Nuclear Holocaust

December 3, 2024 by Dr Rajiv Desai

Nuclear Holocaust:

No one person can be credited with producing the world’s first atomic bomb but two men (figure above) had outsize achievements in that effort: physicist J. Robert Oppenheimer and Army Lt. Gen. Leslie Groves.

The movement of survivors of the atomic bombs in Hiroshima and Nagasaki, known as hibakusha, receives the 2024 Nobel Peace Prize for its efforts to achieve a world without nuclear weapons and for demonstrating through personal testimony that nuclear weapons must never be used again.

“So long as any state has nuclear weapons, others will want them. So long as any such weapons remain, there is a risk that they will one day be used, by design or accident. And any such use would be catastrophic.”

—Weapons of Mass Destruction Commission

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Section-1

Prologue:

Hiram Maxim, the inventor of the machine gun, declared, “Only a general who was a barbarian would send his men to certain death against the concentrated power of my new gun.” But they did send them. In World War One, the machine gun often mowed down tens of thousands of men in a single day.

Orville Wright saw a similar vision: “When my brother and I built and flew the first man-carrying flying machine, we thought we were introducing into the world an invention that would make further wars practically impossible.” Far from ending war, however, the airplane increased the ability to maim and kill. In firebombing raids on London, Hamburg and Tokyo the airplane wrought previously unimaginable levels of destruction. In a single night, March 9, 1945, 25 percent of Tokyo was destroyed, 80,000 people were killed, and over 1 million left homeless.

History shows the folly in hoping that each new, more destructive weapon will not be used. And yet we dare to hope that this time it will be different. We have amassed a combined arsenal of 13,000 nuclear weapons, capable of reaching their targets in a matter of minutes, able to destroy every major city in the world and have the capacity to destroy most life on earth several times over. All in the belief that they will never be used. But unless we make a radical shift in our thinking about war, this time will be no different. On our current path, nuclear war is inevitable.

Nuclear weapons are unique in their destructive power, in the unspeakable human suffering they cause, in the impossibility of controlling their effects in space and time, in the risks of escalation and in the threat they pose to the environment, to future generations, indeed, to the survival of humanity. There is only one scenario other than an asteroid strike that could end the world as we know it in a matter of hours: nuclear war. Despite witnessing their effects in Hiroshima and Nagasaki, countries continue to attempt to protect their right to retain and use nuclear weapons. A great deal of research has been done to highlight the catastrophic impacts of nuclear weapons on humans, animals, plants, and other natural features like water bodies, soil, etc. The known effects of nuclear weapons involve causing death, blunt trauma, thermal radiation, firestorms, radioactive fallout to neighbouring territories (that can cause additional casualties and destruction), radiation sickness, cancer, and genetic diseases. In the case of animals and plants, nuclear weapons can destroy marine and land life by causing contamination through nuclear radiation. Other consequences include nuclear winter that result in more fatalities across the globe than the better-understood effects of blast, prompt radiation, and fallout; and electromagnetic pulse effects, which could range from minor electrical disturbances to the complete collapse of the electric grid.

The world faces two existential threats: climate change, and nuclear holocaust. Action on both is required urgently. Tackling the first will impose significant economic costs and lifestyle adjustments, while tackling the second will bring economic benefits without any lifestyle implications. Those who reject the first are derided as denialists; those dismissive of the second are praised as realists. Although action is needed now in order to keep the world on this side of the tipping point, a climate change-induced apocalypse will not occur until decades into the future. A nuclear catastrophe could destroy us at any time, although, if our luck holds out, it could be delayed for decades. The uncomfortable reality is that nuclear peace has been upheld, owing as much to good luck as to sound stewardship. Because we have learned to live with nuclear weapons for 80 years, we have become desensitized to the gravity and immediacy of the threat.

Nuclear weapons are the most destructive technology ever developed. How can we prevent their use? How can we keep them from evil men? Can we hope to eliminate them entirely? Although these are really questions about human institutions, they cannot be answered without a deep understanding of what nuclear weapons are, and aren’t. The topic is complex and technical: steeped in physics, mathematics, and esoteric engineering. The subject has been highly classified from the beginning making it even more inaccessible. Yet this complexity and secrecy has not prevented their acquisition by any nation with an industrial infrastructure advanced enough to build them, and a matching desire. The obstacle to would-be members to the nuclear club has not been discovering how they work, but simply obtaining the tools and materials to make them.

As former Soviet leader Nikita Khrushchev poignantly stated in the aftermath of Cuban missile crisis, “Peace is the most important goal in the world. If we don’t have peace and the nuclear bombs start to fall, what difference will it make whether we are Communists or Catholic or Capitalists or Chinese or Russians or Americans? Who could tell us apart? Who will be left to tell us apart?” In 1985, US President Ronald Reagan and USSR President Mikhail Gorbachev declared in a joint statement that “a nuclear war cannot be won and must never be fought”. Notwithstanding, Russian President Vladimir Putin and his close associate Dmitry Medvedev have repeatedly warned publicly that Moscow possesses the largest nuclear arsenal in the world, has new means of delivering bombs, and will not hesitate to use them if it deems that the survival or territorial integrity of Russia is threatened. And Iran is persistently seeking to acquire nuclear technology, ostensibly to use it to generate electricity, but more likely to join the nuclear forces, which would put it on par with Israel. North Korea has been developing its atomic arsenal for years, and often tests missiles, which poses a major nuclear threat to South Korea and Japan, as well as to the United States – countries it considers hostile. Both India and Pakistan have their atomic bombs – neighbors that chronically have territorial disputes and border skirmishes with casualties. The United States, the United Kingdom, France and China today do not threaten anyone with their nuclear arsenal, but are ready to retaliate if attacked with such weapons. But as long as they have bombs in the hangars and in the submarines, they are also a general threat. And no one can guarantee that in the White House, in the Elysée Palace or in Downing 10 in the near or distant future there will not be a leader with “nervous fingers” who would easily press the red button.

Nuclear weapons killed about 210,000 people when the United States used them against the Japanese cities of Hiroshima and Nagasaki in August 1945. They have come close to being used again more than a dozen times since. There are more than 13,000 nuclear weapons in the world controlled by nine nations. States with nuclear weapons, including the United States, Russia, China, India, and Pakistan, have recently embarked on plans to modernize or expand their nuclear arsenals, while North Korea has developed, and Iran is at risk of developing new nuclear weapons capabilities. The presence of these weapons creates a risk that they will be launched intentionally or by mistake, by unstable leaders, hackers, or computer failure. Humanity is just one misunderstanding, one miscalculation away from nuclear annihilation.

The development of nuclear weapons has been justified by arguing that they are cheaper than equivalent conventional weapons. In terms of destructive power, this is true (they yield ‘more bang for the buck’ or ‘more rubble for the rouble’), but not in terms of buying security: all of the nuclear powers spend a higher fraction of their income for defense than the world average. Some have argued that nuclear weapons have helped prevent war. But in fact, since 1945 the eight countries possessing nuclear weapons have been involved in over eight times as many wars, on average, as all the nonnuclear countries. Some credit nuclear weapons with having prevented nuclear war, which is preposterous: without nuclear weapons, there could be no nuclear war. The losses in the case of a nuclear war would be so enormous that even if the probability is low, it is an issue that cannot be ignored. Astronomer Carl Sagan and collaborators discovered in 1983, with the help of a model of the earth’s atmosphere, that destruction from a nuclear war would go beyond the impact of heat, blast, and radiation disease. The smoke and soot rising into the stratosphere would linger for months, blocking out sunlight and cooling the earth surface in a ‘nuclear winter’. Harvests would fail, and those who survived the immediate impact could die from hunger and cold. It might well bring an end to civilization and endanger human survival itself.

On 8 July 1996, the World Court declared the threat or use of nuclear weapons contrary to international law under almost any conceivable circumstances and unanimously stated that the nuclear nations have the obligation to conduct negotiations leading to complete nuclear disarmament. Other weapons of mass destruction – chemical and biological weapons – have already been banned by treaties. An immediate first step should be the adoption of a policy of no first use. If nobody were to use nuclear weapons first, they would never be used. China and India are the only two nuclear powers to formally maintain a no first use policy. Countries against no-first-use policy include Pakistan, Russia, the United Kingdom, the United States, and France who have asserted the right to use nuclear weapons against nations that do not possess nuclear weapons. Ironically, this gives a strong incentive for such nations to acquire nuclear weapons to deter nuclear attack on them. On 7 July 2017, 122 member states adopted the Treaty on the Prohibition of Nuclear Weapons at the United Nations. Humanity has demonstrated great wisdom to create the first treaty of its kind. However, all nine of the nuclear-armed states and their allied nations, including Japan, declared that they oppose and would not sign the treaty. I support universal nuclear disarmament and this article is my endeavour to create the vision of a nuclear-weapon-free world.

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Abbreviations and synonyms:

U = uranium

NU = natural uranium

DU = depleted uranium

AEC = Atomic Energy Commission

CANDU = Canadian deuterium–uranium reactor

CD = Conference on Disarmament

CTBT= Comprehensive Nuclear Test Ban Treaty

FMCT = Fissile Material Cut-Off Treaty

HEU = Highly enriched uranium

IAEA = International Atomic Energy Agency

ICBM = Intercontinental ballistic missile

MIRV = multiple independently targetable reentry vehicles

LEU = Low-enriched uranium

LWR = Light water reactor

HWR = heavy water reactor

RBMK = reaktor bolshoy moshchnosti kanalniy = light water graphite reactor (LWGR)

MOX = Mixed-oxide fuel

NPT = Treaty on the Non-Proliferation of nuclear weapons

Pu = Plutonium

RepU = Reprocessed uranium

WGU = Weapon-grade uranium

MWd/t = megawatt-days per ton

GWd/t = gigawatt-days per ton

SWU = separative work unit

SALT I = Strategic Arms Limitation Treaty

INF = Intermediate-Range Nuclear Forces Treaty

START = Strategic Arms Reduction Treaty

SORT = Strategic Offensive Reductions Treaty

New START=Treaty on Measures for the Further Reduction and Limitation of Strategic Offensive Arms.

kT = kiloton = energy released by one thousand tons of TNT

Mt = megaton = energy released by one million tons of TNT

psi = pound per square inch

ARS = acute radiation sickness

MAD = mutual assured destruction

NFU = no first use

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Glossary about nuclear weapons:

Radioactivity:

The spontaneous emission of radiation, generally alpha or beta particles, often accompanied by gamma rays, from the nuclei of an (unstable) isotope. As a result of this emission the radioactive isotope is converted (or decays) into the isotope of a different (daughter) element which may (or may not) also be radioactive. Ultimately, as a result of one or more stages of radioactive decay, a stable (nonradioactive) end product is formed.

Isotopes:

Forms of the same element having identical chemical properties but differing in their atomic masses (due to different numbers of neutrons in their respective nuclei) and in their nuclear properties (e.g., radioactivity, fission, etc.). For example, hydrogen has three isotopes, with masses of 1 (hydrogen), 2 (deuterium), and 3 (tritium) units, respectively. The first two of these are stable (nonradioactive), but the third (tritium) is a radioactive isotope. Both of the common isotopes of uranium, with masses of 235 and 238 units, respectively, are radioactive, emitting alpha particles, but their half-lives are different. Furthermore, uranium-235 is fissionable by neutrons of all energies, but uranium-238 will undergo fission only with neutrons of high energy.

Neutron:

A neutral particle (i.e., with no electrical charge) of approximately unit mass, present in all atomic nuclei, except those of ordinary (light) hydrogen. Neutrons are required to initiate the fission process, and large numbers of neutrons are produced by both fission and fusion reactions in nuclear (or atomic) explosions.

Beryllium metal:

A highly toxic steel-grey metal, possessing a low neutron absorption cross-section and high melting point, which can be used in nuclear reactors as a moderator or reflector. In nuclear weapons, beryllium surrounds the fissile material and reflects neutrons back into the nuclear reaction, considerably reducing the amount of fissile material required. Beryllium is also used in guidance systems and other parts for aircraft, missiles or space vehicles.

Fission:

The process whereby the nucleus of a particular heavy element splits into (generally) two nuclei of lighter elements, with the release of substantial amounts of energy. The most important fissionable materials are uranium-235 and plutonium 239; fission is caused by the absorption of neutrons.

Fusion:

The process whereby the nuclei of light elements, especially those of the isotopes of hydrogen, namely, deuterium and tritium, combine to form the nucleus of a heavier element with the release of substantial amounts of energy.

Fission Fraction:

The fraction (or percentage) of the total yield of a nuclear weapon which is due to fission. For thermonuclear weapons the average value of the fission fraction is about 50 percent.

Fission Products:

A general term for the complex mixture of substances produced as a result of nuclear fission. A distinction should be made between these and the direct fission products or fission fragments which are formed by the actual splitting of the heavy-element nuclei. Something like 80 different fission fragments result from roughly 40 different modes of fission of a given nuclear species (e.g., uranium-235 or plutonium-239). The fission fragments, being radioactive, immediately begin to decay, forming additional (daughter) products, with the result that the complex mixture of fission products so formed contains over 300 different isotopes of 36 elements.

Uranium (U):

A radioactive element with the atomic number 92 and, as found in natural ores, an average atomic weight of 238. The two principal natural isotopes are uranium-235 (0.71 per cent of natural uranium), which is fissionable, and uranium-238 (99.27 per cent of natural uranium), which is fertile.

Fertile material:

A fertile material is a material that can be converted into a fissile material through irradiation in a reactor. The two basic fertile materials are thorium-232 and uranium-238. Uranium-238 becomes plutonium-239 after it absorbs a neutron. Fertile material alone cannot sustain a chain reaction. Thorium is more abundant than uranium in nature. It can be used as a nuclear fuel in conjunction with fissile material.

Fissionable material:

Material, whose nuclei can be induced to fission by a neutron.

Fissile material:

Material composed of atoms which fission when irradiated by slow or ‘thermal’ neutrons. The most common examples of fissile materials are uranium-235 and plutonium-239. The term is often used to describe plutonium and HEU, e.g., a cut-off in the production of fissile materials for weapons.

Weapon-grade material:

Nuclear material of the type most suitable for nuclear weapons, i.e., uranium enriched to over 90 per cent 235U or plutonium that is primarily 239Pu.

Weapon-usable material:

Usually separated plutonium or HEU. Because of the use of this term in UN Security Resolution 687, the IAEA Action Team formally defined it as uranium enriched to 20 per cent or more in uranium isotopes 233, 235 or both; plutonium containing less than 80 per cent 239Pu; any of the foregoing in the form of metal, alloy, chemical compound or concentrate; and any other goods containing one or more of the foregoing, other than irradiated fuel.

Separative work:

A measure of the effort required in an enrichment facility to separate uranium of a given uranium-235 content into two fractions, one with a higher percentage and one with a lower percentage of uranium-235. The unit of separative work is the kilogram separative work unit (kg SWU), or separative work unit (SWU) for short. The initial material is called the ‘feed’. The fraction with a higher proportion of uranium-235 is called the ‘product’, the other is called the ‘tails’.

Significant quantity:

The approximate amount of nuclear material (not just fissile material) which the IAEA considers a state would need to manufacture its first nuclear explosive. Eight kilograms of plutonium are considered significant and 25 kilograms of weapon-grade uranium are significant.

Critical Mass:

The minimum mass of a fissionable material that will just maintain a fission chain reaction under precisely specified condition, such as the nature of the material and its purity, the nature and thickness of the tamper (or neutron reflector), the density (or compression), and the physical shape (or geometry). For an explosion to occur, the system must be supercritical (i.e., the mass of material must exceed the critical mass under the existing conditions).

Nuclear Weapon (or Bomb):

A general name given to any weapon in which the explosion results from the energy released by reactions involving atomic nuclei, either fission or fusion or both. Thus, the A- (or atomic) bomb and the H- (or hydrogen) bomb are both nuclear weapons. It would be equally true to call them atomic weapons, since it is the energy of atomic nuclei that is involved in each case. However, it has become more-or-less customary, although it is not strictly accurate. to refer to weapons in which all the energy results from fission as A-bombs or atomic bombs. In order to make a distinction, those weapons in which part, at least, of the energy results from thermonuclear (fusion) reactions of the isotopes of hydrogen have been called H-bombs or hydrogen bombs. A weapon in which neutrons produced by thermonuclear reactions serve to enhance the fission process is called boosted fission weapon. Boosted fission weapons use a small amount of fusion fuel to increase the yield of a fission chain reaction. Thermonuclear weapons, also known as hydrogen bombs, use a series of fission-fusion-fission reactions to produce a much greater yield than fission weapons.

Yield (or Energy Yield):

The total effective energy released in a nuclear (or atomic) explosion. It is usually expressed in terms of the equivalent tonnage of TNT required to produce the same energy release in an explosion. The total energy yield is manifested as nuclear radiation, thermal radiation, and shock (and blast) energy, the actual distribution being dependent upon the medium in which the explosion occurs (primarily) and also upon the type of weapon and the time after detonation.

TNT Equivalent:

A measure of the energy released in the detonation of a nuclear (or atomic) weapon, or in the explosion of a given quantity of fissionable material, expressed in terms of the mass of TNT which would release the same amount of energy when exploded. The TNT equivalent is usually stated in kilotons or megatons. The basis of the TNT equivalence is that the explosion of ton of TNT is assumed to release 10^9 calories of energy.

Kiloton Energy: This is approximately the amount of energy that would be released by the explosion of I kiloton (l000 tons) of TNT.

Megaton Energy: This is approximately the amount of energy that would be released by the explosion of 1,000 kilotons of TNT.

Nuclear (or Atomic) Tests:

Test carried out to supply information required for the design and improvement of nuclear (or atomic) weapons and to study the phenomena and effects associated with nuclear (or atomic) explosions.

Nuclear deterrence:

The strategic use of the threat of nuclear weapons to persuade enemies or potential enemies to refrain from using such weapons.

Nuclear state:

A country that possesses nuclear weapons and the means to deliver them.

Nuclear war:

A war that includes the exchange of nuclear weapons. Some argue that the use of such weapons against Japan did not amount to nuclear war because they were not used by both sides.

Nuclear security:

Security measures for nuclear weapons, materials, and facilities to reduce the chance that nuclear weapons and materials could be stolen and fall into terrorist hands, or that nuclear facilities could be sabotaged.

Nuclear safety:

Preventing an accident at a nuclear reactor, such as Fukushima.

Nuclear non-proliferation:

Preventing the spread of nuclear weapons to additional countries.

Nuclear disarmament:

The process of reducing or eliminating nuclear weapons, and the goal of creating a world without nuclear weapons.

Nuclear power:

Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power also means a country that has nuclear weapons.

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Glossary about nuclear explosion:

Ground Zero:

The point on the surface of land vertically below or above the center of a burst of a nuclear (or atomic) weapon; frequently abbreviated to GZ. For a burst over or under water the corresponding term is surface zero (SZ). Surface zero is also commonly used for ground surface and underground bursts.

Burst:

Explosion or detonation.

Fireball:

A mass of air surrounding a nuclear explosion and heated to luminous temperatures. The luminous sphere of hot gases which forms a few millionths of a second after a nuclear (or atomic) explosion as the result of the absorption by the surrounding medium of the thermal X rays emitted by the extremely hot (several tens of million degrees) weapon residues. The exterior of the fireball in air is initially sharply defined by the luminous shock front and later by the limits of the hot gases themselves.

Air burst:

A nuclear explosion detonated at an altitude—typically, thousands of feet—that maximizes blast damage. Because its fireball never touches the ground, an air burst produces less radioactive fallout than a ground burst.

Height of Burst:

The height above the earth’s surface at which a bomb is detonated in the air. The optimum height of burst for a particular target (or area) is that at which it is estimated a weapon of a specified energy yield will produce a certain desired effect over the maximum possible area.

High-Altitude Burst:

This is defined, somewhat arbitrarily, as a detonation at an altitude over 100,000 feet. Above this level the distribution of the energy of the explosion between blast and thermal radiation changes appreciably with increasing altitude due to changes in the fireball phenomena.

Surface Burst:

The explosion of a nuclear (or atomic) weapon at the surface of the land or water at a height above the surface less than the radius of the fireball at maximum luminosity (in the second thermal pulse). An explosion in which the weapon is detonated actually on the surface is called a contact surface burst or a true surface burst.

Ground burst:

A nuclear explosion detonated at ground level, producing a crater and significant fallout but less widespread damage than an air burst.

Crater:

The pit, depression, or cavity formed in the surface of the earth by a surface or underground explosion. Crater formation can occur by vaporization of the surface material, by the scouring effect of air blast, by throwout of disturbed material, or by subsidence. In general, the major mechanism changes from one to the next with increasing depth of burst. The apparent crater is the depression which is seen after the burst; it is smaller than the true crater (i.e., the cavity actually formed by the explosion), because it is covered with a layer of loose earth, rock, etc.

Contained Underground Burst:

An underground detonation at such a depth that none of the radioactive residues escape through the surface of the ground.

Blast wave:

An abrupt jump in air pressure that propagates outward from a nuclear explosion as blast wave accompanied by winds, damaging or destroying whatever it encounters.

Overpressure:

Excess air pressure encountered in the blast wave of a nuclear explosion. Overpressure of a few pounds per square inch is sufficient to destroy typical wooden houses. Overpressure is transient pressure, usually expressed in pounds per square inch, exceeding the ambient pressure, manifested in the shock (or blast) wave from an explosion. The variation of the overpressure with time depends on the energy yield of the explosion, the distance from the point of burst, and the medium in which the weapon is detonated. The peak overpressure is the maximum value of the overpressure at a given location and is generally experienced at the instant the shock (or blast) wave reaches that location.

Dynamic Pressure:

The air pressure which results from the mass air flow (or wind) behind the shock front of a blast wave. It is equal to the product of half the density of the air through which the blast wave passes and the square of the particle (or wind) velocity behind the shock front as it impinges on the object or structure.

Shock Front (or Pressure Front):

The fairly sharp boundary between the pressure disturbance created by an explosion (in air, water, or earth) and the ambient atmosphere, water, or earth, respectively. It constitutes the front of the shock (or blast) wave.

Shock Wave:

A continuously propagated pressure pulse (or wave) in the surrounding medium which may be air, water, or earth, initiated by the expansion of the hot gases produced in an explosion. A shock wave in air is generally referred to as a blast wave (vide supra), because it resembles and is accompanied by strong, but transient, winds. The duration of a shock (or blast) wave is distinguished by two phases. First there is the positive (compression) phase during which the pressure rises very sharply to a value that is higher than ambient and then decreases rapidly to the ambient pressure. The positive phase for the dynamic pressure is somewhat longer than for overpressure, due to the momentum of the moving air behind the shock front. The duration of the positive phase increases and the maximum (peak) pressure decreases with increasing distance from an explosion of given energy yield. In the second phase, the negative (suction, rarefaction, or tension) phase, the pressure falls below ambient and then returns to the ambient value. The duration of the negative phase may be several times the duration of the positive phase. Deviations from the ambient pressure during the negative phase are never large and they decrease with increasing distance from the explosion.

Mach Stem:

The shock front formed by the merging of the incident and reflected shock fronts from an explosion. The term is generally used with reference to a blast wave, propagated in the air, reflected at the surface of the earth. The Mach stem is nearly perpendicular to the reflecting surface and presents a slightly convex (forward) front. The Mach stem is also called the Mach front.

Triple Point:

The intersection of the incident, reflected, and merged (or Mach) shock fronts accompanying an air burst. The height of the triple point above the surface (i.e., the height of the Mach stem) increases with increasing distance from a given explosion.

Cube Root Law:

A scaling law applicable to many blast phenomena. It relates the time and distance at which a given blast effect is observed to the cube root of the energy yield of the explosion.

Inverse Square Law:

The law which states that when radiation (thermal or nuclear) from a point source is emitted uniformly in all directions, the intensity of radiation at any given distance from the source, assuming no absorption, is inversely proportional to the square of that distance.

Scaling Law:

A mathematical relationship which permits the effects of a nuclear (or atomic) explosion of given energy yield to be determined as a function of distance from the explosion (or from ground zero), provided the corresponding effect is known as a function of distance for a reference explosion (e.g., of 1-kiloton energy yield).

Thermal X-Rays:

The electromagnetic radiation, mainly in the soft (low-energy) X-ray region, emitted by the extremely hot weapon residue in virtue of its extremely high temperature; it is also referred to as the primary thermal radiation. It is the absorption of this radiation by the ambient medium, accompanied by an increase in temperature, which results in the formation of the fireball (or other heated region) which then emits thermal radiation.

Thermal Radiation:

Electromagnetic radiation emitted (in two pulses from an air burst) from the fireball as a consequence of its very high temperature; it consists essentially of ultraviolet, visible, and infrared radiations. In the early stages (first pulse of an air burst), when the temperature of the fireball is extremely high, the ultraviolet radiation predominates; in the second pulse, the temperatures are lower and most of the thermal radiation lies in the visible and infrared regions of the spectrum. For high-altitude bursts (above 100,000 feet), the thermal radiation is emitted as a single pulse, which is of short duration below about 270,000 feet but increases at greater burst heights.

Thermal Energy:

The energy emitted from the fireball (or other heated region) as thermal radiation. The total amount of thermal energy received per unit area at a specified distance from a nuclear (or atomic) explosion is generally expressed in terms of calories per square centimeter.

Thermal flash:

An intense burst of heat radiation in the seconds following a nuclear explosion. The thermal flash of a large weapon can ignite fires and cause third-degree burns tens of miles from the explosion.

Fire Storm:

The many individual fires created by a nuclear explosion can coalesce into one massive fire known as a “firestorm.” The combination of many smaller fires heats the air and causes winds of hurricane strength directed inward toward the fire; the winds keep the fires from spreading while adding fresh oxygen to increase their intensity.

Thermal Energy Yield (or Thermal Yield):

The part of the total energy yield of the nuclear (or atomic) explosion which is received as thermal energy usually within a minute or less. In an air burst, the thermal partition (i.e., the fraction of the total explosion energy emitted as thermal radiation) ranges from about 0.35 to 0.45. The trend is toward the smaller fraction for low yields or low burst heights and toward the higher fraction at high yields or high bursts. Above 100,000 feet burst height, the fraction increases from about 0.45 to 0.6, and then decreases to about 0.25 at burst altitudes of 160,000 to 260,000 feet. At still greater burst heights, the fraction decreases rapidly with increasing altitude.

Initial Nuclear Radiation:

Nuclear radiation (essentially neutrons and gamma rays) emitted from the fireball and the cloud column during the first minute after a nuclear (or atomic) explosion. The time limit of one minute is set, somewhat arbitrarily, as that required for the source of part of the radiations (fission products, etc., in the radioactive cloud) to attain such a height that only insignificant amounts of radiation reach the earth’s surface.

Residual Nuclear Radiation:

Nuclear radiation, chiefly beta particles and gamma rays, which persists for some time following a nuclear (or atomic) explosion. The radiation is emitted mainly by the fission products and other bomb residues in the fallout, and to some extent by earth and water constituents, and other materials, in which radioactivity has been induced by the capture of neutrons.

Nuclear Radiation:

Particulate and electromagnetic radiation emitted from atomic nuclei in various nuclear processes. The important nuclear radiations, from the weapons standpoint, are alpha and beta particles, gamma rays, and neutrons. All nuclear radiations are ionizing radiations, but the reverse is not true; X rays, for example, are included among ionizing radiations, but they are not nuclear radiations since they do not originate from atomic nuclei.

Induced Radioactivity:

Radioactivity produced in certain materials as a result of nuclear reactions, particularly the capture of neutrons, which are accompanied by the formation of unstable (radioactive) nuclei. In a nuclear explosion, neutrons can induce radioactivity in the weapon materials, as well as in the surroundings (e.g., by interaction with nitrogen in the air and with sodium, manganese, aluminium, and silicon in soil and sea water).

Electromagnetic pulse (EMP):

An intense burst of radio waves produced by a high-altitude nuclear explosion, capable of damaging electronic equipment over thousands of miles. The intense electric and magnetic fields can damage unprotected electrical and electronic equipment over a large area. The range of a nuclear electromagnetic pulse (EMP) depends on the altitude at which the nuclear weapon detonates: The most severe consequences of a 10 KT detonation at ground level are expected to travel no more than 2–5 miles (3.2–8 km). A high-altitude nuclear explosion can produce an EMP that can affect a large area of space, with a diameter of thousands of kilometers. The radius of the area on Earth’s surface within line of sight of the blast can be about 440 miles. It has no known effect on living organisms.

Ionosphere:

The region of the atmosphere, extending from roughly 40 to 250 miles altitude, in which there is appreciable ionization. The presence of charged particles in this region profoundly affects the propagation of long-wavelength electromagnetic radiations (radio and radar waves).

Radio Blackout:

The complete disruption of radio (or radar) signals over large areas caused by the ionization accompanying a high-altitude nuclear explosion, especially above about 40 miles.

Fallout:

Radioactive material, mostly fission products, released into the environment by nuclear explosions. Fallout is process or phenomenon of the descent to the earth’s surface of particles contaminated with radioactive material from the radioactive cloud. The term is also applied in a collective sense to the contaminated particulate matter itself.

Contamination:

The deposit of radioactive material on the surfaces of structures, areas, objects, or personnel, following a nuclear (or atomic) explosion. This material generally consists of fallout in which fission products and other weapon debris have become incorporated with particles of dirt, etc. Contamination can also arise from the radioactivity induced in certain substances by the action of neutrons from a nuclear explosion.

Decontamination:

The reduction or removal of contaminating radioactive material from a structure, area, object, or person. Decontamination may be accomplished by (1) treating the surface so as to remove or decrease the contamination; (2) letting the material stand so that the radioactivity is decreased as a result of natural decay; and (3) covering the contamination so as to attenuate the radiation emitted. Radioactive material removed in process must be disposed of by burial on land or at sea, or in other suitable way.

Nuclear winter:

A substantial reduction in global temperature that might result from soot injected into the atmosphere during a nuclear war.

Radius of destruction:

The distance from a nuclear blast within which destruction is near total, often taken as the zone of 5-pound-per-square-inch overpressure.

Radioactive (or Nuclear) Cloud:

An all-inclusive term for the cloud of hot gases, smoke, dust, and other particulate matter from the weapon itself and from the environment, which is carried aloft in conjunction with the rising fireball produced by the detonation of a nuclear (or atomic) weapon.

Mushroom cloud:

Mushroom clouds form after nuclear blasts because of the way the explosion’s convection currents, gravity, and the atmosphere interact: The explosion’s convection currents suck up dust and other materials from the ground into the fireball. Gravity pulls the denser air into the bottom of the fireball, which mixes turbulently to create the cloud’s familiar shape. The fireball reaches a point in the atmosphere where the air is dense and cold enough to slow its ascent. The weight and density of the air flattens the fireball and its smoke. As the cloud rises, a Rayleigh–Taylor instability forms, which draws air upwards into the cloud. This creates strong air currents called “afterwinds”. If the detonation is low enough, the afterwinds can draw in dirt and debris from the ground to form the stem of the mushroom cloud. The height of the mushroom cloud depends on the heat energy of the weapon and the atmospheric conditions. The cloud can be visible for over an hour before the winds disperse it. Mushroom clouds can also form after other large explosions.

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Glossary and Measurement for Radiation Exposure:

There are four types of ionizing radiation produced by nuclear explosions that can cause significant injury: neutrons, gamma rays, beta particles, and alpha particles. Gamma rays are energetic (short wavelength) photons (as are X-rays), beta particles are energetic (fast moving) electrons, and alpha particles are energetic helium nuclei. Neutrons are damaging whether they are energetic or not, although the faster they are, the worse their effects.

They all share the same basic mechanism for causing injury though: the creation of chemically reactive compounds called “free radicals” that disrupt the normal chemistry of living cells. These radicals are produced when the energetic radiation strikes a molecule in the living issue, and breaks it into ionized (electrically charged) fragments. Fast neutrons can do this also, but all neutrons can also transmute ordinary atoms into radioactive isotopes, creating even more ionizing radiation in the body.

The different types of radiation present different risks however. Neutrons and gamma rays are very penetrating types of radiation. They are the hardest to stop with shielding. They can travel through hundreds of meters of air and the walls of ordinary houses. They can thus deliver deadly radiation doses even if an organism is not in immediate contact with the source. See figure below. Beta particles are less penetrating, they can travel through several meters of air, but not walls, and can cause serious injury to organisms that are near to the source. Alpha particles have a range of only a few centimeters in air, and cannot even penetrate skin. Alphas can only cause injury if the emitting isotope is ingested.

Half-value thickness (HVT) and tenth-value thickness (TVT) are the thickness of a material that reduces the intensity of radiation by half and one-tenth, respectively. These values are used to determine the effectiveness of radiation shielding. Successive layers of shielding each reduce the intensity by the same proportion, so three tenth-value thickness reduce the intensity to one-thousandth. Some example tenth-value thicknesses for gamma rays are: steel 8.4-11 cm, concrete 28-41 cm, earth 41-61 cm, water 61-100 cm, and wood 100-160 cm. The thickness ranges indicate the varying shielding effect for different gamma ray energies. Even light clothing provides substantial shielding to beta rays.

Radiation exposures from nuclear weapons occur on three time scales:

The shortest is exposure from the prompt radiation emitted by the fireball which lasts about one minute. This can cause very intense exposures for individuals close to the burst point. Neutron bombs rely on prompt radiation as the primary damage mechanism, in this case the prompt radiation arrives in a fraction of a second.

The second scale is due to early (tropospheric) fallout from ground bursts. Fallout particles begin settling to the ground within an hour to a few hours after an explosion, most of the fallout descend within a day or two. At any particular site, the fallout deposition will last no more than several hours. Radiation exposure is accumulated as long as an individual remains within the fallout deposit zone, but due to the rapid initial decay most of the radiation exposure is incurred within the first few days. Exposures can be very large during the first few days.

The third scale is long term exposure to low levels of radiation, lasting months or years. This may be due to any of several causes:

-prolonged residence in areas contaminated by early fallout;

-exposure to delayed (stratospheric) fallout;

-exposure to radioisotopes absorbed by the body.

Long term exposures are not intense, but large total doses can accumulate over long periods of time.

The effects of radiation exposure of usually divided into acute and latent effects. Acute effects typically result from rapid exposures, the effects show up within hours to weeks after a sufficient dose is absorbed. Latent effects take years to appear, even after exposure is complete. Since the latent effects of radiation exposure are cumulative, and there does not appear to be any threshold exposure below which no risk is incurred, radiation safety standards have been set to minimize radiation exposure over time.

Absorbed Dose:

The amount of energy imparted by nuclear (or ionizing) radiation to unit mass of absorbing material. The unit is the rad. Rad is unit of absorbed dose of radiation; it represents the absorption of 100 ergs of nuclear (or ionizing) radiation per gram of absorbing material, such as body tissue.

Erg:

An erg is the amount of work done by a force of one dyne exerted for a distance of one centimetre. In the CGS base units, it is equal to one gram centimetre-squared per second-squared (g⋅cm2/s2). It is equal to 10^−7 joules or 100 nanojoules (nJ) in SI units.

RBE:

RBE (or Relative Biological Effectiveness): The ratio of the number of rads of gamma (or X) radiation of a certain energy which will produce a specified biological effect to the number of rads of another radiation required to produce the same effect is the RBE of the latter radiation.

Background Radiation:

Nuclear (or ionizing) radiations arising from within the body and from the surroundings to which individuals are always exposed. The main sources of the natural background radiation are potassium-40 in the body, potassium-40 and thorium, uranium, and their decay products (including radium) present in rocks and soil, and cosmic rays. The average background radiation level worldwide is 2.4 millisieverts (mSv) per year. However, this level can vary significantly depending on location. On average, Americans receive a radiation dose of about 0.62 rem (620 millirem) each year. Half of this dose comes from natural background radiation. Radiological Protection (ICRP) recommendation for the limits of exposure for radiation workers for whole-body doses is 20 mSv/year or 0.02 Sv/year.

Note that 1 mSv = 100 mrem

Dose Rate:

As a general rule, the amount of ionizing (or nuclear) radiation which an individual or material would receive per unit of time. It is usually expressed as rads (or rems) per hour or in multiples or submultiples of these units, such as millirads per hour. The dose rate is commonly used to indicate the level of radioactivity in a contaminated area.

Dosimeter:

An instrument for measuring and registering the total accumulated dose of (or exposure to) ionizing radiations. Instruments worn or carried by individuals are called personnel dosimeters.

Flux (or Flux Density):

The product of the particle (neutron or photon) density (i.e., number per cubic centimeter) and the particle velocity. The flux is expressed as particles per square centimeter per second and is related to the absorbed dose rate. It is numerically equal to the total number of particles passing in all directions through a sphere of 1 square centimeter cross-sectional area per second.

Tenth-Value Thickness:

The thickness of a given material which will decrease the intensity (or dose) of gamma radiation to one-tenth of the amount incident upon it. Two tenth-value thicknesses will reduce the dose received by a factor of 100, and so on.

Attenuation:

Decrease in intensity of a signal, beam, or wave as a result of absorption and scattering out of the path of a detector, but not including the reduction due to geometric spreading (i.e., the inverse square of distance effect). As applied to gamma (and X) rays, attenuation refers to the loss of photons (by the Compton, photoelectric, and pair-production effects) in the passage of the radiation through a material.

Three units of measurement have been commonly used for expressing radiation exposure: roentgens (R), rads, rems, the “three r’s” of radiation measurement. In the scientific literature these are dropping out of use in favor of the SI (System Internationale) units grays (Gy) and sieverts (Sv). Each of the “three r’s” measures something different. A rad is a measure of the amount of ionizing. A roentgen measures the amount of ionizing energy, in the form of energetic photons (gamma rays and x-rays) energy to which an organism is exposed. This unit is the oldest of the three and is defined more the convenience of radiation measurement, than for interpreting the effects of radiation on living organisms. Of more interest is the rad, since it includes all forms of ionizing radiation, and in addition measures the dose that is *actually absorbed* by the organism. A rad is defined as the absorption of 100 ergs per gram of tissue (or 0.01 J/kg). The gray measures absorbed doses as well, one gray equals 100 rads. The rem is also concerned with all absorbed ionizing radiations, and also takes into account the *relative effect* that different types of radiation produce. The measure of effect for a given radiation is its Radiation Biological Effect (RBE). A rem dose is calculated by multiplying the dose in rads for each type of radiation by the appropriate RBE, then adding them all up. The sievert is similar to the rem, but is derived from the gray instead of the rad. Sieverts use a somewhat simplified system of measuring biological potency – the quality factor (Q). The rem and the sievert are the most meaningful unit for measuring and discussing the effects of radiation injury.

1 sievert = 100 rems

1 gray = 100 rads = 1 joule/kg absorbed dose

sievert = gray x Q

rem = rad x RBE

Type Of Radiation RBE Q

Gamma rays/X-rays 1 1

Beta Particles 1 1

Alpha Particles 10-20 20 (ingested emitter)

Neutrons (fast) – 10 Overall effects

1 Immediate Effect

4-6 Delayed cataract formation

10 Cancer Effect

20 Leukemia Effect

Types of Radiation Exposure:

A wide range of biological changes may follow the irradiation of animals. These vary from rapid death following high doses of penetrating whole-body radiation, to essentially normal lives for a variable period of time until the development of delayed radiation effects, in a portion of the exposed population, following low dose exposures.

An important concept to understand is the distinction between whole body doses and radiation exposures concentrated in particular organs. The radiation dose units described above are defined per unit weight of tissue. An exposure of 1000 rems can thus refer to an exposure of this intensity for the whole body, or for only a small part of it. The total absorbed radiation energy will be much less if only a small part of the body is affected, and the overall injury will be reduced.

Not all tissues are exposed equally even in whole body exposures. The body provides significant shielding to internal organs, so tissues located in the center of the body may receive doses that are only 30-50% of the nominal total body dose rate. For example, there is a 50% chance of permanent female sterility if ovaries are exposed to 200 rems, but this internal exposure is only encountered with whole body doses of 400-600 rems.

Units of radioactivity:

Curie:

A “Curie” is an amount of radioactivity, given the same decay rate as 1 gram of Radium-226, and is numerically equal to 3.7 x 10^10 decays per second. 1 Ci also equals 37 billion (3.7 x 10^10) Bequerels (Bq).

Can we convert Curie to Gray?

No.

Grays is the amount of energy absorbed by something (per mass). Curie/Becquerels is a measure of radioactivity – how many decays are there per unit time. The two are quite obviously related, but not directly: a radioactive source that undergoes more radioactive decays will pump out more ionizing radiation energy, and hence you can accumulate more Gy standing in front of it than if you were standing in front of a source whose material was one in which fewer decays were occurring but that is not the only factor. When an atom decays, it emits ionizing radiation (It may be α or β and most of the time it comes with γ). How much energy got absorbed by another material or human being depends on a lot of parameters. For example, how close is the material to the radioactive substance? For how much time did the exposure take place? Geometry considerations and so on.

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Guide to SI Units:

The International System of Units (SI) has been adopted in the publications of several scientific and technical societies in the United States and other countries. It is expected that in due course that these units will come into general use.

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Section-2

Uranium (U) and Plutonium (Pu):

Fissile materials:

Fissile materials are composed of atoms that can be split by neutrons in a self-sustaining chain-reaction to release enormous amounts of energy. In nuclear reactors, the fission process is controlled and the energy is harnessed to produce electricity. In nuclear weapons, the fission energy is released all at once to produce a violent explosion. The most important fissile materials for nuclear energy and nuclear weapons are an isotope of plutonium, plutonium-239, and an isotope of uranium, uranium-235. Uranium-235 occurs in nature. For all practical purposes, plutonium-239 does not.

Nuclear reactors and nuclear weapons derive power through the fission (splitting) of nuclei of uranium or plutonium atoms, a process that releases large amounts of energy. These fissile materials are used for a variety of civil and military purposes, as shown in the table below.

Types of Fissile Material	Main Uses
Natural Uranium	some power reactors military plutonium production reactors
Low-Enriched Uranium (LEU)	most operating power reactors, some research reactors, naval propulsion reactors
Highly Enriched Uranium (HEU)	many research reactors, naval propulsion reactors, nuclear weapons, military plutonium and tritium production reactors
Mixed Plutonium- Uranium Oxide (MOX)	some research and experimental reactors, some power reactors
Plutonium	nuclear weapons

Whereas the U-235 atom is ‘fissile’, the U-238 atom is said to be ‘fertile’. This means that it can capture a neutron and become (indirectly) plutonium-239, which is fissile. Pu-239 is very much like U-235, in that it can fission following neutron capture, also yielding a lot of energy. Because there is so much U-238 in a reactor core (most of the fuel), these reactions occur frequently, and in fact about one-third of the energy yield typically comes from burning bred Pu-239. A very small amount of U-238 also fissions from fast neutrons, contributing about 7% of the energy in a reactor. In certain reactors fuelled with natural uranium, bred plutonium provides about 60% of the energy.

Both uranium and plutonium were used to make bombs before they became important for making electricity and radioisotopes. But the type of uranium and plutonium for bombs is different from that in a nuclear power plant. Bomb-grade uranium is highly enriched (>90% U-235, instead of about 3.5-5.0% in a power plant); bomb-grade plutonium is fairly pure (>90%) Pu-239 and is made in special reactors. Plutonium-239 is more frequently used in nuclear weapons than uranium-235, as it is easier to obtain in a quantity of critical mass. Both plutonium-239 and uranium-235 are obtained from Natural uranium, which primarily consists of uranium-238 but contains traces of other isotopes of uranium such as uranium-235. The process of enriching uranium, i.e. increasing the ratio of 235U to 238U to weapons grade, is generally a more lengthy and costly process than the production of plutonium-239 from 238U and subsequent reprocessing.

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Nuclear Fuel Cycle:

The stepwise process of mining uranium, making it into nuclear fuel, irradiating the fuel in a nuclear power plant and disposing of the resulting waste is called the nuclear fuel cycle as seen in the figure below.

The nuclear fuel cycle is an industrial process involving various activities to produce electricity from uranium in nuclear power reactors. Exploration for uranium is followed by mining and milling of the raw uranium ore. Raw uranium must then be processed, and sometimes enriched, in order to maximise its efficiency as fuel. After being irradiated in reactors, the spent fuel needs to be stored to cool down before being disposed of, or can be recycled as reprocessed uranium (RepU), to be reused as a potential source for more power production. The waste generated after recycling and depleted uranium also needs to be disposed of. RepU is mostly U-238 with about 1% U-235, so it needs to be converted and re-enriched for recycling into most reactors. This is complicated by the presence of impurities and two isotopes in particular, U-232 and U-236, which are formed by or following neutron capture in the reactor, and increase with higher burn-up levels.

How is uranium made into nuclear fuel?

On its path to becoming nuclear fuel, uranium goes through solid, liquid and gaseous states of matter. Solid uranium ore is dissolved into a liquid and extracted through in-situ leaching, turned into a solid as yellowcake, converted into uranium hexafluoride gas, centrifuged and enriched and then processed into uranium dioxide, which makes up uranium pellets that form the basis of nuclear fuel assemblies for nuclear power plants. Uranium dioxide is a black powder-like substance. The substance is compressed and sintered through heating to make up uranium pellets. The pellets are then inserted one by one into long metal tubes, which are stacked together to make fuel assemblies — the main source of fuel for nuclear reactors.

Nuclear weapon fuel cycle:

Nuclear weapons fuel cycle is focused on processing the fuel to those isotopes most effective in weapons. Uranium weapons require simpler and shorter fuel cycle than plutonium weapons.

Plutonium weapons require processing of spent reactor fuel and extraction, purification, and engineering of plutonium.

Figure above shows nuclear weapon fuel cycle.

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Uranium:

Uranium is a dense, silver-white, naturally occurring mineral that contains three main isotopes:

U238 (99.27 percent by mass)
U235 (0.72 percent by mass)
U234 (0.0054 percent by mass)

Uranium enrichment facilities produce enriched uranium, mainly used in fuel for nuclear reactors, by extracting U235 from natural uranium. Natural uranium is enriched to increase its U235 content from 0.72 percent to between 2 percent and 5 percent for low enriched uranium (used for power reactors) and about 93.5 percent for highly enriched uranium (mainly used in military applications). The material left over from the production of enriched uranium is classified as depleted uranium DU. DU typically contains U238 (99.8 percent by mass), U235 (0.2 percent by mass) and U234 (0.001 percent by mass).

Uranium (U) has 92 electrons and 92 protons (the atomic number). Of the 14 isotopes in the sequence 227U to 240U (the mass numbers), 235U and 238U are the most important.

With half-lives of 700 million and 4500 million years respectively, 235U and 238U are relatively stable isotopes. They are not strongly radioactive and can be handled by industrial workers without the need for substantial protection. In these respects, uranium contrasts with plutonium (Pu) whose principal isotopes have much shorter half-lives and workers handling this material require extensive protection.

Naturally occurring uranium consists of 99.28 per cent of 238U and of 0.71 per cent of 235U. Moreover 235U, like 239Pu and 241Pu, fissions when irradiated with relatively low energy (‘thermal’) neutrons, allowing heat to be released under controlled conditions in a class of reactor called ‘thermal’. In thermal reactors, neutrons are slowed down or ‘moderated’ by materials such as graphite and water.

Uranium enrichment is the process, through which the isotopic proportion of U-235 is increased from 0.72 per cent to up to 94 per cent. Uranium is considered low-enriched if its isotopic proportion of U-235 remains below 20 per cent. Most commercial reactors use low-enriched uranium (LEU) below five per cent as fuel, which is also often referred to as “reactor-grade uranium”. LEU does not deteriorate and can be safely stored for many years. If uranium is enriched beyond 20 per cent, it is considered highly enriched. Uranium with such high isotopic proportions of U-235 is mostly used in naval propulsion reactors (for example in submarines), nuclear weapons and some research reactors. HEU is defined as uranium containing over 20 per cent 235U. For fission-type nuclear weapons, 235U concentrations of 90 per cent and over are usually desired. HEU at this level of enrichment is often referred to as ‘weapon-grade uranium’. HEU with lower enrichments is also used in thermonuclear weapons.

The following five grades of uranium are commonly recognized:

-1. Depleted uranium, containing less than 0.71 per cent 235U.

-2. Natural uranium, containing 0.71 per cent 235U.

-3. Low-enriched uranium, containing more than 0.71 per cent and less than 20 per cent 235U.

-4. Highly enriched uranium, containing more than 20 per cent 235U.

-5. Weapon-grade uranium, HEU containing more than 90 per cent 235U.

It should be stressed that a self-sustaining chain reaction in a nuclear weapon cannot occur in depleted or natural or low-enriched uranium and is only theoretically possible in LEU of roughly 10 per cent or greater. The critical mass of uranium which can give rise to explosive releases of energy can only be constructed in practice from materials containing high proportions of the fissile isotope 235 U. Thus the enriched uranium burned in conventional nuclear power reactors has no direct military value. For countries with enrichment plants, the possession of LEU can, however, reduce the time and cost involved in producing HEU since fewer separative work units are required to produce weapon-grade material if LEU is used as feed. Nevertheless, LEU’s worthlessness as a weapon material is recognized in the two tiers of safeguards and physical protection measures applied to enriched uranium. Less stringent standards are applied when enrichment levels fall below 20 per cent. In contrast, a single set of regulations is applied to plutonium since it can be used in nuclear weapons in most available isotopic mixes.

The corollary is that none of today’s thermal power reactor designs require HEU fuels. The HEU-fuelled high-temperature reactor (HTR), prototypes of which were built in the Federal Republic of Germany (FRG) and the USA, is in abeyance. HEU is only used in submarine reactors, in a small number of breeder reactors and in a few large research reactors. Since the mid-1970s, many research reactors around the world have been converted to operate with uranium enriched to levels below 20 per cent. In France and the former Soviet Union, some submarine reactors have also been designed so that they can be fuelled with LEU.

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Highly enriched uranium (HEU):

The important fissile material that has been used for nuclear weapons is highly enriched uranium (HEU), usually defined as uranium whose proportion of uranium-235, the fissile isotope of uranium, has been increased to over 20%. In reality, nearly all HEU is 90% or higher. The natural uranium mined from the earth consists of about 0.7% uranium-235 (U-235), and about 99.3% uranium-238 (U-238), and enrichment is the process of increasing the ratio of U-235 to U-238. The half life of uranium-235 is 704 million years, while the half life of U-238 is about 4.5 billion years. It is important to note that most nuclear reactors run on low-enriched uranium (LEU), which is usually 3%-5% uranium-235. LEU cannot be used in nuclear weapons. HEU produced for weapons (“weapon-grade” uranium) is typically enriched to 90 percent uranium-235 or greater, but all HEU can be used to make nuclear weapons. Fission of a kilogram of uranium-235 can produce an explosion equivalent to 17,000 tons of TNT. In a conventional nuclear reactor, one kilogram of U-235 can produce sufficient heat to generate nearly 24 million kilowatt-hours of electricity.

Australia is estimated to have the largest uranium reserves, followed by Kazakhstan, Canada, and Russia. Traditionally, uranium has been extracted from underground and open pit mines. This natural uranium is processed and then enriched. Numerous technologies have been developed to enrich uranium, such as gaseous-diffusion, centrifuges, and electromagnetic separation. All of these technologies require a large initial investment and large amounts of energy to operate. Enriching uranium is both technically difficult and expensive, as it requires separating isotopes that have very similar chemical and physical properties. The enrichment process is thus the main barrier to producing uranium suitable for use in nuclear weapons. The difficulty and expense of the enrichment process has an important consequence: HEU can be diluted with natural uranium to produce LEU, effectively eliminating the risk that it could be used to make a nuclear weapon.

HEU was first developed for use in nuclear weapons. It can be combined with plutonium to form the “pit”, or core of a nuclear weapon, or it can be used alone as the nuclear explosive. The bomb dropped on Hiroshima used only HEU. About 15-20 kgs of HEU are sufficient to make a bomb without plutonium.

HEU also has non-weapon uses. It is used as a fuel in research reactors and the nuclear reactors that power some naval vessels.

HEU can, in theory, be produced in any enrichment plant. Several countries operate enrichment plants to produce LEU for nuclear reactors, but not all of these countries have used their plants to make highly enriched uranium. The International Atomic Energy Agency, a United Nations agency, is charged with ensuring that uranium from civilian nuclear programs is not diverted to weapons-purposes only in non-nuclear weapon states who are signatories to the Non-Proliferation Treaty.

As of 2023, the global stockpile of unirradiated highly enriched uranium (HEU) was estimated to be about 1245 metric tons. Most of this material – about 1,100 metric tons – is in weapons or available for use in weapon programs.

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HEU Production:

In order to use uranium in nuclear weapons or a fuel in nuclear reactors it is necessary to increase the concentration of uranium 235. This process is known as “enrichment.” The 1.27% difference in mass between U-235 and U-238 allows the isotopes to be separated and makes it possible to increase or “enrich” the percentage of U-235. All present and historic enrichment processes, directly or indirectly, make use of this small mass difference. One tonne of natural uranium feed might end up: as 120-130 kg of uranium for power reactor fuel, as 26 kg of typical research reactor fuel, or conceivably as 5.6 kg of weapons-grade material. There are several techniques that can be employed to enrich uranium. Three basic types of uranium enrichment are depicted in the figure below.

Uranium enrichment is the process of concentrating or increasing the fraction of the 235U isotope, compared with the 238U isotope. Different methods can be used to increase the isotopic proportion of U-235. Yellowcake is a powdered uranium concentrate that is produced during the processing of uranium ore. Yellowcake is created by crushing uranium ore in a mill and then chemically treating it to remove the uranium. The uranium is then concentrated into a yellow-colored powder. The color of yellowcake can vary from yellow to orange to dark green depending on the drying temperature. Typically, the yellow cake is converted into a gaseous form, called uranium hexafluoride. This gas is then pumped into fast spinning cylinders — centrifuges — where heavier isotopes, such as U-238, are pushed towards the walls of the cylinders, and the lighter U-235 stays in the centre of the cylinders. When the rotors are spun rapidly, at 50,000 to 70,000 rpm, the heavier molecules with U-238 increase in concentration towards the cylinder’s outer edge. There is a corresponding increase in concentration of U-235 molecules near the centre. This enables to “filter out” and collect the gas with higher concentrations of U-235. The process can be repeated until the isotopic proportion of U-235 is sufficient. The acquired gas then goes through a process of re-conversion, which enables it to turn U-235 into the form of black power — uranium dioxide. When converting uranium hexafluoride to metal, 0.3% is lost during manufacturing. European centrifuges produce 40-100 SWU/yr. All major commercial civil enrichment facilities today employ some form of gas centrifuge to achieve isotope separation (i.e., enrichment) of 235U from 238U. The degree of separation achieved by a single machine is small, so the process needs to be repeated hundreds of times to achieve 235U concentrations in final product up to 5% assay required for typical nuclear power plants. In industrial facilities, many machines are connected in series and in parallel trains to achieve the required enrichment of uranium hexafluoride feedstock in tonne quantities.

Gaseous diffusion exploits the property of gases whereby heavy molecules travel more slowly than light molecules. If parts of the vessel containing the gas are made permeable, in the form of a barrier, the lighter molecules will pass through the diffusion barrier more rapidly, causing escaping gas to be enriched in the lighter components. Thus, the uranium hexafluoride gas emanating at the end of the diffusion stage will be slightly enriched in the isotope uranium 235. The final degree of enrichment attained depends on the number of stages hooked together by pipes in a “cascade,” and on the enrichment of the initial feed.

Aerodynamic enrichment has two variants. The Becker jet nozzle, developed in the Federal Republic of Germany and Brazil, exploits the mass dependence of the centrifugal force in a fast, curved flow of uranium hexafluoride. The gas expands into a curved duct and the flow is split into heavier and lighter fractions by means of a skimmer. In the South African process uranium hexafluoride is allowed to swirl in a separating element that acts as a stationary-walled centrifuge. Neither aerodynamic technique has been shown to be commercially viable.

Electromagnetic separation was used to produce HEU for the first U.S. atomic weapon and was also applied in Iraq. In a device originally called a calutron, heavy and light uranium ions (atoms carrying electrical charges) follow trajectories with different curvatures in a strong magnetic field.

There has been speculation since the early 1970s that laser enrichment will provide the basis for the next generation of enrichment plants. In this process, high-energy lasers can selectively excite the isotopes of uranium. Two routes can be taken. In the first, the atomic route, uranium 235 is selectively excited using tunable lasers, and the resulting ionized atoms are separated electromagnetically. In the second process, the molecular route, selective infrared absorption of uranium 235 hexafluoride gas is followed by further irradiation at infrared or ultraviolet frequencies, allowing dissociation of the excited molecules or their chemical separation.

Two other enrichment techniques are in the research and development stage. The first is the plasma separation process. The second is called the chemical exchange process. Pilot plants employing chemical processes have been built in France and Japan.

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Enrichment capacity:

Uranium enrichment is strategically sensitive and capital intensive, creating significant barriers to entry for any new supplier. Hence, there are relatively few commercial enrichment suppliers operating a limited number of facilities worldwide. There are three major producers at present: Orano, Rosatom, and Urenco operating large commercial enrichment plants in France, Germany, Netherlands, UK, USA, and Russia. CNNC is a major domestic supplier and is pursuing export sales. In Japan and Brazil, domestic fuel cycle companies manage modest supply capability. Elsewhere, small non-safeguarded facilities are subject to international opposition.

World enrichment capacity – operational in 2020 and planned:

Operator	Capacity (thousand SWU/yr)
Operator	2020	2025	2030
CNNC	6300	11,000	17,000
Orano	7500	7500	7500
Rosatom	27,700	26,200	24,800
Urenco	18,600	17,300	16,300
Other	66	375	525
Total	60,166	62,375	66,125

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Uranium Enrichment and Separative Work Unit:

Naturally occurring uranium comprises about 99.29% of the isotope 238U (146 neutrons, 92 protons) and 0.71% of the isotope 235U (143 neutrons, 92 protons). 238U is mildly radioactive, undergoing alpha decay to 234Th, but it is not fissile, that is, it cannot be used on its own to sustain a nuclear chain reaction. 235U, on the other hand, is a less stable isotope that undergoes fission when a thermal neutron collides with the nucleus. More neutrons are emitted and, in the right quantity and concentration, 235U is capable of sustaining a nuclear chain reaction; for example, as is required for a power generating nuclear reactor.

Uranium enrichment is the name given to any isotope separation process applied to natural uranium resulting in a product in which the concentration of 235U is increased above the natural concentration of 0.71%. The capacity of any equipment or installation to enrich uranium in measured in separative work units (SWUs).

The Separative Work Unit (SWU) is a unit that defines the effort required in the uranium enrichment process, in which uranium-235 and -238 are separated. Separative work performed to enrich uranium is defined by a mathematical formula, but in essence it is a measure of work performed by a process to take a quantity of feed material at a certain 235U concentration and convert it into a quantity of enriched product with a higher 235U concentration and a balancing quantity of depleted “tails” with a lower 235U concentration.

The separative work in an enrichment plant indicates the energy expended in separating the uranium feed into enriched product and depleted uranium waste, commonly called the tails. The tails assay is the concentration of 235U left in this waste. The unit of measurement is the kilogram separative work unit (kg SWU, usually abbreviated to SWU). The capacities of enrichment plants are expressed in SWU per year. It takes approximately 200 SWU to make 1 kg of weapon grade uranium (uranium enriched to 90 per cent) using natural uranium feed and a tails assay of 0.3 per cent.

An example is shown in figure below where the feed is 0.71% 235U, enriched product is 4% 235U, and depleted tails are 0.3% 235U.

Precise calculation of SWUs involves differential equations.

The isotope-separation work required to produce an enriched product depends on the tails assay of the depleted uranium streams but is independent of the method of separation used. It is usually measured in kilogram separative work units (SWUs). Thus, for example, to produce 1 kg of 90% uranium starting from natural uranium and with a tails assay of 0.2% requires 225 SWU and 180 kg of natural uranium (see table below). To put this in perspective, the kind of centrifuges that the Iraqis were assembling in 1990 each had a capacity of approximately 1 SWU per year. Thus, to produce one critical mass per year, for example, 25 kg of 90% uranium, would require more than 5000 centrifuges.

Uranium Enrichment Requirements for 0.2% tails assay:

Feed enrichment	Product (1 kg)	Uranium feed (kg)	SWUs
Natural U	Weapon-grade U (90%)	180	225
Natural U	4% U	7.6	6.6
Natural U	8% U	15.6	17
4% U	Weapon-grade U	23.6	72
8% U	Weapon-grade U	11.3	38

In addition to the separative work units provided by an enrichment facility, the other important parameter to be considered is the mass of natural uranium (NU) that is needed to yield a desired mass of enriched uranium. As with the number of SWUs, the amount of feed material required will also depend on the level of enrichment desired and upon the amount of 235U that ends up in the depleted uranium. However, unlike the number of SWUs required during enrichment, which increases with decreasing levels of 235U in the depleted stream, the amount of NU needed will decrease with decreasing levels of 235U that end up in the DU.

For example, in the enrichment of LEU for use in a light water reactor it is typical for the enriched stream to contain 3.6% 235U (as compared to 0.7% in NU) while the depleted stream contains 0.2% to 0.3% 235U. In order to produce one kilogram of this LEU it would require approximately 8 kilograms of NU and 4.5 SWU if the DU stream was allowed to have 0.3% 235U. On the other hand, if the depleted stream had only 0.2% 235U, then it would require just 6.7 kilograms of NU, but nearly 5.7 SWU of enrichment. Because the amount of NU required and the number of SWUs required during enrichment change in opposite directions, if NU is cheap and enrichment services are more expensive, then the operators will typically choose to allow more 235U to be left in the DU stream whereas if NU is more expensive and enrichment is less so, then they would choose the opposite.

A typical large nuclear power plant with an electrical output of 1300 MW requires about 25 t pa of enriched uranium with 235U concentration of 4%. This is produced from about 210 t of natural uranium feed using about 120 tSWU. An enrichment facility with a capacity of 1000 tSWU pa is therefore able to enrich uranium sufficient to fuel about eight large nuclear power plants.

Note: t = ton and pa = per annum

Other nuclear materials can be used as fuel for power reactors, specifically plutonium mixed with uranium known as mixed oxide (MOX) fuel and thorium. Use of MOX is factored into the uranium enrichment demand forecasts. Thorium is not yet used routinely.

Uranium from thorium:

Thorium can be used as a nuclear fuel. Although not fissile itself, Th-232 will absorb slow neutrons to produce uranium-233 (U-233), which is fissile (and long-lived). The irradiated fuel can then be unloaded from the reactor, the U-233 separated from the thorium, and fed back into another reactor as part of a closed fuel cycle. Alternatively, thorium can be incorporated into the fuel salt of a molten salt reactor (MSR) and the U-233 burned as it is bred.

U-233 has higher neutron yield per neutron absorbed than U-235 or Pu-239. Given a start with some other fissile material (U-233, U-235 or Pu-239) as a driver, a breeding cycle similar to but more efficient than that with U-238 and plutonium (in conventional thermal neutron reactors) can be set up. U-233 has a 95% probability of fission when struck by a neutron of any energy level (a higher probability than Pu-239), though some U-234 is formed. The driver fuels provide all the neutrons initially, but are progressively supplemented by U-233 as it forms from the thorium. However, the intermediate product protactinium-233 (Pa-233) is a neutron absorber which diminishes U-233 yield.

Thorium-based nuclear power generation is fueled primarily by the nuclear fission of the isotope uranium-233 produced from the fertile element thorium. A thorium fuel cycle can offer several potential advantages over a uranium fuel cycle—including the much greater abundance of thorium found on Earth, superior physical and nuclear fuel properties, and reduced nuclear waste production. One advantage of thorium fuel is its low weaponization potential. It is difficult to weaponize the uranium-233 that is bred in the reactor. Plutonium-239 is produced at much lower levels and can be consumed in thorium reactors. Several uranium-233 bombs have been tested, but the presence of uranium-232 tended to “poison” the uranium-233 in two ways: intense radiation from the uranium-232 made the material difficult to handle, and the uranium-232 led to possible pre-detonation. Separating the uranium-232 from the uranium-233 proved very difficult, although newer laser isotope separation techniques could facilitate that process. The world’s thorium reserves are estimated to be around 12 million tons, with the largest resources found in India.

Tails re-enrichment:

In most commercial enrichment contracts, the customer agrees to supply the enricher with a given quantity of feed material in return for a given quantity of enriched product and pays for the services provided by the enricher. The tails arising from the enrichment performed are owned by the enricher. The enrichment contract will specify the tails assay, quite typically in the range 0.2–0.3% 235U. Clearly the tails still contain residual 235U and it is possible to use such tails as feedstock in a further enrichment cycle, producing additional enriched product and “tails of the tails” or “secondary tails.” The economics of tails re-enrichment depend, among other factors, on the price of natural uranium feedstock, the price of enrichment services, and the marginal costs of operating enrichment facilities. However, in the case of any surplus of enrichment capacity, there are drivers to devote some enrichment capacity to the re-enrichment of tails to regenerate natural uranium feedstock or additional enriched product for sale.

An alternative to re-enriching tails is a mode of operating enrichment plants known as “underfeeding.” In this mode, an enricher can choose to use more SWU than specified in the contact to provide the required quantity of enriched product to the customer, but strip the tails to a lower assay than specified in the contract and thereby consume less feedstock than is provided by the contract. The saved feedstock is then owned by the enricher and can be sold on the market.

Underfeeding and tails re-enrichment are somewhat interchangeable in terms of their utilization of enrichment capacity and both are labeled tails re-enrichment in assessing demand/supply balance. Because it is desirable to keep capital intensive gas centrifuge plants in continuous operation, enrichers tend to underfeed/re-enrich tails at times when demand for primary enrichment is suppressed, such as the post-Fukushima period.

In the case that natural uranium was cheap compared to enrichment services, based on economics, enrichers could choose to “overfeed” plants. This involves enrichers acquiring additional feedstock, compared to that supplied in a contract, and using less SWU than specified in the contract to provide the customer with the required quantity of enriched product. Overfeeding has only been undertaken when uranium is cheap and/or enrichment capacity is in short supply compared to demand, or if, as with gas diffusion in the past, the enrichment process is expensive to operate.

Depleted uranium (DU):

Centrifuges produce uranium that contains a higher isotopic proportion of U-235. That also means, that the remaining material contains less of this isotope. If such a byproduct of enrichment has an isotopic proportion of U-235 below 0.7 per cent, it is considered depleted. Every tonne of natural uranium produced and enriched for use in a nuclear reactor gives about 130 kg of enriched fuel (3.5% or more U-235). The balance is depleted uranium tails (U-238, typically with 0.22% U-235 if from Western enrichment plants, 0.10% from Russian ones). This major portion has been depleted in its fissile U-235 isotope (and, incidentally, U-234) by the enrichment process. It is commonly known as DU if the focus is on the actual material, or enrichment tails if the focus is on its place in the fuel cycle and its U-235 assay. DU is less radioactive than natural uranium because it has less U-235 per unit of mass. All traces of decay products have been removed during the chemical purification of uranium prior to enrichment. DU can be disposed of as low-level radioactive waste or used in the fabrication of mixed oxide fuels (MOX) with separated plutonium stemming from the reprocessing of spent nuclear fuels. Depleted uranium (DU) can be used for armour, kinetic energy penetrators, radiation shielding and ballast. The world has about 1.2 million metric tons of depleted uranium (DU) in storage. The majority of this is stored in the United States and Russia, and is in the form of depleted uranium hexafluoride (DUF6) but can be deconverted back to U3O8, which is more benign chemically and thus more suited for long-term storage. It is also less chemically toxic.

The distinction between LEU and HEU at 20 wt% 235U is arbitrary. It is a conservative value that suggests that LEU is adequate for nuclear reactor fuel but is wholly inadequate for nuclear weapons production. Weapons grade uranium is generally considered >90 wt% 235U, but enrichment levels lower than this value can be weaponized. As the enrichment level is decreased, more uranium is needed for criticality. At some point these diminishing effects mean that too much uranium is needed for a practical weapon. Therefore, in a very conservative manner LEU is considered a non-weaponizable material. Consequently, the security requirements for handling LEU are much less than those for HEU. And NU and DU are of no concern in this regard and have no special security requirements. The LEU cannot be used for weapons but the use of even LEU raises two proliferation concerns: The enrichment facilities used to produce the low-enriched fuel can be used to produce HEU, and if the low-enriched fuel is used as input to an enrichment cascade, the quantity of work required to produce HEU would be much reduced.

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Plutonium:

Plutonium is a radioactive metallic element with the atomic number 94. It was discovered in 1940 by scientists studying how to split atoms to make atomic bombs. Plutonium (94Pu) is an artificial element, except for trace quantities resulting from neutron capture by natural uranium. Plutonium is created in a reactor when uranium atoms absorb neutrons. Nearly all plutonium is man-made. Plutonium predominantly emits alpha particles – a type of radiation that is easily stopped and has a short range. It also emits neutrons, beta particles and gamma rays. It is considered toxic, in part, because if it were to be inhaled it could deposit in the lungs and eventually cause damage. ‘There are five “common” isotopes of plutonium, Pu-238, Pu-239, Pu-240, Pu-241, and Pu-242. 239Pu and 241Pu are fissile; meaning their nuclei can split by being bombarded by slow thermal neutrons, releasing energy, gamma radiation and more neutrons. It can therefore sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. The different isotopes have different “half-lives” – the time it takes to lose half of its radioactivity. Pu-239 has a half-life of 24,100 years and Pu-241’s half-life is 14.4 years. Substances with shorter half-lives decay more quickly than those with longer half-lives, so they emit more energetic radioactivity. Like any radioactive isotopes, plutonium isotopes transform when they decay. They might become different plutonium isotopes or different elements, such as uranium or neptunium. Many of these “daughter products” are themselves radioactive. There are several tonnes of plutonium in our biosphere, a legacy of atmospheric weapons testing in the 1950s and 1960s.

If you take U-238, which makes up the overwhelming fraction of natural uranium and bombard it with neutrons, some nuclei will absorb a neutron, transforming them into U-239 (a nucleus with the same 92 protons as U-238 but an additional neutron). But this nucleus has too many neutrons to be stable, and decays with a half-life of 23.5 minutes by beta decay: the emission of a beta particle (electron), transforming one of the neutrons in the nucleus to a proton, which transmutes the U-239 into element 93, Neptunium, yielding the isotope Np-239. Np-239, while more stable than U-239, remains unstable and with a half-life of 2.36 days, also undergoes beta decay, resulting in Pu-239 which, with its half-life of 24,000 years, can be considered as stable on the human time scale. Plutonium is a radioactive actinide metal whose isotope, plutonium-239, is one of the three primary fissile isotopes (uranium-233 and uranium-235 are the other two); plutonium-241 is also highly fissile. To be considered fissile, an isotope’s atomic nucleus must be able to break apart or fission when struck by a slow moving neutron and to release enough additional neutrons to sustain the nuclear chain reaction by splitting further nuclei.

Pure plutonium-239 may have a multiplication factor (keff) larger than one, which means that if the metal is present in sufficient quantity and with an appropriate geometry (e.g., a sphere of sufficient size), it can form a critical mass. Keff is the ratio of the number of neutrons resulting from fission in each generation to the total number lost by both absorption and leakage in the preceding generation. During fission, a fraction of the nuclear binding energy, which holds a nucleus together, is released as a large amount of electromagnetic and kinetic energy (much of the latter being quickly converted to thermal energy). Fission of a kilogram of plutonium-239 can produce an explosion equivalent to 19,000 tons of TNT (82,000 GJ). It is this energy that makes plutonium-239 useful in nuclear weapons and reactors.

The presence of the isotope plutonium-240 in a sample limits its nuclear bomb potential, as 240Pu has a relatively high spontaneous fission rate (~440 fissions per second per gram; over 1,000 neutrons per second per gram), raising the background neutron levels and thus increasing the risk of predetonation. Plutonium is identified as either weapons-grade, fuel-grade, or reactor-grade based on the percentage of 240Pu that it contains. Weapons-grade plutonium contains less than 7% 240Pu. Fuel-grade plutonium contains 7%–19%, and power reactor-grade contains 19% or more 240Pu. Plutonium-238 is not fissile but can undergo nuclear fission easily with fast neutrons as well as alpha decay. All plutonium isotopes can be “bred” into fissile material with one or more neutron absorptions, whether followed by beta decay or not. This makes non-fissile isotopes of plutonium a fertile material.

Over one-third of the energy produced in most nuclear power plants comes from plutonium. It is created in the reactor as a by-product. Plutonium is formed in nuclear power reactors from uranium-238 by neutron capture.
Plutonium recovered from reprocessing normal reactor fuel is recycled as mixed-oxide fuel (MOX).
Plutonium is the principal fuel in a fast neutron reactor, and in any reactor it is progressively bred from non-fissile U-238 that comprises over 99% of natural uranium.
Plutonium-238 is a vital power source for deep space missions.

In practical terms, there are two different kinds of plutonium to be considered: reactor-grade and weapons-grade. The first is recovered as a by-product of typical used fuel from a nuclear reactor, after the fuel has been irradiated (‘burned’) for about three years. The second is made specially for the military purpose, and is recovered from uranium fuel that has been irradiated for only 2-3 months in a plutonium production reactor. The two kinds differ in their isotopic composition but must both be regarded as a potential proliferation risk, and managed accordingly.

Plutonium, both that routinely made in power reactors and that from dismantled nuclear weapons, is a valuable energy source when integrated into the nuclear fuel cycle. In a conventional nuclear reactor, one kilogram of Pu-239 can produce sufficient heat to generate nearly 8 million kilowatt-hours of electricity.

Different uses have been found for plutonium. Plutonium-238 has been used to power batteries for some heart pacemakers, as well as provide a long-lived heat source to power NASA space missions. Like uranium, plutonium can also be used to fuel nuclear power plants. Today’s light water reactors – used to make commercial power – create plutonium when the uranium in their fuel fissions. Some of the neutrons released by uranium interact with other uranium atoms to form plutonium. Some of the plutonium itself fissions – part of the chain reaction of splitting atoms that is the basis of nuclear power. Any plutonium that does not fission stays in the spent fuel. Spent nuclear fuel from reactors contains about 1 percent plutonium by weight. When operating, a typical 1000 MWe nuclear power reactor contains within its uranium fuel load several hundred kilograms of plutonium.

Figure below shows reaction in standard UO2 fuel:

There are many metric tons of plutonium in spent nuclear fuel stored around the world. To be usable, plutonium would need to be separated from the other products in spent fuel. This process, known as reprocessing, uses chemicals to separate plutonium from uranium and other fission products. Once separated, plutonium oxide can be mixed with uranium oxide to produce mixed oxide or MOX fuel. MOX fuel can be used in power reactors. Reprocessing is controversial internationally, because the plutonium can also be used to make nuclear weapons.

Like all other heavy elements, plutonium has a number of isotopes, differing in the number of neutrons in the nucleus. All 15 plutonium isotopes are radioactive, because they are to some degree unstable and therefore decay, emitting particles and some gamma radiation as they do so. All plutonium isotopes are fissionable with fast neutrons, though only two are fissile (with slow neutrons). For this reason all are significant in a fast neutron reactor (FNR), but only one – Pu-239 – has a major role in a conventional light water power reactor. Each fission yields a little over 200 MeV, or about 82 TJ/kg.

The most common plutonium isotope formed in a typical nuclear reactor is the fissile Pu-239, formed by neutron capture from U-238 (followed by beta decay), and which when fissioned yields much the same energy as the fission of U-235. Well over half of the plutonium created in the reactor core is ‘burned’ in situ and is responsible for about one-third of the total heat output of a light water reactor (LWR) and about 60% of the heat in a pressurized heavy water reactor (PHWR) such as CANDU. Of the rest in the LWR, about one-third through neutron capture becomes Pu-240 (and Pu-241). In a fast reactor this proportion is much less.

Plutonium-240 is the second most common isotope, formed by neutron capture by Pu-239 in about one-third of impacts. Its concentration in nuclear fuel builds up steadily, since it does not undergo fission to produce energy in the same way as Pu-239. (In a fast neutron reactor it is fissionable, which means that such a reactor can utilize recycled plutonium more effectively than a LWR.) While of a different order of magnitude to the fission occurring within a nuclear reactor, Pu-240 has a relatively high rate of spontaneous fission with consequent neutron emissions. This makes reactor-grade plutonium entirely unsuitable for use in a bomb. Reactor-grade plutonium is defined as that with 19% or more of Pu-240. This is also called ‘civil plutonium’.

Plutonium-238, Pu-240 and Pu-242 emit neutrons as a few of their nuclei spontaneously fission, albeit at a low rate. They and Pu-239 also decay, emitting alpha particles and heat.

A 1000 MWe light water reactor gives rise to about 25 tonnes of used fuel a year, containing up to 290 kilograms of plutonium. If the plutonium is extracted from used reactor fuel it can be used as a direct substitute for U-235 in the usual fuel, the Pu-239 being the main fissile part, but Pu-241 also contributing. In order to extract it for recycle, the used fuel is reprocessed and the recovered plutonium oxide is mixed with depleted uranium oxide to produce mixed oxide (MOX) fuel, with about 8% Pu-239 (this corresponds with uranium enriched to 5% U-235).

Plutonium can also be used in fast neutron reactors, where a much higher proportion of Pu-239 fissions and in fact all the plutonium isotopes fission, and so function as a fuel. As with uranium, the energy potential of plutonium is more fully realized in a fast reactor. Four of the six ‘Generation IV’ reactor designs currently under development are fast neutron reactors and will thus utilize plutonium in some way. In these, plutonium production will take place in the core, where burn-up is high and the proportion of plutonium isotopes other than Pu-239 will remain high.

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Plutonium-239:

Plutonium-239 (hereafter referred to as “plutonium”) is a heavy element consisting of 94 protons and 145 neutrons. It can have a number of chemical forms. Nuclear weapons use plutonium metal. Plutonium dioxide is used as a component of some nuclear fuels. Plutonium has a half-life of over 24,000 years (a half-life is the time it takes for half of a given amount of radioactive material to decay into other elements).

Two key facilities are needed to obtain plutonium. First, in a nuclear reactor, uranium-238 absorbs a neutron. This leads to nuclear reactions which convert it to plutonium. The plutonium ends up in the spent nuclear fuel along with unused uranium and highly radioactive fission products. Essentially all nuclear reactors in the world produce plutonium in this way, but plutonium in spent fuel is not usable for nuclear energy or nuclear weapons. To get plutonium into a usable form, a second key facility, a reprocessing plant, is needed to chemically separate out the plutonium from the other materials in spent fuel. Reprocessing is generally regarded as one of the key links between civilian nuclear power capability and nuclear weapons production capability (the other is uranium enrichment).

Countries producing plutonium for weapons have generally operated their reactors to maximize the production of plutonium-239—the isotope most useful for nuclear weapons—and to minimize the production of other plutonium isotopes such as plutonium-240. Weapon-grade plutonium contains less than 7 percent plutonium-240. Under normal nuclear power plant operation, the plutonium in spent reactor fuel contains roughly 24 percent plutonium-240; such plutonium is often referred to as “reactor-grade.” However, essentially all isotopic mixtures of plutonium—including reactor-grade plutonium—can be used for nuclear weapons.

In order to use plutonium in nuclear weapons or nuclear fuel, however, it must be separated from the rest of the spent fuel in a reprocessing facility. Plutonium separation is easier than uranium enrichment because it involves separating different elements rather than different isotopes of the same element, and it uses well known chemical separation techniques. However, since the spent fuel is highly radioactive, this process requires heavily shielded facilities with remote-handling equipment.

Relatively large amounts of plutonium-240, as would be contained in reactor-grade plutonium, can cause a weapon to detonate early and “fizzle,” causing a smaller explosion than intended. However, even a weapon that fizzles would cause an explosion roughly equivalent to 1,000 tons (1 kiloton) of TNT. A weapon of this size could kill tens of thousands of people if detonated in a city, which clearly demonstrates that even reactor-grade plutonium would present a potent danger.

Once plutonium is separated, it can be processed and fashioned into the fission core of a nuclear weapon, called a “pit”. Nuclear weapons typically require three to five kilograms of plutonium239.

Plutonium can also be converted into an oxide and mixed with uranium dioxide to form mixed-oxide (MOX) fuel for nuclear reactors. While MOX fuel itself is unlikely to be used to make nuclear weapons, the plutonium can be separated from the uranium by a straightforward chemical process. Moreover, MOX does not contain the highly radioactive components that make spent fuel difficult and dangerous to reprocess. As a result, MOX is as a proliferation concern as plutonium itself.

As of 2023, the global stockpile of separated plutonium was about 560 tons. Of this material, 420 metric tons were produced outside of weapon programs, covered by obligations not to use it in weapons, or not directly suitable for weapons. This leaves about 140 metric tons of plutonium in weapons or available for weapons. The countries with the largest civilian inventories of separated plutonium are the United Kingdom, France, India, Japan, Russia, and the United States.

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Plutonium applications:

Explosives:

239Pu is a key fissile component in nuclear weapons, due to its ease of fission and availability. Encasing the bomb’s plutonium pit in a tamper (a layer of dense material) decreases the critical mass by reflecting escaping neutrons back into the plutonium core. This reduces the critical mass from 16 kg to 10 kg, which is a sphere with a diameter of about 10 centimeters (4 in). This critical mass is about a third of that for uranium-235.

The Fat Man plutonium bombs used explosive compression of plutonium to obtain significantly higher density than normal, combined with a central neutron source to begin the reaction and increase efficiency. Thus only 6 kg of plutonium was needed for an explosive yield equivalent to 20 kilotons of TNT. Hypothetically, as little as 4 kg of plutonium—and maybe even less—could be used to make a single atomic bomb using very sophisticated assembly designs.

Mixed oxide fuel:

Spent nuclear fuel from normal light water reactors contains plutonium, but it is a mixture of plutonium-242, 240, 239 and 238. The mixture is not sufficiently enriched for efficient nuclear weapons, but can be used once as MOX fuel. Accidental neutron capture causes the amount of plutonium-242 and 240 to grow each time the plutonium is irradiated in a reactor with low-speed “thermal” neutrons, so that after the second cycle, the plutonium can only be consumed by fast neutron reactors. If fast neutron reactors are not available (the normal case), excess plutonium is usually discarded, and forms one of the longest-lived components of nuclear waste. The desire to consume this plutonium and other transuranic fuels and reduce the radiotoxicity of the waste is the usual reason nuclear engineers give to make fast neutron reactors.

The most common chemical process, PUREX (Plutonium–URanium EXtraction), reprocesses spent nuclear fuel to extract plutonium and uranium which can be used to form a mixed oxide (MOX) fuel for reuse in nuclear reactors. Weapons-grade plutonium can be added to the fuel mix. MOX fuel is used in light water reactors and consists of 60 kg of plutonium per tonne of fuel; after four years, three-quarters of the plutonium is burned (turned into other elements). MOX fuel has been in use since the 1980s, and is widely used in Europe. Breeder reactors are specifically designed to create more fissionable material than they consume.

Plutonium recovered from spent reactor fuel poses little proliferation hazard, because of excessive contamination with non-fissile plutonium-240 and plutonium-242. Separation of the isotopes is not feasible. A dedicated reactor operating on very low burnup (hence minimal exposure of newly formed plutonium-239 to additional neutrons which causes it to be transformed to heavier isotopes of plutonium) is generally required to produce material suitable for use in efficient nuclear weapons. While “weapons-grade” plutonium is defined to contain at least 92% plutonium-239 (of the total plutonium), the United States have managed to detonate an under-20Kt device using plutonium believed to contain only about 85% plutonium-239, so called ‘”fuel-grade” plutonium. The “reactor-grade” plutonium produced by a regular LWR burnup cycle typically contains less than 60% Pu-239, with up to 30% parasitic Pu-240/Pu-242, and 10–15% fissile Pu-241. It is unknown if a device using plutonium obtained from reprocessed civil nuclear waste can be detonated, however such a device could hypothetically fizzle and spread radioactive materials over a large urban area. The International Atomic Energy Agency (IAEA) is conservative on this matter so that, for the purpose of applying IAEA safeguards measures, all plutonium (other than plutonium comprising 80% or more of the isotope Pu-238) is defined by the IAEA as a ‘direct-use’ material, that is, “nuclear material that can be used for the manufacture of nuclear explosives components without transmutation or further enrichment”. The ‘direct use’ definition applies also to plutonium which has been incorporated into commercial MOX fuel, which as such certainly could not be made to explode.

Power and heat source:

Plutonium-238 has a half-life of 87.74 years. It emits a large amount of thermal energy with low levels of both gamma rays/photons and neutrons. Being an alpha emitter, it combines high energy radiation with low penetration and thereby requires minimal shielding. A sheet of paper can be used to shield against the alpha particles from 238Pu. One kilogram of the isotope generates about 570 watts of heat. These characteristics make it well-suited for electrical power generation for devices that must function without direct maintenance for timescales approximating a human lifetime. It is therefore used in radioisotope thermoelectric generators and radioisotope heater units such as those in the Cassini, Voyager, Galileo and New Horizons space probes, and the Curiosity and Perseverance (Mars 2020) Mars rovers.

Plutonium and americium:

Civil plutonium stored over several years becomes contaminated with the Pu-241 decay product americium-241, which interferes with normal fuel fabrication procedures. After long storage, Am-241 must be removed before the plutonium can be used in a MOX fuel fabrication plant because it emits intense gamma radiation (in the course of its alpha decay to Np-237). Americium-241 from plutonium stockpile is used for 10-watt (e) radioisotope thermoelectric generators (RTGs), as the isotope is much less expensive than Pu-238 (now scarce).

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Plutonium Production:

The production of plutonium is carried out in two main industrial stages. The first involves the irradiation of uranium fuels by neutrons in nuclear reactors. The second involves the chemical separation of plutonium from the uranium, transuranic elements and fission products contained in discharges of irradiated fuel. The second techniques is usually referred to as “reprocessing” when applied commercially and “plutonium separation” when carried out for military purposes.

Irradiation of Reactor Fuel:

Although they can overlap, plutonium is produced in two different contexts. In the military context, the reason for irradiating nuclear fuel is to acquire stocks of weapon-grade material for use in nuclear warheads; plutonium supply is the raison d’être, and typically dedicated “production reactors” are used to make weapon-grade plutonium. In the civilian context, the purpose is to generate electricity, plutonium being a by-product which may or may not have further uses. The power reactor is typically optimized for electricity production. The isotopic content of discharged plutonium is a serious concern of nuclear weapon designers, but is less important to electricity producers.

As distinct from the production of uranium with high concentrations of uranium 235, the technique of isotopic enrichment has not been used to produce weapon-grade plutonium from lower-grade material. Research was carried out in the 1960s in the United States and the Soviet Union using calutrons (and centrifuges) to separate the plutonium isotopes. More substantial research and development programs were launched in the 1980s to develop laser techniques for enriching plutonium by these means. These plans came to naught because of the reduced demand for weapon-grade plutonium as weapon programs were curtailed.

Instead, the nuclear weapons producers have achieved the desired isotopic content of plutonium mainly by controlling the extent to which uranium fuel elements are irradiated with neutrons in nuclear reactors. This is known as the fuel burn-up, whose unit of measurement is megawatt-days per ton (MWd/t) of uranium fuel. Weapon-grade plutonium is produced by operating reactors at low burnup–400 MWd/t is typical–so that insufficient time elapses for a substantial build-up of plutonium 240 and other plutonium isotopes.

Civil power reactors are operated at higher burnups in order to optimize the energy output from a given amount of fissile material. Power reactors fueled with natural uranium, such as the gas-cooled, graphite-moderated reactor developed in Britain and France, and the Canadian deuterium-uranium (CANDU) reactor, have burnups in the range 3,000-8,000 MWd/t. The most common type of thermal power reactor, the pressurized water reactor (PWR) which is fueled with low-enriched uranium, is typically operated at 30,000-40,000 MWd/t. The concentrations of the even-numbered isotopes become substantial at these burnups. It should also be noted that the concentrations of total fissile plutonium (plutonium 239 plus plutonium 241) are not dissimilar for these reactor types, but that PWR fuel contains relatively low concentrations of plutonium 239 and high concentrations of plutonium 241.

The trend is towards still higher burnups, with many utilities aiming for 50,000-60,000 MWd/t for light water reactor (LWR) fuel in the coming decade. As the irradiation period is extended, the energy extracted from the fissioning of plutonium 239 and plutonium 241 increases as that from uranium 235 decreases. In effect, a high burnup strategy is a cheap and energy-efficient substitute for recycling plutonium from lower burnup fuels. These high burnup spent fuels will also have increasing concentrations of the isotopes plutonium 238, plutonium 240, plutonium 241 and plutonium 242, which have detrimental consequences for the economics of plutonium recycling in light water reactors. In general, the commercial attractions of reprocessing and plutonium recycling diminish with increasing burnups.

Spent Fuel Reprocessing:

In the nuclear weapons context, all plutonium is routinely separated from the irradiated fuels discharged from production reactors. In contrast, most of the spent fuel emanating from civil power reactors is today held in store. By the end of the century, one-fifth or less of world plutonium arisings will have been separated. Nevertheless, the reprocessing of spent fuels, particularly at facilities in France, Russia, and the United Kingdom, is giving rise to large amounts of separated plutonium.

In contrast to enrichment, only one process is currently used to extract plutonium from spent reactor fuels. This is the Purex (plutonium-uranium extraction) process developed in the United States in the late 1940s and early 1950s. Plutonium separation occurs in three main stages. In the first, the spent fuel assemblies are dismantled and the fuel rods are chopped into short segments (after the cladding has been removed mechanically in the case of gas-graphite reactor fuel). In the second stage, the extracted fuel is dissolved in hot nitric acid. In the third and most complex stage, the plutonium and uranium are separated from other actinides and fission products, and then from each other, by a technique known as “solvent extraction.” Tributyl phosphate is commonly used as the organic solvent in a kerosene-type dilutant in the Purex process. The plutonium and uranium are usually taken through several solvent-extraction cycles to reach the required levels of purity.

In modern reprocessing plants, less than 1 percent of the plutonium contained in spent fuel may end up in wastes. In older plants, the fraction was often several percent.

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Plutonium is classified according to the percentage of the contaminant plutonium-240 that it contains:

Supergrade 2–3%
Weapons grade 3–7%
Fuel grade 7–18%
Reactor grade 18% or more

A nuclear reactor that is used to produce plutonium for weapons therefore generally has a means for exposing 238U to neutron radiation and for frequently replacing the irradiated 238U with new 238U. A reactor running on unenriched or moderately enriched uranium contains a great deal of 238U. However, most commercial nuclear power reactor designs require the entire reactor to shut down, often for weeks, in order to change the fuel elements. They therefore produce plutonium in a mix of isotopes that is not well-suited to weapon construction. Such a reactor could have machinery added that would permit 238U slugs to be placed near the core and changed frequently without shutdown, so proliferation is a concern; for this reason, the International Atomic Energy Agency inspects licensed reactors often. A few commercial power reactor designs, such as the reaktor bolshoy moshchnosti kanalniy (RBMK) and pressurized heavy water reactor (PHWR), do permit refueling without shutdowns, and they may pose a proliferation risk. By contrast, the Canadian CANDU heavy-water moderated, natural-uranium fueled reactor can also be refueled while operating, but it normally consumes most of the 239Pu it produces in situ; thus, it is not only inherently less proliferative than most reactors, but can even be operated as an “actinide incinerator”

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Plutonium recycling:

Fissile plutonium (notably 239Pu and 241Pu) can be used as an alternative to fissile uranium (235U) in reactor fuel. In the 1970s, the future expansion of nuclear power seemed predicated upon the recycling of plutonium, since it was believed that reserves of low-cost uranium would soon be depleted at the growth rates of nuclear electricity production then envisaged. Today, however, uranium is cheap and abundant, and the stock of nuclear power stations is not increasing rapidly. The real price of uranium is not expected to rise substantially for many years or even decades, while the economics of plutonium recycling are generally unfavourable.

In terms of nuclear physics, plutonium is more suitable for recycling in fast reactors than in thermal reactors. The fission and capture cross-sections of an isotope are the technical terms used to indicate the probability of neutron absorption by an atomic nucleus. As they imply, the former indicates the probability that absorbed neutrons will fission nuclei, while the latter indicates the probability that neutrons will be captured without fissions occurring. When the fission cross section is greater than the capture cross section, fission will occur more often than capture.

Neutron cross-sections:

Cross-sections are expressed in barns.*

	Thermal neutrons			Fast neutrons
			Fission/			Fission/
	Fission	Capture	total	Fission	Capture	total
	cross-	cross-	cross-	cross-	cross-	cross-
Isotope	section	section	section (%)	section	section	section (%)
235U	579	100	85	2.0	0.5	80
238U	. .	3	–	0.05	0.3	17
239Pu	741	267	74	1.9	0.6	76
240Pu	. .	290	–	0.4	0.6	40
241Pu	1009	368	73	2.6	0.6	81
242Pu	. .	19	–	0.3	0.4	43
241Am	3	832	0.4	0.4	1.9	17

* A barn is the unit of effective cross-sectional area of the nucleus equal to 10^–28 m2.

In a thermal reactor, around 85 per cent of the neutrons absorbed by 235U cause fissions (the remainder are captured to produce 236U), while the proportion for 239Pu is 74 per cent. Moreover, 240Pu and 241Pu also have high capture cross-sections, as does 241Am. As a result, a larger amount of fissile plutonium than fissile uranium is required for a given energy output in thermal reactors.

Plutonium is not used on its own to fuel reactors. It is typically blended with natural or depleted uranium in so-called mixed-oxide (MOX) fuels. The costs of fabricating MOX fuels for thermal reactors are today several times higher than the costs of fabricating ordinary uranium fuels, so that the prices of MOX fuel are higher even when the plutonium used in them is regarded as a free good. The isotope 239Pu also emits fewer delayed neutrons than 235U, limiting the quantity of plutonium (typically to one-third core) that can be recycled in a reactor core designed for uranium fuelling without major modifications to the reactor control system. Utilities wishing to raise the burnups of new fuels such as MOX may also face licensing delays, causing them to lag behind those allowed with uranium fuels. In some contexts, spent MOX fuels may also have to be kept in cooling ponds at reactor sites for longer periods than spent uranium fuels because of their higher heat output, increasing the amount of storage capacity that is required there. For all these reasons, MOX fuels will not generally be competitive with uranium fuels when used in thermal reactors, unless uranium prices rise steeply and offset the higher costs associated with their manufacture and usage.

In fast reactors, plutonium is in physical terms a slightly better fuel than enriched uranium, although the fabrication of fast reactor fuels from plutonium is again more costly because of its radioactivity. Table above shows that, unlike in thermal reactors, all isotopes of uranium and plutonium are fissioned by fast neutrons, so that all contribute to the reactor’s energy output. However, this is largely offset by the much lower fission and capture cross-sections exhibited by the fissile isotopes 235U, 239Pu and 241Pu when they are bombarded by fast neutrons rather than by thermal neutrons. Table above also explains why higher enrichment levels are required in fast reactors. The total cross-section of 239Pu is about 300 times that of 238U in thermal reactors, but only seven times that of 238U in fast reactors. Although the spread of neutron energies and resonances tends to reduce this differential, thermal neutrons are still 10 times more likely than fast neutrons to be absorbed by 239Pu rather than by 238U (the same applies to 235U). Concentrations of 235U or 239Pu in the range of 15–25 per cent, compared to 3–6 per cent with LWR fuel, are therefore required in fast reactors. This is one reason why the start-up costs of fast reactors are so high.

Although fast reactor cores therefore require large initial inventories of plutonium or HEU, fast reactors also seemed attractive because the high neutron flux could be exploited to ‘breed’ plutonium. Once running, it was expected that they would produce more fissile fuel than they consumed, mainly through neutron capture in 238U ‘blankets’ placed adjacent to the reactor core.

Despite these advantages, the prospects for fast reactors have diminished greatly in recent years. High capital costs, operational difficulties and doubts over safety have led all countries with fast reactor programmes to revise their plans. No government or utility now claims that it will construct fast reactors in significant numbers before the middle decades of the next century.

The heavy demand for plutonium to fuel fast reactors that was forecast in the 1970s has therefore largely evaporated. Utilities in Europe and Japan have turned to MOX recycling in thermal reactors as a means of consuming the large quantities of plutonium that they will soon acquire as their spent fuels are reprocessed in France and the UK. The main reason for using MOX fuels today is to reduce stocks of plutonium arising from reprocessing contracts. Especially if they were located in or transferred to non-nuclear weapon states, the stocks would become political liabilities if left standing.

Plutonium from dismantled US and Soviet weapons might also become available for recycling. As it is weapon-grade material, it is easier to handle than the plutonium from reactor spent fuels because of the relatively low concentrations of 241Pu and of the other higher-numbered isotopes of plutonium. However, the USA has reservations about plutonium recycling, and it is questionable whether Russia, despite its desire to utilize its redundant weapon material, will have the technical or financial resources to use its large plutonium stock in this way except with foreign assistance. The amounts of plutonium emerging from weapon dismantlement and civil reprocessing that will end up being recycled, are very uncertain. With strong economic disincentives to plutonium recycling, the majority of plutonium arisings from these sources might have to be stored and eventually treated as wastes. It should be noted, however, that plutonium storage also has its problems.

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Plutonium and weapons:

A nuclear reactor produces abundant neutrons, with enough left over from the fissioning of U-235 to irradiate U-238 and start the sequence of reactions which will yield Pu-239. Furthermore, by using a neutron moderator of graphite or heavy water, it is possible to build a nuclear reactor which will sustain fission using natural uranium, eliminating the need for uranium enrichment. (For reasons of cost and efficiency, most nuclear power stations use regular light water as moderator and coolant, but this requires enriched fuel.) In principle, you build a graphite or heavy water moderated reactor, fuel it with natural uranium refined from uranium ore, start it up, let it run for a while, then remove the fuel elements, which will now contain Pu-239 bred from the U-238 in the natural uranium you started with, and chemically separate the plutonium and hand it off to the bomb builders.

As U-238 is irradiated by neutrons in a reactor, Pu-239 is produced but that isn’t the end of the story. In a neutron-rich environment, Pu-239 can capture an additional neutron and be transformed into the Pu-240 isotope. Pu-240 is chemically identical to Pu-239, but has a shorter half-life of 6,563 years and, more importantly, undergoes spontaneous fission at a rate 41,500 times greater than that of Pu-239. All of these spontaneous fissions release neutrons, which can provoke predetonation (or a fizzle), in which the nuclear weapon blows itself apart before the intended explosion occurs. This neutron background from Pu-240 rules out the simple gun assembly weapon design possible with U-235, and requires a much more complicated and difficult to perfect implosion design. The higher the degree of contamination of the plutonium with Pu-240, the more sophisticated the weapon design must be to avoid a fizzle in which a small explosion occurs, destroying the weapon but not causing fission of a significant fraction of the fuel. Moreover, 239Pu and 240Pu cannot be chemically distinguished, so expensive and difficult isotope separation would be necessary to separate them.

It takes about 10 kilograms of nearly pure Pu-239 to make a bomb (though the Nagasaki bomb in 1945 used less). Producing this requires 30 megawatt-years of reactor operation, with frequent fuel changes and reprocessing of the ‘hot’ fuel. Hence ‘weapons-grade’ plutonium is made in special production reactors by burning natural uranium fuel to the extent of only about 100 MWd/t (effectively three months), instead of the 45,000 MWd/t typical of LWR power reactors. Allowing the fuel to stay longer in the reactor increases the concentration of the higher isotopes of plutonium, in particular the Pu-240 isotope.

Figure below shows Plutonium in the reactor core:

For weapons use, Pu-240 is considered a serious contaminant, due to higher neutron emission and higher heat production. It is not feasible to separate Pu-240 from Pu-239.

The operational requirements of power reactors and plutonium production reactors are quite different, and so therefore is their design. No weapons material has ever been produced from PWR, BWR, or PHWR power reactors (96% of the worldwide fleet by capacity). An explosive device could be made from plutonium extracted from low burn-up reactor fuel (i.e. if the fuel had only been used for a short time), but any significant proportions of Pu-240 in it would make it hazardous to the bomb makers, as well as probably unreliable and unpredictable. Typical ‘reactor-grade’ plutonium recovered from reprocessing used power reactor fuel has about one-third non-fissile isotopes (mainly Pu-240).

The following Table contrasts the plutonium or plutonium mixture separated out from three different fuel cycles: short cycle/low burn-up uranium fuel, normal high burn-up uranium fuel, and high burn-up fast reactor fuel. As can be discerned from the attributes of each, it is the first which produces weapons-usable material.

Type	Composition	Thermal power w/kg	Spontaneous neutrons /second/gram	Origin	Use
Weapons-grade	Pu-239 with less than 8% Pu-240	2-3	60	From military ‘production’ reactors with metal fuel operated for production of low burn-up Pu. Purex separation.	Nuclear weapons (can be recycled as fuel in fast neutron reactor or as ingredient of MOX)
Reactor-grade from high-burnup fuel	55-70% Pu-239; more than 19% Pu-240 (typically about 30-35% non-fissile Pu)	5-10	200	Comprises about 1% of used fuel from normal operation of civil nuclear reactors with oxide fuel used for electricity generation	As ingredient (c. 5-8%) of MOX fuel for normal reactor
IFR-grade actinide	Pu + minor actinides + U, 50% Pu fissile	80-100	300,000	From fast reactor used metal fuel by pyroprocessing	recycle

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How much is needed to build a bomb?

The amount of HEU needed to make a nuclear weapon varies with the degree of enrichment and the sophistication of the weapon design. In general, the higher the enrichment level, the less HEU is needed to make a bomb. For a HEU-based nuclear weapon, there are two basic design options: a “gun-type” weapon where two pieces of HEU are brought together quickly and explode, and an “implosion weapon,” where a sphere of HEU is rapidly compressed in a highly symmetrical manner. Gun-type weapons are far simpler in design and can be built by some terrorist groups. The second is more difficult technically but requires less HEU. Plutonium-based nuclear weapons only work as implosion weapons, with more sophisticated weapons using less plutonium.

The core of an implosion weapon – the fissile material and any reflector or tamper bonded to it – is known as the pit. Some weapons tested during the 1950s used pits made with U-235 alone, or in composite with plutonium, but all-plutonium pits are the smallest in diameter and have been the standard since the early 1960s.

Amount of fissile material needed to build an atomic bomb:

HEU (enriched to 90 percent U-235)	Simple gun-type nuclear weapon	90 to 110 lbs. (40 to 50 kg)
	Simple implosion weapon	33 lbs (15 kg)
	Sophisticated implosion weapon	20 to 26 lbs. (9 to 12 kg)
Plutonium	Simple implosion weapon	14 lbs. (6 kg)
	Sophisticated implosion weapon	4.5 to 9 lbs. (2 to 4 kg)

The IAEA defines the amounts of fissile material “required for a single nuclear device” as 8 kg of plutonium, 8 kg of U-233, and 25 kg of U-235. But that apparently depends on the skills and technical capability of the producer.

The first uranium bomb, Little Boy, dropped by the United States on Hiroshima in 1945, used 64 kilograms (141 lb) of 80% enriched uranium. Wrapping the weapon’s fissile core in a neutron reflector (which is standard on all nuclear explosives) can dramatically reduce the critical mass. Because the core was surrounded by a good neutron reflector, at explosion it comprised almost 2.5 critical masses. Neutron reflectors, compressing the fissile core via implosion, fusion boosting, and “tamping”, which slows the expansion of the fissioning core with inertia, allow nuclear weapon designs that use less than what would be one bare-sphere critical mass at normal density. The presence of too much of the 238U isotope inhibits the runaway nuclear chain reaction that is responsible for the weapon’s power. The critical mass for 85% highly enriched uranium is about 50 kilograms (110 lb), which at normal density would be a sphere about 17 centimetres (6.7 in) in diameter.

Later U.S. nuclear weapons usually use plutonium-239 in the primary stage, but the jacket or tamper secondary stage, which is compressed by the primary nuclear explosion often uses HEU with enrichment between 40% and 80% along with the fusion fuel lithium deuteride. This multi-stage design enhances the efficiency and effectiveness of nuclear weapons, allowing for greater control over the release of energy during detonation. For the secondary of a large nuclear weapon, the higher critical mass of less-enriched uranium can be an advantage as it allows the core at explosion time to contain a larger amount of fuel. This design strategy optimizes the explosive yield and performance of advanced nuclear weapons systems. The 238U is not said to be fissile but still is fissionable by fast neutrons (>2 MeV) such as the ones produced during D-T fusion.

HEU is also used in fast neutron reactors, whose cores require about 20% or more of fissile material, as well as in naval reactors, where it often contains at least 50% 235U, but typically does not exceed 90%. These specialized reactor systems rely on highly enriched uranium for their unique operational requirements, including high neutron flux and precise control over reactor dynamics. The Fermi-1 commercial fast reactor prototype used HEU with 26.5% 235U. Significant quantities of HEU are used in the production of medical isotopes, for example molybdenum-99 for technetium-99m generators. The medical industry benefits from the unique properties of highly enriched uranium, which enable the efficient production of critical isotopes essential for diagnostic imaging and therapeutic applications.

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Section-3

Introduction to Nuclear weapons:

History of nuclear weapon:

Leo Szilard was waiting to cross the road near Russell Square in London when the idea came to him. It was 12 September 1933. A little under 12 years later, the US dropped an atom bomb on Hiroshima, killing an estimated 135,000 people. The path from Szilard’s idea to its deadly realisation is one of the most remarkable chapters in the history of science and technology. It features an extraordinary cast of characters, many of them refugees from Fascism who were morally opposed to the bomb but driven by the dreadful prospect of Nazi Germany getting there first.

Szilard himself was a Hungarian-born Jew who had fled Germany for the UK two months after Adolf Hitler became chancellor. He arrived in a country that was then at the forefront of nuclear physics. James Chadwick had just discovered the neutron and Cambridge physicists soon “split the atom”. They broke a lithium nucleus in two by bombarding it with protons, verifying Albert Einstein’s insight that mass and energy were one and the same, as expressed by the equation E = mc2. Szilard’s eureka moment was based on this groundbreaking experiment. He reasoned that if you could find an atom that was split by neutrons and in the process emitted two or more neutrons, then a mass of this element would emit vast amounts of energy in a self-sustaining chain reaction.

Szilard pursued the idea with little success. It wasn’t until 1938 that the breakthrough came – ironically in the Nazi capital Berlin, where German physicists Otto Hahn and Fritz Strassman bombarded uranium atoms with neutrons. When they analysed the debris they were stunned to find traces of the much lighter element barium. As luck would have it, Hahn and Strassman were opponents of the regime. Hahn wrote to the Austrian chemist Lise Meitner, who had worked with him in Berlin until she fled to Sweden after the Nazis occupied Vienna in 1938. Meitner wrote back explaining that the uranium nucleus was splitting into two roughly equal parts. She called the process “fission”. The next piece of the puzzle came when Italian physicist Enrico Fermi, who had fled Fascism and was working at Columbia University in New York, discovered that uranium fission released the secondary neutrons that were needed to make the chain reaction happen. Szilard soon joined Fermi in New York. Together they calculated that a kilogram of uranium would generate about as much energy as 20,000 tonnes of TNT. Szilard already saw the prospect of nuclear war. “There was very little doubt in my mind that the world was headed for grief,” he later recalled.

Others did have doubts, however. In 1939 the Danish physicist Niels Bohr – who was actively helping German scientists escape via Copenhagen – poured cold water on the idea. He pointed out that uranium-238, the isotope which makes up 99.3 per cent of natural uranium, would not emit secondary neutrons. Only a very rare isotope of uranium, uranium-235, would split in this way. However, Szilard remained convinced that the chain reaction was possible, and feared that the Nazis knew it too. He consulted fellow Hungarian émigrés Eugene Wigner and Edward Teller. They agreed that Einstein would be the best person to alert President Roosevelt to the danger. Einstein’s famous letter was sent soon after the outbreak of war in Europe, but had little impact.

Things changed dramatically in 1940, when news filtered through that two German physicists working in the UK had proved Bohr wrong. Rudolf Peierls and Otto Frisch had worked out how to produce uranium-235 in large quantities, how it could be used to produce a bomb, and what the appalling consequences of dropping it would be. Peierls and Frisch – who Bohr had helped escape – were also horrified at the prospect of a Nazi bomb, and in March they wrote to the British government urging prompt action. Their “Memorandum on the Properties of a Radioactive ‘Super-Bomb‘” was more successful than Einstein’s letter to Roosevelt. It led to the initiation of the British bomb project, codenamed Tube Alloys.

The letter also galvanised the US into action. In April 1940 the government appointed the veteran physicist Arthur Compton to head a nuclear weapons programme, which eventually became the Manhattan Project. One of his first moves was to bring together various chain reaction research groups under one roof in Chicago. That summer the team began a series of experiments to make the chain reaction happen. The bombing of Pearl Harbor in December 1941 added further impetus. A year later the Manhattan Project team was ready to attempt a chain reaction in a pile of uranium and graphite they had assembled in a squash court underneath a stand of the University of Chicago’s football field. On Wednesday, 2 December 1942, they did it. Celebrations were muted. Once the reaction was confirmed, Szilard shook hands with Fermi and said: “This will go down as a black day in the history of mankind.”

Over the next four years the US, UK and Canada poured vast resources into the Manhattan Project. Tube Alloys continued for a while but was eventually absorbed into the US project. The Nazis initiated a nuclear weapons programme but made little progress. On 16 July 1945 the US detonated the world’s first nuclear bomb in the New Mexico desert. The test was final, terrible proof that nuclear energy could be weaponised, and prompted Robert Oppenheimer to recall a passage from the Hindu scripture, Bhagavad Gita: “I am become death, the destroyer of worlds.” The attacks on Japan started a worldwide arms race. Following 1945, the US developed massively destructive hydrogen bombs, which exploited nuclear fusion rather than fission. The Soviets developed and tested their own bomb in 1949. The world’s nuclear arsenal now stands at about 12,000 to 13,000 bombs.

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Nuclear weapon:

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter. The first test of a fission (“atomic”) bomb released an amount of energy approximately equal to 20,000 tons of TNT (84 TJ). The first thermonuclear (“hydrogen”) bomb test released energy approximately equal to 10 million tons of TNT (42 PJ). Nuclear bombs have had yields between 10 tons TNT (the W54) and 50 megatons for the Tsar Bomba. A thermonuclear weapon weighing as little as 600 pounds (270 kg) can release energy equal to more than 1.2 megatons of TNT (5.0 PJ). A nuclear device no larger than a conventional bomb can devastate an entire city by blast, fire, and radiation. Since they are weapons of mass destruction, the proliferation of nuclear weapons is a focus of international relations policy.

There are many ways of categorising nuclear weapons (by fission/fusion, by delivery mechanism, by yield, etc.). One common distinction is between ‘strategic’ and ‘tactical’ (or ‘non-strategic’) weapons. Today, this distinction usually refers to different categories of explosive yield: ‘tactical’ nuclear weapons are generally smaller (up to around 50 kilotons of TNT equivalent), while ‘strategic’ nuclear weapons generally have yields between 100 and 50,000 kilotons of TNT. The smaller yields are usually associated with tactical nuclear weapons – intended for threatening an opponent’s military forces on the battlefield – and the larger yields are associated with strategic nuclear weapons – intended for threats against an opponent’s homeland using long-range delivery vehicles.

Testing and deployment:

Nuclear weapons have only twice been used in warfare, both times by the United States against Japan at the end of World War II. On August 6, 1945, the United States Army Air Forces (USAAF) detonated a uranium gun-type fission bomb nicknamed “Little Boy” over the Japanese city of Hiroshima; three days later, on August 9, the USAAF detonated a plutonium implosion-type fission bomb nicknamed “Fat Man” over the Japanese city of Nagasaki. These bombings caused injuries that resulted in the deaths of approximately 200,000 civilians and military personnel. The ethics of these bombings and their role in Japan’s surrender are to this day, still subjects of debate.

Since the atomic bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated over 2,000 times for testing and demonstration. Only a few nations possess such weapons or are suspected of seeking them. The only countries known to have detonated nuclear weapons—and acknowledge possessing them—are (chronologically by date of first test) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, China, India, Pakistan, and North Korea. Israel is believed to possess nuclear weapons, though, in a policy of deliberate ambiguity, it does not acknowledge having them. Germany, Italy, Turkey, Belgium, the Netherlands, and Belarus are nuclear weapons sharing states. South Africa is the only country to have independently developed and then renounced and dismantled its nuclear weapons.

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There are three existing basic design types for nuclear weapons:

pure fission weapons are the simplest, least technically demanding, were the first nuclear weapons built, and so far the only type ever used in warfare, by the United States on Japan in World War II
boosted fission weapons increase yield beyond that of the implosion design, by using small quantities of fusion fuel to enhance the fission chain reaction. Boosting can more than double the weapon’s fission energy yield.
staged thermonuclear weapons are arrangements of two or more “stages”, most usually two. The first stage is normally a boosted fission weapon (except for the earliest thermonuclear weapons, which used a pure fission weapon instead). Its detonation causes it to shine intensely with x-radiation, which illuminates and implodes the second stage filled with a large quantity of fusion fuel. This sets in motion a sequence of events which results in a thermonuclear, or fusion, burn. This process affords potential yields up to hundreds of times those of fission weapons.

Pure fission weapons have been the first type to be built by new nuclear powers. Large industrial states with well-developed nuclear arsenals have two-stage thermonuclear weapons, which are the most compact, scalable, and cost effective option, once the necessary technical base and industrial infrastructure are built. Most known innovations in nuclear weapon design originated in the United States, though some were later developed independently by other states.

In early news accounts, pure fission weapons were called atomic bombs or A-bombs and weapons involving fusion were called hydrogen bombs or H-bombs. Practitioners of nuclear policy, however, favor the terms nuclear and thermonuclear, respectively.

Nuclear Warhead types with yield:

Gun-type fission weapon: uses chemical explosives to combine two subcritical masses of HEU into one supercritical mass of HEU. 50-60 kg (110-132 lbs)

Example: Hiroshima bomb (yield: ~13.5 kt).

Single-stage, fission weapon: uses chemical explosives to compress HEU (12-18 kg; 26-39 lbs) or Pu (4-6 kg;

8-13 lbs) subcritical mass into supercritical mass.

Example: Nagasaki bomb (yield: ~22 kt).

Can be “boosted” by deuterium-tritium gas to ~80 kt.

Two-stage, thermonuclear weapon: combines fission device (primary or trigger) with fusion device (secondary or Canned Sub-Assembly). All US nuclear weapon designs current are of this type. Yields range from 0.3 to 1,200 kilotons; most yield comes from secondary.

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The destructive force associated with a nuclear explosion vary with the location of the point of burst in relation to the surface of the earth.

The main types are:

High Altitude Burst:

Detonation above 100,000 feet. Destructive forces do no significantly affect the ground. The biggest risk is not radiation to the living things, but electromagnetic pulse (EMP) that effects electronic systems such as communications.

Air Burst:

The fireball does not touch the ground. Detonation is below 100,000 feet. For the Hiroshima bomb, an air burst 550 to 610 m (1,800 to 2,000 ft) above the ground was chosen “to achieve maximum blast effects, and to minimize residual radiation on the ground as it was hoped U.S. troops would soon occupy the city”.

Surface Burst:

Detonation occurs at or slightly above the actual surface of the earth. One of the greatest results of the type of burst is the amount of radioactive debris and fallout, and the force of the blast wave.

Sub-surface Burst:

Detonation occurs under ground or under water. Depth determines destructive forces on the surface.

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Fission and fusion:

All matter is composed of atoms: incredibly small structures that house different combinations of three particles, known as protons, neutrons, and electrons. At the center of each atom is a “nucleus” (the plural of which is “nuclei”), where neutrons and protons are bound in close proximity together. Most nuclei are relatively stable, meaning the makeup of their neutrons and protons is comparatively static and unchanging.

During fission, the nuclei of certain heavy atoms split into smaller, lighter nuclei, releasing excess energy in the process. This can sometimes occur spontaneously, but can also, in certain nuclei, be induced from outside. A neutron is shot at the nucleus and is absorbed, causing instability and fission. In some elements—such as certain isotopes of uranium and plutonium—the fission process also releases excess neutrons, which can trigger a chain reaction if they’re absorbed by nearby atoms. The most commonly used fissile materials for nuclear weapons applications have been uranium-235 and plutonium-239. Less commonly used has been uranium-233. Neptunium-237 and some isotopes of americium may be usable for nuclear explosives as well, but it is not clear that this has ever been implemented, and their plausible use in nuclear weapons is a matter of dispute.

Fusion works in reverse: when exposed to extremely high temperatures and pressures, some lightweight nuclei can fuse together to form heavier nuclei, releasing energy in the process. The released neutron can, if necessary, be used to drive another fission event.

A nuclear weapon uses one or a combination of these two processes. Both reactions generate roughly a million times more energy than comparable chemical reactions, making nuclear bombs a million times more powerful than non-nuclear bombs.

In modern nuclear weapons, which use both fission and fusion, a single warhead can release more explosive energy in a fraction of a second than all of the weapons used during World War II combined—including Fat Man and Little Boy, the two atom bombs dropped on Japan.

In some ways, fission and fusion are opposite and complementary reactions, but the particulars are unique for each. To understand how nuclear weapons are designed, it is useful to know the important similarities and differences between fission and fusion.

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Fission:

When a free neutron hits the nucleus of a fissile atom like uranium-235 (235U), the uranium nucleus splits into two smaller nuclei called fission fragments, plus more neutrons (for 235U three about as often as two; an average of just under 2.5 per fission). The fission chain reaction in a supercritical mass of fuel can be self-sustaining because it produces enough surplus neutrons to offset losses of neutrons escaping the supercritical assembly. Most of these have the speed (kinetic energy) required to cause new fissions in neighboring uranium nuclei. The key to extracting large amounts of energy from a macroscopic amount of fissile material, for example, in nuclear bombs or nuclear power reactors, is to create a chain reaction, as depicted in Figure below. In a chain reaction the neutrons released from an initial fission reaction are absorbed by neighboring U235 nuclei, which subsequently undergo fission. This process keeps multiplying until nearly all the U235 (or Pu239) is consumed. Of course, some neutrons will escape without hitting other U235 nuclei. If too many neutrons escape, the chain reaction will not proceed very far. Therefore the shape and amount of U235 present influences the amount of energy released. The amount of material needed for a self-sustaining chain reaction is called the critical mass, which is the approximate amount required for a simple fission bomb.

Fission chain reaction is depicted below:

Critical mass:

Any weapons-grade nuclear material must have a critical mass that is small enough to justify its use in a weapon. The critical mass for any material is the smallest amount needed for a sustained nuclear chain reaction. Moreover, different isotopes have different critical masses, and the critical mass for many radioactive isotopes is infinite, because the mode of decay of one atom cannot induce similar decay of more than one neighboring atom. For example, the critical mass of uranium-238 is infinite, while the critical masses of uranium-233 and uranium-235 are finite.

The critical mass for any isotope is influenced by any impurities and the physical shape of the material. The shape with minimal critical mass and the smallest physical dimensions is a sphere. Bare-sphere critical masses at normal density of some actinides are listed in the table below. Most information on bare sphere masses is classified, but some documents have been declassified. However, the critical mass can be reduced to less than half of that by using neutron reflectors, triggers, implosion geometry, and tampers. Compressing the fissile core by implosion reduces critical mass because at higher densities, emitted neutrons are more likely to strike a fissionable nucleus before escaping.

Nuclide	Half-life (y)	Critical mass (kg)	Diameter (cm)
uranium-233	159,200	15	11
uranium-235	703,800,000	52	17
neptunium-236	154,000	7	8.7
neptunium-237	2,144,000	60	18
plutonium-238	87.7	9.04–10.07	9.5–9.9
plutonium-239	24,110	10	9.9
plutonium-240	6561	40	15
plutonium-241	14.3	12	10.5
plutonium-242	375,000	75–100	19–21
americium-241	432.2	55–77	20–23
americium-242m	141	9–14	11–13
americium-243	7370	180–280	30–35
curium-243	29.1	7.34–10	10–11
curium-244	18.1	13.5–30	12.4–16
curium-245	8500	9.41–12.3	11–12
curium-246	4760	39–70.1	18–21
curium-247	15,600,000	6.94–7.06	9.9
berkelium-247	1380	75.7	11.8-12.2
berkelium-249	0.9	192	16.1-16.6
californium-249	351	6	9
californium-251	900	5.46	8.5
californium-252	2.6	2.73	6.9
einsteinium-254	0.755	9.89	7.1

The uranium-235 nucleus can split in many ways, provided the charge numbers add up to 92 and the mass numbers add up to 236 (uranium-235 plus the neutron that caused the split). The following equation shows one possible split, namely into strontium-95 (95Sr), xenon-139 (139Xe), and two neutrons (n), plus energy:

235U + n = 95Sr + 139Xe + 2n + 180MeV

The immediate energy release per atom is about 180 million electron volts (MeV); i.e., 74 TJ/kg. Only 7% of this is gamma radiation and kinetic energy of fission neutrons. The remaining 93% is kinetic energy (or energy of motion) of the charged fission fragments, flying away from each other mutually repelled by the positive charge of their protons (38 for strontium, 54 for xenon). This initial kinetic energy is 67 TJ/kg, imparting an initial speed of about 12,000 kilometers per second. The charged fragments’ high electric charge causes many inelastic coulomb collisions with nearby nuclei, and these fragments remain trapped inside the bomb’s fissile pit and tamper until their motion is converted into heat. Given the speed of the fragments and the mean free path between nuclei in the compressed fuel assembly (for the implosion design), this takes about a millionth of a second (a microsecond), by which time the core and tamper of the bomb have expanded to plasma several meters in diameter with a temperature of tens of millions of degrees Celsius.

This is hot enough to emit black-body radiation in the X-ray spectrum. These X-rays are absorbed by the surrounding air, producing the fireball and blast of a nuclear explosion.

Most fission products have too many neutrons to be stable so they are radioactive by beta decay, converting neutrons into protons by throwing off beta particles (electrons) and gamma rays. Their half lives range from milliseconds to about 200,000 years. Many decay into isotopes that are themselves radioactive, so from 1 to 6 (average 3) decays may be required to reach stability. In reactors, the radioactive products are the nuclear waste in spent fuel. In bombs, they become radioactive fallout, both local and global.

Meanwhile, inside the exploding bomb, the free neutrons released by fission carry away about 3% of the initial fission energy. Neutron kinetic energy adds to the blast energy of a bomb, but not as effectively as the energy from charged fragments, since neutrons do not give up their kinetic energy as quickly in collisions with charged nuclei or electrons. The dominant contribution of fission neutrons to the bomb’s power is the initiation of subsequent fissions. Over half of the neutrons escape the bomb core, but the rest strike 235U nuclei causing them to fission in an exponentially growing chain reaction (1, 2, 4, 8, 16, etc.). Starting from one atom, the number of fissions can theoretically double a hundred times in a microsecond, which could consume all uranium or plutonium up to hundreds of tons by the hundredth link in the chain. Typically in a modern weapon, the weapon’s pit contains 3.5 to 4.5 kilograms (7.7 to 9.9 lb) of plutonium and at detonation produces approximately 5 to 10 kilotons of TNT (21 to 42 TJ) yield, representing the fissioning of approximately 0.5 kilograms (1.1 lb) of plutonium.

Materials which can sustain a chain reaction are called fissile. The two fissile materials used in nuclear weapons are: 235U, also known as highly enriched uranium (HEU), “oralloy” meaning “Oak Ridge alloy”, or “25” (a combination of the last digit of the atomic number of uranium-235, which is 92, and the last digit of its mass number, which is 235); and 239Pu, also known as plutonium-239, or “49” (from “94” and “239”). Once sufficient fissile material is obtained, two designs can be used to make a bomb. The first is the ‘gun-type’ design where a subcritical mass of U235 is shot into another subcritical mass, thereby creating a supercritical mass for a brief time. A neutron source injects a few neutrons to start the chain reaction at the proper moment. For technical reasons, this relatively simple assembly technique works only with U235. A bomb of this design was dropped on Hiroshima on 6 August 1945, exploding with a force of approximately 12500 tons (12.5 kilotons (kT)) of TNT, killing approximately 70000 people and wounding another 80000. Because of its simplicity, this bomb design was not tested before it was used, which makes it of interest to states that wish to develop fission bombs covertly because nuclear tests are not essential. South Africa took this approach to build an arsenal of six gun-type U235 bombs in the 1980s.

Modern nuclear weapons work slightly differently. Critical mass depends on the density of the material: as the density increases, the critical mass decreases. Instead of colliding two sub-critical pieces of nuclear fuel, modern weapons detonate chemical explosives around a sub-critical sphere (or “pit”) of uranium-235 or plutonium-239 metal. The force from the blast is directed inward, compressing the pit and bringing its atoms closer together. Once dense enough to reach the critical mass, neutrons are injected, initiating a fission chain reaction and producing an atomic explosion. This fission bomb design creates a critical mass by crushing a sphere of fissile material, thereby creating very high densities. This implosion design is more challenging technically, but is more efficient with respect to the use of fissile material. Moreover, it works with both U235 and Pu239. A bomb of this design was tested at Alamogordo, NM on 16 July 1945 and a second bomb of this design was dropped on Nagasaki on 9 August 1945 which exploded with a force of nearly 20 kT of TNT. It missed the center of the city and killed approximately 40000 people and wounded another 20000.

The two basic fission weapon designs are depicted in figure below:

The major technical hurdle to developing implosion bombs, besides acquiring the fissile material, is to perfect the implosion mechanism, that is, to develop explosive lenses that can crush a sphere of fissile material in a perfectly symmetric manner to create a supercritical mass. Small deviations from spherical symmetry cause the bomb to fail. Hence, implosion designs are usually tested. A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range from the equivalent of just under a ton to upwards of 500,000 tons (500 kilotons) of TNT (4.2 to 2.1×10^6 GJ). The former Soviet Union was the second country to test an implosion device in August 1949. Great Britain followed suit in 1952, France in 1960, and China in 1964. India tested a ‘peaceful nuclear device’ probably of this design, in 1974, and again in May 1998. Pakistan followed suit later that same month, although it is not clear whether their tests involved implosion or gun-type uranium devices. Israel is also thought to have developed implosion bombs; however, the evidence for an Israeli test is equivocal. On 9 October 2006, North Korea became the latest country to test a nuclear weapon based on a plutonium design, although the test was a partial failure because the yield was less than 1 kT.

In fusion weapons (also called “thermonuclear” or “hydrogen” weapons), the energy from an initial fission explosion is used to “fuse” hydrogen isotopes together.

All fission reactions generate fission products, the remains of the split atomic nuclei. Many fission products are either highly radioactive (but short-lived) or moderately radioactive (but long-lived), and as such, they are a serious form of radioactive contamination. Fission products are the principal radioactive component of nuclear fallout. Another source of radioactivity is the burst of free neutrons produced by the weapon. When they collide with other nuclei in the surrounding material, the neutrons transmute those nuclei into other isotopes, altering their stability and making them radioactive.

Uranium’s most common isotope, 238U, is fissionable but not fissile, meaning that it cannot sustain a chain reaction because its daughter fission neutrons are not (on average) energetic enough to cause follow-on 238U fissions. However, the neutrons released by fusion of the heavy hydrogen isotopes deuterium and tritium will fission 238U. This 238U fission reaction in the outer jacket of the secondary assembly of a two-stage thermonuclear bomb produces by far the greatest fraction of the bomb’s energy yield, as well as most of its radioactive debris.

For national powers engaged in a nuclear arms race, this fact of 238U’s ability to fast-fission from thermonuclear neutron bombardment is of central importance. The plenitude and cheapness of both bulk dry fusion fuel (lithium deuteride) and 238U (a byproduct of uranium enrichment) permit the economical production of very large nuclear arsenals, in comparison to pure fission weapons requiring the expensive 235U or 239Pu fuels. Most nuclear weapons in the arsenals of the five declared nuclear powers (i.e., the United States, Russia, France, Great Britain, and China) are fusion bombs with yields ranging between a few kTs to 1000 kT or more.

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Fusion:

Fusion produces neutrons which dissipate energy from the reaction. In weapons, the most important fusion reaction is called the D-T reaction. Using the heat and pressure of fission, hydrogen-2, or deuterium (2D), fuses with hydrogen-3, or tritium (3T), to form helium-4 (4He) plus one neutron (n) and energy:

2H + 3H –> 4He + n + 17.6 MeV

The total energy output, 17.6 MeV, is one tenth of that with fission, but the ingredients are only one-fiftieth as massive, so the energy output per unit mass is approximately five times as great. In this fusion reaction, 14 of the 17.6 MeV (80% of the energy released in the reaction) shows up as the kinetic energy of the neutron, which, having no electric charge and being almost as massive as the hydrogen nuclei that created it, can escape the scene without leaving its energy behind to help sustain the reaction – or to generate x-rays for blast and fire.

The only practical way to capture most of the fusion energy is to trap the neutrons inside a massive bottle of heavy material such as lead, uranium, or plutonium. If the 14 MeV neutron is captured by uranium (of either isotope; 14 MeV is high enough to fission both 235U and 238U) or plutonium, the result is fission and the release of 180 MeV of fission energy, multiplying the energy output tenfold.

For weapon use, fission is necessary to start fusion, helps to sustain fusion, and captures and multiplies the energy carried by the fusion neutrons. In the case of a neutron bomb, the last-mentioned factor does not apply, since the objective is to facilitate the escape of neutrons, rather than to use them to increase the weapon’s raw power.

The explosions used in thermonuclear weapons are often described as a primary (the chemical and fission explosions) and secondary (the subsequent fusion blast). However, the actual mechanisms are considerably more complicated.

For example, a pure fission primary is inefficient—the plutonium pit will blow itself apart before most of the plutonium-239 can fission. Instead, the reaction can be “boosted” by including hydrogen gas (consisting of the isotopes deuterium and tritium) in the center of a hollow pit. As the surrounding plutonium fissions, the hydrogen gas undergoes fusion and releases neutrons, inducing additional fission.

Similarly, the secondary doesn’t consist purely of fusion fuel; layered within it is a fission “spark plug,” consisting of either plutonium-239 or uranium-235. As the primary explosion compresses the fuel from the outside, the spark plug material becomes supercritical and fissions, heating the hydrogen from the inside and facilitating further fusion reactions.

Fusion releases neutrons. These neutrons hit a layer of depleted uranium (uranium-238) surrounding the fusion fuel causing atoms in it to fission; this fissioning generally contributes more than half of the weapon’s total explosive yield.

Figure below shows basics of the Teller–Ulam design for a hydrogen bomb: a fission bomb uses radiation to compress and heat a separate section of fusion fuel.

Thermonuclear bombs work by using the energy of a fission bomb to compress and heat fusion fuel. In the Teller-Ulam design, which accounts for all multi-megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel (tritium, deuterium, or lithium deuteride) in proximity within a special, radiation-reflecting container. When the fission bomb is detonated, gamma rays and X-rays emitted first compress the fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-speed neutrons, which can then induce fission in materials not normally prone to it, such as depleted uranium. Each of these components is known as a “stage”, with the fission bomb as the “primary” and the fusion capsule as the “secondary”. In large, megaton-range hydrogen bombs, about half of the yield comes from the final fissioning of depleted uranium.

Virtually all thermonuclear weapons deployed today use the “two-stage” design described above, but it is possible to add additional fusion stages—each stage igniting a larger amount of fusion fuel in the next stage. This technique can be used to construct thermonuclear weapons of arbitrarily large yield. This is in contrast to fission bombs, which are limited in their explosive power due to criticality danger (premature nuclear chain reaction caused by too-large amounts of pre-assembled fissile fuel). The largest nuclear weapon ever detonated, the Tsar Bomba of the USSR, which released an energy equivalent of over 50 megatons of TNT (210 PJ), was a three-stage weapon. Most thermonuclear weapons are considerably smaller than this, due to practical constraints from missile warhead space and weight requirements.

The critical challenge with fusion weapon designs is heating the deuterium and tritium to temperatures high enough so the kinetic energy overcomes the electrostatic repulsion between these two positively charged nuclei. This is done by detonating a fission bomb next to the fusion fuel (usually Li6D, which creates D and T when bombarded with neutrons). Acquiring Li6D is less difficult than U235 or Pu239. Fusion bombs usually require testing because of the difficulty coupling the energy from the fission trigger to heat the fusion fuel sufficiently before the bombs blow apart. Finally, the neutron emitted from the fusion reaction is of sufficient energy to fission U238. Therefore, if the fusion bomb is surrounded by a U238 jacket (or tamper), a fission–fusion–fission reaction occurs. Although a relatively small fraction of a fusion bomb’s yield comes from the fission trigger (e.g., several kTs), fission within the U238 tamper can contribute a significant amount to the total weapon yield (e.g., several hundred kTs for a megaton-size fusion bomb).

Very large fusion bombs (also called hydrogen bombs or thermonuclear bombs) can be made by increasing the amount of fusion fuel. Typically, fusion bombs are 100 to 1000 times more powerful than fission bombs. The first US fusion bomb test occurred in November 1952. The Soviet Union was quick to follow in August 1953. The largest fusion bomb ever tested was one of Soviet design which detonated with an explosive force equivalent to 60 megatons (MT) of TNT, or 3000 times the yield of the bomb dropped on Nagasaki.

Only six countries—the United States, Russia, the United Kingdom, China, France, and India—have conducted thermonuclear weapon tests. Whether India has detonated a “true” multi-staged thermonuclear weapon is controversial. North Korea claims to have tested a fusion weapon as of January 2016, though this claim is disputed. Thermonuclear weapons are considered much more difficult to successfully design and execute than primitive fission weapons. Almost all of the nuclear weapons deployed today use the thermonuclear design because it results in an explosion hundreds of times stronger than that of a fission bomb of similar weight.

Neutron bomb:

Thermonuclear weapons that don’t include this uranium “blanket” are called neutron bombs, as the neutrons freed by fusion are released from the weapon. Neutron bombs therefore create a larger amount of radiation than a normal weapon of the same yield. A neutron bomb, technically referred to as an enhanced radiation weapon (ERW), is a type of tactical nuclear weapon designed specifically to release a large portion of its energy as energetic neutron radiation. During the Cold War such weapons were considered for use against tank attacks, with the goal of disabling tank crews without having to physically destroy the tank. In terms of yield, ERWs typically produce about one-tenth that of a fission-type atomic weapon. Even with their significantly lower explosive power, ERWs are still capable of much greater destruction than any conventional bomb. Meanwhile, relative to other nuclear weapons, damage is more focused on biological material than on material infrastructure (though extreme blast and heat effects are not eliminated). When the yield of a nuclear weapon is less than one kiloton, its lethal radius from blast, 700 m (2,300 ft), is less than that from its neutron radiation. However, the blast is more than potent enough to destroy most structures, which are less resistant to blast effects than even unprotected human beings. Blast pressures of upwards of 20 PSI are survivable, whereas most buildings will collapse with a pressure of only 5 PSI.

Commonly misconceived as a weapon designed to kill populations and leave infrastructure intact, these bombs are still very capable of levelling buildings over a large radius. The intent of their design was to kill tank crews – tanks giving excellent protection against blast and heat, surviving (relatively) very close to a detonation. Given the Soviets’ vast tank forces during the Cold War, this was the perfect weapon to counter them. The neutron radiation could instantly incapacitate a tank crew out to roughly the same distance that the heat and blast would incapacitate an unprotected human (depending on design). The tank chassis would also be rendered highly radioactive, temporarily preventing its re-use by a fresh crew.

A neutron bomb is only feasible if the yield is sufficiently high that efficient fusion stage ignition is possible, and if the yield is low enough that the case thickness will not absorb too many neutrons. This means that neutron bombs have a yield range of 1–10 kilotons, with fission proportion varying from 50% at 1-kiloton to 25% at 10-kilotons (all of which comes from the primary stage). The neutron output per kiloton is then 10–15 times greater than for a pure fission implosion weapon.

These neutron bombs were never deployed in Europe, and U.S. production ceased in the 1980s. By the 1990s, with the Cold War confrontation over, both the missile warheads and artillery shells were withdrawn.

What limits the minimum size and yield of fission bombs?

Fission works by a runaway chain reaction of uranium or plutonium nuclei splitting and emitting enough neutrons to split more. It takes “critical mass” for that chain reaction to happen. How much is highly classified for very good reasons. If your block is too small you can never compress it enough for the runaway reaction to happen. That’s way nukes have a lower limit on their size. There are several ways to achieve a lower yield fission bomb while maintaining critical mass, including:

-1. Fractional critical mass: This technique uses a fissile core that’s a fraction of critical mass, but is compressed to a higher density to achieve a supercritical mass. An implosion fission weapon with an explosive yield of one kiloton can be constructed with as little as 1 to 2 kg (2.2 to 4.4 pounds) of plutonium or with about 5 to 10 kg (11 to 22 pounds) of highly enriched uranium.

-2. Boosting: This technique uses fusion reactions to create neutrons that induce fissions at a higher rate.

-3. Neutron reflector: This technique reduces the loss of neutrons and critical mass.

There are technical challenges in creating a nuclear explosion with a yield significantly below 0.1 kt, as the fundamental physics of fission and fusion requires a certain amount of fissile material to sustain a chain reaction. Additionally, extremely low-yield nuclear devices may not produce a reliable or effective explosion due to the complexities of nuclear reactions. Fusion (thermonuclear) bombs require a minimum yield for the primary of about 250 tons (boosted implosive fission bomb) to release energy to compresses the secondary (deuterium-tritium fuel) through the process of radiation implosion, at which point it is heated and undergoes nuclear fusion.

Fusion reactions do not create fission products, and thus contribute far less to the creation of nuclear fallout than fission reactions, but because all thermonuclear weapons contain at least one fission stage, and many high-yield thermonuclear devices have a final fission stage, thermonuclear weapons can generate at least as much nuclear fallout as fission-only weapons. Furthermore, high yield thermonuclear explosions (most dangerously ground bursts) have the force to lift radioactive debris upwards past the tropopause into the stratosphere, where the calm non-turbulent winds permit the debris to travel great distances from the burst, eventually settling and unpredictably contaminating areas far removed from the target of the explosion.

The detonation of any nuclear weapon is accompanied by a blast of neutron radiation. Surrounding a nuclear weapon with suitable materials (such as cobalt or gold) creates a weapon known as a salted bomb. This device can produce exceptionally large quantities of long-lived radioactive contamination. It has been conjectured that such a device could serve as a “doomsday weapon” because such a large quantity of radioactivity with half-lives of decades, lifted into the stratosphere where winds would distribute it around the globe, would make all life on the planet extinct.

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While a number of elements are fissionable (meaning they can undergo fission), only a few are used in nuclear weapons. Most common are the isotopes uranium-235 and plutonium-239. Uranium is found throughout the world and can be mined from mineral deposits (it can also be extracted from seawater, but doing so is currently much more expensive). However, only a small fraction (less than one percent) of naturally occurring uranium is uranium-235. Producing usable uranium requires a process of “enrichment,” in which different uranium isotopes are separated and concentrated (usually using centrifuges). This is extremely costly, difficult, and time-consuming, and is one of the central barriers to constructing a nuclear bomb. For efficient bomb designs, highly-enriched uranium, that is, uranium enriched to approximately 90% U235 or more, is required, although one can fashion a crude fission bomb with uranium enriched to only 20% U235.

Plutonium can also be used, but only occurs naturally in trace amounts. It can, however, be produced as a fission byproduct in nuclear reactors, then separated by a process called “reprocessing.” Plutonium separation is easier than uranium enrichment—it involves separating different elements, not different isotopes of the same element—but it’s a highly radioactive process that requires heavily shielded facilities with remote-handling equipment.

Modern nuclear weapon designs are much smaller and lighter than the original US and Soviet fission bombs, ranging in size from that of a suitcase to a refrigerator and in weight from around 100 to 2000 lbs. The fact that they are small and light imply that they can be delivered in a variety of ways (e.g., ballistic missiles, aircraft, cruise missiles, artillery shells, torpedoes, etc.). Finally, nuclear weapons are relatively cheap. The initial investment cost to produce fission weapons is around $2 to $10 billion for indigenous programs; however, the marginal cost thereafter can be as low as $1–2 million per nuclear bomb for large programs of the sort that existed in the United States and the former Soviet Union during the Cold War.

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Tactical vs strategic nuclear weapons:

A strategic nuclear weapon (SNW) refers to a nuclear weapon that is designed to be used on targets often in settled territory far from the battlefield as part of a strategic plan, such as military bases, military command centers, arms industries, transportation, economic, and energy infrastructure, and countervalue targets such areas such as cities and towns. It is in contrast to a tactical nuclear weapon, which is designed for use in battle as part of an attack with and often near friendly conventional forces, possibly on contested friendly territory. As of 2024, strategic nuclear weapons have been used twice in the 1945 United States bombings of Hiroshima and Nagasaki. As of 2024, no tactical nuclear weapons have ever been used in combat.

Tactical weapons are sometimes called “battlefield nukes,” smaller weapons that can be shot out of a mortar or even exploded like a mine, as opposed to “strategic” weapons that are put on intercontinental ballistic missiles. Russia has a large arsenal of tactical weapons; the United States keeps comparatively few. Low-yield nuclear weapons have been designed to produce a fairly small explosion, which sometimes blurs the difference between conventional and nuclear weapons. Tactical nuclear weapons have burst onto the international stage as Russian President Vladimir Putin, facing battlefield losses in eastern Ukraine, has threatened that Russia will “make use of all weapon systems available to us” if Russia’s territorial integrity is threatened. Putin has characterized the war in Ukraine as an existential battle against the West, which he said wants to weaken, divide and destroy Russia. U.S. President Joe Biden criticized Putin’s overt nuclear threats against Europe. Meanwhile, NATO Secretary-General Jens Stoltenberg downplayed the threat, saying Putin “knows very well that a nuclear war should never be fought and cannot be won.” This is not the first time Putin has invoked nuclear weapons in an attempt to deter NATO.

The United States has about 200 tactical nuclear gravity bombs with explosive yields adjustable between 0.3 and 170 kilotons. The Pentagon deploys about 100 of those bombs, called the B61, in five European countries: Italy, Germany, Turkey, Belgium, and the Netherlands. Russia has retained more tactical nuclear weapons, estimated to be around 2,000, and relied more heavily on them in its nuclear strategy than the U.S. has, mostly due to Russia’s less advanced conventional weaponry and capabilities. Russia’s tactical nuclear weapons can be deployed by ships, planes and ground forces. Most are deployed on air-to-surface missiles, short-range ballistic missiles, gravity bombs and depth charges delivered by medium-range and tactical bombers, or naval anti-ship and anti-submarine torpedoes. These missiles are mostly held in reserve in central depots in Russia. Russia has updated its delivery systems to be able to carry either nuclear or conventional bombs. Tactical nuclear weapons are substantially more destructive than their conventional counterparts even at the same explosive energy, as they leave deadly radiation fallout that would contaminate air, soil, water and food supplies, similar to the disastrous Chernobyl nuclear reactor meltdown in 1986.

Unlike strategic nuclear weapons, tactical weapons are not focused on mutually assured destruction through overwhelming retaliation or nuclear umbrella deterrence to protect allies. While tactical nuclear weapons have not been included in arms control agreements, medium-range weapons were included in the now-defunct Intermediate-range Nuclear Forces treaty (1987–2018), which reduced nuclear weapons in Europe. Both the U.S. and Russia reduced their total nuclear arsenals from about 19,000 and 35,000 respectively at the end of the Cold War to about 3,700 and 4,480 as of January 2022. Russia’s reluctance to negotiate over its nonstrategic nuclear weapons has stymied further nuclear arms control efforts.

In the framework of the nuclear Strategic Arms Limitation Talks (SALT) agreements, nuclear weapons were defined as ‘strategic’ whose land-based delivery systems could deliver a nuclear warhead on targets 5,500 km or more away. Then, the nuclear means of delivery of the classical ‘triad’ were listed. Heavy strategic bomber with nuclear bombs or cruise missiles, land-based intercontinental ballistic missiles (ICBMs) and sea-based long-range submarine-launched ballistic missiles (SLBMs). When considering the deterrence ratio between Pakistan and India, India and China, France and Russia, nuclear weapons with a range far less than 5,500 km can indeed be strategic weapons. The distance between Islamabad and New Delhi is less than 700 km; between Beijing and New Delhi, it is about 3,800 km, and between Paris or London and Moscow, it is approx. 2,500 km. Russia is particularly affected by this scenario. Besides the three Western nuclear potentials, it also has to take into account those of China, Pakistan and India. There is about 3,650 km between Moscow and Islamabad. One can hardly say that just because states do not possess any intercontinental missiles, they do not possess any strategic nuclear weapons. So whether nuclear weapons are considered to be strategic or tactical also lies in the eyes of the beholder.

Why are tactical nuclear weapons so dangerous?

The United States and Russia hold 90% of the world’s stockpile of almost 13,000 nuclear weapons. Neither has the capability to wipe out the other’s nuclear arsenal in an initial attack. Both countries understand that any use of strategic nuclear weapons would invite a nuclear counterattack, and the potential of a civilization-ending nuclear exchange.

Tactical nuclear weapons, however, introduce greater ambiguity, raising the possibility that a country might think it could get away with a limited attack, such as using a low-yield tactical nuclear weapon to strike an isolated military target where few civilians would be harmed. Another possibility is a demonstration strike, without any military utility. For example, Russia could explode a nuclear weapon over the Black Sea to warn NATO countries against aiding its adversaries, such as Ukraine.

Because tactical nuclear weapons are considered more “useable,” they increase the risk of nuclear war. US wargames predict that a conflict involving use of tactical nuclear weapons will quickly spiral out of control. A Princeton University simulation of a US-Russian conflict that begins with the use of a tactical nuclear weapon predicts rapid escalation that would leave more than 90 million people dead and injured. In fact, then-Secretary of Defense James Mattis notably stated in 2018: “I do not think there is any such thing as a tactical nuclear weapon. Any nuclear weapon use any time is a strategic game changer.”

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Energy yield of nuclear weapon:

The destructive effect of nuclear weapons is unlike any other created by human beings. The most powerful U.S. conventional bomb – the GBU-43/B Massive Ordnance Air Blast (MOAB) – has an explosive yield of approximately 0.011 kt TNT, roughly 30 times less than the lowest yield setting (0.3 kt) on the B61 nuclear bomb. The B61-12 weighs 850 lbs (385 kg), nearly thirty times less that the MOAB’s 22,600 lbs (10,300 kg). 100% fission of 1 kg Pu-239 or U-235 can produce an explosion equivalent to more than 17,500 tons of TNT.

The energy yield and the types of energy produced by nuclear bombs can be varied. Energy yields in current arsenals range from about 0.1 kT to 20 MT, although the Soviets once detonated a 67 MT device. Nuclear bombs differ from conventional explosives in more than size. Figure below shows the approximate fraction of energy output in various forms for conventional explosives and for two types of nuclear bombs. Nuclear bombs put a much larger fraction of their output into thermal energy than do conventional bombs, which tend to concentrate the energy in blast. Another difference is the immediate and residual radiation energy from nuclear weapons. This can be adjusted to put more energy into radiation (the so-called neutron bomb) so that the bomb can be used to irradiate advancing troops without killing friendly troops with blast and heat.

The figure below shows three pie charts. The first shows the energy distribution of a conventional chemical bomb as ten percent thermal and ninety percent blast. The second shows fifty percent blast, thirty five percent thermal, ten percent delayed radiation, and five percent prompt radiation in the case of conventional nuclear bomb. The third shows forty percent blast, thirty percent prompt radiation, twenty five percent thermal, and five percent delayed radiation in the case of neutron bomb.

Figure above shows approximate fractions of energy output by conventional and two types of nuclear weapons. In addition to yielding more energy than conventional weapons, nuclear bombs put a much larger fraction into thermal energy. This can be adjusted to enhance the radiation output to be more effective against troops. An enhanced radiation bomb is also called a neutron bomb.

The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would produce the same energy discharge), either in kilotons (kt—thousands of tonnes of TNT), in megatons (Mt—millions of tonnes of TNT), or sometimes in terajoules (TJ). An explosive yield of one terajoule is equal to 0.239 kilotons of TNT. Because the accuracy of any measurement of the energy released by TNT has always been problematic, the conventional definition is that one kiloton of TNT is held simply to be equivalent to 10^12 calories.

The fission weapons have a theoretical limit to their yield, and the largest such weapon ever developed had a yield of 500 kilotons. Fusion weapons have no such upper limit, and the largest one ever tested yielded 50 megatons – that’s 50,000 kilotons, or 100,000,000 pounds of TNT equivalent. Such enormous weapons have little practical value, and today’s strategic weapons are in the 100 to 500 kiloton range, still many times more destructive than the weapons used on Hiroshima and Nagasaki.

The two nuclear weapons dropped on Hiroshima and Nagasaki, had an explosive yield of the equivalent of about 15 kilotons of TNT and 20 kilotons of TNT respectively. In modern nuclear arsenals, those devastating weapons are considered “low-yield.” Many of the modern nuclear weapons in Russian and U.S. nuclear weapons are thermonuclear weapons and have explosive yields of the equivalent at least 100 kilotons of TNT – and some are much higher. One 100-kiloton nuclear weapon dropped on New York City could lead to roughly 583,160 fatalities.

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Log–log plot comparing the yield (in kilotons) and mass (in kilograms) of various nuclear weapons developed by the United States is depicted in figure below:

The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. The practical maximum yield-to-weight ratio for fusion weapons (thermonuclear weapons) has been estimated to six megatons of TNT per tonne of bomb mass (25 TJ/kg). Yields of 5.2 megatons/tonne and higher have been reported for large weapons constructed for single-warhead use in the early 1960s. Since then, the smaller warheads needed to achieve the increased net damage efficiency (bomb damage/bomb mass) of multiple warhead systems have resulted in increases in the yield/mass ratio for single modern warheads.

Yield limits:

The yield-to-mass ratio is the amount of weapon yield compared to the mass of the weapon. The highest achieved values are somewhat lower, and the value tends to be lower for smaller, lighter weapons, of the sort that are emphasized in today’s arsenals, designed for efficient MIRV use or delivery by cruise missile systems.

The 25 Mt yield option reported for the B41 would give it a yield-to-mass ratio of 5.1 megatons of TNT per tonne. While this would require a far greater efficiency than any other current U.S. weapon (at least 40% efficiency in a fusion fuel of lithium deuteride), this was apparently attainable, probably by the use of higher than normal lithium-6 enrichment in the lithium deuteride fusion fuel. This results in the B41 still retaining the record for the highest yield-to-mass weapon ever designed.
The W56 demonstrated a yield-to-mass ratio of 4.96 kt per kilogram of device mass, and very close to the predicted 5.1 kt/kg achievable in the highest yield-to-mass weapon ever built, the 25-megatonne B41. Unlike the B41, which was never proof-tested at full yield, the W56 demonstrated its efficiency in the XW-56X2 Bluestone shot of Operation Dominic in 1962, thus, from information available in the public domain, the W56 may hold the distinction of demonstrating the highest efficiency in a nuclear weapon to date.
In 1963 DOE declassified statements that the U.S. had the technological capability of deploying a 35 Mt warhead on the Titan II, or a 50–60 Mt gravity bomb on B-52s. Neither weapon was pursued, but either would require yield-to-mass ratios superior to a 25 Mt Mk-41.
For current smaller US weapons, yield is 600 to 2200 kilotons of TNT per tonne. By comparison, for the very small tactical devices such as the Davy Crockett it was 0.4 to 40 kilotons of TNT per tonne. For historical comparison, for Little Boy the yield was only 4 kilotons of TNT per tonne, and for the largest Tsar Bomba, the yield was 2 megatons of TNT per tonne (deliberately reduced from about twice as much yield for the same weapon, so there is little doubt that this bomb as designed was capable of 4 megatons per tonne yield).
The largest pure-fission bomb ever constructed, Ivy King, had a 500 kiloton yield, which is probably in the range of the upper limit on such designs. Fusion boosting could likely raise the efficiency of such a weapon significantly, but eventually all fission-based weapons have an upper yield limit due to the difficulties of dealing with large critical masses. (The UK’s Orange Herald was a very large boosted fission bomb, with a yield of 800 kilotons.) However, there is no known upper yield limit for a fusion bomb.

Large single warheads are seldom a part of today’s arsenals, since smaller MIRV warheads, spread out over a pancake-shaped destructive area, are far more destructive for a given total yield, or unit of payload mass. This effect results from the fact that destructive radius of a single warhead on land scales approximately only as the cube root of its yield, due to blast “wasted” over a roughly hemispherical blast volume, while the strategic target is distributed over a circular land area with limited height and depth. This effect more than makes up for the lessened yield/mass efficiency encountered if ballistic missile warheads are individually scaled down from the maximal size that could be carried by a single-warhead missile.

Multiple Independently-targetable Reentry Vehicle (MIRV) technology allows a single missile to carry multiple warheads that can hit different targets simultaneously. MIRVs are more difficult to defend against than traditional missiles and are considered effective countermeasures to ballistic missile defenses.

Yield efficiency:

The efficiency of an atomic bomb is the ratio of the actual yield to the theoretical maximum yield of the atomic bomb. Not all atomic bombs possess the same yield efficiency as each individual bombs design plays a large role in how efficient it can be. In order to maximize yield efficiency, one must make sure to assemble the critical mass correctly, as well as implementing instruments such as tampers or initiators in the design. A tamper is typically made of uranium and it holds the core together using its inertia. It is used to prevent the core from separating too soon to generate maximum fission, so as not to cause a “fizzle”. The initiator is a source of neutrons either inside of the core, or on the outside of the bomb, and in this case it shoots neutrons at the core at the moment of detonation. It is essentially kick starting the reaction so the maximum fission reactions can occur to maximize yield.

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Nuclear weapon delivery system:

The system used to deliver a nuclear weapon to its target is an important factor affecting both nuclear weapon design and nuclear strategy. The design, development, and maintenance of delivery systems are among the most expensive parts of a nuclear weapons program; they account, for example, for 57% of the financial resources spent by the United States on nuclear weapons projects since 1940. According to an audit by the Brookings Institution, between 1940 and 1996, the U.S. spent $11.3 trillion in present-day terms on nuclear weapons programs and 57% of which was spent on building nuclear weapons delivery systems.

The simplest method for delivering a nuclear weapon is a gravity bomb dropped from aircraft; this was the method used by the United States against Japan in 1945. This method places few restrictions on the size of the weapon. It does, however, limit attack range, response time to an impending attack, and the number of weapons that a country can field at the same time. With miniaturization, nuclear bombs can be delivered by both strategic bombers and tactical fighter-bombers. This method is the primary means of nuclear weapons delivery; the majority of U.S. nuclear warheads, for example, are free-fall gravity bombs, namely the B61, which is being improved upon to this day.

Preferable from a strategic point of view is a nuclear weapon mounted on a missile, which can use a ballistic trajectory to deliver the warhead over the horizon. Although even short-range missiles allow for a faster and less vulnerable attack, the development of long-range intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) has given some nations the ability to plausibly deliver missiles anywhere on the globe with a high likelihood of success.

More advanced systems, such as multiple independently targetable reentry vehicles (MIRVs), can launch multiple warheads at different targets from one missile, reducing the chance of a successful missile defense. Today, missiles are most common among systems designed for delivery of nuclear weapons. Making a warhead small enough to fit onto a missile, though, can be difficult.

Tactical weapons have involved the most variety of delivery types, including not only gravity bombs and missiles but also artillery shells, land mines, and nuclear depth charges and torpedoes for anti-submarine warfare. An atomic mortar has been tested by the United States. Small, two-man portable tactical weapons (somewhat misleadingly referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty of combining sufficient yield with portability limits their military utility.

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Delivery systems―such as ballistic and cruise missiles, combat aircraft, and drones―determine how, when, and against whom a country can use conventional, nuclear, chemical, or biological weapons. Today over 30 countries possess ballistic missiles, over 20 have cruise missiles, many more operate combat aircraft, and others are pursuing these technologies.

-1. Ballistic Missiles:

A ballistic missile is a rocket-powered delivery vehicle that is initially guided for a brief period but then follows a trajectory governed by gravity and air resistance for most of its flight path. Ballistic missiles can be launched from fixed-position silos, road-mobile launchers, or at sea from surface ships or ballistic missile submarines. Ballistic missiles can carry a single or multiple warheads containing nuclear, chemical, biological, or conventional payloads. Several nuclear-armed countries employ missiles with Multiple Independently-targetable Re-Entry Vehicles (MIRVs), a system with multiple warheads, each of which can strike a separate target.

Ballistic missiles are divided into four categories depending on their range as seen in the figure below:

-2. Cruise Missiles:

Cruise missiles are essentially small unmanned, fixed-wing aircraft. They use a jet engine and wings to fly a warhead to a target. While generally smaller and slower than ballistic missiles, cruise missiles can be extremely accurate and fly at very low altitude, enabling them to avoid detection. Cruise missiles are usually categorized based on their intended targets or their launch platforms. They can attack targets on land (land-attack cruise missiles, LACM), in the air (surface-to-air missiles, SAM), or ships at sea (anti-ship cruise missile, ASCM), and can be ground-launched (GLCM), air-launched (ALCM), or sea-launched (SLCM).

-3. Combat Aircraft:

Manned combat aircraft can deliver gravity bombs (like the ones used on Hiroshima and Nagasaki) or air-launched cruise missiles (ALCM).

Combat aircraft include heavy bombers and strike aircraft. Heavy bombers typically have longer ranges and can carry heavier payloads than strike aircraft, which often serve other roles such as air-to-air combat and close air support.

All countries with nuclear weapons possess combat aircraft, although the degree to which they rely on this delivery method varies from country to country.

-4. Unmanned Aerial Vehicles (UAV):

Often referred to as drones, UAVs are unmanned, self-propelled aircraft that can be flown autonomously or remotely by pilots thousands of miles away. The key difference between UAVs and cruise missiles is that UAVs are reusable, whereas cruise missiles are destroyed upon delivering a payload to their target. However, there is a type of one-way attack, or “kamikaze,” UAV that, like a cruise missile, is destroyed upon hitting the target.

UAVs are often used where manned flight is deemed too risky or impractical. They can perform intelligence, surveillance, and reconnaissance (ISR) missions; attack enemy forces; or provide close air support for ground troops. While no country has used UAVs to deliver nuclear weapon to date, they could be used for this purpose in the future.

-5. Hypersonic missiles:

Hypersonic glide vehicle (HGV) are missile warheads which maneuver and glide through the atmosphere at high speeds after an initial ballistic launch phase. Hypersonic cruise missile are cruise missiles which use air-breathing engines such as scramjets to reach high speeds. These state-of-the-art missiles can reach up to Mach 5, or 4,000 miles per hour, to deliver their payload in minutes from across the Pacific or Atlantic. Traditional ballistic missiles, may achieve hypersonic speeds but are not typically classified as hypersonic weapons due to lacking the use of aerodynamic lift to allow their reentry vehicles to maneuver under guided flight within the atmosphere.

-6. Crude Non-State Actor Delivery Methods:

Lacking the resources of a state, non-state actors, such as terrorists, would likely resort to simpler delivery methods to carry out WMD attacks. While less damaging than a state’s delivery system, these crude methods are uncontrolled, widely available, and thus far easier for a terrorist group to acquire.

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Each system has its advantages and disadvantages from a military point of view:

ICBMs can be positioned in silos (stationary) or on lorries (mobile). They are ready to be deployed within a short span of time, have short flying times, and there are no reliable means of intercepting them. Their disadvantage is that their positions are known and that they, therefore, become a primary target for the enemy. This is why the owner will be prepared to have these weapons ready for takeoff at all times and to launch them before they can be destroyed on the ground. If this were to occur due to a false alarm, the danger of a ‘nuclear war by accident’ would become real. Once launched, a missile can no longer return.

Sea-based long-range submarine-launched ballistic missiles (SLBMs), too, can quickly attack targets with multiple warheads at nearly all distances; only in the recent decades, though, have they become as precise as ICBMs. Their greatest advantage is the fact that they are virtually invulnerable. Once launched, SLBMs cannot return, either.

A country’s decision to acquire a particular delivery system depends on its unique political and military circumstances. This decision can be driven by a system’s availability, the type of WMD to be delivered, the intended targets, and perceptions about what is required for deterrence. A country’s decision may also be impacted by internal bureaucratic dynamics as well as an adversarial country’s development of certain delivery systems. More technologically advanced countries tend to develop multiple types of delivery systems. For example, the U.S. strategic nuclear arsenal consists of land-based ICBMs, submarine-launched ballistic missiles (SLBMs), and heavy bombers, which collectively form the U.S. nuclear triad. Attributes affecting the suitability of a delivery system for a particular country include range, accuracy, payload weight and type, ability to penetrate enemy defenses, survivability in case of a preemptive attack, as well as cost and the availability of assistance.

Modern strategic nuclear weapons are usually thermonuclear (hydrogen bombs), meaning they have a second stage of detonation fuelled by the fusion. Strategic nuclear weapons can be delivered in a variety of ways:

Land-based missile silos launching ICBMs (intercontinental ballistic missiles), IRBMs (intermediate-range ballistic missiles), or MRBMs (medium-range ballistic missiles)
SLBMs (submarine-launched ballistic missiles) or SLCMs (sea-launched cruise missiles)
Aircraft carrying nuclear bombs or ALCMs (air-launched cruise missiles)
GLCMs (ground-launched cruise missiles)

In general ballistic missiles are powered initially by a rocket, but then follow an unpowered trajectory arching extremely high before falling back down to earth. Cruise missiles are propelled by jet engines, meaning they fly low to the surface of the earth and are harder to detect, but use much more fuel and move at slower speeds.

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Nuclear triad:

A nuclear triad is a three-pronged military force structure of land-based intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and strategic bombers with nuclear bombs and missiles. Countries build nuclear triads to eliminate an enemy’s ability to destroy a nation’s nuclear forces in a first-strike attack, which preserves their own ability to launch a second strike and therefore increases their nuclear deterrence. Only four countries are known to have the nuclear triad: the United States, Russia, India, and China. Israel is suspected to possess a nuclear triad, but its status is not confirmed. While traditional nuclear strategy holds that a nuclear triad provides the best level of deterrence from attack, most nuclear powers do not have the military budget to sustain a full triad. The only two countries that have successfully maintained a strong nuclear triad for most of the nuclear age are the United States and Russia.

For more than six decades, the United States has emphasized the need for a nuclear force that credibly deters adversaries, assures allies and partners, and would achieve U.S. objectives should deterrence fail. Since the 1960s, these objectives have been met by the U.S. nuclear triad through forces operating at sea, on land, and in the air. Today’s nuclear triad consists of: 14 ballistic missile submarines (SSBNs) armed with 240 submarine-launched ballistic missiles (SLBMs); 400 land-based intercontinental ballistic missiles (ICBMs); and 60 nuclear-capable heavy bomber aircraft capable of delivering gravity bombs and cruise missiles.

Note:

Nuclear-powered ballistic missile submarines (SSBNs) are stealthy submarines that launch intercontinental missiles.

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For decades now, there have been efforts to make the spread of means of delivery more difficult or to curb it. The Missile Technology Control Regime (MTCR), established in 1987, is a voluntary agreement with which most countries that were capable of making means of delivery committed themselves to stopping the export of such systems (ballistic missiles, cruise missiles, drones) with a range of more than 300 km and a payload of more than 500 kg and to preventing the transfer of components and manufacturing technology for such systems. In 2002, this agreement was supplemented by the Hague Code of Conduct to which 134 member states have committed themselves politically—but not legally—to counter the spread of ballistic missiles and to be transparent with regard to their missiles. This code of conduct, however, does not apply to cruise missiles and drones. Despite all efforts to keep the number of countries with means of delivery with sufficient payload for nuclear weapons small, the number of countries possessing such systems is growing. Today, more than ten countries respectively possess ballistic missiles with more than 300 km range and a load of more than 500 kg or cruise missiles of comparable specifications. More countries are developing such weapons or try to purchase the technology needed.

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How quickly can nuclear weapons be deployed?

As for how quickly a nuclear weapon could be deployed and how many are on “high alert,” there is a bit of a spectrum. The U.S. and Russia keep a portion of their nuclear weapons on prompt alert, meaning they could be ready to launch in under 15 minutes. A 2015 paper by the Union of Concerned Scientists estimated that the U.S. and Russia each had around 900 weapons on such hair-trigger alert. Other countries—including China, Israel, India and Pakistan—keep their nuclear weapons in central storage, meaning they would have to be taken out and mated to their delivery systems in a crisis. This could take days, or even weeks, to arrange. And others, such as the United Kingdom, have nuclear weapons deployed at all times on ballistic missile submarines, but these are kept in detargeted mode and would require hours or days to be brought to launch-ready status.

How are nuclear weapons stored?

While each country has its own specific storage system, storage facilities are generally blast-resistant and are often buried underground to limit the damage of an accidental detonation and to protect from an attack. In the United States, nuclear weapons are kept under cryptographic combination lock to prevent unauthorized use. In theory, only the president has the authority to sanction their use.

Future without nuclear weapons:

Given that the launch of a nuclear weapon would, in all likelihood, be met with immediate retaliation and could lead to all-out global nuclear war, is there a chance that all nuclear weapons could be decommissioned for the greater good? Could there ever be a future without nuclear weapons?

“I don’t think this is going to happen,” said Holger Nehring, chair in contemporary European history at the University of Stirling in Scotland. “Nuclear weapons are mainly a form of deterrence against nuclear attack, so states have no real interest in getting rid of them. Entirely getting rid of nuclear weapons would mean a very high level of trust between all states in the international system, and this is unlikely to be achieved.”

Andrew Futter, a professor of international politics at the University of Leicester in England, agreed. “We have probably reached a point now where further big reductions are unlikely,” he said.

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Global Nuclear Weapons Spending in USD:

A cumulative $387 billion has been spent by these nine countries to build and maintain their nuclear arsenals over the past five years as seen in the figure below. Funding allocated to disarmament efforts is minuscule by comparison.

The billions of dollars being squandered on nuclear weapons is a profound and unacceptable misallocation of public funds which should have been used for humanitarian needs like global hunger eradication or environmental conservation efforts. Nuclear weapons programmes divert public funds from health care, education, disaster relief and other vital services. The nine nuclear-armed nations spend many tens of billions of dollars each year maintaining and modernizing their nuclear arsenals. According to the International Campaign to Abolish Nuclear Weapons (ICAN), in 2023 they squandered $91.4 billion on their nuclear weapons; a total of $2,898 per second. At the top of the list is the United States, which spent $51.5 billion – more than all of the other nations combined. That amounts to nearly $100,000 per minute aimed at developing new intercontinental ballistic missiles, new airplanes to drop bombs and new submarines, according to ICAN report. Other big spenders were China with $11.9 billion; Russia with $8.3 billion; and the United Kingdom with $8.1 billion. The increase in worldwide spending in 2023 is the greatest ICAN has recorded in a single year.

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Nuclear Devices in Space:

Nuclear devices in space have the potential to prove indispensable tools, ideal for protecting the planet from asteroid impacts. They are, however, currently forbidden, unless the 1967 Outer Space Treaty is properly amended. This is because they are viewed as destructive weapons of war. Recent scientific research at Sandia National Laboratories proves that carefully aimed nuclear detonations in space, early enough in an object’s approach to Earth, can deflect a threatening comet or asteroid by enough to put it on a safe trajectory. However, nuclear devices can also be deadly weapons of war. They are indeed being looked at for purposes of space-based coercion and blackmail and even warfighting in space. Examples include Russia’s “Sputnuke” and China’s fractional orbital bombardment system.

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Section-4

Civil and military nuclear power: two sides of the same coin:

Civil nuclear power means electricity generated from nuclear power and military nuclear power means construction of nuclear weapons and its delivery system. Data from the Stockholm International Peace Research Institute (SIPRI) show that global military expenditures in real terms rose for the third consecutive year to 1917 billion USD in 2019. This year-on-year increase of 3.6 percent confirms that global defense spending has reached the highest level since the data became publicly available across all countries in 1988. Six out of the ten states with the highest military expenditures in 2018 possess nuclear weapons and nine use nuclear power. Initial nuclear development in the United States, Great Britain, France, and the former Soviet Union was influenced by the technological and nuclear expertise gained from strategic and military activities. In part, the global civilian nuclear industry was established to legitimatize the development of nuclear weapons. Modern supply chains involving nuclear skills, education, research, design, and engineering helped to introduce or sustain military capabilities. China, Russia, India, the UK, and the US have the largest nuclear reactor new-build programs. Both Russia and the US are upgrading their nuclear arsenals, China, India, and Pakistan, are expected to gradually increase the size of their arsenals in the next decade, and thirty states are considering, planning, or building civilian nuclear power facilities.

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Civil nuclear power:

About 10% of the world’s electricity is generated from uranium in nuclear reactors. This amounts to over 2600 billion kWh, as much as from all sources worldwide a few decades ago. It comes from about 440 nuclear reactors with a total output capacity of about 390,000 MWe operating in 32 countries plus Taiwan. Over 50 more reactors are under construction and about another 100 are planned. A typical 1000 megawatt (MWe) reactor can provide enough electricity for a modern city of close to one million people, about 8 billion kWh per year. A dozen countries get 25% or more of their electricity from nuclear reactors. Germany and Japan have derived a similar amount of their electricity from uranium in the past. The USA has over 90 reactors operating, supplying 20% of its electricity. France generates about 70% of its electricity from nuclear power.

Nuclear power stations and fossil-fuelled power stations of similar capacity have many features in common. Both require heat to produce steam to drive turbines and generators. In a nuclear power station, however, the fissioning of uranium atoms replaces the burning of coal or gas. The chain reaction that takes place in the core of a nuclear reactor is controlled by rods which absorb neutrons. They are inserted or withdrawn to set the reactor at the required power level. The fuel elements are surrounded by a substance called a moderator to slow the speed of the emitted neutrons and thus enable the chain reaction to continue. Water, graphite and heavy water are used as moderators in different types of reactors.

Reactors for Electricity Generation:

In nuclear power plants the fission energy released in the reactor is used to produce steam, which in turn is used to generate electricity. There are several types of nuclear power reactors.

Light Water Reactor:

The most widely used reactor is the light water reactor (LWR) which is moderated and cooled by ordinary water (light water). Light water is an excellent moderator; however, light water reactors require uranium fuel that is enriched. There are two types of light water reactors, the pressurized water reactor (PWR) and the boiling water reactor (BWR). In the PWR, water passes through the reactor core but is under high pressure and does not boil. The water then passes through steam generators which exchange the heat, boiling the water in a secondary circuit which drives the turbines which produce electricity. In the BWR the water boils as it passes through the reactor core and the resulting steam drives the turbines.

Heavy Water Reactor:

Another type of reactor is the heavy water moderated reactor (HWR). Heavy water (water in which hydrogen atoms have been replaced by deuterium) does not absorb neutrons as readily as light water and so natural uranium can be used as the fuel. Natural uranium fuel is readily available, but deuterium is expensive. The Canadian reactor design, known as the CANDU, has been successful and has been exported outside of Canada. HWRs do not have to be shut down to refuel but can be reloaded while running. Both Germany and Japan have developed their own HWR designs.

Gas-Graphite Reactors:

Other nuclear reactors use graphite as a moderator and a gas as the coolant. This type of reactor was the basis for nuclear power production in France and Great Britain. These gas-graphite reactors are cooled by carbon dioxide gas and use a natural uranium metal fuel that is clad in a magnesium alloy. This fuel corrodes when stored in water. The British gas-graphite, known as the Magnox reactor, was replaced by the advanced gas reactors (AGRs). AGRs are also cooled by carbon dioxide but use slightly enriched, ceramic uranium dioxide fuel.

Water-Graphite Reactor:

The Russian RBMK uses graphite as its moderator but light water as its coolant and slightly enriched uranium for fuel. The Chernobyl reactors are of this design.

Fast Breeder Reactors:

A breeder reactor makes more fissile material than it consumes and does not use a moderator. For example, a breeder core might contain 15 to 25 percent plutonium mixed with uranium, surrounded by a blanket of natural or depleted uranium. Plutonium in the core is consumed, but neutrons emanate from the core and produce plutonium 239 through the capture of neutrons by the uranium 238 in the blanket. This creates a net increase in plutonium. Breeder reactors can also have a core of highly enriched uranium. The liquid metal fast breeder reactor (LMFBR) uses sodium as a coolant and the gas-cooled fast breeder reactor (GCFR) uses helium as a coolant.

Green advantages of nuclear power:

Six major environmental advantages of current or future nuclear power plants are central to the vision for future energy systems. (1) Nuclear is low-carbon — Nuclear power plants produce no greenhouse gas emissions during operation, and over the course of its life-cycle, nuclear produces about the same amount of carbon dioxide-equivalent emissions per unit of electricity as wind, and one-third of the emissions per unit of electricity when compared with solar; (2) clean air—emits no air pollution; (3) clean drinking water—in addition to making electricity, can convert seawater into safe drinking water; (4) preservation of natural resources—uses far less land than any other energy source for 24/7 energy; (5) minimal waste—advanced reactor technologies minimize waste, and some use it as fuel; and (6) support to renewable energy—provides electricity when the wind doesn’t blow and the sun doesn’t shine.

When the commercial nuclear industry began in the 1960s, there were clear boundaries between the industries of the East and West. Today, the nuclear industry is characterized by international commerce. A reactor under construction in Asia today may have components supplied from South Korea, Canada, Japan, France, Germany, Russia, and other countries. Similarly, uranium from Australia or Namibia may end up in a reactor in the UAE, having been converted in France, enriched in the Netherlands, deconverted in the UK and fabricated in South Korea.

Nuclear provides about one-quarter of the world’s low-carbon electricity. The uses of nuclear technology extend well beyond the provision of low-carbon energy. It helps control the spread of disease, assists doctors in their diagnosis and treatment of patients, and powers our most ambitious missions to explore space. These varied uses position nuclear technologies at the heart of the world’s efforts to achieve sustainable development. Over 50 countries utilize nuclear energy in about 220 research reactors. In addition to research, these reactors are used for the production of medical and industrial isotopes, as well as for training.

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The links between nuclear power and nuclear weapons:

Nuclear weapons and nuclear power share several common features and there is a danger that having more nuclear power stations in the world could mean more nuclear weapons. The long list of links includes their histories, similar technologies, skills, health and safety aspects, regulatory issues and radiological research and development. For example, the process of enriching uranium to make it into fuel for nuclear power stations is also used to make nuclear weapons. Plutonium is a by-product of the nuclear fuel cycle and is still used by some countries to make nuclear weapons. There is always the danger that countries acquiring nuclear power technology may subvert its use to develop a nuclear weapons programme. Nuclear materials may also get into the wrong hands and be used to make a crude nuclear device or a so-called ‘dirty bomb’.

Some radioactive materials (such as plutonium-239 and uranium-235) fission and their nuclei split apart giving off very large amounts of energy. Inside a warhead, trillions of such fissions occur inside a small space within a fraction of a second, resulting in a massive explosion. Inside a nuclear reactor, the fissions are slower and more spread out, and the resulting heat is used to boil water, to make steam, to turn turbines which generate electricity. However, the prime use of plutonium-239 and uranium-235, and the reason they were produced in the first place, is to make nuclear weapons. The connections between nuclear power and nuclear weapons have always been very close and are largely kept secret. Most governments take great pains to keep their connections well hidden. The civil nuclear power industry grew out of the atomic bomb programme in the 1940s and the 1950s. Many nations used civil nuclear power programme as a cover for military activities. Nuclear weapons and nuclear power remain inextricably linked. For example:

All the processes at the front of the nuclear fuel cycle, i.e. uranium ore mining, uranium ore milling, uranium ore refining, and U-235 enrichment are still used for both power and military purposes.
Factory that makes nuclear fuel for reactors also makes nuclear fuel for nuclear submarines.
Nuclear reactors are used to create tritium (the radioactive isotope of hydrogen) necessary for nuclear weapons.

It is important to remember that nuclear technologies are dual-use and offer opportunities for energy production and weapons development. Early civilian nuclear energy programs, like those of the United States and the Soviet Union, were byproducts of classified initiatives to build atomic weapons. Low-enriched uranium consisting of 3–5% isotope U-235 can fuel a nuclear reactor, but a highly-enriched level of 90% U-235 is considered “weapons-grade.” A critical mass enriched to this higher level can sustain a fission chain reaction to power a bomb. Further, neutron absorption by uranium-238 in a nuclear reactor produces plutonium (typically isotope Pu-239). Reprocessing spent reactor fuel can recover unused plutonium to serve as fissile material for nuclear weapons. Enrichment and reprocessing thus enabled the Cold War nuclear arms race and risk of cities being destroyed in minutes by nuclear-tipped ballistic missiles.

Since its founding by the United Nations in 1957, the International Atomic Energy Agency (IAEA) has promoted two, sometimes contradictory, missions: on the one hand, the Agency seeks to promote and spread internationally the use of civilian nuclear energy; on the other hand, it seeks to prevent, or at least detect, the diversion of civilian nuclear energy to nuclear weapons, nuclear explosive devices or purposes unknown. The IAEA now operates a safeguards system as specified under Article III of the Nuclear Non-Proliferation Treaty (NPT) of 1968, which aims to ensure that civil stocks of uranium and plutonium, as well as facilities and technologies associated with these nuclear materials, are used only for peaceful purposes and do not contribute in any way to proliferation or nuclear weapons programs. It is often argued that the proliferation of nuclear weapons to many other states has been prevented by the extension of assurances and mutual defence treaties to these states by nuclear powers, but other factors, such as national prestige, or specific historical experiences, also play a part in hastening or stopping nuclear proliferation.

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How to get an atomic bomb: Two technical alternatives:

Whoever wants to build nuclear weapons can do this in two ways: Either, one can aim at constructing a nuclear weapon that is based on fission, requiring highly enriched uranium, or one can try to construct a hydrogen bomb that is based on the principle of fusion and needs plutonium. Both materials must first be sourced. In its natural state, uranium only contains a small share of the fissile isotope U-235 that first will have to be enriched to a higher concentration through great technical effort. The element plutonium, on the contrary, is only created when uranium is irradiated in a nuclear reactor.

Both ways to build a nuclear weapon, therefore, are inherently difficult. The implementation of how to construct a uranium bomb is relatively easy. Yet, the uranium enrichment process needed for a uranium bomb is a highly complex technical process and is very expensive. The opposite is the case for the hydrogen bomb. The technological requirements to create plutonium are quite basic whereas the construction of such a weapon is far more complex. The knowledge gleaned from the civilian use of nuclear energy and research- or nuclear fuel cycle facilities can be useful for any of the two. Whoever, for example, needs fuel elements for nuclear reactors, research reactors or nuclear propulsion for vessels has to enrich uranium. The same goes for whoever wants to build nuclear weapons with a uranium core. These differences are more gradual than fundamental. Light water reactors, for instance, require two- to five per cent enriched uranium while research or ship reactors more often than not use much more highly enriched uranium, or even uranium that is just as highly enriched as weapons-grade uranium (20 to over 90 per cent).

There are various technologies to enrich uranium—the use of centrifuges is the most common. They can enrich uranium to various degrees, that is, prepare it both for civilian and military purposes. Uranium enrichment plants are operated by the five traditional nuclear powers (United States, Russia, Great Britain, France and China) as well as by Pakistan, Iran, Germany, the Netherlands, Japan, South Africa and Brazil. There are smaller (experimental) plants in Australia and South Korea, amongst others. It is suspected that North Korea has an undeclared military enrichment programme. Research reactors operated with weapons-grade, highly enriched uranium also constitute a high risk. Research or ship reactors can be used for legitimate reasons to produce more highly enriched uranium than would be necessary for nuclear power plants.

A similar scenario applies when looking at the production of plutonium. Irradiating uranium fuel elements in nuclear reactors either results in plutonium for power reactors or weapons-grade plutonium. The outcome depends on the type of reactor, used fuel and length of irradiation. While light water reactors are not the ideal choice for producing weapons-grade plutonium, heavy water reactors and some other reactor types are much better suited. When irradiated fuel elements are reprocessed, the plutonium generated in that process can be chemically isolated and used for weapons construction. Technically, it is even possible to build a device with plutonium from power reactors. The building of reactors that are well suited for the production of plutonium and the use of reprocessing technology often raises concerns about proliferation. Military reprocessing plants not only exist in the five acknowledged nuclear weapons states but also in Israel, India, Pakistan and North Korea. Commercially-run plants were built in Great Britain, France, Russia and Japan. There are smaller (experimental) plants in other countries.

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Dual-Use Technology:

Dual-use technology refers to the possibility of military use of civilian nuclear power technology. Many technologies and materials associated with the creation of a nuclear power program have a dual-use capability, in that several stages of the nuclear fuel cycle allow diversion of nuclear materials for nuclear weapons. When this happens a nuclear power program can become a route leading to the atomic bomb or a public annex to a secret bomb program. The crisis over Iran’s nuclear activities is a case in point. Many UN and US agencies warn that building more nuclear reactors unavoidably increases nuclear proliferation risks. A fundamental goal for global security is to minimize the proliferation risks associated with the expansion of nuclear power. If this development is “poorly managed or efforts to contain risks are unsuccessful, the nuclear future will be dangerous”. For nuclear power programs to be developed and managed safely and securely, it is important that countries have domestic “good governance” characteristics that will encourage proper nuclear operations and management. These characteristics include low degrees of corruption (to avoid officials selling materials and technology for their own personal gain as occurred with the A.Q. Khan smuggling network in Pakistan), high degrees of political stability (defined by the World Bank as “likelihood that the government will be destabilized or overthrown by unconstitutional or violent means, including politically-motivated violence and terrorism”), high governmental effectiveness scores (a World Bank aggregate measure of “the quality of the civil service and the degree of its independence from political pressures [and] the quality of policy formulation and implementation”), and a strong degree of regulatory competence.

The civilian and military use of nuclear technology can be compared to Siamese twins. They are so closely connected that one can hardly separate them. The civilian use of nuclear technology can create knowledge, materials and technology that can also be used for a military nuclear programme. Comprehensive nuclear programmes – even if they are purely civilian by nature – therefore often create concern that the real intention is the desire to possess nuclear weapons. The proliferation of nuclear weapons is a risk that must be taken very seriously. The presence of a broad range of specific export controls and non-proliferation regulations attests to this. The long dispute over the nuclear programme of Iran is a current example of this.

A forthright U.S. Department of Energy official once remarked that the only difference between civilian and military applications of nuclear energy was psychological. This stark assessment contravenes the conventional wisdom that the risks of diverting civilian nuclear technology and materials to nuclear weapons can be managed. On the civilian nuclear energy side of the equation, governments and the nuclear industry have invested enormous time and money in distinguishing between peaceful uses of nuclear energy and military uses to help manage public perceptions and expectations. A system of nuclear governance for states with only civilian nuclear sectors has evolved over time to sharpen their boundaries so that non-compliance is easier to discern and can be more quickly addressed. Sharper boundaries will never prevent diversion of civilian nuclear material to military purposes, but they can help strengthen the ability of the multilateral system of checks and balances to respond quickly, effectively, and appropriately.

When it comes to the separation of military and civilian nuclear energy activities in nuclear weapon states, the strategic nature of nuclear weapons tends to overpower the need to keep the two separate and inhibits transparency. This has certainly been the historical case for all five nuclear weapon states, and to a large extent for India and Pakistan (less so for Israel and North Korea, which have few purely civilian nuclear assets).

Types of Co-mingling:

There are several ways in which states with nuclear weapons have co-mingled material, technologies, facilities and sites for defense and civilian purposes. Four particular examples have been common:

Military facilities providing civilian services, such as military production reactors providing heat and/or electricity to local communities or enrichment plants producing for weapons and for commercial fuel;
“Conversion” of military facilities to primarily civilian use without application of international safeguards;
Civilian facilities providing military products such as tritium for weapons; and
Civilian facilities providing fissile material for nuclear weapons (i.e., reactors, uranium enrichment or spent fuel reprocessing plants) or fissile material for military purposes.

The table below gives a rough comparison of the state of separation of military nuclear production facilities from civilian nuclear energy activities in the five nuclear weapon states under the NPT plus India, Pakistan, Israel and North Korea. The table divides production facilities into three types (although there clearly are many more facilities involved in the nuclear fuel cycle and nuclear weapons programs): reactors, reprocessing and uranium enrichment.

It uses four separate criteria: a) whether the facilities were used for dual military and civilian production; b) whether they were physically separated from civilian sites; c) whether there was administrative separation; and d) whether international safeguards have ever been applied at the site. Sites are considered physically separate when military sites do not contain civilian facilities on-site. They are considered administratively separate when budgets, personnel and programs are kept separate, minimizing the potential for material or facilities to fluidly shift from one to the other.

Separation between civil and military nuclear facilities in nuclear weapon states:

Types of facility	US	UK	France	Russia	China	India	Pakistan	Israel	North Korea
PRODUCTION REACTORS: Dual civilian uses?	✔	✔	✔	✔	X	✔	X	X	X
Physical separation?	✔	X	X	✔	X	X	✔	✔	X
Administrative separation?	>1974	> 1973	X	✔	X	?	For safety	✔	X
International safeguards on converted reactors?	X	?	X	X	X	Some	X	None	None
REPROCESSING: Dual civilian processing?	X	<1969	✔	✔	✔	✔	X	X	X
Physical separation?	✔	Some	X		X	X	X	✔	X
Administrative separation?	> 1974	Some	X	X	X	X	> 2001	✔	X
International safeguards?	NA	Some	Some	X	X	Some	X	X	X
ENRICHMENT: Dual civilian uses?	Converted	✔	✔	Converted	Converted	X	X	X	X
Physical separation?	✔	X	X	X	X	✔	X	✔	X
Administrative separation?	> 1974	> 1993	X	X	X	✔	X	✔	X
International safeguards?	Some	Some	Some	X	Some	X	X	X	X

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Nuclear power’s advocates and opponents often ignore links with nuclear weapons:

According to the International Atomic Energy Agency, 442 nuclear power reactors in 30 countries provide over 2,560 terawatt hours of electricity annually. This 2020 figure accounts for approximately 10% of global electrical power. Despite the 2011 Fukushima Daiichi nuclear disaster in Japan, 53 reactors are under construction in 19 countries. Meanwhile, pro-nuclear groups advocate nuclear energy as a solution to human-induced climate change and shrinking fossil fuel supplies. Major environmentalist groups and various experts disagree, arguing that rapid nuclear expansion would heighten accident risks and long-term waste disposal problems.

Most polls indicate a majority of US residents oppose building commercial power reactors and producing nuclear energy. Informative, but generally dated, public opinion studies point to construction costs and safety concerns such as waste storage as drivers of skepticism. Others highlight the influence of the environmentalist movement on public opinion and institutional decision-making. Notwithstanding these rationales, a critical area of public opinion remains understudied: the relationship between nuclear power and nuclear weapons. This tie has been central to policy in the nuclear age, as technologies used in nuclear power generation can contribute to nuclear weapons development. Today, nine countries possess nearly 13,000 nuclear weapons, which could be used with catastrophic effects. Public concerns about links between nuclear energy and the spread of nuclear weapons to additional states also remain salient. Civilian nuclear energy technologies are potential facilitators of nuclear weapons proliferation to new states. Nuclear power programs can be instrumental in the accumulation of technical knowledge and diversion of fissile materials for use in parallel military nuclear weapons programs. Indeed, beyond the nine nuclear-armed states, an additional 26 have explored development of nuclear weapons. Recent scholarship has shown that these countries may leverage civilian nuclear programs as a threat to build nuclear weapons. Considering the dual-use dilemma, the spread of this so-called “nuclear latency” may combine with the risk of nuclear weapons use to cast a long shadow over public opinion on nuclear energy.

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Civil nuclear power to nuclear proliferation:

The problem of nuclear proliferation is global, and any effective response must also be multilateral. Nine states (China, France, India, Israel, North Korea, Pakistan, Russia, the United Kingdom, and the United States) are known or believed to have nuclear weapons, and more than thirty others (including Japan, Germany, and South Korea) have the technological ability to quickly acquire them. Amid volatile energy costs, the accompanying push to expand nuclear energy, growing concerns about the environmental impact of fossil fuels, and the continued diffusion of scientific and technical knowledge, access to dual-use technologies seems destined to grow.

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Can a peaceful use of nuclear power be expanded without affecting the world’s nuclear proliferation?”

This question was qualitatively examined by Yim, comparing today’s world situation with the past situation during the AFPI (2006). It has been over 71 years since the Atoms for Peace Initiative (AFPI) begun. It was a grand global vision presented by US President Eisenhower to spread the benefits of nuclear energy while locking up the military use of the technology. Initially under the AFPI, 37 countries explored the use of civilian nuclear power technology between 1954 and 1962. The list was then expanded to 57 countries by 1973. Among these, a number of countries were also interested in nuclear weapons and pursued related developmental activities. Today, out of these 57 countries, three are known to possess nuclear weapons, and only 17 of them have operating nuclear power plant(s). Among those countries with operating nuclear power plants, the size of the country’s civilian nuclear generating capacity varies significantly depending upon each country’s situation.

Two questions arise in this observation:

-1) Does the interest or development in nuclear weapons have relationship with civilian nuclear power development, or vice versa?

-2) Is it possible to characterize the success of civilian nuclear power development in relation to nuclear weapons proliferation or other national attributes?

Regarding the first question, Fuhrmann (2009) investigated the relationship between civilian nuclear cooperation and nuclear weapons proliferation by using a data set compiled by Singh and Way (2004). Both the demand and the supply side of nuclear proliferation were represented in the data. Through case studies and statistical analysis of the data, he argued that all types of civilian nuclear assistance raise the risks of nuclear proliferation and that peaceful nuclear cooperation and proliferation are causally connected because of the dual-use nature of nuclear technology and know-how. But in a subsequent work, Fuhrmann (2012) indicated that the evidence does not support the argument that countries pursue civilian nuclear power to augment nuclear weapons programs.

By using a similar but expanded data set, a related work was performed by another research group (Li et al., 2010a). The goal of this work was to develop statistical models to project nuclear proliferation decisions of countries against the historical records from 1945 through 2000. The expanded section included the description of nuclear technological capabilities of the nations. In this work, proliferation events were considered as a continuum covering four distinct stages: 1) “no noticeable interest in nuclear weapons”, 2) “explore”, 3) “pursue”, and 4) “acquire.” The variables that affected the proliferation decisions at different stages were identified. This work showed that having research nuclear reactors and having experiences with them could contribute to the decision to “explore” or “pursue” nuclear weapons. The study also showed that “electricity generation capacity from nuclear power reactors” may work against nuclear weapons proliferation. This implies that, as the electricity generation capacity of nuclear power increases, the motivation for nuclear weapons proliferation may decrease. According to this result, it is expected that a country with a large established infrastructure of civilian nuclear power program would abstain from nuclear proliferation decisions.

In relation to the second question, Nelson and Sprecher (Nelson and Sprecher, 2000) made an attempt to characterize the importance of various factors in the development of nuclear energy. It was based on statistical analysis of 86 nuclear candidate states by using stepwise regression applied to a set of fourteen candidate independent variables as predictors of the percentage of electrical power that a state derives from nuclear energy (so called, nuclear reliance, in the paper). In this analysis, the unit of analysis is the state with variables represented by the most recently available data. Five independent variables were found to be significant in affecting a country’s nuclear reliance. The study found that three variables, international commercialization, level of democracy, and being unable to provide nuclear materials and technology domestically, each contributed to increase the nuclear reliance of a country. Two other variables, indigenous coal reserve and presence of fuel cycle production plants, were found to have potentially negative effect on nuclear reliance. The findings seem reasonable although the observation that presence of fuel cycle production plants had a negative effect on nuclear reliance can be argued. The study did not include the examination of the effect of nuclear weapons interest in the analysis.

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Plutonium proliferation dangers:

While electricity systems based on breeder reactors have not been built, it is still possible to use plutonium as a fuel in light water and other power reactors not designed to breed plutonium. In any case, about one-fourth to one-third of the energy in an LWR is derived from plutonium created in the course of reactor operation from the uranium-238 in the fuel rods. Further, the spent fuel rods from LWRs typically contain about 0.7 percent fissile isotopes of plutonium. This plutonium, while far less than the amount of fissile material used in the reactor, can be re-extracted for use as fuel. However, most reactors are not designed to operate on pure plutonium. The total amount of fissile material (uranium-235 plus fissile isotopes of plutonium) must be kept below the design level — in the vicinity of five percent for most LWRs. The plutonium is put into oxide form, mixed with depleted uranium oxide (mainly uranium-238 with about 0.2 percent uranium-235) to make a mixed oxide fuel (“MOX fuel”). Thus, it would appear that even without breeder reactors, plutonium can be useful as a nuclear reactor fuel.

While this argument is theoretically correct from the point of view of physics, it fails on economic grounds. The costs of MOX fuel fabrication, assuming that the plutonium was free (that is, obtained as surplus from the nuclear weapons program) is higher than the cost of processing and fabricating low enriched uranium oxide reactor fuel (4.4 percent enrichment). Further, the costs of disposing of MOX spent fuel are likely to be higher than those for uranium spent fuel because the MOX spent fuel will be more radioactive and contain two to three times more residual plutonium than uranium spent fuel. It is clear that so long as uranium prices are relatively low, the use of MOX fuel is uneconomical even under the most favorable circumstances: when the plutonium itself is free and uranium is assumed to be more expensive than current spot market prices. The cost difference is even greater when the cost of reprocessing is taken into account, because reprocessing would add hundreds of millions of dollars to lifetime fuel costs for each reactor. The fact that plutonium has a fuel value in physical terms does not make it economically practical. In addition, plutonium poses some proliferation liability which, although difficult to quantify, is a serious cost.

Although civilian plutonium has a different isotopic composition from plutonium that has been produced for weapons, it can be used to make a nuclear explosive, as demonstrated in a successful 1962 test by the United States Atomic Energy Commission. Continued reprocessing and use of plutonium pose a two-fold proliferation danger.

First, growing stockpiles of commercial separated plutonium undermine disarmament commitments under international treaties. Even if carried out for commercial reasons, reprocessing of plutonium can be perceived as simply adding to weapons-usable materials stockpiles. In the short-term, this could undermine effective global negotiations on a fissile material cut-off, and in the long-term, the Non-Proliferation Treaty, in which, under Article VI, signatories commit to “pursue negotiations in good faith on effective measures relating to the cessation of the arms race at an early date and to nuclear disarmament . . .”

Second is the danger of plutonium being diverted to a black market. The value of the plutonium would undoubtedly be far greater on a potential black market where the objective would be to make a weapon. The danger of plutonium diversion to a black market is particularly acute in Russia where the weakening of central control, combined with the rise of organized crime and poor economic conditions heighten the chances of diversion.

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Uranium proliferation dangers:

Most of the about 500 commercial nuclear power reactors operating or under construction in the world today require uranium ‘enriched’ in the U-235 isotope for their fuel. The commercial process employed for this enrichment involves gaseous uranium in centrifuges. Prior to enrichment, uranium oxide must be converted to a fluoride so that it can be processed as a gas, at low temperature. Uranium enriched to concentrations above 0.7% but less than 20% uranium-235 is defined as low enriched uranium (LEU). Most civil and commercial nuclear reactors use LEU that is about 3-5% uranium-235. Uranium enriched to more than 20% uranium-235 is defined as highly enriched uranium (HEU). All HEU is weapons-usable, but the lower the enrichment level the greater the amount of material required to achieve a critical mass—the amount of material required to build a bomb. States with nuclear weapons typically use so-called weapons-grade HEU, which is typically defined as 90% HEU or above, to minimize weapons’ size. Smaller and lighter nuclear weapons are much easier to deliver; ballistic missiles in particular can only deliver highly miniaturized nuclear weapons. From a non-proliferation standpoint, uranium enrichment is a sensitive technology needing to be subject to tight international control. In recent years there has been a significant surplus of world enrichment capacity.

Why does enrichment technology pose a proliferation risk?

Uranium enrichment poses a nuclear proliferation risk because the same technology that can produce LEU for reactor fuel can also be used to produce HEU for nuclear weapons. There are no technical barriers to prevent countries with enrichment capabilities from using them to enrich uranium to the higher levels required for nuclear weapons, only legal prohibitions.
The Treaty on the Non-Proliferation of Nuclear Weapons (NPT) prohibits non-nuclear weapon states (NNWS) from developing or acquiring nuclear weapons, and commits the five treaty-recognized nuclear-weapon states to pursuing nuclear disarmament. The NPT also requires NNWS to negotiate and conclude safeguards agreements with the International Atomic Energy Agency (IAEA), whose inspectors are tasked with monitoring states’ programs to verify that their declarations about their nuclear materials and activities are correct and complete. The NPT does not expressly prohibit non-nuclear weapon states from possessing enrichment facilities, as long as these facilities are used for peaceful purposes, declared, and placed under IAEA safeguards. Covert enrichment facilities, which have not been declared by a state to the IAEA, are a serious proliferation concern.
EMIS and gaseous diffusion are not ideal technologies for covert proliferators, as they are easily detected using satellite imagery analysis and other intelligence tools because of their large infrastructure requirements. Nonetheless, Iraq successfully hid an EMIS-based enrichment program from the world in the 1980s, perhaps in part because the U.S. and other intelligence communities assumed proliferating countries would not consider EMIS.
Centrifuges pose a unique proliferation challenge because detecting covert facilities in a timely manner is very difficult and existing centrifuges can be quickly reconfigured to produce HEU.
Currently, France, the United Kingdom, the Netherlands, Germany, the United States, Russia, Argentina, Brazil, India, Pakistan, and Iran are known to have uranium enrichment capabilities.
Breakout time is the theoretical amount of time required for a country to reconfigure an existing enrichment plant to produce enough HEU for a nuclear weapon. Breakout time only becomes relevant if a country makes the political decision to pursue nuclear weapons. While breakout time is regularly used in news reports about non-proliferation, states attempting to create a nuclear weapon are unlikely to base any real policy on breakout time calculations.
Breakout time is less when starting from an existing stockpile of uranium enriched to 3-5% uranium-235—the level used for nuclear power—than when starting with natural uranium. Enrichment removes unwanted uranium-238, making the concentration of uranium-235 atoms higher. It takes much more work to enrich uranium to 3-5% uranium-235 (typical power reactor fuel), than it does to further enrich uranium from 3-5% to 90% uranium-235 (weapons-grade material).

-Starting out with natural uranium, a facility with nearly 6,000 early-generation centrifuges could produce about 40 kg of weapons-grade uranium within a year.

-If material pre-enriched to 3.5% uranium-235 is used, a facility with the same capacity could produce about 180 kg of weapons-grade uranium per year.

Breakout time calculations do not take into account the other steps involved in acquiring nuclear weapons, such as designing, fabricating, testing, and deploying nuclear weapons on delivery systems. Although these steps could be pursued in parallel with the production of fissile material, they should be considered when assessing a country’s breakout potential.
A country could also “sneak out” by covertly constructing a small undeclared facility dedicated to the production of HEU to avoid IAEA safeguards altogether. A covert centrifuge plant could be small, underground, and therefore very difficult to detect remotely.

What are the chances that a country attempting to either “breakout” or “sneak out” would be discovered?

History shows countries are far more likely to “sneak out” than “breakout” precisely because breaking out is not covert. If a non-nuclear weapon state party to the NPT breaks out using a declared facility safeguarded by the IAEA, international inspectors would almost certainly detect the production of weapons-grade HEU or the diversion of LEU for further enrichment elsewhere. Although the time between detection and production of enough material for a nuclear weapon might be short, particularly if centrifuges are used, the proliferating country would still risk international pressure, including economic sanctions and possible military action.
Sneaking out might not be detected by the international community in a timely manner. Although a number of covert nuclear facilities have been revealed in recent years through intelligence sources and methods, some programs have remained undetected longer than others. All six countries found to have violated their NPT obligations with illicit nuclear activities did so by maintaining covert facilities (Iran, Iraq, North Korea, Libya, Romania, and Syria).

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Military interests are pushing new nuclear power plants:

Nuclear power is associated with radioactive waste, and characterized by substantially longer construction times compared to solar and wind making it too slow for reducing climate disruption. Spending on nuclear power also detracts from investing in renewable energy which presents opportunity costs. Investments in nuclear power thus not only tend to crowd-out spending on renewables, the resistance and resilience of nuclear production regimes moreover downsizes the benefits from increasing renewables deployment. With renewables and storage significantly cheaper, climate goals are achieved faster, more affordably and reliably by diverse other means. Nuclear power stations under construction are still not finished, running ten years late and many times over budget.

So why does this technology enjoy such intense and persistent generosity?

French president Emmanuel Macron summarises: “without civil nuclear power, no military nuclear power, without military nuclear, no civil nuclear”. This is largely why nuclear-armed France is pressing the European Union to support nuclear power. This is why non-nuclear-armed Germany has phased out the nuclear technologies it once led the world in. This is why other nuclear-armed states are so disproportionately fixated by nuclear power. It is the military interests of some nations that are pushing for new nuclear power plants.

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Examining relationship between nuclear proliferation and civilian nuclear power development, a 2013 study:

This paper attempts to examine the relationship between nuclear weapons proliferation and civilian nuclear power development based on the history of Atoms for Peace Initiative. To investigate the relationship, a database was established by compiling information on a country’s civilian nuclear power development and various national capabilities and situational factors. The results of correlation analysis indicated that the initial motivation to develop civilian nuclear power could be mostly dual purpose. However, for a civilian nuclear power program to be ultimately successful, the study finds the role of nuclear non-proliferation very important. The analysis indicated that the presence of nuclear weapons in a country and serious interest in nuclear weapons have a negative effect on the civilian nuclear power program. The study showed the importance of state level commitment to nuclear non-proliferation for the success of civilian nuclear power development. NPT ratification and IAEA safeguards were very important factors in the success of civilian nuclear power development. In addition, for a country’s civilian nuclear power development to be successful, the country needs to possess strong economic capability and be well connected to the world economic market through international trade. Mature level of democracy and presence of nuclear technological capabilities were also found to be important for the success of civilian nuclear power program.

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Warheads of Energy: Exploring the linkages between civilian nuclear power and nuclear weapons in seven countries, 2021 study:

This paper focuses on the causal determinants of the accumulation of nuclear weapons, also known as vertical nuclear proliferation, in China, France, India, Pakistan, Russia, UK, and the US. It empirically analyzes the causal relationships between the civilian uses of nuclear energy, military expenditures, trade openness, and the stockpiling of nuclear warheads. Results from the Toda and Yamamoto (1995) version of the Granger non-causality test suggest a causal relationship in five of the seven states. A potential nuclear power lock-in into their energy systems induced by vertical proliferation aspirations is also plausible for some of the states. Authors suggest that military nuclear relationships affect energy system developments and impede a nuclear phase-out in the seven states. Emphasizing the mutually beneficial relationship between a state’s nuclear warhead stockpiles and its civil nuclear capabilities helps to explain nuclear incumbency and the future use of nuclear power in nuclear armed states. Authors also discuss the implications from their results for sociotechnical transition theories which usually neglect the role of military nuclear related factors in describing energy system trajectories.

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Nuclear weapon to civil nuclear power:

Nuclear weapon to nuclear fuel:

Megatons to Megawatts, the Russian HEU deal:

Commitments by the USA and Russia to convert nuclear weapons into fuel for electricity production was known as the Megatons to Megawatts program. Surplus weapons-grade HEU resulting from the various disarmament agreements led in 1993 to an agreement between the US and Russian governments. Under this Russia would convert 500 tonnes of HEU from warheads and military stockpiles (equivalent to around 20,000 bombs) to LEU to be bought by the USA for use in civil nuclear reactors. HEU metal is first removed from a warhead, machined into shavings, oxidized and fluorinated. The resulting highly enriched uranium hexafluoride is then mixed in a gaseous stream with slightly enriched uranium to form LEU suitable for commercial nuclear reactors. The LEU is transferred to shipping cylinders. The whole deal is equivalent to 20,000 nuclear warheads and 89 million SWU. The 1993 agreement significantly depressed uranium exploration activities and the uranium price, which took until about 2003 to recover.

Downblending:

The opposite of enriching is downblending; surplus HEU can be downblended to LEU to make it suitable for use in commercial nuclear fuel. Downblending is a key process in nuclear non-proliferation efforts, as it reduces the amount of highly enriched uranium available for potential weaponization while repurposing it for peaceful purposes. Highly-enriched uranium from weapons stockpiles has been displacing some 8850 tonnes of U3O8 production from mines each year, and met about 13% to 19% of world reactor requirements through to 2013. Weapons-grade uranium and plutonium surplus to military requirements in the USA and Russia is being made available for use as civil fuel. Weapons-grade uranium is highly enriched, to over 90% U-235 (the fissile isotope). Weapons-grade plutonium has over 93% Pu-239 and can be used, like reactor-grade plutonium, in fuel for electricity production.

For more than five decades, concern has centred on the possibility that uranium intended for commercial nuclear power might be diverted for use in weapons. This gave way to a focus on the role of military uranium as a major source of fuel for commercial nuclear power. Since 1987 the United States and countries of the former USSR have signed a series of disarmament treaties to reduce the nuclear arsenals by about 80%. Nuclear materials declared surplus to military requirements by the USA and Russia have been converted into fuel for commercial nuclear reactors. This continues. With the disintegration of the Soviet Union, a unique opportunity arose to deploy military weapons material for making electricity. A 1993 agreement covered essentially the enrichment component of this material, but left unresolved the question of feed from mines, and a 1999 agreement dealt with what happened to the feed material.

The main weapons material is highly enriched uranium (HEU), containing at least 20% uranium-235 (U-235) and usually about 90% U-235. HEU can be blended down with uranium containing low levels of U-235 to produce low-enriched uranium (LEU), less than 5% U-235, fuel for power reactors. It is blended with depleted uranium (mostly U-238), natural uranium (0.7% U-235), or partially-enriched uranium.

Highly-enriched uranium in US and Russian weapons and other military stockpiles amounts to about 1500 tonnes, equivalent to about seven times annual world mine production. World stockpiles of weapons-grade plutonium are reported to be some 260 tonnes, which if used in mixed oxide fuel in conventional reactors would be equivalent to a little over one year’s world uranium production. Military plutonium can blended with uranium oxide to form mixed oxide (MOX) fuel. After LEU or MOX is burned in power reactors, the spent fuel is not suitable for weapons manufacture without reprocessing plant.

Nuclear weapon to plutonium and MOX fuel:

Disarmament will also give rise to some 150-200 tonnes of weapons-grade plutonium (Pu). Weapons-grade plutonium has over 93% of the fissile isotope, Pu-239, and can be used, like reactor-grade Pu, in fuel for electricity production. Options considered for it included:

Immobilisation with high-level waste – treating plutonium as waste,
Fabrication with uranium oxide as a MOX fuel for burning in existing reactors,
Fabrication with thorium as a fuel for existing Russian reactors,
Fuelling fast-neutron reactors.

Weapons-grade plutonium entering the civil fuel cycle needs to be kept under very tight security, and there are some technical measures needed to achieve this.

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Section-5

Nuclear stockpile and arms race:

The nuclear powers refer to the countries with a sizable nuclear arsenal. Nuclear power also means electricity generated by power plants that derive their heat from fission in a nuclear reactor. At present there are 9 countries in the world that possess nuclear weapons. They are:

Russia
United States
China
France
United Kingdom
Pakistan
India
Israel
North Korea

The exact number of nuclear weapons in each country’s possession is a closely held national secret, so the estimates presented here come with significant uncertainty. Most nuclear-armed states provide essentially no information about the sizes of their nuclear stockpiles. Yet the degree of secrecy varies considerably from country to country. Between 2010 and 2018, the United States disclosed its total stockpile size, but in 2019 the Trump administration stopped that practice. In 2020, the Biden administration restored nuclear transparency – a brief victory for nuclear accountability in a democratic country – but then declined to declassify any US stockpile data for 2021, 2022, or 2023. Similarly, in 2021 the United Kingdom announced that it would no longer disclose public figures for its operational stockpile, deployed warhead or deployed missile numbers. Additionally, as of 2024 both the United States and Russia have elected to no longer exchange publicly-available data about their deployed strategic warheads and launchers as mandated by the New START Treaty. Despite these limitations, however, publicly available information, careful analysis of historical records, and occasional leaks make it possible to make best estimates about the size and composition of the national nuclear weapon stockpiles. Nuclear weapon states have roughly 12,121 nuclear warheads, with over 9,585 in active military stockpiles and the average size of the 12,121 nuclear weapons is 200 kt. While this is a significant decline from the approximately 70,000 warheads owned by the nuclear-armed states during the Cold War, nuclear arsenals are expected to grow over the coming decade and today’s forces are vastly more capable.

Russia has the most confirmed nuclear weapons, with over 5,580 nuclear warheads. The United States follows behind with 5,044 nuclear weapons, hosted in the US and 5 other nations: Turkey, Italy, Belgium, Germany and the Netherlands. Total nuclear warheads owned by these 2 countries alone counts for nearly 90% of nuclear weapons in the world. Total number of warheads for North Korea and Israel is unconfirmed. However, it has been estimated that North Korea has enough fissile material to develop between 40-50 individual weapons, whilst Israel has material for up to 200, with an estimated 90 existing warheads.

Nuclear attacks can devastate any country in the world, but it’s important to take extra caution if you live near an important military base, airport, financial district, or any major industry. In warfare, nuclear weapons are deployed strategically to maximize impact, so beware of important landmarks that could make possible targets. A single nuclear warhead could kill hundreds of thousands of people, with lasting and devastating humanitarian and environmental consequences. Detonating just one 100 kt nuclear weapon alone over New York would cause an estimated 583,160 fatalities. Combined, Russia, the United States, the United Kingdom, France, China, India, Pakistan, Israel and North Korea possess over 12,000 nuclear weapons, most of which are many times more powerful than the nuclear weapon dropped on Hiroshima. Thirty-two other states are also part of the problem, with 6 nations hosting nuclear weapons, and a further 28 endorsing their use.

Tactical nuclear weapons:

A tactical nuclear weapon is any weapon that’s not been classified as “strategic” under US- Russian arms control agreements. The Federation of American Scientists currently estimates Russian non-strategic nuclear warheads at 1,912, and approximately 100 U.S. non-strategic warheads deployed in five European countries. While these are often framed as “smaller” or “low yield” nuclear weapons, and it’s implied that they would cause less damage, these warheads can have explosive yields up to 300 kilotons, or 20 times that of the bomb that destroyed Hiroshima.

The six states hosting another country’s nuclear weapons:

Belgium, Germany, Italy, the Netherlands and Turkey all host U.S. nuclear weapons. The United States insists that it maintains operational control of these weapons but their stationing in these countries helps U.S. nuclear war planning. In 2023, the president of Belarus, Alexander Lukashenko, announced that his country had started taking delivery of Russian tactical nuclear weapons.

The 28 Other Nuclear Endorsers:

Twenty-eight countries (plus the six hosts) also “endorse” the possession and use of nuclear weapons by allowing the potential use of nuclear weapons on their behalf as part of defence alliances, including the North Atlantic Treaty Organisation (NATO) and the Collective Security Treaty Organisation (CSTO).

All thirty-four countries that endorse nuclear weapon usage are:

Albania, Armenia, Australia, Belarus, Belgium, Bulgaria, Canada, Croatia, Czech, Denmark, Estonia, Finland, Germany, Greece, Hungary, Iceland, Italy, Japan, Latvia, Lithuania, Luxembourg, Montenegro, The Netherlands, North Macedonia, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, South Korea, Spain, Sweden and Turkey.

The end of World War II heralded the atomic age, and many countries embarked on a nuclear arms race. From 1945 to 1964, the United States, the Union of Soviet Socialist Republics (USSR), the United Kingdom, France, and China successively became nuclear-armed countries. By early 2022, nine countries possessed a total of approximately 13,000 warheads. (Figure below). The danger of use of nuclear weapons is greater than ever before due to proliferation of nuclear weapons, terrorism, and political instabilities. Russia’s recent invasion of Ukraine has heightened the nuclear war risks thus the public is increasingly concerned about nuclear weapons.

Figure above shows estimated global nuclear warhead inventories.

Combined, the United States and Russia now possess approximately 88 percent of the world’s total inventory of nuclear weapons, and 84 percent of the stockpiled warheads available for use by the military. Currently, no other nuclear-armed state sees a need for more than a few hundred nuclear weapons for national security, although many of these states are increasing their nuclear stockpiles. Globally, the overall inventory of nuclear weapons is declining, but the pace of reductions is slowing compared with the past 30 years. Moreover, these reductions are happening only because the United States and Russia are still dismantling previously retired warheads.

In contrast to the overall inventory of nuclear weapons, the number of warheads in global military stockpiles – which comprises warheads assigned to operational forces – is increasing once again. The United States is still reducing its nuclear stockpile slowly. France and Israel have relatively stable inventories. But China, India, North Korea, Pakistan and the United Kingdom, as well as possibly Russia, are all thought to be increasing their stockpiles.

Of the world’s approximate 12,121 nuclear warheads, roughly 9,585 are in the military stockpiles for use by missiles, aircraft, ships and submarines. The remaining warheads have been retired but are still relatively intact and are awaiting dismantlement. Of the 9,585 warheads in the military stockpiles, some 3,904 are deployed with operational forces (on missiles or bomber bases). Of those, approximately 2,100 US, Russian, British and French warheads are on high alert, ready for use on short notice. (see table below):

Country	Deployed Strategic	Deployed Nonstrategic	Reserve/ Nondeployed	Military Stockpile	Total Inventory
Russia	1,710	0	2,670	4,380	5,580
United States	1,670	100	1,938	3,708	5,044
France	280	n.a.	10	290	290
China	24	n.a.	476	500	500
United Kingdom	120	n.a.	105	225	225
Israel	0	n.a.	90	90	90
Pakistan	0	n.a.	170	170	170
India	0	n.a.	172	172	172
North Korea	0	n.a.	50	50	50

Table above shows breakdown of the nuclear warhead categories of the different nuclear-armed states.

How to read this table:

“Deployed strategic warheads” are those deployed on intercontinental missiles and at heavy bomber bases. “Deployed nonstrategic warheads” are those deployed on bases with operational short-range delivery systems. “Reserve/Nondeployed” warheads are those not deployed on launchers but in storage (weapons at bomber bases are considered deployed). The “military stockpile” includes active and inactive warheads that are in the custody of the military and earmarked for use by commissioned deliver vehicles. The “total inventory” includes warheads in the military stockpile as well as retired, but still intact, warheads in the queue for dismantlement.

In historical context, the number of nuclear weapons in the world has declined significantly since the Cold War: down from a peak of approximately 70,300 in 1986 to an estimated 12,100 in early-2024. Government officials often characterize that accomplishment as a result of current or recent arms control agreements, but in reality the overwhelming portion of the reduction happened in the 1990s. Some also compare today’s numbers with those of the 1950s, but that is like comparing apples and oranges; today’s forces are vastly more capable. The pace of reduction has slowed significantly compared with the 1990s and appears to continue only because of dismantlement of retired weapons; the trend is that the military stockpiles (useable nuclear weapons) are increasing again. Overall, the total number of weapons deployed this century is highly uncertain. But it’s important to note that the number of weapons and the chances of nuclear war aren’t independent. Greater the number of warheads being built, higher the risk for nuclear war.

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Decline in number of nuclear weapons and its destructiveness:

The number of nuclear weapons has declined substantially since the end of the Cold War. After increasing for almost half a century after their creation in the 1940s, nuclear arsenals reached over 70,000 warheads in 1986. Since then we have seen a reversal of this trend, as the chart below shows. The nuclear powers reduced their arsenals a lot in the following decades, and the number of warheads fell below 20,000 in the 2010s. The decline has slowed since then, and the total stockpile still consists of more than 12,000 warheads. Some countries have also been expanding their arsenals.

Note: The exact number of countries’ warheads is secret, and the estimates are based on publicly available information, historical records, and occasional leaks.

The destructiveness of nuclear arsenals has also declined.

A simple count of the number of warheads, as shown in the above chart, does not consider that these weapons differ in their explosive power. It also does not consider that not all of them can be used at once. The data shown in the following chart attempts to take this into account. It considers the destructiveness and deployment of nuclear warheads to arrive at an estimate of the explosive power of nuclear weapons deliverable in a first strike.

We can see that the United States rapidly developed much more powerful warheads in the 1950s. The Soviet Union increased the destructiveness of its weapons more slowly but ultimately reached similar levels. The destructive potential of first-strike warheads peaked at more than 15,000 Mt in the early 1980s. This amounts to more than a million Hiroshima bombs. At this peak, first-strike weapons could destroy more than 40% of the total urban land worldwide. However, the destructiveness of first strikes has been steadily declining for decades, for both the United States and the Soviet Union/Russia. Yet, it has still been more than 2,500 Mt, with the potential to directly destroy almost 7% of the total urban land worldwide.

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NPT nuclear weapon states:

At the dawn of the nuclear age, the United States hoped to maintain a monopoly on its new weapon, but the secrets and the technology for building the atomic bomb soon spread. The United States conducted its first nuclear test explosion in July 1945 and dropped two atomic bombs on the cities of Hiroshima and Nagasaki, Japan, in August 1945. Just four years later, the Soviet Union conducted its first nuclear test explosion. The United Kingdom (1952), France (1960), and China (1964) followed. Seeking to prevent the nuclear weapon ranks from expanding further, the United States and other like-minded countries negotiated the nuclear Nonproliferation Treaty (NPT) in 1968 and the Comprehensive Nuclear Test Ban Treaty (CTBT) in 1996.

The nuclear-weapon states (NWS) are the five states—China, France, Russia, the United Kingdom, and the United States—officially recognized as possessing nuclear weapons by the NPT. The treaty recognizes these states’ nuclear arsenals, but under Article VI of the NPT, they are not supposed to build and maintain such weapons in perpetuity. In 2000, the NWS committed themselves to an “unequivocal undertaking…to accomplish the total elimination of their nuclear arsenals.”

Non-NPT Nuclear Weapons Possessors:

India, Pakistan, and Israel never joined the NPT and are known to possess nuclear weapons. India first tested a nuclear explosive device in 1974. That test spurred Pakistan to ramp up work on its secret nuclear weapons program. India and Pakistan both publicly demonstrated their nuclear weapon capabilities with a round of tit-for-tat nuclear tests in May 1998. Israel has not publicly conducted a nuclear test but is universally believed to possess nuclear arms. Their arsenal estimates are based on the amount of fissile material—highly enriched uranium and plutonium—that each of the states is estimated to have produced. Fissile material is the key element for making nuclear weapons. India and Israel are believed to use plutonium in their weapons, while Pakistan is thought to use highly enriched uranium.

North Korea joined the NPT as a non-nuclear weapon state but announced its withdrawal from the NPT in 2003 –a move that has not been legally recognized by the other NPT member states. North Korea has tested nuclear devices and nuclear-capable ballistic missiles. North Korea is estimated to have approximately 30 nuclear warheads and likely possesses additional fissile material that is not weaponized, but there is a high degree of uncertainty surrounding these estimates. North Korea currently operates its 5-megawatt heavy-water graphite-moderated reactor to extract plutonium for its nuclear warheads. North Korea has uranium enrichment technology and a known uranium enrichment facility at Yongbyon. It likely operates additional covert uranium enrichment facilities at other locations. North Korea has developed nuclear capable missiles of various ranges, including ICBMs, and claims to have developed tactical nuclear warheads.

States of Immediate Proliferation Concern:

Iran is a threshold state—it has developed the necessary capacities to build nuclear weapons. Tehran has threatened to withdraw from the NPT and to pursue a nuclear deterrent if its security considerations shift. Iran ratified the NPT in 1970 but pursued illicit nuclear activities, including an organized nuclear weapons program, through 2003, according to the International Atomic Energy Agency (IAEA) and the US intelligence community. In July 2015, Iran and six world powers negotiated an agreement to limit the country’s nuclear program and enhance transparency in exchange for relief from sanctions directed at Iran for breaching its NPT commitments. In May 2018, the United States withdrew from the JCPOA and reimposed sanctions on Iran. The following year Iran began breaching the JCPOA’s nuclear restrictions. Tehran maintains that it does not intend to pursue nuclear weapons and that its actions are a response to the U.S. withdrawal from the nuclear deal and reimposition of sanctions. Iran has accumulated enough uranium enriched to 60 percent to build nuclear weapons, but the warhead would be large, unwieldy, and inconsistent with the weapons-related work Iran did prior to 2003.

States that had nuclear weapons or Nuclear Weapons Programs at one time:

Belarus, Kazakhstan, and Ukraine inherited nuclear weapons following the Soviet Union’s 1991 collapse but returned them to Russia and joined the NPT as non-nuclear-weapon states.
The apartheid South African government secretly developed a small number of nuclear weapons. South Africa joined the NPT in 1991 and dismantled its entire nuclear weapons program prior to its transition to a multi-racial democracy in 1994.
Iraq had an active nuclear weapons program prior to the 1991 Persian Gulf War but was forced to verifiably dismantle it under the supervision of UN inspectors. The United States invaded Iraq in 2003 under the Bush administration’s rationale of preventing Iraq from acquiring weapons of mass destruction. However, Iraq’s nuclear program had remained dormant since its dismantlement in the 1990s and the country did not have ready stockpiles of chemical or biological weapons.
Libya voluntarily renounced its secret nuclear weapons efforts in December 2003.
The IAEA is seeking clarification from Syria regarding its nuclear program. In 2007, Israel bombed a reactor under construction at Al Kibar. Evidence suggests Syria was constructing the reactor as part of an illicit nuclear weapons effort.
Argentina, Brazil, South Korea, Sweden, Australia, and Taiwan also once pursued nuclear weapons programs.

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Arms race:

An arms race occurs when two or more groups compete in military superiority. It consists of a competition between two or more states to have superior armed forces, concerning production of weapons, the growth of a military, and the aim of superior military technology. Unlike a sporting race, which constitutes a specific event with winning interpretable as the outcome of a singular project, arms races constitute spiralling systems of on-going and potentially open-ended behavior. The existing scholarly literature is divided as to whether arms races correlate with war. International-relations scholars explain arms races in terms of the security dilemma, engineering spiral models, states with revisionist aims, and deterrence models.

Nuclear Arms Race during the Cold War:

The Cold War marked a period of rising tensions between the Soviet Union and the United States of America. Throughout the second half of the 20th century, these two superpowers held extremely different economic and political beliefs, which further deepened the divide between the states. The Soviet Union practiced a communist form of government, with complete governmental control of property, wealth, and education. On the other hand, the United States promoted a free and capitalist form of government, characterized by democratic elections and privately held businesses or organizations. This ideological difference between the superpowers put them in direct opposition to one another. As a result, competition arose in many areas including the development of new technology and military weapons- the most important being the nuclear bomb. This contest of the advancement of offensive nuclear capabilities occurred during the Cold War, an intense period between the Soviet Union and the United States and some other countries. During the second half of the 20th century, the two superpowers competed for superiority in the development and accumulation of nuclear weapons. Four years after the U.S. successfully dropped its first bomb, the Soviets developed theirs. With deterrence at the core of foreign policy, both sides worked to increase their arms stock. This resulted in the U.S. spending six trillion dollars on its nuclear weapons program, containing ten thousand nuclear warheads, while Russia had only half as many. Although the arms race was meant to increase each state’s security, it backfired in several instances. For example, in the 1950s, the Soviets issued nuclear threats against Western allies, including the British and French during the Suez crisis. Tensions rose and consequentially cumulated in the Cuban Missile Crisis in 1962, which was the closest the world has ever been to nuclear war. This period marks an intense time in history when two countries were racing to stockpile the most deadly weapon in the world: the nuclear bomb. The perceived advantages of the adversary by both sides (such as the “missile gap” and “bomber gap”) led to large spending on armaments and the stockpiling of vast nuclear arsenals. Proxy wars were fought all over the world (e.g. in the Middle East, Korea, and Vietnam) in which the superpowers’ conventional weapons were pitted against each other. After the dissolution of the Soviet Union and the end of the Cold War, tensions decreased and the nuclear arsenal of both countries were reduced.

21st century nuclear arms race:

On 13 December 2001, George W. Bush gave Russia notice of the United States’ withdrawal from the Anti-Ballistic Missile Treaty. This led to the eventual creation of the American Missile Defense Agency. Russian President Vladimir Putin responded to the withdrawal by ordering a build-up of Russia’s nuclear capabilities, designed to counterbalance U.S. capabilities.

On April 8, 2010, U.S. President Barack Obama and Russian President Dmitry Medvedev signed the New START Treaty, which called for a fifty percent reduction of strategic nuclear missile launchers and a curtailment of deployed nuclear warheads. The U.S. Senate ratified the treaty in December 2010 by a three-quarter majority.

On December 22, 2016, U.S. President Donald Trump proclaimed in a tweet that “the United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes,” effectively challenging the world to re-engage in a race for nuclear dominance. The next day, Trump reiterated his position to Morning Joe host Mika Brzezinski of MSNBC, stating: “Let it be an arms race. We will outmatch them at every pass and outlast them all.”

In October 2018, the former Soviet leader Mikhail Gorbachev commented that U.S. withdrawal from the INF nuclear treaty is “not the work of a great mind” and that “a new arms race has been announced”.

In 2019, Russian Deputy Foreign Minister Sergey Ryabkov warned about the risk of nuclear war, as negative dynamics had been noticeable over the previous year. He urged the nuclear states to build channels on forestalling potential incidents in order to lower the risks.

On February 21, 2023, Russian President Vladimir Putin suspended Russia’s participation in the New START nuclear arms reduction treaty with the United States, saying that Russia would not allow the US and NATO to inspect its nuclear facilities.

In July 2024, the Biden administration announced its intention to deploy long-range missiles in Germany starting in 2026 that could hit Russian territory within 10 minutes. In response, Russian President Putin warned of a Cold War-style missile crisis and threatened to deploy long-range missiles within striking distance of the West. US weapons in Germany would include SM-6 and Tomahawk cruise missiles and hypersonic weapons. The United States’ decision to deploy long-range missiles in Germany has been compared to the deployment of Pershing II launchers in Western Europe in 1979. Critics say the move would trigger a new arms race. According to Russian military analysts, it would be extremely difficult to distinguish between a conventionally armed missile and a missile carrying a nuclear warhead, and Russia could respond by deploying longer-range nuclear systems targeting Germany.

In August 2024, The Economist reported that “a new nuclear arms race draws closer”, as the U.S. is considering increasing its nuclear forces in response to escalating threats and rapid nuclear expansions by China and Russia, as well as North Korea’s advancements in missile technology and Iran’s advancement as a “threshold” nuclear state. China is expanding its nuclear force and is on pace to nearly quadruple the number of warheads it has by 2035, rapidly closing its gap with the United States. China is also closely watching how the international community reacts to Russia’s threat to use nuclear weapons in Ukraine. If Russia is able to gain its objectives by means of nuclear threats, China will derive lessons from that and could be potentially making these kinds of threats against Taiwan or other neighboring countries in connection with China’s territorial ambitions.

Arms race in south Asia:

Indian and Pakistani nuclear developments are the main cause of arms race concerns. Ideally, the best measure of whether the two are in fact in a classic, reciprocal nuclear arms competition would be the rate at which both sides are deploying nuclear-armed missiles or bombs (or, perhaps, “deployable” missiles, given the going assumption that both countries keep their nuclear weapons in a recessed posture, with warheads and delivery vehicles stored separately). But these data are not public. The U.S. and Soviet nuclear data was eventually reported under their bilateral arms control treaties, but no analogous process or mechanism yet exists in South Asia under which India and Pakistan might share or publish such information. The best estimates from Western nongovernmental experts put the number of weapons in each state’s arsenal at 80–100 for India and 90–110 for Pakistan, and they suggest that India and Pakistan have both doubled their nuclear inventories over the last decade. Indeed, scholars have cited this apparent growth to argue that an arms race does indeed exist. These are useful estimates, but they are assessments based primarily on calculations of fissile material and delivery vehicle production, rather than hard data. An analysis of aggregated missile test data since 1998 reveals that the armament dynamic is far more complex. The types and ranges of missiles under development provide concrete evidence of the divergence in their nuclear objectives and security strategies. India and Pakistan are indeed racing toward their respective national security objectives, but they are running on different tracks and chasing vastly different goals. Pakistan is building weapons systems to deter India from conventional military operations below the nuclear threshold. India is developing systems primarily to strengthen its strategic deterrent against China, meaning this dynamic is not confined to the subcontinent.

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Rationale for nuclear arms race:

The successful exercise of power depends on both possession of the means of power and demonstration of the will to use it. Stronger will has often been a more important determinant of the victory than arms—witness Hitler’s successful invasion of the Rhineland in the face of vastly stronger French military power and the victory of the North Vietnamese over the United States. The more conventional weapons a nation had the more powerful it appeared to be and, indeed, the more powerful it really was. The accumulation of nuclear weapons, beyond the level where each nuclear opponent can destroy the other many times over, no matter how large or sophisticated the other’s nuclear arsenal (a level long since exceeded by the United States and the Soviet Union), conveys only the appearance of security and power. As a result, the main function of nuclear weapons has become to demonstrate determination to prevail. To put it bluntly, with nuclear weapons appearance is really all that counts: . . objective reality, whatever that may be, is simply irrelevant: only the subjective phenomena of perception and value-judgment count (Luttwak, 1977). Furthermore, an arsenal that is continually innovating is a more convincing demonstration of will than one that is static: “A growing and innovative arsenal will be perceived as more powerful than one which is static—even if the latter retains an advantage in purely technical terms” (Kline, 1975). These arguments, incidentally, provide intellectual justification for the pursuit of an endless arms race not only with the military establishments of other nations but also within the military establishment of each of them. Under the spur of the drive for power each of the military services competes with the other for a larger share of the military budget, and each goes to great length to justify its need for ever new and more sophisticated weaponry. A possibly hopeful consequence of the universal recognition that the use of nuclear weapons in combat carries an inordinately high risk is that, in contrast to previous arms races, the major purpose of both nuclear superpowers is not to win a nuclear war but to avoid or prevent one. Unfortunately, this goal itself becomes a justification for pursuit of the nuclear arms race.

The justification goes something like this: Prudence requires that military policy be based on the worst case assessment, the worst case in this instance being that the opponents believe they can win a nuclear war. Each side can quote ample evidence for this possibility in the form of public statements by military and political leaders, military directives, elaborate preparations to enable essential leaders to function during a prolonged nuclear war, and the like. Should the opponents come to believe that they could prevail in a nuclear war, the argument continues, they might threaten to attack. Our side would then be faced with the dread alternatives of yielding to this nuclear blackmail or launching a nuclear holocaust. Therefore our side must maintain escalation dominance—that is, sufficient superiority at every level of armaments and in all nuclear weapon systems, so that the opponents could not possibly believe blackmail would succeed.

The detonation of any tactical nuclear weapon would be an unprecedented test of the dogma of deterrence, a theory that has underwritten America’s military policy for the past 70 years. The idea stipulates that adversaries are deterred from launching a nuclear attack against the United States — or more than 30 of its treaty-covered allies — because by doing so they risk an overwhelming counterattack. Possessing nuclear weapons isn’t about winning a nuclear war, the theory goes; it’s about preventing one. It hinges upon a carefully calibrated balance of terror among nuclear states. After the nuclear age began in 1945, the United States and the Soviet Union were locked in an arms race. Each side amassed tens of thousands of nuclear arms. Over time, nuclear weapons became symbols of national power and prestige. Other nations in Europe and Asia developed their own arsenals. The dangerous, costly arms buildup pushed Washington and Moscow to the brink of confrontation, before a gradual warming in relations led to mutual reductions. In the decades since, overall nuclear stockpiles have shrunk, but the number of nuclear powers has increased to nine.

Charles Glaser argues that numerous cases of arms races were suboptimal, as they entailed a waste of resources, damaged political relations, increased the probability of war, and hindered states in accomplishing their goals. However, arms races can be optimal for security-seeking states in situations when the offense-defense balance favours offense, when a declining state faces a rising adversary, and when advances in technology make existing weapons obsolete for the power that had an advantage in the existing weaponry.

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National Pragmatic Safety Limit for Nuclear Weapons:

In the past, the size of the nuclear weapons arsenal for a given nation was determined through a military and policy analysis of deterrence and the ability to fund the stockpile. Realizing there are fundamental limits to safety, studies have looked at the implications of “close calls” including technical glitches, misinterpretation of military exercises, inadvertent nuclear war (where one side believes it is being attacked), accidental nuclear detonation, escalation of convention war and other accidental potential paths to nuclear Armageddon. Despite strong arguments for limiting nuclear weapons inventories because of the risks of accidents, full-scale nuclear war or threats of retaliation for first strikes would need large arsenal of nuclear weapons. However, there is a fundamental upper limit for the number of nuclear weapons needed by any country. This fundamental limit, defined as the pragmatic limit, is based on the direct physical negative consequences of a large number of nuclear weapons being used anywhere on the globe. The nuclear pragmatic limit means the direct physical negative consequences of nuclear weapons use are counter to national interests. Stated simply: no country should have more nuclear weapons than the number necessary for unacceptable levels of environmental blow-back on the nuclear power’s own country if they were used. A 2018 study, National Pragmatic Safety Limit for Nuclear Weapon Quantities attempts to provide a general answer to that question by analyzing the limit set by the number of nuclear weapons that could create a global nuclear winter severe enough to destabilize the source nation. The results found that 100 nuclear warheads is adequate for nuclear deterrence in the worst case scenario, while using more than 100 nuclear weapons by any aggressor nation (including the best positioned strategically to handle the unintended consequences) even with optimistic assumptions (including no retaliation) would cause unacceptable damage to their own society. Thus, 100 nuclear warheads is the pragmatic limit and use of government funds to maintain more than 100 nuclear weapons does not appear to be rational.

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Section-6

Nuclear warfare strategy:

Nuclear warfare strategy is a set of policies that deal with preventing or fighting a nuclear war. The policy of trying to prevent an attack by a nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence. The goal in deterrence is to always maintain a second strike capability (the ability of a country to respond to a nuclear attack with one of its own) and potentially to strive for first strike status (the ability to destroy an enemy’s nuclear forces before they could retaliate). During the Cold War, policy and military theorists considered the sorts of policies that might prevent a nuclear attack, and they developed game theory models that could lead to stable deterrence conditions.

Different forms of nuclear weapons delivery allow for different types of nuclear strategies. The goals of any strategy are generally to make it difficult for an enemy to launch a pre-emptive strike against the weapon system and difficult to defend against the delivery of the weapon during a potential conflict. This can mean keeping weapon locations hidden, such as deploying them on submarines or land mobile transporter erector launchers whose locations are difficult to track, or it can mean protecting weapons by burying them in hardened missile silo bunkers. Other components of nuclear strategies included using missile defense to destroy the missiles before they land or implementing civil defense measures using early-warning systems to evacuate citizens to safe areas before an attack.

Critics of nuclear war strategy often suggest that a nuclear war between two nations would result in mutual annihilation. From this point of view, the significance of nuclear weapons is to deter war because any nuclear war would escalate out of mutual distrust and fear, resulting in mutually assured destruction. This threat of national, if not global, destruction has been a strong motivation for anti-nuclear weapons activism. Critics from the peace movement and within the military establishment have questioned the usefulness of such weapons in the current military climate. According to an advisory opinion issued by the International Court of Justice in 1996, the use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, but the court did not reach an opinion as to whether or not the threat or use would be lawful in specific extreme circumstances such as if the survival of the state were at stake.

Another deterrence position is that nuclear proliferation can be desirable. In this case, it is argued that, unlike conventional weapons, nuclear weapons deter all-out war between states, and they succeeded in doing this during the Cold War between the U.S. and the Soviet Union. In the late 1950s and early 1960s, Gen. Pierre Marie Gallois of France, an adviser to Charles de Gaulle, argued in books like The Balance of Terror: Strategy for the Nuclear Age (1961) that mere possession of a nuclear arsenal was enough to ensure deterrence, and thus concluded that the spread of nuclear weapons could increase international stability. Some prominent neo-realist scholars, such as Kenneth Waltz and John Mearsheimer, have argued, along the lines of Gallois, that some forms of nuclear proliferation would decrease the likelihood of total war, especially in troubled regions of the world where there exists a single nuclear-weapon state. Aside from the public opinion that opposes proliferation in any form, there are two schools of thought on the matter: those, like Mearsheimer, who favored selective proliferation, and Waltz, who was somewhat more non-interventionist. Interest in proliferation and the stability-instability paradox that it generates continues to this day, with ongoing debate about indigenous Japanese and South Korean nuclear deterrent against North Korea.

The threat of potentially suicidal terrorists possessing nuclear weapons (a form of nuclear terrorism) complicates the decision process. The prospect of mutually assured destruction might not deter an enemy who expects to die in the confrontation. Further, if the initial act is from a stateless terrorist instead of a sovereign nation, there might not be a nation or specific target to retaliate against. It has been argued, especially after the September 11, 2001, attacks, that this complication calls for a new nuclear strategy, one that is distinct from that which gave relative stability during the Cold War. Since 1996, the United States has had a policy of allowing the targeting of its nuclear weapons at terrorists armed with weapons of mass destruction. Robert Gallucci argues that although traditional deterrence is not an effective approach toward terrorist groups bent on causing a nuclear catastrophe, Gallucci believes that “the United States should instead consider a policy of expanded deterrence, which focuses not solely on the would-be nuclear terrorists but on those states that may deliberately transfer or inadvertently leak nuclear weapons and materials to them. By threatening retaliation against those states, the United States may be able to deter that which it cannot physically prevent.”.

Graham Allison makes a similar case, arguing that the key to expanded deterrence is coming up with ways of tracing nuclear material to the country that forged the fissile material. “After a nuclear bomb detonates, nuclear forensics cops would collect debris samples and send them to a laboratory for radiological analysis. By identifying unique attributes of the fissile material, including its impurities and contaminants, one could trace the path back to its origin.” The process is analogous to identifying a criminal by fingerprints. “The goal would be twofold: first, to deter leaders of nuclear states from selling weapons to terrorists by holding them accountable for any use of their weapons; second, to give leaders every incentive to tightly secure their nuclear weapons and materials.”

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Conventional vs nuclear weapon use:

Over the years, technological advances have made conventional weapons more deadly and accurate. Missiles and bombs carrying powerful conventional munitions can be redirected in flight and guided precisely to their target by satellite positioning data, laser spotters, and terminal seekers. With such accuracy, less explosive power is required to destroy many targets, reducing the military imperative for nuclear weapons.

Yet while the general trend has been to conventional weapons substituting for nuclear, certain capabilities would provide a significant advantage over conventional alternatives in some circumstances.

First, some military targets, such as hardened, deep targets, will resist all but nuclear weapons.

Second, nuclear weapons compensate for inaccuracy, delivering greater explosive yield and farther lethality. In ideal conditions, high-tech conventional munitions can destroy targets with conventional ordnances delivered accurately. In wartime, however, you may have sparse intelligence, surveillance, and reconnaissance information on adversary possibly because of disruptions caused by space and cyberspace attacks, or may discover that terminal seekers are less effective than expected. Nuclear weapons can disable many forces over a wide area by delivering significant blast, overpressure, and radiation; the affected area may be wider still if the you optimize strikes to emit a strong electromagnetic pulse (EMP).

Third, nuclear forces can compensate for lack of available firepower. As a conflict develops, you may be short of conventional-strike options, either because munitions stocks have been depleted or the location and disposition of its conventional forces are disadvantageous.

You may consider the benefits of nuclear employment before or during a conflict. You are risk-prone and may conduct nuclear strikes to overcome conventional shortfalls, hoping that the combined instrumental and suggestive effect of nuclear use will force adversary to back down. Alternatively, you might enter a conflict expecting to win via conventional means, but discover that its non-nuclear military capabilities are insufficient. In these circumstances, the pressure of war may push political and military leaders to explore military operations that incorporate nuclear weapons.

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Nuclear Employment Strategies:

Simply speaking, there are two general types of nuclear employment strategies; counterforce doctrine, the targeting of an opponent’s military infrastructure with a nuclear strike. The counterforce doctrine is differentiated from the countervalue doctrine, which targets the enemy’s cities, destroying its civilian population and economic base. The counterforce doctrine asserts that a nuclear war can be limited and that it can be fought and won.

Counter-force employs nuclear forces to destroy the military capabilities of an enemy or render them impotent. Typical counter force targets include: bomber bases, ballistic missile submarine bases, intercontinental ballistic missile (ISBM) silos, antiballistic and air defense installations, command and control centers, and weapons of mass destruction storage facilities. Generally, the nuclear forces required to implement a counter-force target strategy are larger and more accurate than those required to implement a counter-value strategy. Counter-force targets generally tend to be harder, more protected, more difficult to find, and more mobile than counter-value targets.

In response to the 1950s strategy of massive retaliation, which maintained that the United States would respond to Soviet aggression with an all-out nuclear attack, counterforce strategies sought to give the United States more options in countering communist threats. Counterforce targeting was developed with the idea of limiting damage and protecting cities in the event of a nuclear war. The “city avoidance” principle was the driving force behind counterforce targeting, and the hope was that both the United States and the Soviet Union could establish some ground rules to be followed in the event of a nuclear exchange. The idea was to create rules for a limited nuclear exchange to prevent escalation to an all-out general nuclear war.

The Berlin crisis of 1961 and the Cuban missile crisis of 1962 created the sense that nuclear war with the Soviet Union was a real possibility. The United States wanted to be able to minimize costs and limit damage should deterrence fail. The idea was to reassure the Soviet Union that the United States would not target its cities and to give the Soviets an incentive to refrain from striking American cities. For counterforce to work, the United States would have to convince the Soviets that they would both benefit from fighting a nuclear war in these limited, structured terms. This implied a mutual understanding.

The main problem with the counterforce doctrine lay in its inevitable association with a pre-emptive first strike. A first strike aimed at an opponent’s military facilities and weapons systems could effectively disarm the enemy. The United States assured the Soviet Union that it had no intention of launching a first strike, but these assurances were not enough. Counterforce continued to be associated with an offensive first strike, not a defensive doctrine. It was hard for the Soviets to believe that the United States intended counterforce to be used only in a second strike. And for counterforce to work, the United States had to successfully convince the Soviet Union that it would not launch a first strike.

Another issue with counterforce targeting was that an incredible level of precision would be needed to accurately target missiles so that they would hit only military installations. Collateral damage would be unavoidable, though, because many military bases and missile installations were located in close proximity to cities, in both the United States and the Soviet Union. Even “limited” counter-force attacks would create extensive collateral damage. Large-scale attacks, even purely counterforce, would have devastating civilian consequences and cause climate effects and famine on a global scale.

Alpha strike:

Alpha strike is a pre-emptive attack on a hostile enemy, first targeting their nuclear weapons and military assets. This, in theory, would prevent the enemy from retaliating with their entire arsenal, cutting projected deaths to more “acceptable” levels (albeit still in the millions, in most cases). The catch with an alpha strike is that it would have to be comprehensive. In other words, you’d have to wipe out most, if not all, of the enemy’s weapons before they had the chance to retaliate. And since both American and Russian leaders have their own versions of a “nuclear football” on hand to initiate a launch at any time, you’d have to be extremely quick.

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Potential benefits of limited nuclear strike:

There are two rationales by which to improve your position through limited nuclear strikes.

First, taking nuclear action suggests the potential for yet further escalation: if gradually increasing nuclear threats fail to arrest the adversary, a nuclear strike might increase the credibility of escalation threats. Potentially suggestive nuclear attacks could range from a single strike against a remote military target to strikes that inflict significant collateral damage against a number of military targets. Further escalation might be threatened by signaling a willingness to impose higher costs on the adversary until they back down or by warning that further escalation could not be meaningfully restrained should the adversary counter-escalate. With either approach, the goal is to terrorize adversary’s political and military decision makers and populations.

A second rationale for using nuclear weapons is to achieve instrumental benefits in the conflict. Rather than coercing decision makers and populations via the spectre of an escalating nuclear war, instrumental escalation coerces by decisively improving the aggressor’s military position. Instrumental use might seem particularly attractive, insofar as the tactical benefits of limited nuclear strikes would translate to operational or strategic effects. If you can use nuclear weapons to degrade the adversary’s ability to command and control forces, flow surge forces to the battlefield, or project air- and naval power in the conflict area, the cost to the adversary of restoring the status quo ante would significantly increase.

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Logic of Nuclear Superiority:

What role do nuclear weapons play in international crisis politics?

How does nuclear superiority affect the likelihood that a state achieves its goals in an international crisis?

Scholars have long been sceptical about the benefits of nuclear superiority. In 1987, Glenn H. Snyder and Paul Diesing argued that even states with small nuclear arsenals should be able to successfully threaten superior opponents, since the costs of nuclear war for any state, regardless of nuclear capability, would be massive. In 1945, Bernard Brodie wrote that “it would make little difference if one power had more bombs and were better prepared to resist them than the opponent,” as any nuclear war would be so destructive to both sides. An important implication is articulated in The Illogic of American Nuclear Strategy, an influential work where Robert Jervis argues that, though second-strike capabilities were essential to deterrence, capabilities much beyond this point held little practical utility. Jervis explains: “It does not matter which side has more nuclear weapons … Deterrence comes from having enough weapons to destroy the other’s cities; this capability is an absolute, not a relative one. In a world where nuclear war would be all-out, completely devastating, and irreversible, nuclear superiority ought not to matter.

Scholars and politicians have disputed the idea that nuclear wars can be won. President Ronald Reagan stated that “a nuclear war cannot be won and must never be fought. Similarly, by the end of his presidency, Harry Truman believed that “starting an atomic war [would be] totally unthinkable for rational men. In 1982, McGeorge Bundy, George F. Kennan, Robert S. McNamara, and Gerard Smith famously wrote: “Any use of nuclear weapons … carries with it a high and inescapable risk of escalation into the general nuclear war which would bring ruin to all and victory to none. If this is correct, then even nuclear superiority cannot allow states to meaningfully win a nuclear war. In turn, superior states should have few advantages over their inferior opponents, so long as those inferior opponents can credibly demonstrate that they are willing to risk nuclear escalation.”

More recent academic literature echoes this argument. Barry M. Blechman and Robert Powell argue nuclear superiority is not useful once a nuclear country has a second-strike capability. According to Todd S. Sechser and Matthew Fuhrmann, “nuclear weapons are uniquely poor instruments of compellence,” meaning nuclear states do not have an advantage over nonnuclear ones in an effort to compel opponents to make concessions or act in certain ways. Charles L. Glaser also concludes that superiority ought not to affect crisis outcomes, writing that the case for nuclear superiority is weak, proponents have done little to support their claims, and efforts to fill in the logical gaps in their arguments encounter overwhelming difficulties. Studying crises from 1900 to 1980, Paul Huth and Bruce Russett determine that a quest for strategic nuclear superiority is unlikely to be the most effective means for providing security to America’s friends and allies in a crisis, or to America itself.

Yet policymakers still invest in “overkill” capabilities and seemingly believe in the importance of nuclear superiority. Many policymakers have, for example, attributed American success in the Cuban Missile Crisis to nuclear superiority over the USSR. Similarly, strategists argued the United States should fear Soviet nuclear superiority, as it could threaten the US ability to make credible threats. David S. McDonough has covered the history of US nuclear strategists’ interest in strategic superiority. Kier A. Lieber and Daryl G. Press explain that, throughout the Cold War, both superpowers were well aware of the benefits of nuclear primacy, and neither was willing to risk falling behind. This logic suggests nuclear superiority lowers a state’s expected costs should nuclear war break out. Therefore, a superior state can demonstrate stronger resolve, providing a crisis advantage over states with more to lose. Bryan R. Early and Victor Asal make a similar argument, explaining that when superior states can levy existential threats against states with “significant existential vulnerability,” then superior states’ nuclear deterrence policies should work. Early and Asal explain that the inability to impose reciprocal existential threats makes inferior states vulnerable.

Using a quantitative approach, Matthew Kroenig has linked nuclear superiority and political victory during crises. Kroenig argues that nuclear superiority provides states with significant strategic advantages. Because a superior state would win a nuclear war against an inferior opponent, a superior state can more credibly threaten nuclear escalation. As a result, we might expect that the greater a state’s nuclear superiority over its opponent, the larger an advantage the state has in competitions of brinkmanship.

Mark S. Bell and Julia Macdonald offer an alternative pathway toward the same conclusion by suggesting there may be far greater incentives for counterforce operations by the superior state and “use them or lose them” pressures for the inferior state in asymmetric circumstances. This reality, in turn, could increase the likelihood of a nuclear exchange in asymmetric crises relative to symmetric ones and thereby increase the utility of nuclear superiority in asymmetric cases. This is because superiority becomes more valuable as the likelihood of a nuclear exchange increases; the utility of superiority is related to damage limitation in a nuclear war through the ability to minimize an opponent’s retaliatory capabilities.

The Disadvantage of Nuclear Superiority, a 2023 study:

When crises occur between nuclear-armed states, do relative nuclear capabilities affect the outcome? The literature offers no consensus about nuclear superiority’s effect on crisis victory, but this article demonstrates that this effect depends on the size of the disparity between states’ nuclear arsenals. Although superiority is correlated with victory in crises between states with similarly sized nuclear arsenals, superiority provides no advantage in asymmetric crises. Because a vastly inferior state risks annihilation in a nuclear conflict, it will acquiesce to an opponent’s demands before the crisis occurs, unless backing down implies an existential threat as well. Given an asymmetric crisis has emerged, therefore, the inferior side will be willing to bid up the risk of nuclear war, deterring superior opponents. Using quantitative analyses of crisis data, this article shows that the positive association between nuclear superiority and crisis victory decreases as the disparity between competing states’ arsenals increases.

The study findings show that seeking nuclear superiority will not help states achieve better crisis outcomes. In a Cold War world, where it was essential for the United States to maintain parity with the Soviet Union to achieve general deterrence, the pursuit of nuclear superiority may have been strategic. But today, immediate deterrence takes precedence. Parity with Russia has already been achieved, and the United States boasts a far superior nuclear arsenal than all remaining nuclear states. Yet, despite its immense nuclear capabilities, the United States is struggling to curb North Korean and Chinese threats. Nuclear superiority provides few benefits in these settings. Further pursuit of superiority may even be counterproductive, harming the United States’ ability to achieve its objectives in this increasingly important geopolitical sphere.

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No first use:

In nuclear ethics and deterrence theory, no first use (NFU) refers to a type of pledge or policy wherein a nuclear power formally refrains from the use of nuclear weapons or other weapons of mass destruction (WMD) in warfare, except for as a second strike in retaliation to an attack by an enemy power using WMD. Such a pledge would allow for a unique state of affairs in which a given nuclear power can be engaged in a conflict of conventional weaponry while it formally forswears any of the strategic advantages of nuclear weapons, provided the enemy power does not possess or utilize any such weapons of their own. The concept is primarily invoked in reference to nuclear mutually assured destruction but has also been applied to chemical and biological warfare, as is the case of the official WMD policy of India.

China and India are currently the only two nuclear powers to formally maintain a no first use policy, adopting pledges in 1964 and 1998 respectively. Both NATO and a number of its member states have repeatedly rejected calls for adopting a NFU policy, as during the lifetime of the Soviet Union a pre-emptive nuclear strike was commonly argued as a key option to afford NATO a credible nuclear deterrent, compensating for the overwhelming conventional weapon superiority enjoyed by the Soviet Army in Eurasia. In 1993, Russia dropped a pledge against first use of nuclear weapons made in 1982 by Leonid Brezhnev, with Russian military doctrine later stating in 2000 that Russia reserves the right to use nuclear weapons “in response to a large-scale conventional aggression”. Pakistan has also made similar statements, largely in reference to intermittent military tensions with India. North Korea has publicly pledged to refrain from a pre-emptive nuclear strike, while threatening retaliation up to and including WMD against conventional aggression.

Pakistan, Russia, the United Kingdom, the United States, and France say that they will use nuclear weapons against either nuclear or non-nuclear states only in the case of invasion or other attack against their territory or against one of their allies. Historically, NATO military strategy, taking into account the numerical superiority of Warsaw Pact conventional forces, assumed that tactical nuclear weapons would have to be used to defeat a Soviet invasion.

At the 16th NATO summit in April 1999, Germany proposed that NATO adopt a no-first-use policy, but the proposal was rejected. In 2022, leaders of the five NPT nuclear-weapon states issued a statement on prevention of nuclear war, saying “We affirm that a nuclear war cannot be won and must never be fought.”

During the 2022 Russian invasion of Ukraine, observers expressed concern that Russia would pre-emptively use tactical nuclear weapons after President Vladimir Putin announced the mobilization of Russian nuclear forces to “combat-ready” status. In December 2022, Putin claimed that Russia would not be the first to use nuclear weapons or the second, and that “Russian nuclear doctrine is premised on self-defence.”

Russia and China do maintain a mutual agreement to have a no first use policy which was developed under the Treaty of Good-Neighborliness and Friendly Cooperation. Under the second paragraph of article two, China and Russia agreed that “The contracting parties reaffirm their commitment that they will not be the first to use nuclear weapons against each other nor target strategic nuclear missiles against each other.”

The United States has refused to adopt a no first use policy and says that it “reserves the right to use” nuclear weapons first in the case of conflict. This was partially to provide a nuclear umbrella over its allies in NATO as a deterrent against a conventional Warsaw Pact attack during the Cold War, and NATO continues to oppose a no-first-use policy. Not only did the United States and NATO refuse to adopt a no first use policy, but until 1967 they maintained a nuclear doctrine of “massive retaliation” in which nuclear weapons would explicitly be used to defend North America or Western Europe against a conventional attack. Although this strategy was revised, they both reserved the right to use nuclear weapons first under the new doctrine of “flexible response”.

North Korea’s stated policy position is that nuclear weapons “will never be abused or used as a means for pre-emptive strike”, but if there is an “attempt to have recourse to military force against us” North Korea may use their “most powerful offensive strength in advance to punish them”.

Although Israel does not officially confirm or deny having nuclear weapons, the country is widely believed to be in possession of them. Its continued ambiguous stance puts it in a difficult position since to issue a statement pledging ‘no first use’ would confirm their possession of nuclear weapons. Israel has said that it ‘would not be the first country in the Middle East to formally introduce nuclear weapons into the region’. If Israel’s very existence is threatened, some speculate that Israel would use a ‘Samson Option’, a ‘last resort’ deterrence strategy of massive retaliation with nuclear weapons, should the State of Israel be substantially damaged and/or near destruction.

Debates in the international community on strategic no-first-use of nuclear weapons include legal, ethical, moral and political arguments from intergovernmental organizations, regional blocs, non-governmental organizations and civil society actors as well as countries. In 2023, former IPPNW program director John Loretz wrote: “With the risk of nuclear war greater than at any time since the Cold War of the 1980s (Bulletin of the Atomic Scientists 2023)—exacerbated even further by the prolonged war in Ukraine—it comes as no surprise that academics, diplomats, and nuclear strategists are focusing anew on risk reduction proposals. One idea that has been in circulation for some time is a global-no-first-use agreement (GNFU), with unilateral or bilateral NFUs as another option.” According to SIPRI’s 1984 analysis, first use of nuclear weapons as a right of self-defence in warfare is the “most controversial” under international law—a right, in their view, not unlimited. Highlighted also were the views of “religious, political and military authorities” who questioned a first-use doctrine. SIPRI concluded that a meaningful no-first-use declaration “would have to be accompanied—or preferably preceded—by changes in the deployment of both nuclear and conventional forces”.

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Deterrence:

Strategy is the art of mustering all available resources in a concerted effort to alter an opponent’s political preferences so they correspond to one’s liking. Deterrence is an exquisite example of strategy because it is intended to alter an opponent’s political preferences without fighting in an effort to preserve the status quo, guarantee the peace, or ensure that diplomacy, not war, is the method of change in international affairs. The goal of deterrence is to prevent war or the occurrence of some unwanted fait accompli. The onset of war constitutes the failure of deterrence and a total and potentially catastrophic failure of deterrence as a strategy.

Deterrence theory refers to the scholarship and practice of how threats of using force by one party can convince another party to refrain from initiating some other course of action. The topic gained increased prominence as a military strategy during the Cold War with regard to the use of nuclear weapons and is related to but distinct from the concept of mutual assured destruction, according to which a full-scale nuclear attack on a power with second-strike capability would devastate both parties. The central problem of deterrence revolves around how to credibly threaten military action or nuclear punishment on the adversary despite its costs to the deterrer. Deterrence in an international relations context is the application of deterrence theory to avoid conflict.

The concept of deterrence can be defined as the use of threats in limited force by one party to convince another party to refrain from initiating some course of action. In Arms and Influence (1966), Schelling offers a broader definition of deterrence, as he defines it as “to prevent from action by fear of consequences.” Deterrence is widely defined as any use of threats (implicit or explicit) or limited force intended to dissuade an actor from taking an action (i.e. maintain the status quo). Deterrence is unlike compellence, which is the attempt to get an actor (such as a state) to take an action (i.e. alter the status quo). Both are forms of coercion. Compellence has been characterized as harder to successfully implement than deterrence. Deterrence also tends to be distinguished from defense or the use of full force in wartime. Deterrence is most likely to be successful when a prospective attacker believes that the probability of success is low and the costs of attack are high. Central problems of deterrence include the credible communication of threats and assurance. Deterrence does not necessarily require military superiority.

“General deterrence” is considered successful when an actor who might otherwise take an action refrains from doing so due to the consequences that the deterrer is perceived likely to take. “Immediate deterrence” is considered successful when an actor seriously contemplating immediate military force or action refrains from doing so. Scholars distinguish between “extended deterrence” (the protection of allies) and “direct deterrence” (protection of oneself). Rational deterrence theory holds that an attacker will be deterred if they believe that:

(Probability of deterrer carrying out deterrent threat × Costs if threat carried out) > (Probability of the attacker accomplishing the action × Benefits of the action)

This model is frequently simplified in game-theoretic terms as:

Costs × P(Costs) > Benefits × P(Benefits)

The starting point for any deterrent strategy is capability. In other words, unless one is prepared to rely on bluff, one has to possess the military forces needed to execute threats if deterrence fails. For that matter, the likelihood of deterrence success increases if the opponent is aware that the party making a deterrent threat actually possesses the military capability needed to execute that threat. Capability, in turn, contributes to credibility, the idea in the mind of the opponent that a threat would actually be executed if certain redlines are crossed. Deterrent threats that rely on nuclear or conventional weapons are based on fundamentally different types of military capability, which, in turn, embody their own strengths and weaknesses when it comes to instilling the credibility of a threat in the mind of the opponent. Regardless of the weapons employed or the strategy adopted, capability and credibility are the key ingredients of deterrence success. Opponents must believe that the side issuing deterrent threats has the capability to make good on those threats and will actually execute them in the wake of deterrence failure. As Michael Codner explains, the fundamental components of deterrence are “the perception of capability to deliver violence, perception of will, and reputation of the ability to implement intentions effectively”. So long as a nation perceives intolerable consequences resulting from a potential conflict, the incentive to initiate any such conflict vanishes. Deterrence theory relies on the assumptions that all interested parties act both rationally and possess all relevant information. All nations must not only play by the rules, but they must fully understand the rules in the first place. In such cases, a weaker nation should not attack a militarily superior enemy, since doing so would almost certainly result in resounding defeat.

Nuclear deterrence theory:

Nuclear deterrence theory states that nations with nuclear weapons will not be subject to attack, especially nuclear attack, because the prospect of a retaliatory nuclear strike is too terrible to contemplate.

According to Kenneth Waltz, there are three requirements for successful nuclear deterrence:

-1. Part of a state’s nuclear arsenal must appear to be able to survive an attack by the adversary and be used for a retaliatory second strike

-2. The state must not respond to false alarms of a strike by the adversary

-3. The state must maintain command and control

The stability–instability paradox is a key concept in rational deterrence theory. It states that when two countries each have nuclear weapons, the probability of a direct war between them greatly decreases, but the probability of minor or indirect conflicts between them increases. This occurs because rational actors want to avoid nuclear wars, and thus they neither start major conflicts nor allow minor conflicts to escalate into major conflicts—thus making it safe to engage in minor conflicts. For instance, during the Cold War the United States and the Soviet Union never engaged each other in warfare, but fought proxy wars in Korea, Vietnam, Angola, the Middle East, Nicaragua and Afghanistan and spent substantial amounts of money and manpower on gaining relative influence over the third world.

Bernard Brodie wrote in 1959 that a credible nuclear deterrent must be always ready but never used. Scholars have debated whether having a superior nuclear arsenal provides a deterrent against other nuclear-armed states with smaller arsenals. Matthew Kroenig has argued that states with nuclear superiority are more likely to win nuclear crises, whereas Todd Sechser, Matthew Fuhrmann and David C. Logan have challenged this assertion. A 2023 study found that a state with nuclear weapons is less likely to be targeted by non-nuclear states, but that a state with nuclear weapons is not less likely to target other nuclear states in low-level conflict. A 2022 study by Kyungwon Suh suggests that nuclear superiority may not reduce the likelihood that nuclear opponents will initiate nuclear crises.

Proponents of nuclear deterrence theory argue that newly nuclear-armed states may pose a short- or medium-term risk, but that “nuclear learning” occurs over time as states learn to live with new nuclear-armed states. Mark S. Bell and Nicholas L. Miller have however argued that there is a weak theoretical and empirical basis for notions of “nuclear learning.”

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Nuclear Deterrence vs Conventional Deterrence:

The fact that battle outcomes with conventional weapons are so difficult to predict highlights the observation that conventional deterrent threats are “contestable.” The contestability of conventional threats can raise doubts in the minds of those targeted by conventional deterrence concerning the capability of the side issuing deterrent threats to actually succeed. Contestability is the Achilles’ heel of conventional deterrence. By contrast, deterrent threats based on nuclear weapons are largely uncontestable. They offer an ideal deterrent capability because they tend to eliminate optimism about a positive war outcome. The fact that nuclear threats are uncontestable does not guarantee that they will be viewed as credible, while the contestable nature of conventional threats does not preclude their credibility.

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Extended Deterrence:

Extended deterrence is defined as “a confrontation in which the policymakers of one state (‘defender’ [patron]) threaten the use of force against another state (‘potential attacker’ [enemy]) in an attempt to prevent that state from using military force against an ally (‘protégé’ [client]) … of the defender.” Notably, in contrast to central deterrence (also known as direct deterrence), which refers to “attempts to discourage attacks upon the deterrer’s own homeland,” in extended deterrence a deterrer (patron) is inherently different from a beneficiary of deterrence (client). This inherent discordance produces a canonical commitment problem. That is, even if a patron’s commitment appears credible today, a client cannot be convinced the patron will honor its prior security commitments in times of contingency. Therefore, in extended deterrence, a patron should play a double role: (1) assuring a client of its security [(re)assuring a client of a patron’s unwavering commitment to the client’s protection], while (2) deterring a potential aggressor from invading a client.

Extending security commitments to allies has been a cornerstone of the United States’ efforts to maintain international peace and forestall the worldwide cascade of nuclear proliferation. Close inspection reveals that nuclear patrons have employed different extended deterrence strategies across disparate clients, and those for the protection of individual clients have varied over time. For example, since the formation of the North Atlantic Treaty Organization (NATO) in 1949, the US security commitment to NATO Europe has relied on forward-deployed nuclear weapons coupled with large-scale conventional troops on the European Continent. The US security umbrella over South Korea resembled the case of NATO during the Cold War. However, it underwent a considerable change in the early 1990s, moving away from the NATO model. Specifically, America’s nuclear umbrella over the Korean Peninsula shifted from onshore to offshore. In contrast, US extended deterrence to the Philippines during the Cold War was conventional: the United States pre-positioned robust conventional troops in the archipelago without employing nuclear assets for the protection of the Philippines. In short, the security umbrellas provided have not been one-size-fits-all. Instead, they have been tailored to individual clients’ unique security needs and circumstances.

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Breakdown of nuclear deterrence:

It’s true that these are reasons to think that nuclear war is unlikely. But unfortunately, there are lots of ways in which nuclear deterrence could break down.

-1. First, deterrence relies on the possibility of a retaliatory strike strong enough to destroy a nuclear state. But there are ways this could fail. For example, a strong missile defence system might mean that one nuclear state could attack a second nuclear state in the knowledge that their defences mean they’ll likely survive any retaliatory strike. Alternatively, states’ military capabilities could be sufficiently imbalanced such that one nuclear state could destroy a second state’s nuclear capabilities before a retaliatory strike is launched.

-2. Second, decision makers could believe that the results of not launching a nuclear strike would be even worse than launching. For example, this could be because individual decision makers’ positions or power are at risk. Or there could be an escalating large-scale conventional war (especially one between nuclear powers) which threatens the existence of a nuclear state.

-3. Third, and perhaps most importantly, the decision-making process could lead to mistakes in a number of ways, for instance:

Someone involved in the process makes a mistake (the arguments for deterrence assume that states are rational decision makers) — for example, there has been substantial discussion over whether Putin’s decisions to invade Ukraine, and subsequently make nuclear threats show that he is making these kinds of mistakes.
False information, such as computer errors or mistaking clouds for nuclear missiles, could interfere with the decision making process.
We aren’t rational and we can’t read minds. For nuclear deterrence to work, all stakeholders must be perceived to act “rationally” and “predictably” but we know that’s not how people work – particularly in the fog of war.

-4. Nuclear deterrence makes nuclear use more likely because the threat of use of nuclear weapons must be credible, and so the nuclear armed states are always poised to launch nuclear weapons.

-5. Nuclear weapons don’t keep the peace. History shows that the existence of nuclear weapons has done nothing to prevent the many terrible conflicts since 1945, including acts of aggression against countries with nuclear weapons. In reality, nuclear weapons haven’t been used due solely to good luck – which cannot be expected to last forever.

Although the logic of deterrence theory is compelling, history nonetheless provides numerous instances of deterrence failing. For example, despite the clear latent power advantage enjoyed by the United States, Japan initiated war with its attack on Pearl Harbor in 1941. In the face of world condemnation, Saddam Hussein refused to withdraw from Kuwait in 1991 despite certain defeat against overwhelming coalition forces certain to attack. More recently, Gazan militants routinely escalated their attacks against Israel despite withering retaliation by a far superior Israeli military throughout the 2000s. In fact, a historical lookback reveals weaker countries initiated more than 33 percent of all major conflicts during the 20th century. Whether these attacks occurred because the weaker side perceived a window of opportunity to achieve victory or perhaps miscalculated the capabilities of their opponent altogether, the historical implication remains the same. Militarily superior nations often fail to deter their adversaries from initiating conventional war. If conventional deterrence often fails, can the same be said about nuclear deterrence? A preliminary review of historical data suggests nuclear weapons do indeed possess a higher deterrence effect than conventional forces alone. Perhaps nuclear deterrence works because nuclear weapons fundamentally change conflict escalation.

If nuclear weapons have diminished the chances of a World War III scenario, then they have dramatically increased the stakes of such a calamity as well. While there is reason to believe that a link exists between nuclear weapons and fewer wars between major powers, as Keith Payne notes: “It is [also] impossible to predict the next failure in deterrence.” As long as rational actors remain in control of nuclear weapons (and do not make mistakes,) it seems the current status quo can persist indefinitely. Unfortunately, there exists no guarantee that mature nuclear powers will always act rationally or not make mistakes. Furthermore, emerging nuclear powers such as North Korea, Iran, and possibly others could significantly impart further uncertainty. Precisely because of these unknown unknowns, nuclear deterrence cannot guarantee a future nuclear attack will not occur. By solely relying on a massive retaliation deterrence strategy, we accept a simplified world model and intentionally avoids fully preparing for the ultimate black swan event.

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MAD:

Mutual assured destruction (MAD) is a doctrine of military strategy and national security policy which posits that a full-scale use of nuclear weapons by an attacker on a nuclear-armed defender with second-strike capabilities would result in the complete annihilation of both the attacker and the defender. It is based on the theory of rational deterrence, which holds that the threat of using strong weapons against the enemy prevents the enemy’s use of those same weapons. The strategy is a form of Nash equilibrium in which, once armed, neither side has any incentive to initiate a conflict nor to disarm.

The result may be a nuclear peace, in which the presence of nuclear weapons decreases the risk of crisis escalation, since parties will seek to avoid situations that could lead to the use of nuclear weapons. Proponents of nuclear peace theory therefore believe that controlled nuclear proliferation may be beneficial for global stability. Critics argue that nuclear proliferation increases the chance of nuclear war through either deliberate or inadvertent use of nuclear weapons, as well as the likelihood of nuclear material falling into the hands of violent non-state actors.

During the Cold War, the important thinking about using nuclear weapons didn’t come from old military wisdom but from game theory, a new way to understand strategic decision-making. This analytical approach suggested that the standoff between the U.S. and USSR represented a Nash equilibrium: Neither superpower had reason to pre-emptively launch a nuclear attack, as it would surely provoke a devastating counterattack. At the same time, neither would disarm significantly enough to leave itself unable to retaliate to a pre-emptive strike. The doctrine of mutually assured destruction seemed to keep the superpowers at a peaceful balance point. But it’s unsettling to live in a world whose existence is maintained only by the threatening logic of the Nash equilibrium.

The term “mutual assured destruction”, commonly abbreviated “MAD”, was coined by Donald Brennan, a strategist working in Herman Kahn’s Hudson Institute in 1962. Brennan conceived the acronym cynically, spelling out the English word “mad” to argue that holding weapons capable of destroying society was irrational. Proponents of MAD as part of the US and USSR strategic doctrine believed that nuclear war could best be prevented if neither side could expect to survive a full-scale nuclear exchange as a functioning state. Since the credibility of the threat is critical to such assurance, each side had to invest substantial capital in their nuclear arsenals even if they were not intended for use. In addition, neither side could be expected or allowed to adequately defend itself against the other’s nuclear missiles. This led both to the hardening and diversification of nuclear delivery systems (such as nuclear missile silos, ballistic missile submarines, and nuclear bombers kept at fail-safe points) and to the Anti-Ballistic Missile Treaty.

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Section-7

Nuclear war:

Nuclear war refers to a catastrophic conflict in which nuclear weapons are used, resulting in widespread destruction, loss of life, and devastation. It is characterized by long-distance attacks and uncontrollable consequences, surpassing the scale and impact of conventional warfare. The use of nuclear weapons is widely considered morally indefensible, but the concept of nuclear deterrence is debated as an ethically acceptable means of preventing their deployment. Nuclear war is perhaps the worst thing we can imagine humankind bringing about, and almost everyone agrees that initiating such a war could not be morally defended. If it should ever occur, it will be much messier, and much less controllable, than wars waged with conventional weapons; many more people will die, and much more devastation will be caused. Usually when nuclear war is debated, people have in mind destruction of a kind that is outside our understanding. It is because the destruction caused by the nuclear attacks on Hiroshima and Nagasaki was at a level that is similar to that wrought by concerted conventional warfare, such as the fire bombing of Dresden or the Blitz to which London was subjected, that they are often not considered as the first examples of nuclear warfare but, rather, as unilateral one-off uses of nuclear weapons.

Nuclear war would not be fought by individual combatants but entirely at long distance, and it could not be carried on in the relatively cautious way that wars could be conducted in the past. A single nuclear weapon would destroy not only the intended targets (mostly heavily populated cities) but also the surrounding countryside and infrastructure for many miles; few people believe that once a nuclear conflict has begun, it will be possible to contain it. A nuclear war would involve hundreds to thousands of explosions, creating a situation for which we simply have no relevant experience. Despite decades of arms reduction treaties, there are still thousands of nuclear weapons in the world’s arsenals. Detonating only a tiny fraction of these would cause mass casualties.

Conservative estimates published in the Journal of Medicine in 1998 suggest that even an intermediate-sized launch of weapons accidentally released from a single Russian submarine would result in the death of nearly 7 million people in eight U.S. cities, with millions of others being exposed to potentially lethal radiation from fallout. In 2003, the Johnston’s Archive suggested that the worse-case scenario in the event of an all-out attack would result in an estimated 110 million U.S. dead and 30 million injured, with approximately 20 million killed in the United Kingdom. Within 3 months, the number of dead in the United States would increase to 140 million. Could such a level of human casualties ever be justified from any ethical point of view? This question is important because the central plank in arguments against deterrence is that unless it is possible to give an account of circumstances in which such an attack would be morally justifiable, the use of nuclear threats cannot be justified.

After the dissolution of the Soviet Union in 1991 and the resultant end of the Cold War, the threat of a major nuclear war between the two nuclear superpowers was generally thought to have declined. Since then, concern over nuclear weapons has shifted to the prevention of localized nuclear conflicts resulting from nuclear proliferation, and the threat of nuclear terrorism. However, the threat of nuclear war is considered to have resurged after the Russian invasion of Ukraine, particularly with regard to Russian threats to use nuclear weapons during the invasion.

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Key factors influencing the probability of nuclear war include:

-1. Geopolitical Tensions: Fluctuating relationships between nuclear-armed nations like the United States, Russia, China, India, and Pakistan.

-2. Nuclear Policies: Each nation’s doctrines regarding the use of nuclear weapons, including pre-emptive strikes and retaliatory measures.

-3. Accidental Launches: The ever-present risk of human error, technical failures, or cyberattacks leading to unintended launches.

-4. Diplomatic Efforts: Ongoing treaties, agreements, and international dialogue aimed at nuclear disarmament and non-proliferation.

-5. Regional Conflicts: Localized conflicts involving nuclear-armed states, which can escalate tensions and heighten the risk of nuclear engagement.

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Various types of nuclear war:

(a) Limited nuclear war in the periphery.

A war breaks out in the Middle East, and resort is made to nuclear weapons, killing a few hundred thousand people. The United States and Russia place their nuclear forces on the highest alert. As the tension continues to build up, a state of emergency is declared in the US. Normal democratic procedures are suspended, and ‘dissidents’ are rounded up. A similar process occurs in many countries allied militarily to the US, and also within the Soviet bloc. A return to the pre-crisis state of affairs does not occur for years or decades. As well as precipitating bitter political repression, the crisis contributes to an increased arms race, especially among nonnuclear and small nuclear powers, as no effective sanctions are applied to those who used nuclear weapons. Another similar limited nuclear war and superpower crisis becomes likely … or perhaps the scene shifts to scenario b or c.

(b) Limited nuclear war between the superpowers.

A limited exchange of nuclear weapons between the US and Russia occurs, either due to accident or as part of a threat-counterthreat situation. A sizable number of military or civilian targets are destroyed, either in the US or the Soviet Union or in allied states, and perhaps 5 or 10 million people are killed. As in scenario a, states of emergency are declared, political dissent repressed and public outrage channelled into massive military and political mobilisation to prepare for future confrontations and wars. Scenario c becomes more likely.

A massive nuclear exchange occurs, killing 200 million people in the US, Russia and Europe. National governments, though decimated, survive and apply brutal policies to obtain economic and military recovery, brooking no dissent. In the wake of the disaster, authoritarian civilian or military regimes take control in countries relatively unscathed by the war, such as Australia, Japan and Spain. The road is laid to an even more devastating World War IV.

Many other similar scenarios could be presented. One feature of these scenarios is familiar: the enormous scale of physical destruction and human suffering, which is only dimly indicated by the numbers of dead and injured, whether this is hundreds, or hundreds of millions. This destruction and suffering is familiar largely because many people have repeatedly warned of the human consequences of nuclear war. What has been almost entirely absent from peace movement analysis and planning is any consideration of the political consequences of nuclear war.

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Military violence:

The actual or threatened use of violence is one of the essential characteristics of the military. More precisely, the military is a “social organization for the achievement of political aims through the threatened and actual use of armed force” (Wachtler, 1988:268). The armed forces, in the words of Carl von Clausewitz, are an instrument of the modern state. They are recruited, paid and deployed in the interests of the security of an individual state, the term “security” here referring primarily to the external security of one state against threats from other states. Traditionally, the functions of the armed forces are defined in two different ways. While the deterrent and defensive capability can be regarded as a defensive role, the ability to launch an attack on another state, in order to assert national interests and claims of political domination, can be seen as an offensive role.

There are many plausible scenarios that might pit the United States against Russia, China, or North Korea. Following its playbook of recent interventions in Ukraine, Russia may invade Estonia, Latvia, or Lithuania. Russia’s goal may be conquering the Baltics, securing a land bridge to its exclave in Kaliningrad, or simply demonstrating that NATO will not or cannot defend all its members. China may attempt to deny Japan or the Philippines control of maritime territory in the East- or South China Sea (respectively) or, in a political or economic dispute, restrict maritime commerce through the first island chain. In an even more critical scenario, China may attempt to invade and occupy Taiwan. North Korea has a long history of using military violence to coerce South Korea, Japan, and the United States and may become emboldened to once again attempt the reunification of the Korean peninsula by force. Short of that, North Korea may embark on a limited military campaign such as challenging the Northern Limit Line by occupying one of South Korea’s five northwest islands.

In an ongoing conventional conflict, the United States and its allies would compete with an adversary over the terms of a cessation of hostilities. Each side would have a strong interest in keeping the conflict limited to minimize costs, yet both would seek to maximally benefit from the peace that ensued. The country that perceived a higher stake in the conflict would presumably endure higher costs to achieve a preferred outcome. But in addition to the relative importance of what is being fought over, each side’s resolve would be regulated by its perception of its military position and capability. The side that objectively has more at stake ultimately may have less resolve if it believes its inferior military position makes the likely costs and risk too great.

Each side’s incentive to maximize postwar benefits while minimizing wartime costs means that future wars between nuclear-armed adversaries are likely to be competitions over limits on violence. In an interactive process of tacit bargaining, each side will seek to establish a level of military violence below which it can achieve its political and military objectives at the lowest cost, while deterring the other side from escalating to higher levels. Either side might, for example, withhold attacks on the other’s territory or against space-based capabilities to keep a local conflict limited. Both are likely to attempt to shape other’s perceptions—and the perceptions of the international community—to reinforce their preferred limitations in the conflict and discredit limitations their opponents may advance.

Figure below depicts potential stances opponents could take in tacit conflict bargaining, from tightly controlled to very permissive.

Immediate effects of nuclear war:

Nuclear weapons could be fired at a range of targets: cities, natural resources, government buildings, nuclear silos, conventional militaries, war-supporting infrastructure and industry, and more. Roughly, the more nuclear weapons fired at densely populated civilian areas, the more devastating the conflict would be — there would be more people killed in the initial detonations and more smoke released means increased chances of a nuclear winter. In a nuclear war, hundreds or thousands of detonations would occur within minutes of each other. Regional nuclear war between India and Pakistan that involved about 100 15-kiloton nuclear weapons launched at urban areas would result in 27 million direct deaths. A global all-out nuclear war between the United States and Russia with over four thousand 100-kiloton nuclear warheads would lead, at minimum, to 360 million quick deaths. In an all-out nuclear war between Russia and the United States, the two countries would not limit to shooting nuclear missiles at each other’s homeland but would target some of their weapons at other countries, including ones with nuclear weapons. These countries could launch some or all their weapons in retaliation. Together, the United Kingdom, China, France, Israel, India, Pakistan, and North Korea currently have an estimated total of over 12000 nuclear warheads.

As horrific as those statistics are, the tens to hundreds of millions of people dead and injured within the first few days of a nuclear conflict would only be the beginnings of a catastrophe that eventually will encompass the whole world. Global climatic changes, widespread radioactive contamination, and societal collapse virtually everywhere could be the reality that survivors of a nuclear war would contend with for many decades. Two years after any nuclear war—small or large—famine alone could be more than 10 times as deadly as the hundreds of bomb blasts involved in the war itself. Even a limited nuclear exchange between India and Pakistan could put one billion people at risk of starvation and another 1.3 billion at risk of severe food insecurity due to global cooling, according to a 2013 study by International Physicians for the Prevention of Nuclear War.

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How much time Americans would have between a nuclear alert and strike:

If your city was under attack, you’d likely receive a Wireless Emergency Alert (WEA) text on your cell phone stating that missiles were on the way and to seek shelter immediately. The Emergency Alert System (EAS) would also send out the same alert message as the WEA across all types of television and radio broadcasts, including satellite, cable, and wireless systems. On top of that, the President may choose to send out a “Presidential Alert” to cell phones nationwide.

Russia’s nuclear arsenal is capable of striking just about anywhere on the planet. Were Russia to launch a nuclear-armed intercontinental ballistic missile at the US, residents would have roughly 30 minutes, or less, to find shelter, assuming they were immediately warned of the attack. Some weapons, such as submarine-launched missiles, could potentially have shorter delivery times. In theory you could park a submarine closer to North America, thereby lessening the warning and flight time. If Russia launched a weapon from international waters just off the East Coast, people in cities like New York, Boston, and Washington, DC, might have just 10 to 15 minutes to prepare. Arguably, the American public is not as prepared or educated on what to do in the event of a nuclear attack as Americans were during the Cold War, when stocked fallout shelters, nuclear drills, and air raid sirens were in place across the nation.

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Limited Nuclear War:

One form of limited nuclear war would be like a conventional battlefield conflict but using low-yield tactical nuclear weapons. Here’s a hypothetical scenario: After its 2014 annexation of Crimea, Russia attacks a Baltic country with tanks and ground forces while the United States is distracted by a domestic crisis. NATO responds with decisive counterforce, destroying Russian tanks with fighter jets, but this doesn’t quell Russian resolve. Russia responds with even more tanks and by bombing NATO installations, killing several hundred troops. NATO cannot tolerate such aggression and to prevent further Russian advance launches low-yield tactical nuclear weapons with their dial-a-yield positions set to the lowest settings of only 300 tons TNT equivalent. The goal is to signal Russia that it has crossed a line and to deescalate the situation. NATO’s actions are based on fear that if the Russian aggression weren’t stopped the result would be all-out war in northern Europe.

This strategy is actually being discussed in the higher echelons of the Pentagon. The catchy concept is that use of a few low-yield nuclear weapons could show resolve, with the hoped-for outcome that the other party will back down from its aggressive behavior (this concept is known as escalate to deescalate). The assumption is that the nuclear attack would remain limited, that parties would go back to the negotiating table, and that saner voices would prevail. However, this assumes a chain of events where everything unfolds as expected. It neglects the incontrovertible fact that, as the Prussian general Carl von Clausewitz observed in the 19th century, “Three quarters of the factors on which action in war is based are wrapped in a fog of greater or lesser uncertainty.” Often coined fog of war, this describes the lack of clarity in wartime situations on which decisions must nevertheless be based. In the scenario described, sensors could have been damaged or lines of communication severed that would have reported the low-yield nature of the nuclear weapons. As a result, Russia might feel its homeland threatened and respond with an all-out attack using strategic nuclear weapons, resulting in millions of deaths.

There is every reason to believe that a limited nuclear war wouldn’t remain limited:

A 1983 war game known as Proud Prophet involved top-secret nuclear war plans and had as participants high-level decision makers including President Reagan’s Secretary of Defense Caspar Weinberger. The war game followed actual plans but unexpectedly ended in total nuclear annihilation with more than half a billion fatalities in the initial onslaught — not including subsequent deaths from starvation. The exercise revealed that a limited nuclear strike may not achieve the desired results! In this case, that was because the team playing the Soviet Union responded to a limited U.S. nuclear strike with a massive all-out nuclear attack.

What about an attack on North Korea?

In 2017, some in the U.S. cabinet advocated for a “bloody nose” strategy in dealing with North Korea’s flagrant violations of international law. This is the notion that in response to a threatening action by North Korea, the U.S. would destroy a significant site to “bloody Pyongyang’s nose.” This might employ a low-yield nuclear attack or a conventional attack. The “bloody nose” strategy relies on the expectation that Pyongyang would be so overwhelmed by U.S. might that they would immediately back down and not retaliate. However, North Korea might see any type of aggression as an attack aimed at overthrowing their regime, and could retaliate with an all-or-nothing response using weapons of mass destruction (including but not necessarily limited to nuclear weapons) as well as their vast conventional force.

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All-Out Nuclear War:

Whether from escalation of a limited nuclear conflict or as an outright full-scale attack, an all-out nuclear war remains possible as long as nuclear nations have hundreds to thousands of weapons aimed at one another. What would be the consequences of all-out nuclear war?

Within individual target cities, conditions described for single explosions would prevail. (Most cities, though, would likely be targeted with multiple weapons.) Government estimates suggest that over half of the United States’ population could be killed by the prompt effects of an all-out nuclear war. For those within the appropriate radii of destruction, it would make little difference whether theirs was an isolated explosion or part of a war. But for the survivors in the less damaged areas, the difference could be dramatic.

Consider the injured. After all-out nuclear war, unsheltered persons would receive weekly radiation doses in excess of 1 Sv (1,000 mSv or 100 rem), some 400 times annual background; 60 percent would receive fatal doses in excess of 10 Sv. Thermal flash burns extend well beyond the 5-psi radius of destruction. A single nuclear explosion might produce 10,000 cases of severe burns requiring specialized medical treatment; in an all-out war there could be several million such cases. Yet the United States has facilities to treat fewer than 2,000 burn cases — virtually all of them in urban areas that would be levelled by nuclear blasts. Burn victims who might be saved, had their injuries resulted from some isolated cause, would succumb in the aftermath of nuclear war. The same goes for fractures, lacerations, missing limbs, crushed skulls, punctured lungs, and myriad other injuries suffered as a result of nuclear blast. Where would be the doctors, the hospitals, the medicines, the equipment needed for their treatment? Most would lie in ruin, and those that remained would be inadequate to the overwhelming numbers of injured. Again, many would die whom modern medicine could normally save.

In an all-out war, lethal fallout would cover much of the United States. Survivors could avoid fatal radiation exposure only when sheltered with adequate food, water, and medical supplies. Even then, millions would be exposed to radiation high enough to cause lowered disease resistance and greater incidence of subsequent fatal cancer. Lowered disease resistance could lead to death from everyday infections in a population deprived of adequate medical facilities. And the spread of diseases from contaminated water supplies, non-existent sanitary facilities, lack of medicines, and the millions of dead could reach epidemic proportions. Small wonder that the international group Physicians for Social Responsibility has called nuclear war “the last epidemic.”

Attempts to contain damage to cities, suburbs, and industries would suffer analogously to the treatment of injured people. Firefighting equipment, water supplies, electric power, heavy equipment, fuel supplies, and emergency communications would be gone. Transportation into and out of stricken cities would be blocked by debris. The scarcity of radiation-monitoring equipment and of personnel trained to operate it would make it difficult to know where emergency crews could safely work. Most of all, there would be no healthy neighboring cities to call on for help; all would be crippled in an all-out war.

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Survivability in nuclear war:

More than half the United States’ population might be killed outright in an all-out nuclear war. What about the survivors?

Recent studies have used detailed three-dimensional, block-by-block urban terrain models to study the effects of 10-kiloton detonations on Washington, D.C. and Los Angeles. The results settle an earlier controversy about whether survivors should evacuate or shelter in place: Staying indoors for 48 hours after a nuclear blast is now recommended. That time allows fallout levels to decay by a factor of 100. Furthermore, buildings between a survivor and the blast can block the worst of the fallout, and going deep inside an urban building can lower fallout levels still further. The same shelter-in-place arguments apply to survivors in the non-urban areas blanketed by fallout.

These new studies, however, consider only single detonations as might occur in a terrorist or rogue attack. In considering all-out nuclear war, we have to ask a further question: Then what?

Individuals might survive for a while, but what about longer term, and what about society as a whole? Extreme and cooperative efforts would be needed for long-term survival, but would the shocked and weakened survivors be up to those efforts? How would individuals react to watching their loved ones die of radiation sickness or untreated injuries? Would an “everyone for themselves” attitude prevail, preventing the cooperation necessary to rebuild society? How would residents of undamaged rural areas react to the streams of urban refugees flooding their communities? What governmental structures could function in the postwar climate? How could people know what was happening throughout the country? Would international organizations be able to cope?

Some students of nuclear war see postwar society in a race against time. An all-out war would have destroyed much of the nation’s productive capacity and would have killed many of the experts who could help guide social and physical reconstruction. The war also would have destroyed stocks of food and other materials needed for survival.

On the other hand, the remaining supplies would have to support only the much smaller postwar population. The challenge to the survivors would be to establish production of food and other necessities before the supplies left from before the war were exhausted. Could the war-shocked survivors, their social and governmental structure shattered, meet that challenge? That is a very big nuclear question — so big that it’s best left unanswered, since only an all-out nuclear war could decide it definitively.

Climatic Effects:

Ozone depletion, nuclear winter and nuclear famine:

A large-scale nuclear war would pump huge quantities of chemicals and dust into the upper atmosphere. The upper atmosphere includes a layer enhanced in ozone gas, an unusual form of oxygen that vigorously absorbs the Sun’s ultraviolet radiation. In the absence of this ozone layer, more ultraviolet radiation would reach Earth’s surface, with a variety of harmful effects. A nuclear war would produce huge quantities of ozone-consuming chemicals, and studies suggest that even a modest nuclear exchange would result in unprecedented increases in ultraviolet exposure. Marine life might be damaged by the increased ultraviolet radiation, and humans could receive blistering sunburns. More UV radiation would also lead to a greater incidence of fatal skin cancers and to general weakening of the human immune system.

Simulations have shown that a regional nuclear war that lasted three days and injected 5 Tg of soot into the stratosphere would reduce the ozone layer by 25 percent globally; recovery would take 12 years. A global nuclear war injecting 150 Tg of stratospheric smoke would cause a 75 percent global ozone loss, with the depletion lasting 15 years.

The loss of the Earth’s protective ozone layer would result in several years of extremely high ultraviolet (UV) light at the surface, a hazard to human health and food production. Most recent estimates indicate that the ozone loss after a global nuclear war would lead to a tropical UV index above 35, starting three years after the war and lasting for four years. The US Environmental Protection Agency considers a UV index of 11 to pose an “extreme” danger; 15 minutes of exposure to a UV index of 12 causes unprotected human skin to experience sunburn. Globally, the average sunlight in the UV-B range would increase by 20 percent. High levels of UV-B radiation are known to cause sunburn, photoaging, skin cancer, and cataracts in humans. They also inhibit the photolysis reaction required for leaf expansion and plant growth.

Stratospheric soot injection:

Even more alarming is the fact that soot from the fires of burning cities after a nuclear exchange would be injected high into the atmosphere. A 1983 study by Richard Turco, Carl Sagan, and others (the so-called TTAPS paper) shocked the world with the suggestion that even a modest nuclear exchange — as few as 100 warheads — could trigger drastic global cooling as airborne soot blocked incoming sunlight. In its most extreme form, this nuclear winter hypothesis raised the possibility of extinction of the human species. (This is not the first dust-induced extinction pondered by science. Current thinking holds that the dinosaurs went extinct as a result of climate change brought about by atmospheric dust from an asteroid impact; indeed, that hypothesis helped prompt the nuclear winter research.)

Recent studies with modern climate models show that an all-out nuclear war between the United States and Russia, even with today’s reduced arsenals, could put over 150 million tons of smoke and soot into the upper atmosphere. That’s roughly the equivalent of all the garbage the U.S. produces in a year! The result would be a drop in global temperature of some 8°C (more than the difference between today’s temperature and the depths of the last ice age), and even after a decade the temperature would have recovered only 4°C. In the world’s “breadbasket” agricultural regions, the temperature could remain below freezing for a year or more, and precipitation would drop by 90 percent. The effect on the world’s food supply would be devastating.

Even a much smaller nuclear exchange could have catastrophic climate consequences. The research also suggests that a nuclear exchange between India and Pakistan, involving 100 Hiroshima-sized weapons, would shorten growing seasons and threaten annual monsoon rains, jeopardizing the food supply of a billion people. The image below shows the global picture one month after this hypothetical 100-warhead nuclear exchange.

Figure above shows global smoke distribution from a 100-warhead nuclear exchange between India and Pakistan one month after the event. Darker shading indicates greater sunlight absorption. Smoke from mass fires after a nuclear war could inject massive amounts of soot into the stratosphere, the Earth’s upper atmosphere. An all-out nuclear war between India and Pakistan, with both countries launching a total of 100 nuclear warheads of an average yield of 15 kilotons, could produce a stratospheric loading of some 5 million tons (or teragrams, Tg) of soot. This is about the mass of the Great Pyramid of Giza, pulverized and turned into superheated dust. But these lower-end estimates date back to the late 2000s. Since then, India and Pakistan have significantly expanded their nuclear arsenals, both in the number of nuclear warheads and yield. By 2025, India and Pakistan could have up to 250 nuclear weapons each, with yields of 12 kilotons on the low end, up to a few hundred kilotons. A nuclear war between India and Pakistan with such arsenals could send up to 47 Tg of soot into the stratosphere.

For comparison, the recent catastrophic forest fires in Canada in 2017 and Australia in 2019 and 2020 produced 0.3 Tg and 1 Tg of smoke respectively. Chemical analysis showed, however, that only a small percentage of the smoke from these fires was pure soot—0.006 and 0.02 Tg respectively. This is because only wood was burning. Urban fires following a nuclear war would produce more smoke, and a higher fraction would be soot.

The climatic response from volcanic eruptions also continues to serve as a basis for understanding the long-term impacts of nuclear war. Volcanic blasts typically send ash and dust up into the stratosphere where it reflects sunlight back into space, resulting in the temporary cooling of the Earth’s surface. Likewise, in the theory of nuclear winter, the climatic effects of a massive injection of soot aerosols into the stratosphere from fires following a nuclear war would lead to the heating of the stratosphere, ozone depletion, and cooling at the surface under this cloud. Volcanic eruptions are also useful because their magnitude can match—or even surpass—the level of nuclear explosions. For instance, the 2022 Hunga Tonga’s underwater volcano released an explosive energy of 61 megatons of TNT equivalent— more than the Tsar Bomba, the largest human-made explosion in history with 50 Mt. Its plume reached altitudes up to about 56 kilometers (35 miles), injecting well over 50 Tg—even up to 146 Tg— of water vapor into the stratosphere where it will stay for years. Such a massive injection of stratospheric water could temporarily impact the climate—although differently than soot.

Since Russia’s war in Ukraine started, President Putin and other Russian officials have made repeated nuclear threats, in an apparent attempt to deter Western countries from any direct military intervention. If Russia were to ever start—voluntarily or accidentally—nuclear war with the United States and other NATO countries, the number of devastating nuclear explosions involved in a full exchange could waft more than 150 Tg of soot into the stratosphere, leading to a nuclear winter that would disrupt virtually all forms of life on Earth over several decades.

Stratospheric soot injections associated with different nuclear war scenarios would lead to a wide variety of major climatic and biogeochemical changes, including transformations of the atmosphere, oceans, and land. Such global climate changes will be more long-lasting than previously thought because models of the 1980s did not adequately represent the stratospheric plume rise. It is now understood that soot from nuclear firestorms would rise much higher into the stratosphere than once imagined, where soot removal mechanisms in the form of “black rains” are slow. Once the smoke is heated by sunlight it can self-loft to altitudes as high as 80 kilometers (50 miles), penetrating the mesosphere.

Even a nuclear exchange between India and Pakistan—causing a relatively modest stratospheric loading of 5 Tg of soot—could produce the lowest temperatures on Earth in the past 1,000 years—temperatures below the post-medieval Little Ice Age. A regional nuclear war with 5-Tg stratospheric soot injection would have the potential to make global average temperatures drop by 1 degree Celsius. Even though their nuclear arsenals have been cut in size and average yield since the end of the Cold War, a nuclear exchange between the United States and Russia would still likely initiate a much more severe nuclear winter, with much of the northern hemisphere facing below-freezing temperatures even during the summer. A global nuclear war that injected 150 Tg of soot into the stratosphere could make temperatures drop by 8 degrees Celsius—3 degrees lower than Ice Age values.

In any nuclear war scenario, the temperature changes would have their greatest effect on mid- and high-latitude agriculture, by reducing the length of the crop season and the temperature even during that season. Below-freezing temperatures could also lead to a significant expansion of sea ice and terrestrial snowpack, causing food shortages and affecting shipping to crucial ports where sea ice is not now a factor. Global average precipitation after a nuclear war would also drop significantly because the lower amounts of solar radiation reaching the surface would reduce temperatures and water evaporation rates. The precipitation decrease would be the greatest in the tropics. For instance, even a 5-Tg soot injection would lead to a 10 percent drops in rainfall.

Changes in the ocean:

The longest-lasting consequences of any nuclear war would involve oceans. Regardless of the location and magnitude of a nuclear war, the smoke from the resulting firestorms would quickly reach the stratosphere and be dispersed globally, where it would absorb sunlight and reduce the solar radiation to the ocean surface. The ocean surface would respond more slowly to changes in radiation than the atmosphere and land due to its higher specific heat capacity (i.e., the quantity of heat needed to raise the temperature per unit of mass).

Global ocean temperature decrease will be the greatest starting three to four years after a nuclear war, dropping by approximately 3.5 degrees Celsius for an India-Pakistan war (that injected 47 Tg of smoke into the stratosphere) and six degrees Celsius for a global US-Russia war (150 Tg). Once cooled, the ocean will take even more time to return to its pre-war temperatures, even after the soot has disappeared from the stratosphere and solar radiation returns to normal levels. The delay and duration of the changes will increase linearly with depth. Abnormally low temperatures are likely to persist for decades near the surface, and hundreds of years or longer at depth. For a global nuclear war (150 Tg), changes in ocean temperature to the Arctic sea-ice are likely to last thousands of years—so long that researchers talk of a “nuclear Little Ice Age.”

Because of the dropping solar radiation and temperature on the ocean surface, marine ecosystems would be highly disrupted both by the initial perturbation and by the new, long-lasting ocean state. This will result in global impacts on ecosystem services, such as fisheries. For instance, the marine net primary production (a measure of the new growth of marine algae, which makes up the base of the marine food web) would decline sharply after any nuclear war. In a US-Russia scenario (150 Tg), the global marine net primary production would be cut almost by half in the months after the war and would remain reduced by 20 to 40 percent for over 4 years, with the largest decreases being in the North Atlantic and North Pacific oceans.

Impacts on food production:

Changes in the atmosphere, surface, and oceans following a nuclear war will have massive and long-term consequences on global agricultural production and food availability. Agriculture responds to the length of growing seasons, the temperature during the growing season, light levels, precipitation, and other factors. A nuclear war will significantly alter all of those factors, on a global scale for years to decades.

Using new climate, crop, and fishery models, researchers have now demonstrated that soot injections larger than 5 Tg would lead to mass food shortages in almost all countries, although some will be at greater risk of famine than others. Globally, livestock production and fishing would be unable to compensate for reduced crop output. After a nuclear war, and after stored food is consumed, the total food calories available in each nation will drop dramatically, putting millions at risk of starvation or undernourishment. Mitigation measures—shifts in production and consumption of livestock food and crops, for example—would not be sufficient to compensate for the global loss of available calories.

The impacts of nuclear war on agricultural food systems would have dire consequences for most humans who survive the war and its immediate effects. The overall global consequences of nuclear war—including both short-term and long-term impacts—would be even more horrific causing hundreds of millions—even billions—of people to starve to death. Two years after a nuclear war ends, nearly everyone might face starvation.

The aforementioned food production impacts do not account for the long-term direct impacts of radioactivity on humans or the widespread radioactive contamination of food that could follow a nuclear war. International trade of food products could be greatly reduced or halted as countries hoard domestic supplies. But even assuming a heroic action of altruism by countries whose food systems are less affected, trade could be disrupted by another effect of the war: sea ice. Cooling of the ocean’s surface would lead to an expansion of sea ice in the first years after a nuclear war, when food shortages would be highest. This expansion would affect shipping into crucial ports in regions where sea ice is not currently experienced, such as the Yellow Sea.

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Table below shows possible impacts of nuclear war:

Theme	Possible impact
Health	Burn injury, flash blindness, retinal burn, hemorrhaging, embolisms, other injuries, acute radiation syndrome, direct morbidity, and mortality
	Chronic health harms, illness, food poisoning, cancer, sunburn, other human health harms, patient death
	Healthcare supply chain, healthcare disruption
	Malnourishment, infectious disease
Infrastructure/energy	Fire, infrastructure damage
	Energy supply shift (fossil fuel, geothermal, nuclear power, wind, solar)
	Damage to electronics, fiber optics, satellite disruption
	Disruption to energy supply, telecommunications, transport, mobility, emergency services, supply chains, heating/cooling
	Loss of industries
Food/water	Water supply disruption (including freezing pipes), lack of potable water, dehydration
	Consumption of stockpiles, agriculture disruption, impact on ocean foods, food price rise, crop substitutions
	Food insecurity, hoarding of food (local/national), export bans, failure to trade, food riots, global food conflict, starvation
Society	Migration, evacuation, territory abandonment, refugee arrival, loss of law and order, smaller less centralized communities
	Unemployment, reduced outdoor activity, labor shortage, disrupted financial markets, disrupted trade, long-term collapse, violent conflict, human extinction (by indirect means)
	Diplomatic reactions, military reactions, shifted norms about nuclear weapons, nuclear electricity and other risks, survivor mental health
Climate/Environment	Smoke/soot, reduced sunlight, reduced temperature and precipitation, increased UV radiation, radiological contamination (e.g., food chain), decrease in phytoplankton productivity, ocean surface temperature change, ecological harm, biodiversity loss, shifted wind, change in greenhouse gas emissions

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Section-8

Introduction to nuclear holocaust:

The term “nuclear holocaust” refers to the catastrophic consequences that arise from the extensive use of nuclear weapons. It signifies a scenario where nuclear warfare leads to widespread destruction and loss of life. Nuclear holocaust refers to a possible nearly complete annihilation of human civilization by nuclear warfare. Under such a scenario, all or most of the Earth is made uninhabitable by nuclear weapons in future world wars. The threat of a nuclear holocaust plays an important role in the anti-nuclear movement and the development of popular perception of nuclear weapons. It features in the security concept of mutually assured destruction (MAD) and is a common scenario in survivalism. Nuclear holocaust is a common feature in literature and film, especially in speculative genres such as science fiction, dystopian and post-apocalyptic fiction.

A nuclear holocaust, also known as a nuclear apocalypse, nuclear annihilation, nuclear Armageddon, or atomic holocaust, is a theoretical scenario where the mass detonation of nuclear weapons causes widespread destruction and radioactive fallout. Such a scenario envisages large parts of the Earth becoming uninhabitable due to the effects of nuclear warfare, potentially causing the collapse of civilization, the extinction of humanity, and/or the termination of most biological life on Earth. Nuclear holocaust became an anti-nuclear issue with the start of nuclear weapons testing, which caused a global fallout due to atmospheric nuclear tests conducted between 1945 and 1980, resulting in deaths of an estimated 2.4 million people from cancers.

Besides the immediate destruction of cities by nuclear blasts, the potential aftermath of a nuclear war could involve firestorms, a nuclear winter, widespread radiation sickness from fallout, and/or the temporary (if not permanent) loss of much modern technology due to electromagnetic pulses. Some scientists, such as Alan Robock, have speculated that a thermonuclear war could result in the end of modern civilization on Earth, in part due to a long-lasting nuclear winter. In one model, the average temperature of Earth following a full thermonuclear war falls for several years by 7 – 8 °C (13 to 15 degrees Fahrenheit) on average. Early Cold War- era studies suggested that billions of humans would survive the immediate effects of nuclear blasts and radiation following a global thermonuclear war. The International Physicians for the Prevention of Nuclear War believe that nuclear war could indirectly contribute to human extinction via secondary effects, including environmental consequences, societal breakdown, and economic collapse.

Nuclear weapons are the most terrifying weapon ever invented; no weapon is more destructive; no weapon causes such unspeakable human suffering; and there is no way to control how far the radioactive fallout will spread or how long the effects will last. Nuclear reactions, whether fission or fusion, allow nuclear weapons to harness far greater energy than conventional explosives, which rely upon chemical reactions. Fissioning one kilogram of a fissile material, such as uranium-235 or plutonium-239, can generate about 15 million times more energy than one kilogram of the conventional explosive TNT. Nuclear explosions are typically measured using a standard unit known as tons of TNT equivalent. For example, the W87, a modern U.S. nuclear weapon, has an explosive yield of 300 kilotons, which is equivalent to 300,000 tons of TNT. The difference is not just about the size of a nuclear explosion, but also the unique effects it generates. The enormous destructive power of a nuclear weapon comes from the blast (which causes shock waves); thermal radiation (which generates enormous heat); nuclear radiation (which has both short and long-term effects), and the Electromagnetic Pulse (which is a short burst of electromagnetic energy that disrupts and damages electronics and other infrastructure). The humanitarian, economic, and environmental consequences of nuclear war are unimaginable. While the likelihood of a full-scale nuclear exchange has decreased significantly since the end of U.S.-Soviet Cold War, the continued existence of around 12,100 nuclear weapons poses ongoing risks of intentional, accidental or unauthorized nuclear weapons use.

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Why are nuclear weapons the worst:

-1. They cause a lot of destruction and death.

A single nuclear weapon can destroy a city and kill most of its people. The bombings of Hiroshima and Nagasaki are prime examples of the fatality caused by an atomic bomb. Several nuclear explosions over modern cities would kill tens of millions of people. Casualties from a major nuclear war between the US and Russia would reach hundreds of millions.

-2. Civilians are the main victims.

The extreme destruction caused by nuclear weapons cannot be limited to military targets or to combatants. Civilians are more often the majority of casualties from a nuclear attack; those within range are either killed or suffer long-term health implications from a nuclear blast and resulting radiation. Even those in neighbouring cities or countries would suffer from the impact of a nuclear detonation.

-3. They lead to high levels of radiation.

Nuclear weapons produce ionizing radiation, which kills or sickens those exposed, contaminates the environment, and has long-term health consequences, including cancer and genetic damage. The legacy of nuclear testing means that up to 2.4 million people worldwide will die from illnesses linked to nuclear testing in the twentieth century. Even the production of nuclear weapons has an effect on the environment. Producing the explosive materials used in nuclear weapons leads to long-lasting radioactive pollution.

-4. They could lead to climate disruption and worldwide famine.

Use of less than one percent of the nuclear weapons in the world could disrupt the global climate and threaten as many as two billion people with starvation in a nuclear famine. The thousands of nuclear weapons possessed by the US and Russia could bring about a nuclear winter, destroying the essential ecosystems on which all life depends.

-5. Humanitarian aid wouldn’t be provided to victims.

There would be no humanitarian response. Physicians and first responders would be unable to work in devastated, radioactively contaminated areas. Even a single nuclear detonation in a modern city would strain existing disaster relief resources to the breaking point; a nuclear war would overwhelm any relief system we could build in advance. Displaced populations from a nuclear war will produce a refugee crisis that is orders of magnitude larger than any we have ever experienced.

-6. Widespread implications to health and the environment.

Whether or not they are detonated, nuclear weapons cause widespread harm to health and to the environment.

-7. Misuse of public funds.

Spending on nuclear weapons detracts limited resources away from vital social services. Currently states that are armed with nuclear weapons spend close to US $225 million a day on nuclear forces.

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Difficulties in developing nuclear weapon:

Developing nuclear weapons is a complex endeavour, requiring substantial financial, technical, and human resources; however, these barriers are not insurmountable, and many countries could develop nuclear weapons if they chose to do so.

Step 1: Acquiring Fissile Material

Acquiring fissile material is the most significant hurdle to a nuclear weapons capability, requiring a country to enrich uranium, produce plutonium, or illicitly procure such materials through theft or purchase.

Step 2: Weapons Fabrication

Individuals with expertise in chemistry, physics, metallurgy, electronics, and explosives would be required to design and fabricate a nuclear weapon. Many non-nuclear components and high-end manufacturing techniques are also required. However, the basic design concepts are in the public domain, and many of the components and manufacturing techniques could be procured legitimately because of their dual-use nature. Modern proliferators would benefit from advances in high-performance computing (supercomputers), which were unavailable to the first nuclear weapons programs.

Step 3: Testing

Countries use nuclear testing to validate whether a particular nuclear weapon design works. For an unsophisticated design, such as a gun-type weapon, nuclear testing is not necessary to provide high confidence a bomb will detonate. Weapons designers would need to test the non-nuclear components in an implosion-based weapon, but might not need to conduct a full-scale nuclear text. Testing at full nuclear yield would be required for a country seeking very low-weight weapons, or thermonuclear weapons.

All five nuclear weapon states recognized by the NPT and at least three of the four additional nuclear weapons possessing states have conducted nuclear tests. All but one of these countries (North Korea) currently observe testing moratoria. Because of the Comprehensive Nuclear Test Ban Treaty Organization’s (CTBTO) International Monitoring System, conducting clandestine nuclear tests is extremely difficult.

Step 4: Delivery Systems

In addition to the nuclear weapon’s design, the sophistication of a country’s delivery systems—such as missiles, combat aircraft and drones—determine how, when and against whom a country can use nuclear weapons. These systems also enable states to deploy their nuclear forces for deterrence and signaling purposes. States prefer aerial methods of delivering nuclear weapons (and especially ballistic missiles) because they are fast, cover large distances, carry large payloads and can penetrate an adversary’s defenses. Long-range systems place tight constraints on the size and weight of nuclear weapons. Miniaturization to fit a nuclear weapon atop a missile, for example, can pose significant challenges to a proliferating country, and would require nuclear testing.

Non-state actors such as terrorists may resort to crude delivery methods to carry out attacks. Were such groups to build a crude nuclear device, a human carrier, truck, cargo shipping container, or a civilian aircraft could be sufficient to deliver it to a target.

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Countries having nuclear weapons:

Nine countries are known or believed to possess nuclear weapons: the United States, China, France, India, Israel, North Korea, Pakistan, Russia, and the United Kingdom. Those countries are called nuclear weapons states. Several other countries started nuclear weapons programs but gave them up, either voluntarily or because of external pressure. A few have had nuclear weapons and later destroyed them or turned them over to another nuclear state.

Countries banning nuclear weapons:

Since the 1960s, some countries have come together to create nuclear weapon-free zones (NWFZs), specified areas where countries pledge not to build, receive, test, or store nuclear weapons. NWFZs do not prevent peaceful nuclear technology use. Five treaties have created NWFZs in Africa, Central Asia, Latin America, Southeast Asia, and the South Pacific. Together, those zones span the entire Southern Hemisphere and parts of the Northern Hemisphere. Additionally, three treaties create a nuclear weapon–free global common space for research, exploration, and the general advancement of humankind:

The Seabed Treaty bans weapons of mass destruction on the ocean floor.
The Antarctic Treaty bans any military activity in Antarctica, including the testing of nuclear weapons.
The Outer Space Treaty bans weapons of mass destruction from the earth’s orbit, the moon, or any other object in outer space.

Countries that have security guarantees to help protect them against nuclear weapons:

The global divide isn’t as simple as nuclear and nuclear free. Many countries without nuclear weapons want to protect themselves against nuclear threats without developing nuclear weapons themselves. One way to do that is through a security guarantee, a pledge from a country to protect an ally using military means. A security guarantee extends the perceived security a nuclear arsenal provides to allied countries that do not possess nuclear weapons. Because of that provision, a security guarantee provided by a nuclear-armed country is also called a nuclear umbrella. The U.S. nuclear umbrella covers several countries.

Australia: Since 1951, the United States and Australia have been part of a collective security alliance, but the related treaty is nonbinding and its language not as strong as that in the North Atlantic Treaty: whether the alliance requires the U.S. military to actually come to Australia’s defense is unclear. Still, most experts consider Australia to be protected by the U.S. nuclear umbrella.
Japan: In 1951, at the end of the Allied occupation, the United States and Japan signed a security treaty that provisionally allowed the United States to maintain armed forces in and around Japan. In 1960, the two countries revised that agreement, which then allowed the United States to set up military bases in Japanese territories in exchange for U.S. protection and security, including nuclear weapons.
South Korea: Two months after fighting stopped in the Korean War in 1953, the United States and South Korea signed a mutual defense treaty creating a military alliance that continues to this day.
North Atlantic Treaty Organization (NATO) members: NATO member countries that do not have nuclear weapons (i.e., all except France and the United Kingdom) are protected by the umbrella.

A nuclear umbrella is also meant to be a tool of nonproliferation: if countries without nuclear weapons are protected under a security guarantee from a nuclear-armed country, then those countries will be less inclined to start nuclear weapons programs of their own.

Security guarantees and nuclear umbrellas both illustrate an important point: even countries that have committed to nonproliferation understand that they live in a nuclear world. The different ways countries deal with that reality—acquiring nuclear weapons, declaring NWFZs, or seeking security guarantees—reflect the paradoxical goal of most countries: a peaceful future secured by weapons as necessary.

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Many dimensions of nuclear threat:

Nuclear war is low in most people’s priorities. But according to the World Economic Forum Global Risks Report 2021, weapons of mass destruction are still the greatest long-term existential threat to the world. Nuclear war could dwarf a pandemic in terms of health impacts, pressure on health services, difficulties in protecting essential workers, societal effects, and overwhelming global ramifications. Implicit or explicit nuclear threats have been the default position of states possessing nuclear weapons for decades. Such threats are the essence of deterrence: if you attack, we will destroy your society or your most vital military assets. All the same, making a nuclear threat is unusual and alarming. For that reason, explicit threats and the raising of nuclear alert levels have become rare since the 1962 Cuban missile crisis. Chinese nuclear threats against Japan and U.S. President Donald Trump’s “fire and fury” threats to North Korea were shocking. The implied nuclear threats that Russian President Vladimir Putin made to the United States and NATO as he pressed his full-scale invasion of Ukraine are also startling. A durable end to Russia’s war in Ukraine seems distant, and the use of nuclear weapons by Russia in that conflict remains a serious possibility. In February 2023, Russian President Vladimir Putin announced his decision to “suspend” the New Strategic Arms Reduction Treaty (New START). In March, he announced the deployment of tactical nuclear weapons in Belarus. In June, Sergei Karaganov, an advisor to Putin, urged Moscow to consider launching limited nuclear strikes on Western Europe as a way to bring the war in Ukraine to a favorable conclusion. In October, Russia’s Duma voted to withdraw Moscow’s ratification of the Comprehensive Nuclear Test Ban Treaty, as the US Senate continued to refuse even to debate ratification.

MIT Professor Ted Postol, a former scientific adviser to the chief of naval operations, has warned that Russia’s missile detection capabilities are not as advanced as the ones that the United States has, which he described as a “terrible and dangerous technology shortfall.” Especially, he warns, if nuclear radar facilities are under attack, as they were recently, Russia could falsely assume it is being targeted by nuclear weapons and could unleash the full power of its 5,500+ warhead arsenal. Make that partial, it’s still enough to not only destroy the United States, but the whole world. Mikhail Gorbachev and Ronald Reagan jointly stated in 1985 that “nuclear war cannot be won and must never be fought.” Despite leaders of the five original nuclear weapon states explicitly reaffirming this in January 2022 prior to Russia’s invasion of Ukraine, many of those same leaders seem to have forgotten these wise words and have recklessly pushed the world to the brink of nuclear war.

Nuclear spending programs in the three largest nuclear powers—China, Russia, and the United States—threaten to trigger a three-way nuclear arms race as the world’s arms control architecture collapses. Russia and China are expanding their nuclear capabilities, and pressure mounts in Washington for the United States to respond in kind. Meanwhile, other potential nuclear crises fester. Iran continues to enrich uranium to close to weapons grade while stonewalling the International Atomic Energy Agency on key issues. Efforts to reinstate an Iran nuclear deal appear unlikely to succeed, and North Korea continues building nuclear weapons and long-range missiles. Nuclear expansion in Pakistan and India continues without pause or restraint. And the war in Gaza between Israel and Hamas has the potential to escalate into a wider Middle Eastern conflict that could pose unpredictable threats, regionally and globally.

Top nuclear issues of 2024:

-1. Russia’s Nuclear Threats and the War in Ukraine

-2. China’s Nuclear Buildup

-3. Tensions with North Korea

-4. Nuclear Modernization

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Modernising and expanding nuclear arsenals at enormous and escalating cost:

All nine nuclear-armed states are investing massively in modernising and expanding their nuclear arsenals. Modernisation means new, faster, stealthier, more flexible and accurate capacities. A missile can be armed with either conventional or nuclear warheads, indistinguishable until point of impact. These changes lower the overall threshold for use of nuclear weapons. Both Russia and the USA, owning between them 90% of all nuclear weapons, are comprehensively replacing and modernising their warheads, missiles and launch platforms. They are also increasing the role of nuclear weapons in their military policies, and the range of circumstances in which they might be used, including against conventional and cyber-attacks. Russia is testing and deploying entirely new types of nuclear weapons including nuclear-powered cruise missiles, hypersonic delivery vehicles atop ballistic missiles, and long-range nuclear torpedoes designed to explode in waters close to cities. The US is producing new nuclear warheads for the first time in three decades, modernising all types of nuclear weapons—ballistic and cruise missiles, bombs delivered by aircraft, and the submarines, ships and aircraft that carry them. It is also upgrading the nuclear weapons it provides to the UK and the nuclear bombs it stations in Belgium, Germany, Italy, Netherlands and Turkey.

Current estimates of global spending on development and production of nuclear weapons reached US$72.6 billion in 2020, an increase of $1.4 billion from 2019, even given constraints of the pandemic. The total cost of nuclear weapons programs, including environmental clean-up and legacy costs, is far greater. The US spends the most on military and nuclear weapons: in FY 2021 its nuclear weapons-related costs reached US$74.75 billion. Military spending consumes half of all discretionary US government spending. In the US, nuclear warhead spending is currently at an all-time record high, with projected expenditures over the next three decades of over US$2 trillion to comprehensively refurbish the nuclear arsenal and the facilities that produce nuclear weapons. While Russia’s military spending in 2020 ($61.7 billion) was estimated to be only 8% of that of the US ($778 billion), the proportion it spends on nuclear weapons is more than 2.5 times as great as the US.

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Cyberwarfare increases vulnerability of nuclear arms systems:

Attacks on civilian and military nuclear facilities included extensive hacking in December 2020 of the US National Nuclear Security Administration which maintains US nuclear weapons. Complex global systems of early warning, command, control, communications, and intelligence are related to nuclear weapons. They are complex, dispersed, and interlinked—and vulnerable to cyberattack. As General James Cartwright, former head of US Strategic Command stated, it: “might be possible for terrorists to hack into Russian or American command and control systems and launch nuclear missiles, with a high probability of triggering a wider nuclear conflict.”

British, French, Russian, and US authorities keep 2000 nuclear warheads on high alert, all mounted on delivery vehicles and ready for use within minutes of a launch order. These warheads are particularly vulnerable to digital sabotage and inadvertent or unauthorised launch. Many states, including China, Iran, Israel, North Korea, Russia, and the US, engage in offensive cyber operations. Buyers may include governments, government proxies, and terrorist organisations. Frequently buyers find tools in a lucrative global black and grey market offering hacking tools, especially ‘Zero-day exploits’. These tools exploit software or hardware flaws and vulnerabilities for which no corrective patch yet exists. Government staff, as part of their work, or moonlighting staff, or government contractors can develop offensive digital tools. Individual or organised hackers and cybercriminals, or private for-profit companies can also produce them almost anywhere. Targets of hacking and digital sabotage to date include banking and health systems, Sony Corporation, electricity grids, water treatment facilities, airports, electoral systems, oil company computer systems, uranium enrichment centrifuges, and nuclear power plants. Increasing digital sophistication of nuclear weapons and delivery systems may increase their vulnerability to digital sabotage.

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Source materials for nuclear weapons are not under adequate control:

Vast stocks of fissile materials, the highly enriched uranium and plutonium from which nuclear weapons can be built, persist in civilian and military stockpiles in tens of countries. There are no effective international constraints on the production of these materials. Every state with a civilian nuclear industry is also capable of producing fissile materials; and any state that can enrich uranium to reactor grade can enrich it to weapons grade. Nuclear reactors inevitably convert some of the uranium in the fuel into plutonium. The average modern nuclear weapon contains around 4 kg of plutonium and/or 15 kg of highly enriched uranium (HEU). With the global fissile material stockpile at the start of 2020 estimated by the International Panel on Fissile Materials to contain 1330 tonnes of HEU and 540 tonnes of separated plutonium, this equates to more than 225,000 nuclear weapon equivalents of material. Apart from removal of relatively modest quantities of highly enriched uranium from civilian stockpiles in 34 countries plus Taiwan, the challenges of ceasing production of these materials, eliminating them where possible, and keeping the remaining quantities in consolidated storage in the safest possible form at the highest possible levels of security, remain largely unaddressed.

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End nuclear weapons before they end us:

Evidence of the consequences of nuclear war, particularly the global climatic and nutritional effects of the abrupt ice age conditions from even a relatively small regional nuclear war, indicates that these are more severe than previously thought. None of the nine nuclear-armed states is disarming; instead, all invest enormously in new and more hazardous nuclear weapons. Nor has any of the 32 states claiming reliance on another state’s nuclear weapons yet ended such reliance. Risks of a nuclear war are growing. No nuclear-armed state is currently disarming, nor engaged in nuclear disarmament negotiations. First the US, followed by Russia, abrogated hard-won treaties negotiated between them which were fruits of the end of the first Cold War, and which constrained nuclear weapons numbers and types. These factors, abrogation of existing nuclear arms control agreements, policies of first nuclear use and war fighting, growing armed conflicts worldwide, and increasing use of information and cyberwarfare, exacerbate dangers of nuclear war. No health service in any area of the world would be capable of dealing adequately with the hundreds of thousands of people seriously injured by blast, heat or radiation from even a single 1-megaton bomb. The only approach to the treatment of the health effects of nuclear explosions is primary prevention of such explosions, that is, the primary prevention of atomic war.

Mainau Declaration 2024 on nuclear weapons: 30 Nobel Laureates sign Appeal against Nuclear War:

On the closing day of the 73rd Lindau Nobel Laureate Meeting, 5 July 2024, 30 Nobel Laureates in Physics and Chemistry from more than 10 countries signed the “Mainau Declaration 2024 on Nuclear Weapons”. It states:

“In July 1955, eighteen Nobel Laureates in science, meeting in Lindau, issued a declaration warning the world of the immense danger posed by the development of nuclear weapons that give humankind the means to destroy itself. In the subsequent decades, the number of countries with nuclear weapons, as well as the number of warheads and their destructive power, has increased ten-fold. We have been very lucky to have avoided nuclear war until now, but at this time the situation is dire. Nuclear arms are proliferating; arms control agreements are being scrapped; and an accelerated arms race is underway. In today’s fragmented and polarized world, there is a significant probability that, either by accident or by deliberate act, these horrible weapons may be used – with the likelihood of the end of human civilization as we know it. We the undersigned scientists of different countries, different creeds, and different political persuasions, call on the people and leaders of the world to heed our warning and act to prevent this catastrophe. All nations must commit to ensuring that nuclear weapons never be used again. If they are not prepared to do this, they will cease to exist.”

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The Doomsday Clock:

Founded in 1945 by Albert Einstein, J. Robert Oppenheimer, and University of Chicago scientists who helped develop the first atomic weapons in the Manhattan Project, the Bulletin of the Atomic Scientists created the Doomsday Clock two years later, using the imagery of apocalypse (midnight) and the contemporary idiom of nuclear explosion (countdown to zero) to convey threats to humanity and the planet. The Doomsday Clock is set every year by the Bulletin’s Science and Security Board in consultation with its Board of Sponsors, which includes nine Nobel laureates. The Clock has become a universally recognized indicator of the world’s vulnerability to global catastrophe caused by man-made technologies. As a symbol of the unique existential peril posed by thousands of nuclear warheads kept on a hair trigger, the Doomsday Clock is unparalleled, one of the 20th century’s most iconic pieces of graphic art. Its value is its stark simplicity. At a glance, anyone can see how close the Bulletin’s science and security experts, who meet twice a year to determine the Clock’s annual setting, believe the world is to existential catastrophe. The Clock may be wrong — predicting the apocalypse is a near-impossible task — but it cannot be misread. Since its introduction 77 years ago, the hands of the Clock have moved backward and forward in response to geopolitical shifts and scientific advances. In 1953, it was set to two minutes to midnight after the U.S. and Soviet Union both tested thermonuclear weapons for the first time; in 1991, after the collapse of the USSR and the signing of the Strategic Arms Reduction Treaty, it was moved back to 17 minutes to midnight, the furthest it’s been to 12 in its history. The Doomsday Clock was reset at 90 seconds to midnight, still the closest the Clock has ever been to midnight, reflecting the continued state of unprecedented danger the world faces in 2024, for example the Russia-Ukraine war and deterioration of nuclear arms reduction agreements.

The setting of the clock is intended to represent how close the world is to nuclear war, metaphorically midnight. There are multiple problems with taking the clock seriously as an assessment of the likelihood of nuclear war. In setting the clock, there could be motives beyond accurately characterizing the nuclear threat, such as to promote certain policies, especially with respect to arms control treaties, or simply to draw attention to the Bulletin of the Atomic Scientists. The process by which the clock is set is obscure, although brief summaries of the reasons for changing the clock’s setting have been provided. No attempt has been made to define the clock’s scale, which is almost certainly nonlinear. Does ten minutes to midnight indicate half the probability of five minutes to midnight? And finally, the clock is unable to reflect the risks associated with short-duration, high-risk episodes, such as the Cuban missile crisis of 1962 and the coup attempt against Gorbachev in August 1991. Ironically, the former occurred during a period of declining risk, and the latter occurred during the period of least risk. Notwithstanding these points, the Doomsday Clock does seem to have captured the broad trends in the nuclear threat as it derives from the international political climate. Gaining a better understanding of the processes by which the clock has been set could prove useful in developing more scientific approaches. Unfortunately, the clock’s future utility as an indicator of the risk of nuclear war has been diminished since 2007 by the inclusion of climate change and harmful developments in the life sciences as additional harbingers of doomsday.

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Fallible leaders and nuclear war:

It is extremely unfortunate that when international peace and cooperation are needed more than ever before to avoid the most catastrophic situations, the world leadership has been increasingly exposed in recent times for its glaring failures to achieve such peace and cooperation. In fact, it is no exaggeration to say that at a time when the need for moving fast on the path of peace, disarmament and cooperation is the highest, world leadership has been instead moving in the reverse direction, as evident from increasing superpower rivalries and tensions as well as breakdown and non-renewal of important disarmament treaties or agreements. The possibility that military plans could drive a crisis faster than leaders can manage is a classic concern.

How close did India and Pakistan come to nuclear war in February 2019? After a suicide attack in Kashmir that killed 46 policemen, India conducted an airstrike against what it called a “terrorist training camp” in Balakot, Pakistan. The crisis seemed on the verge of spiralling out of control after Pakistan shot down an Indian fighter jet. According to a number of reports, Indian Prime Minister Narendra Modi seriously considered a missile strike in the event that Pakistan did not return the pilot. The accounts vary—was it six missiles? Nine? Twelve? Or was it all a bluff, a threat upon which Modi never intended to follow through? For his part, Modi has repeatedly emphasized that the threat was real and that had Pakistan not returned the pilot, he was prepared to commit what he called “a night of murder.” For their part, Pakistani officials also claim the threat was real and that, had India launched the missiles, Prime Minister Imran Khan was prepared to respond “three times over” to any Indian strike. As it turned out, the pilot was released and the crisis ebbed, another in a recurring series of crises in South Asia.

War scares and nuclear brinkmanship also fueled the Cold War between the United States and the Soviet Union. The world held its breath as leaders squared off over Berlin in 1961 and Cuba in 1962, and as relations collapsed into the War Scare of 1983. Historians still debate how serious each of these crises really were. After all, while each side engaged in nuclear brinksmanship, the two superpowers always pulled back in time. There exists today a kind of confident hindsight that everything was destined to work out, a confidence that would have surprised those who lived through these scares. A similar confidence seems to exist that nuclear crises in South Asia, like their Cold War analogues, are not as frightening as they seem. Perhaps, people say, we exaggerated the danger in February 2019, just as we exaggerated all the other dangers through which we have passed safely.

Many of us, though, remember the Cold War as terrifying. And many of us find that new historical information has done little to reassure that past crises were destined to end well. Robert McNamara recalled learning near the end of his life that, contrary to what he and other officials believed, that there were already Soviet nuclear weapons in Cuba in 1962. McNamara always thought the crisis had been dangerous, but he had not realized that an invasion almost certainly would have met with a nuclear response that could have escalated out of control. He thought he knew where the red lines were that October. He was wrong. McNamara was visibly shaken after learning this at a conference with Fidel Castro in 1992, later telling a reporter that the revelation had been “horrifying.” Kennedy and McNamara, Khrushchev and Castro, like all leaders, were fallible. They made mistakes. They believed things that later turned out not to be true. In other words, they were human. So are Narendra Modi and Imran Khan.

Modi and Khan probably believe that their handling of past crises has been deft, but we now know that even the best American and Soviet leaders during the Cold War made serious mistakes. Like Kennedy and Khrushchev, Modi and Khan may be confident they can approach the brink of nuclear catastrophe, but pull back in time. Their success may depend on whether they realize how close that edge really is. The need to “think the unthinkable” has returned with Vladimir Putin’s veiled threat to launch nuclear missiles if Russia feels alarmed by the West’s response to its invasion of Ukraine. Meanwhile, it is reported that Russia is thinking about putting nuclear weapons in space, while China is rapidly expanding its own nuclear arsenal. In the Middle East, there is an increasingly urgent concern that Iran will develop a nuclear weapon and use it on behalf of its geopolitical designs.

An attacker is far more likely to succeed by going first, attempting to destroy the enemy’s nuclear forces before they can be dispersed. India, in particular, may feel compelled to strike Pakistan while Pakistan’s missiles are still in their garrisons – either striking the missile launchers themselves or, more likely, attempting to kill Pakistan’s political leadership before it can issue orders to disperse, let alone to retaliate. Scholars Christopher Clary and Vipin Narang have noted the signs in Indian discourse of what they call a “flirtation with pre-emptive counterforce,” warning that it could drive Pakistan to respond in ways that accelerate the regional arms race and undermine crisis stability. Many Indian scholars and experts have rejected the idea that India is moving toward a pre-emptive strategy, arguing that Clary and Narang have “misinterpreted” and “cherry-picked” evidence. Clary and Narang’s arguments seem persuasive, but the possibility of such a fundamental dispute over India’s basic approach to deterrence and defense illustrates the need to strengthen confidence building measures. One wonders whether current leaders in South Asia will be as cautious or just plain lucky as Kennedy.

The previous two world wars were fought over several years and involved prolonged battles in many countries. World War 3 can take a very different shape as so much harm is caused within just a few days that it cannot continue beyond this. However, it will be worse than the previous two world wars taken together as within a few days of nuclear warfare and the resulting nuclear winter most people and other life-forms will die or will be left to die. The actual use of just 10% of the existing stock of nuclear weapons will be enough to achieve such a hugely destructive result. It is not just a question of whether the probability of this ever happening is 5% or 10%, more or less. The fact is that by any rational reckoning any probability of this happening even at minimum levels is unacceptable. This is a betrayal by world leadership of their most essential responsibility towards people, towards this generation and the next, towards completely innocent children, towards all forms of life.

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Effects of a single nuclear explosion:

Any nuclear explosion creates radiation, heat, and blast effects that will result in many quick fatalities.

Direct radiation is the most immediate effect of the detonation of a nuclear weapon. It is produced by the nuclear reactions inside the bomb and comes mainly in the form of gamma rays and neutrons. Direct radiation lasts less than a second, but its lethal level can extend over a mile in all directions from the detonation point of a modern-day nuclear weapon with an explosive yield equal to the effect of several hundred kilotons of TNT. If you are exposed to it, people, for example, in Hiroshima were essentially evaporated, leaving shadows.

Microseconds into the explosion of a nuclear weapon, energy released in the form of X-rays heats the surrounding environment, forming a fireball of superheated air. Inside the fireball, the temperature and pressure are so extreme that all matter is rendered into a hot plasma of bare nuclei and subatomic particles, as is the case in the Sun’s multi-million-degree core.

The fireball following the airburst explosion of a 300-kiloton nuclear weapon—like the W87 thermonuclear warhead deployed on the Minuteman III missiles currently in service in the US nuclear arsenal—can grow to more than 600 meters (2,000 feet) in diameter and stays blindingly luminous for several seconds, before its surface cools.

The light radiated by the fireball’s heat—accounting for more than one-third of the thermonuclear weapon’s explosive energy—will be so intense that it ignites fires and causes severe burns at great distances. The thermal flash from a 300-kiloton nuclear weapon could cause first-degree burns as far as 13 kilometers (8 miles) from ground zero.

Then comes the blast wave.

The blast wave—which accounts for about half the bomb’s explosive energy—travels initially faster than the speed of sound but slows rapidly as it loses energy by passing through the atmosphere.

Because the radiation superheats the atmosphere around the fireball, air in the surroundings expands and is pushed rapidly outward, creating a shockwave that pushes against anything along its path and has great destructive power.

The destructive power of the blast wave depends on the weapon’s explosive yield and the burst altitude.

An airburst of a 300-kiloton explosion would produce a blast with an overpressure of over 5 pounds per square inch (or 0.3 atmospheres) up to 4.7 kilometers (2.9 miles) from the target. This is enough pressure to destroy most houses, gut skyscrapers, and cause widespread fatalities less than 10 seconds after the explosion.

The blast area is defined as the area where the shockwaves and the fireball are the most intense. For Hiroshima, that was between 1 and 2 miles. Basically, everything is destroyed in that blast area.

Radioactive fallout:

Shortly after the nuclear detonation has released most of its energy in the direct radiation, heat, and blast, the fireball begins to cool and rise, becoming the head of the familiar mushroom cloud. Within it is a highly-radioactive brew of split atoms, which will eventually begin to drop out of the cloud as it is blown by the wind. Radioactive fallout, a form of delayed radioactivity, will expose post-war survivors to near-lethal doses of ionizing radiation. The nuclear blast creates a mushroom cloud, which can reach as high as 10 miles into the atmosphere. Carried by the wind, the cloud spreads radioactivity far outside the blast area. In a nuclear blast, up to 100 different radioactive elements are produced. These radioactive elements have lifetimes which could be a few seconds, and they could be up to millions of years. … It causes pollution and damage to the body and injuries over a longer period, causing cancer and leukemia, things like this.

As for the blast, the severity of the fallout contamination depends on the fission yield of the bomb and its height of burst. For weapons in the hundreds of kilotons, the area of immediate danger can encompass thousands of square kilometers downwind of the detonation site. Radiation levels will be initially dominated by isotopes of short half-lives, which are the most energetic and so most dangerous to biological systems. The acutely lethal effects from the fallout will last from days to weeks, which is why authorities recommend staying inside for at least 48 hours, to allow radiation levels to decrease.

Because its effects are relatively delayed, estimating casualties from the fallout is difficult; the number of deaths and injuries will depend very much on what actions people take after an explosion. But in the vicinity of an explosion, buildings will be completely collapsed, and survivors will not be able to shelter. Survivors finding themselves less than 460 meters (1,500 feet) from a 300-kiloton nuclear explosion will receive an ionizing radiation dose of 500 Roentgen equivalent man (rem). “It is generally believed that humans exposed to about 500 rem of radiation all at once will likely die without medical treatment,” the US Nuclear Regulatory Commission says.

But at a distance so close to ground zero, a 300-kiloton nuclear explosion would almost certainly burn and crush to death any human being. The higher the nuclear weapon’s yield, the smaller the acute radiation zone is relative to its other immediate effects.

One detonation of a modern-day, 300-kiloton nuclear warhead—that is, a warhead nearly 10 times the power of the atomic bombs detonated at Hiroshima and Nagasaki combined—on a city like New York would lead to over one million people dead and about twice as many people with serious injuries in the first 24 hours after the explosion. There would be almost no survivors within a radius of several kilometers from the explosion site.

Vaults are massive underground bunkers the size of small towns that the luckiest of people get to retreat into when the world ends. The Vaults are several steps above most real-world fallout shelters, but that kind of protection would be necessary if you wanted to stay safe from the kind of radiation released by nuclear weapons, particularly gamma rays that can penetrate several feet of concrete. If you are further away and you keep inside and behind concrete, then you can avoid both the initial flash of the nuclear blast and also could probably withstand the shockwaves and the heatwave that follows, so the survivability becomes larger.

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Effects of nuclear weapons:

Nuclear weapons are the most destructive, inhumane and indiscriminate weapons ever created. Both in the scale of the devastation they cause, and in their uniquely persistent, spreading, genetically damaging radioactive fallout, they are unlike any other weapons. A single nuclear bomb detonated over a large city could kill millions of people. The use of tens or hundreds of nuclear bombs would disrupt the global climate, causing widespread famine.

Short-term effects:

A single nuclear weapon can destroy a city and kill most of its people. Several nuclear explosions over modern cities would kill tens of millions of people. Casualties from a major nuclear war between the US and Russia would reach hundreds of millions. It takes around 10 seconds for the fireball from a nuclear explosion to reach its maximum size. A nuclear explosion releases vast amounts of energy in the form of blast, heat and radiation. An enormous shockwave reaches speeds of many hundreds of kilometres an hour. The blast kills people close to ground zero, and causes lung injuries, ear damage and internal bleeding further away. People sustain injuries from collapsing buildings and flying objects. Thermal radiation is so intense that almost everything close to ground zero is vaporized. The extreme heat causes severe burns and ignites fires over a large area, which coalesce into a giant firestorm. Even people in underground shelters face likely death due to a lack of oxygen and carbon monoxide poisoning.

Long-term effects:

In the long-term, nuclear weapons produce ionizing radiation, which kills or sickens those exposed, contaminates the environment, and has long-term health consequences, including cancer and genetic damage. Their widespread use in atmospheric testing has caused grave long-term consequences. Physicians project that some 2.4 million people worldwide will eventually die from cancers due to atmospheric nuclear tests conducted between 1945 and 1980.

The use of less than one percent of the nuclear weapons in the world could disrupt the global climate and threaten as many as two billion people with starvation in a nuclear famine in the long-term. The detonation of thousands of nuclear weapons could result in a nuclear winter, which would destroy our fragile ecosystem.

Radioactive fallout and toxic chemical contamination from destroyed pipelines and industrial and storage sites would affect large areas of agricultural land. Social, economic, transport and trade turmoil would disrupt global distribution of fertiliser, fuel, machinery and equipment, seeds, pesticides, food storage facilities, and transport on which modern agriculture, food stocks, and distribution depend. And the consequence? The climatic changes alone would cause a decline in net primary productivity (NPP) of between 10 and 20% in the oceans and between 15 and 40% on land over multiple years. NPP is the net amount of carbon per square metre per year converted into plant matter after accounting for what plants use for their own respiration. This loss would be comparable to the total current annual human use of food and fibre. Scientists continue to discover new effects that would exacerbate the harm. Recent findings indicate that various nuclear war scenarios could induce an El Niño-like pattern of unprecedented magnitude across the Pacific, with associated reductions in equatorial Pacific phytoplankton productivity of about 40%.

Physicians and first responders would be unable to work in devastated, radioactively contaminated areas. Even a single nuclear detonation in a modern city would strain existing disaster relief resources to the breaking point; a nuclear war would overwhelm any relief system we could build in advance. Displaced populations from a nuclear war will produce a refugee crisis that is orders of magnitude larger than any we have ever experienced.

Environmental and socio-economic impact of nuclear weapons:

The existence of nuclear weapons has a strong impact on the environment. Nuclear war would mean a climate disruption with devastating consequences. The world would fall under a nuclear winter, be subject to a deadly global famine and exacerbated effects of global warming.

The socio-economic impacts would also be terrible, with developing countries and marginalized groups the ones that will suffer the most. Nuclear weapons are also a vacuum for financial support: in their development, maintenance and dismantlement. This is money that could be better spent funding assets such as renewable technologies and health facilities.

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Simulations of nuclear weapon use:

Plan A:

In 2019, Princeton’s Science and Global Security Program developed a “Plan A” simulation to simulate how limited tactical weapons could rapidly spiral into an all-out nuclear assault and leave 91.5 million dead in a matter of hours. As you can see, what begins with a one-for-one tactical exchange escalates rapidly into counterforce and eventually counter value—wiping out critical infrastructure to keep one’s enemy from recovering in the aftermath of an apocalyptic attack. That means that in a matter of hours, most of Europe, the United States, and Russia would be levelled due to the detonation of multiple nuclear weapons, with nearly 100 million dead in the immediate aftermath. Those who weren’t instantly killed by the blasts or afflicted with radiation sickness, meanwhile, could still be blinded by it from miles away. Note that 35% of a nuclear weapon’s energy is released as heat, which can scorch and leave second and third-degree burns, even miles from the blast. Each impact would vaporize buildings, blowing out windows and ejecting wreckage at 784 miles per hour outward from the blast. The electromagnetic pulse (EMP) would shut down every car, smartphone, computer, and other unshielded electronic devices for miles.

The Princeton simulation, ironically entitled “Plan A,” comes as the United States works to develop brand new low-yield nuclear weapons, despite the opposition of leading Democratic members of Congress, and demonstrates that even lower-yield nuclear weapons can have devastating consequences. The researchers used independent assessments of current U.S. and Russian nuclear force postures, including the number of warheads deployed and their yields, war plans and targets to create the simulation. Equally alarming as the casualty toll of this nuclear war simulation is the growing probability that it becomes a reality.

The risk of nuclear war has increased dramatically in the past two years as the United States and Russia have abandoned long-standing nuclear arms control treaties, started to develop new kinds of nuclear weapons and expanded the circumstances in which they might use nuclear weapons. Plan A shows that there is no sane plan once a nuclear weapon is launched. A better plan is to reject nightmare nuclear scenarios and support the Treaty on the Prohibition of Nuclear Weapons.

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Simulation Study on 16 Kiloton and 1 Megaton Nuclear Bomb Detonations upon One Million Modern City:

Researchers at Nagasaki University and Hiroshima University who had been engaged in the studies on the delayed atomic-bomb effects were asked by the Japanese Ministry of Foreign Affairs to conduct a simulation study to prepare for the second International Conference on the Humanitarian Impact of Nuclear Weapons held in Nayarit in Mexico in 2014. Based on the scientific data obtained from the actual detonations of the 16-kiloton Hiroshima bomb and the 21-kiloton Nagasaki bomb, such as statistics on the deaths caused by leukemia and cancers (Table below), and data from a US government report on the effects of nuclear-weapon detonations, especially for a 1-megaton hydrogen bomb, researchers simulated the effects of nuclear detonations on a virtual modern city with a population of 1 million.

	Fixed population of survivors	No. of death in 50 years	expected No. of death	Excess cases	Percent Radiation-related
Leukemia
all doses	86,611	296	203	93	46%
2 Gy<	2,709	64	8	56	88%
Cancers
all doses	1,05,427	17,448	16,500	853	10.7%
2 Gy<	2,211	185	111	74	61%

Table above shows Population-based study on leukemia and cancer statistics Hiroshima/Nagasaki combined.

As shown in Figure below, the following two cases were examined: a 16-kiloton atomic bomb that explodes 600 meters above the ground, exactly as Hiroshima’s “Little Boy” did, and a 1-megaton hydrogen bomb that explodes 2,400 meters above the ground.

Figure above shows Design of simulation.

As shown in Table below researchers estimated (1) the number of immediate deaths and injuries, (2) the long-term consequences such as leukemia and cancers, (3) the magnitude of damage to city area and infrastructure, and (4) the magnitude of economic collapse.

	16 kiloton atomic bomb	1 megaton hydrogen bomb
Immediate Death	66,000	3,70,000
Immediate Injury	2,05,000	4,60,000
Radiation-affected	1,55,000	36,000
population	(within 2.8 km)	(within 3 km)
Excess Leukemia	220	70
Excess Cancers	12,000	650

Table above shows Comparison of immediate effects and late effects (leukemia/cancer) over 50 years between atomic bomb and hydrogen bomb.

For the 16-kiloton atomic bomb, the area of visible destruction has a radius of 4.5 km from ground zero, exactly the same as the one observed in Hiroshima City in the 1945 bombing. As for the hydrogen bomb, the radius of the completely destroyed area is approximately 18 km, which covers the entire city of 1 million people and additional neighborhood areas with 400,000 people. Heat and radiation rays from the atomic bomb reached 2.8 km, the same as Hiroshima. About 40 percent of the city area is devastated. In the case of the hydrogen bomb, the major destructive powers are blast wind and heat rays. But, curiously, radiation reaches only 3 km from ground zero. This can be explained by the height of the detonation. The radiation beams emitted from a height of 2,400 meters tend to diminish significantly during their transmission through the air as air absorbs radiation. Only a small portion of the total radiation actually reaches the ground surface.

Researchers have also calculated immediate and late casualties. As shown in Table above, the 16-kiloton atomic bomb causes 66,000 immediate deaths and 205,000 severe injuries. The population affected by radiation is 155,000. The excess death cases for leukemia and cancers over 50 years after the bombing are 220 and 12,000, respectively. Explosion of a 1-megaton hydrogen bomb – this is a small hydrogen bomb – at a height of 2,400 meters causes 370,000 immediate deaths and 460,000 injuries. Over 90% of the injured are expected to die soon due to subsequent firestorms. In contrast, the population affected by radiation is 36,000, much smaller than that affected by the 16-kiloton bomb. Also, there are 70 excess leukemia deaths and 670 excess cancer deaths over 60 years after detonation. Again, these are much smaller than the atomic-bomb victims. This is due to the greatly reduced amount of total radiation from the high altitude of 2,400 meters that reaches people on the ground.

These numbers clearly indicate that any relief by rescue teams and medical personnel is not possible because most of these people will be dead or severely injured. Various city buildings will be completely or partially destroyed by the blast and firestorms. City functions such as traffic, electricity, and schools will be totally lost instantaneously. It takes many years to regenerate the city. It may be even impossible in the case of the detonation of a hydrogen bomb.

The abovementioned result of the simulation deals with only one case. In an actual full-scale nuclear war in which several hundred average-size (100-kiloton) atomic bombs are exchanged, the total damage to humanity and urban infrastructure is beyond our imagination and calculation. A possible outcome caused by such a large-scale nuclear war is an extinction of Homo sapiens and end of human civilization.

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Technology advances:

Some technological advances we might see:

Development of hypersonic missiles and increased use of cruise missiles. Cruise missiles get to their target in less time once they’ve been detected, and their targets and payloads are more ambiguous — hypersonic missiles have similar problems. This makes decision making under a possible attack harder and increases risk.
Changing cybersecurity landscape. Cyber attacks on nuclear weapons systems are highly plausible, and many things — including the development of AI — could change this landscape. It’s currently unclear whether these developments will improve states’ offensive capabilities more than their defensive ones.
Improvements in remote sensing and weapons accuracy could make it more likely that nuclear forces can be destroyed by conventional weapons or much lower-yield nuclear weapons on a first strike, which could harm deterrence.
Missile defence systems could improve, preventing one state’s ability to conduct a first strike without substantially increasing their arsenals. This might also mean that any retaliatory strike needs to be launched in a very short period of time. It could also have an effect on the incentives for limited nuclear war by making it unclear how many nuclear weapons are needed to achieve a given result.
Improved early warning systems could increase the time and information available to states under attack, decreasing the chances of mistakes and inadvertent escalation.
New kinds of weapons, such as salted bombs (designed to maximise radiation poisoning as a result of their explosion) or pure fusion bombs, could substantially increase the damage caused by a single strike. That said, one expert said that over the last 50 years, nuclear weapons have become on average less damaging — nuclear thinkers have become more interested in precision than yield.
Autonomous weapons and command and control systems could substantially change the landscape, although we’re not sure how.

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Artificial intelligence and nuclear war:

The connection between nuclear war and artificial intelligence is not new; in fact, the two have an intertwined history. Much of the early development of AI was done in support of military efforts or with military objectives in mind. Many business leaders and experts have warned against the use of AI in a military setting. Military integration of advanced AI by nuclear-armed states has the potential to have an impact on elements of their nuclear deterrence architecture such as missile early-warning systems, intelligence, surveillance and reconnaissance (ISR) and nuclear command, control and communications (NC3), as well as related conventional systems. AI has significant potential to upset the foundations of nuclear stability and undermine deterrence by the year 2040, especially in the increasingly multipolar strategic environment. Dismissing the Hollywood nightmare of malevolent AIs trying to destroy humanity with nuclear weapons, experts are instead concerned with more-mundane issues arising from improving capabilities. AI applications included the ability to track and target adversary launchers for counterforce targeting and the incorporation of AI into decision support systems informing choices about the use of nuclear weapons.

Most nuclear powers favor mobile missile launchers because they are difficult to track and target and therefore are considered survivable. These missiles move regularly via road or rail, and unless the enemy can keep apprised of their locations at all times, the only way to threaten them (other than a first strike destroying the weapons before they are deployed to the field) is by attempting to target their sizable patrol areas with nuclear weapons. Even such bombardment strategies are really practical only if the possible locations of the missiles can be narrowed down at least somewhat. Cold War–era schemes to target Soviet mobile ICBM launchers combined bombardment strategies with intelligence about patterns in the way the Soviet Union moved its missiles. AI could make critical contributions to ISR and analysis systems, upending these assumptions and making mobile missile launchers vulnerable to pre-emption. This possibility seriously alarms Russian and Chinese defense planners because those states rely heavily on mobile ICBMs for deterrence. Even if AI only modestly improves the ability to integrate data about the disposition of enemy missiles, it might substantially undermine a state’s sense of security and undermine crisis stability.

Even with perfect knowledge of the target location, mobile targets can move between the time a weapon is launched and the time it arrives. Weapons for targeting mobile systems might be able to fly faster and adjust course better, but weapons would still need extremely sophisticated terminal guidance capabilities to substantially reduce the amount of ordnance required. As a result, even with advances in image processing and target recognition, many large weapons would be needed, or smaller ones would need to be launched from close range. The figure below shows the number of warheads of various types that would be required to destroy a mobile target with a weapon radius of effect between 0 and 5 kilometers. Despite their huge “kill radius” measuring kilometers in diameter, multiple thermonuclear warheads delivered by ballistic missiles would be required to have a high assurance of destroying a missile launcher. For instance, three 475-kT W88 warheads delivered by Trident II missiles with a ten-minute flight time would be required to cover one target, while five 100-kT W76 warheads would be necessary to cover it. The analysis finds, however, that accurate cruise missiles (CMs) launched from a position close to the targets (30-kT CM and 200-kT CM in the figure) could cover the mobile missile launchers with only one or two warheads. Fired from very close distances (i.e., flight times of a few minutes), even conventional munitions could become viable options, thereby significantly increasing the credibility of pre-emptive counterforce strikes.

Figure above shows Minimum Number of Weapons required to cover Target. AI in conjunction with mobile, possibly autonomous, sensor platforms could enable the development of strategically destabilizing threats to the survivability of mobile ICBM launchers.

ATACM = Army Tactical Missile System; JDAM = Joint Direct Attack Munition; kT = kiloton; MMIII = Minuteman III.

The dangers of the use of AI to take military decisions is more likely than the threat of autonomous drones and other so-called “killer robots.” Some experts fear that an increased reliance on AI could lead to new types of catastrophic mistakes. AI in the future could encourage human actors to make catastrophic decisions. This could break down the notion of mutually assured destruction being a deterrent for the use of nuclear weapons. While peace has been maintained for decades due to the notion that any nuclear attack could trigger mutually assured destruction, the potential for AI and machine-learning to decide military actions could mean that the assurance of stability breaks down. AI could also tempt nations to launch a pre-emptive strike against another nation to gain bargaining power, even if they have no intention of carrying out an attack. There may be pressure to use AI before it is technologically mature, or it may be susceptible to adversarial subversion; or adversaries may believe that the AI is more capable than it is, leading them to make catastrophic mistakes.

On the other hand, if the nuclear powers manage to establish a form of strategic stability compatible with the emerging capabilities that AI might provide, the machines could reduce distrust and alleviate international tensions, thereby decreasing the risk of nuclear war.

At present, we cannot predict which—if any—of these scenarios will come to pass, but we need to begin considering the potential impact of AI on nuclear security before these challenges become acute. Maintaining strategic stability in the coming decades may prove extremely difficult, and all nuclear powers will have to participate in the cultivation of institutions to help limit nuclear risk.

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Nuclear War: A Scenario: Book by Annie Jacobsen:

In a recent book titled “Nuclear War: A Scenario,” author Annie Jacobsen details the 72 minutes that unfold after the U.S. detects a North Korea launch of an intercontinental ballistic missile heading for Washington, DC, until the end of the world as we know it. The hypothesized North Korean attack quickly turns into a nuclear war between the U.S. and Russia, a possibility made even more likely by the Putin-Kim Jong Un agreement. In Jacobsen’s book, the two countries proceed to use a thousand or more warheads to level the other, a prospect that terrified millions of people throughout the Cold War, but which had more recently faded from the public’s consciousness.

In her research-based book “Nuclear War: A Scenario,” Annie Jacobsen reveals how a nuclear holocaust would play out in real time. She uses startling facts most citizens outside the military-industrial complex aren’t privy to and paints vivid second-by-second descriptions of the catastrophic effects that intercontinental ballistic missiles would have if they struck targets, including Washington, D.C., and Southern California’s nuclear power plant in Diablo Canyon. Bodies and buildings instantly convert to ash. Irradiated fuel rods launch into the sky to poison the air for miles in every direction while toxic lava burrows deep into the planet. Fire vortexes consume everything. The country is brought to its knees in less than an hour before the whole world follows. Nothing and no one is spared.

The book uses information that was only recently declassified, and some of what the journalist uncovers — particularly the shortcomings of intercontinental ballistic defense systems and the aggressive war preparations North Korea has made in the last decade — is alarming. North Korea may never strike first, as it does in the book, but the country’s mobile nuclear missile launchers, a satellite that could be carrying a destructive electromagnetic pulse weapon and the decades it has spent building underground tunnels as Armageddon prep suggest that North Korea is more prepared for World War III than most want to imagine.

“For decades, people were under the assumption that the nuclear threat ended when the Berlin Wall went down,” Jacobsen said, before suggesting another reason the existential threat of nuclear weapons has been filtered out of mainstream discourse – it has been turned into a technical debate. “Nuclear weapons and the whole nomenclature around them have been so rarefied it’s been reserved as a subject for those in the know,” she said. In her book, Jacobsen seeks to break through jargon and details in order to tell a terrifying story in a devastatingly straightforward way. The spoiler alert is that it doesn’t end well.

As the book promises on the cover, it presents a single scenario for a nuclear war, set in the present day. North Korea, perhaps convinced it is about to be attacked, launches a surprise missile strike against the US, leading Washington to respond with a salvo of 50 Minuteman III intercontinental ballistic missiles (ICBMs). These are aimed at North Korea’s weapons sites and command centres, but in order to reach their intended targets the missiles have to fly over Russia, because they do not have the range to use any other route. All too aware of the danger of miscalculation, the US president tries to get hold of his Russian counterpart. But the two men and the countries they run are not getting on, and he fails. Making things even worse, Russia’s dodgy satellite early warning system, Tundra, has exaggerated the scale of the US salvo, and from his Siberian bunker, the Russian president (Vladimir Putin in all but name) orders an all-out nuclear attack on the US.

The scenario is based on known facts concerning the world’s nuclear arsenals, systems and doctrine. Those facts are all in the public domain, but Jacobsen believes society has tuned them out, despite (or perhaps because of) how shocking they are. Jacobsen was stunned to find out that an ICBM strike against North Korea would have to go over Russia, and that Russia’s early warning system is beset with glitches, an especially worrying fact when combined with the knowledge that both the US and Russia have part of their nuclear arsenals ready to launch at a few minutes’ notice. Both also have an option in their nuclear doctrine to “launch on warning”, without waiting for the first incoming warhead to land. A US president would have a few minutes to make a decision if American early warning systems signalled an incoming attack. In those few minutes, he or she would have to process an urgent, complex and inevitably incomplete stream of information and advice from top defence officials. Jacobsen points out that in such circumstances the president is likely to be subject to “jamming”, a chorus of military voices urging he or she follows protocols which lead inexorably towards a retaliatory launch.

“My jaw dropped at so much of what I learned, which was not classified but had just been removed or rather sanitised from the public discourse,” she said. “I found myself constantly surprised by the insanity of what I learned, coupled with the fact that it’s all there for the public to know.” Ultimately, only presidents can make the decision and once it is made, no one has the authority to block it. It is called sole authority, and it is almost certainly the most frightening fact in the world today. It means a handful of men each have the power to end the world in a few minutes, without having to consult anyone. It is not a group anyone would choose to have that responsibility, including as it does the likes of Putin and Kim Jong-un. They all bring a lot of human frailty, anger, fear and paranoia to a potential decision that could end the planet. “You would want to have a commander-in-chief who is of sound mind, who is fully in control of his mental capacity, who is not volatile, who is not subject to anger,” Jacobsen said, referring to this year’s presidential election. “These are significant character qualities that should be thought about when people vote for president, for the simple reason that the president has sole authority to launch nuclear weapons.” But American people voted for Donald trump for economic reasons.

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Section-9

Atomic bombings of Hiroshima and Nagasaki:

By July 1945, Germany had surrendered, and the war in Europe was over. Japan, however, refused to submit to the terms outlined in the Allies’ Potsdam Declaration. It appeared to American leaders that the only way to compel Japan’s unconditional surrender was to invade and conquer the Japanese home islands. Although an estimated 300,000 Japanese civilians had already died from starvation and bombing raids, Japan’s government showed no sign of capitulation. Instead, American intelligence intercepts revealed that by August 2, Japan had already deployed more than 560,000 soldiers and thousands of suicide planes and boats on the island of Kyushu to meet the expected American invasion of Japan. Additional reports correctly surmised that the Japanese military intended to execute all American prisoners in Japan in the event of an Allied landing. These frightening figures portended a costlier battle for the United States than any previously fought during the war. By comparison, US forces suffered 49,000 casualties, including 12,000 men killed in action, when facing less than 120,000 Japanese soldiers during the battle for the island of Okinawa from April to June of 1945. At least 110,000 Japanese soldiers and more than 100,000 Okinawan civilians, a third of the island’s prewar population, also perished in the campaign. American casualties on Okinawa weighed heavily on the minds of American planners who looked ahead to the invasion of Japan. Japan’s leaders hoped to prevail, not by defeating American forces, but by inflicting massive casualties and thereby breaking the resolve of the American public.

This was the situation that confronted American President Harry S. Truman in the summer of 1945 when he authorized the use of the world’s first atomic bomb. In light of intelligence reports about Japan’s commitment to continue fighting, Truman and his military advisors were determined to use every weapon at their disposal in order to bring the war to an immediate end. Consequently, neither Truman nor any of his advisors ever debated if the atomic bombs should be used, only how and where they should be used. In the spring of 1945, the American government convened a committee of scientists and military officers to determine how best to use the bombs. This group unanimously declared that there was no guarantee that demonstrating the bombs to the Japanese in a deserted area would convince Japanese leaders to surrender. It was vital that Japan be convinced to surrender as fast as possible because the United States had just two atomic bombs available in July 1945 and additional weapons would not be ready to deploy for several more weeks. Meanwhile, thousands of Chinese, American, and Japanese soldiers continued to die each day the war continued. Consequently, Truman approved the long-standing plans for the US Army Air Force to drop atomic bombs on a list of preselected Japanese cities. The list of targets excluded Tokyo and Kyoto because of their political and historic importance. Instead, the intended target of the first bomb was Hiroshima, a fan-shaped city of approximately 550,000 people that occupied the estuary of the Ota River. The city was also home to the headquarters of the Japanese army that defended the island of Kyushu as well as a number of war industries.

The discovery of nuclear fission in 1938 made the development of an atomic bomb a theoretical possibility. Fears that a German atomic bomb project would develop atomic weapons first, especially among scientists who were refugees from Nazi Germany and other fascist countries, were expressed in the Einstein–Szilard letter to Roosevelt in 1939. This prompted preliminary research in the United States in late 1939. Progress was slow until the arrival of the British MAUD Committee report in late 1941, which indicated that only 5 to 10 kilograms of isotopically-pure uranium-235 were needed for a bomb instead of tons of natural uranium and a neutron moderator like heavy water. Consequently, the work was accelerated, first as a pilot program, and finally in the agreement by Roosevelt to turn the work over to the U.S. Army Corps of Engineers to construct the production facilities necessary to produce uranium-235 and plutonium-239. This work was consolidated within the newly created Manhattan Engineer District, which became better known as the Manhattan Project, eventually under the direction of Major General Leslie R. Groves, Jr.

The work of the Manhattan Project took place at dozens of sites across the United States, and even some outside of its borders. It would ultimately cost over US$2 billion (equivalent to about $27 billion in 2023) and employ over 125,000 people simultaneously at its peak. Groves appointed J. Robert Oppenheimer to organize and head the project’s Los Alamos Laboratory in New Mexico, where bomb design work was carried out. Two different types of bombs were eventually developed: a gun-type fission weapon that used uranium-235, called Little Boy, and a more complex implosion-type nuclear weapon that used plutonium-239, called Fat Man. There was a Japanese nuclear weapon program, but it lacked the human, mineral, and financial resources of the Manhattan Project, and never made much progress towards developing an atomic bomb.

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In the history of warfare, two nuclear weapons have been detonated – both by the United States, during the closing days of World War II.

The first was detonated some 1,800 feet above ground on the morning of 6 August 1945, when the United States dropped a uranium gun-type device code-named “Little Boy” on the Japanese city of Hiroshima. Due to its long, thin shape, the Hiroshima bomb was called ‘Little Boy’. The material used was uranium 235. It is believed that the fission of slightly less than one kilogram of uranium 235 released energy equivalent to approximately 15,000 tons of TNT. The bomb reduced 5 square miles of the city centre to ashes and caused the deaths of an estimated 120,000 people within the first four days following the blast. Many were instantly vaporised by the explosion, others died afterwards from the effects of burns and radiation.

Three days later, just after 11 on the morning of 9th August, a second atomic bomb nicknamed `Fat Man’ exploded above the city of Nagasaki. Although it was even more powerful than `Little Boy’, the destruction caused by this bomb was less than at Hiroshima due to the nature of the terrain (the original target had been the city of Kokura, but the B29 carrying the bomb had been diverted to Nagasaki because of heavy cloud cover). Nonetheless, over 2 square miles of the city were pulverised and some 73,000 people killed. The material used was plutonium 239. The fission of slightly more than one kilogram of plutonium 239 is thought to have released destructive energy equivalent to about 21,000 tons of TNT.

Figure below shows two atomic bombs used in war.

Under the two gigantic mushroom clouds, approximately 350,000 citizens in Hiroshima and 270,000 in Nagasaki were suddenly thrown into chaos and agony. A total of approximately 140,000 in Hiroshima and 73,000 in Nagasaki died instantaneously or within five months due to the combined effects of three components of physical energy generated by nuclear fissions: blast wind (pressure), radiant heat, and ionizing radiation. A total of more than 210,000 remaining victims, 140,000 in Hiroshima and 74,000 in Nagasaki, survived the first five months of death and agony and became hibakusha.

The residents of both cities were mostly noncombatant civilians, including many women and children. Military combatants were only a minority. There were fewer adult males than females, and most of the males worked at military arsenals. Many young men went to war in the later stages of World War II. Young students were employed by military arsenals located close to ground zero; that increased the number of victims. Citizens were suddenly thrown into firestorms at home, factories, and schools; on open roads or on ground; in automobiles and trams; and in city offices, hospitals, pharmacies, fire stations, and almost all city structures. Many survivors spent the night on the road or the ground. Subsequently, many severely injured victims were forced to remain where they survived the first strike without being provided any meaningful medical treatment. Most of them died there.

Seventy-nine years have passed since the atomic bombings of Hiroshima and Nagasaki. Approximately 210,000 victims died, and another 210,000 people survived. The damage to their health has continued, consisting of three phases of late effects: the appearance of leukemia, the first malignant disease, in 1949; an intermediate phase entailing the development of many types of cancer; and a final phase of lifelong cancers for hibakusha who experienced the bombing as a child, as well as a second wave of leukemia for elderly hibakusha and psychological damage such as depression and post-traumatic stress disorder. Thus, the human consequences of the atomic bombings have not ceased; many people are still dying of radiation-induced malignant diseases. Therefore, it is too early to finalize the total death toll. Hibakusha have faced a never-ending struggle to regenerate their lives and families under the fear of disease. As the only group of Homo sapiens experiencing real nuclear attacks, hibakusha have continued to engage in a lifelong movement to eliminate nuclear weapons. Political leaders, especially of nuclear-weapon states, must learn the wisdom of the hibakusha to save Homo sapiens from possible global extinction by nuclear war.

Since the Hiroshima and Nagasaki bombings, nuclear weapons have been detonated on over two thousand occasions for testing purposes and demonstration purposes. The only countries known to have detonated such weapons are (chronologically) the United States, the Soviet Union, the United Kingdom, France, the People’s Republic of China, India, Pakistan, and North Korea.

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The first atomic bomb at Hiroshima:

Figure below shows Hiroshima following the dropping of the atomic bomb on 6 August 1945. The prominent building in the foreground was the Industry Promotional Hall, retained in its ruined state as a peace memorial.

John Hersey’s famous report, published in 1946 by The New Yorker, describes a “noiseless flash.” Blinding light and intense pressure, yes, but sound? “Almost no one in Hiroshima recalls hearing any noise of the bomb,” Hersey wrote at the time.

In general, the noise produced by a nuclear bomb can reach levels of up to 240 decibels at its epicenter. But it doesn’t really matter, because you’re close enough to hear it go off, either the radiation or intense vibrations would kill you instantly.

Figure below shows fire and blast damage following nuclear explosion over Hiroshima:

Studies in Hiroshima (shown on map below) and Nagasaki conducted over the past 75 years have yielded important insights into the health effects of radiation. Researchers went to great lengths to determine survivors’ exposure, which depended partly on their distance from the hypocenter of the bombings.

Figure above shows radiation exposure following nuclear explosion over Hiroshima:

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The second atomic bomb at Nagasaki:

The second was detonated three days later when the United States dropped a plutonium implosion-type device code-named “Fat Man” on the city of Nagasaki. Figure below shows a general view of Nagasaki looking towards the hypocentre, a mile behind the Mitsubish Armament and Steel Works, seen across the Urakami River in the centre background. In the foreground is the shell of the Mitsubishi Woodworking Plant, which was unharmed by the blast, but was gutted by fire.

As shown in Figures Below, three types of physical energy (heat, blast and ionizing radiation) from the detonation were estimated by the US Army Manhattan Project Team (Atomic Bomb Disease Institute, Nagasaki University Citation1995). Many residential areas full of Japanese wooden houses were crushed and burned. The firestorms that continued over to next day finally flattened city areas within a 4 km radius. According to the saddest memory of some survivors, the blast wind tore off the heads of babies who were being carried on their mothers’ backs in the traditional Japanese way. Most of the mothers also died soon. At the same time, the victims were irradiated by 100 grays (Gy) or more of combined gamma and neutron rays generated by nuclear fission. Thus one can say that they were killed in three ways (heat, blast and radiation) at once.

Figure below shows physical energy by heat rays by distance from ground zero in Nagasaki.

Figure below shows physical energy of blast wind due to Nagasaki bomb.

Figure below shows fire and blast damage by nuclear explosion over Nagasaki.

Figure below shows radiation dose by distance from ground zero in Nagasaki: gamma rays and neutron rays.

In areas within 1 kilometer of ground zero, human bodies without any shielding, namely in open air on the roads and ground, were instantaneously squeezed by the blast wind (pressure) against walls, causing multiple fractures of skeletons and ruptures of the abdominal cavity causing escape of colons. Many people in open roads and grounds were carbonized by the direct effect of heat rays within 1.0 km from ground zero. Many residential areas full of Japanese houses were crushed by the wind and burned out in which many victims were also burned to white bones. The skin of people on open roads or grounds within 0.5–1.5 km was deeply flash-burned due to heavy heat rays. The skins were soon peeled off because of necrosis in the deep skin layer. With large areas of skin peeling off, people suffered severe pain and bleeding.

Figure below shows flash burns on a victim’s skin.

In three months after the bombing, these deep skin flash burns began to heal. However, with tissue being regenerated, keloid was quite often formed. It was characterized by marked thickening of the wounds, sometimes resembling cancerous proliferation of the skin.

The people within 1 km of ground zero who finally survived were mostly those who were working inside a concrete building with thick walls or in a basement. Some other survivors were inside private air-raid shelters or military arsenals set in large shelters. Heat rays were effectively blocked by the walls, and radiation and blast were partially shielded before victims were exposed, thus allowing them to survive. But there were only a few hundred of these people. Many of those who survived at various proximal points were severely injured by debris and pieces of glass from damaged houses, heated and irradiated simultaneously. Many of them died within the first three months.

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Surrender of Japan:

The two atomic explosions had the effects desired by the Allies. On 10th August the Japanese government indicated its readiness to accept defeat, subject to certain conditions. On 14th August it finally accepted the demand for unconditional surrender. The following day was declared `Victory over Japan’ or VJ Day, although it was not until 2nd September that the final Japanese surrender was signed, thereby bringing the Second World War to a formal close.

Why had the Allied powers considered it necessary to inflict such unprecedented destruction on Japanese civilians in order to bring the war to an end?

At the Potsdam Conference (17th July – 2nd August 1945) the Allies formulated their terms for ending the war with Japan, which centred on that country’s acceptance of unconditional surrender, as had been the case with Nazi Germany in May. However, the Allies were also aware that whilst the Japanese Emperor Hirohito desired an end to hostilities, and would probably accept the unconditional capitulation demanded, the `hawks’ of the Japanese military and civilian leadership were totally opposed to such a humiliating condition and were ready to fight to the finish – whatever that might look like. It was this knowledge that informed the contents of the Potsdam Declaration, in particular the statement that failure to accept unconditional surrender would result in “prompt and utter destruction” for Japan. It was no coincidence that on 16th July, the day before the opening of the Potsdam Conference, the world’s first nuclear bomb was detonated in the desert of New Mexico. It demonstrated a destructive power never before seen in a man-made device. In one split second, the face of war changed completely.

The cost of victory:

Looking back on these events some time later, Lieutenant General Leslie R Groves, former director of the `Manhattan Project’ that had developed the first A-bomb, commented:

“The atomic bombings of Hiroshima and Nagasaki ended World War II. There can be no doubt of that. While they brought death and destruction on a horrifying scale, they averted even greater losses – American, English, and Japanese”.

It was a view that generated controversy then and after as to the justification or otherwise of the use of such weapons on largely defenceless civilian targets, at such terrible cost. But the nuclear genii, once out of the bottle, could not be put back in. The ever-present threat of a nuclear option in the superpower stand-offs of the Cold War defined global politics after 1945. Hiroshima and Nagasaki raised the spectre of Mutual Assured Destruction (MAD) that has haunted the world into our present times.

Was the decision to bomb Hiroshima and Nagasaki morally wrong?

79 years later, the question is more difficult to answer than first appears. In the early 1980s, the Harvard law professor Roger Fisher proposed a new, gruesome way that nations might deal with the decision to launch nuclear attacks. It involved a butcher’s knife and the president of the United States. Writing in the Bulletin of Atomic Scientists, Fisher suggested that instead of a briefcase containing the nuclear launch codes, the means to launch a bomb should instead be carried in a capsule embedded near the heart of a volunteer. That person would carry a heavy blade with them everywhere the president went. Before authorising a missile launch, the commander-in-chief would first have to personally kill that one person, gouging out their heart to retrieve the codes. When Fisher made this proposal to friends at the Pentagon, they were aghast, arguing out that this act would distort the president’s judgement. But to Fisher, that was the point. Before killing thousands, the leader must first “look at someone and realise what death is – what an innocent death is. Blood on the White House carpet”. Killing a person with a butcher’s knife may be a morally repugnant act, yet in the realm of geopolitics, past leaders have justified their atomic acts as a political or military necessity. Following the nuclear bombs dropped on Hiroshima and Nagasaki – 79 years ago – the decision was justified only in terms of its outcome, not its morality. The bombing ended World War Two, preventing further deaths from a protracted conflict, and arguably discouraged the descent into nuclear war for the rest of the 20th Century.

Yet those positive consequences cannot obscure the fact that on 6 and 9 August 1945, two of humanity’s most destructive objects brought the horrifying power of the atom onto two civilian cities. We can attempt to describe the events through numbers: at least 200,000 people killed by the flashes, blasts, firestorms and radiation; tens of thousands more injured; an unquantifiable inter-generational legacy of radiation, cancer and trauma. We can remember the individual stories – of mothers and children, of priests and doctors, of ordinary lives transformed in a moment.

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Struggle for Survival:

Medical rescue teams perished and hospitals were all destroyed on the first day of the bombing. It therefore was impossible to find any meaningful medical aid. The situation was much severer in Hiroshima where over 90% of medical staffs, doctors, nurses, and pharmacists were dead. The Nagasaki Medical College Hospital, the largest and strongest concrete buildings in Nagasaki City, located 600 meters from ground zero, did provide fairly good shielding effects; the death rate was a relatively as low as 43%. Subsequently 900 lives in total – approximately half of the total number of professors, doctors, nurses and medical students were lost in the entire college facility including the hospital. Most of those who survived were severely injured by the blast wind and heat ray. The hospital had completely ceased to function. Within a few days, medical staffs and medical students who had survived opened first-aid stations around the margin of flattened areas.

In the late afternoon on the first day, several rescue trucks arrived carrying medical teams consisting of military doctors and nurses from Omura Navy Hospital, located 45 km north of Nagasaki City. They brought back approximately 700 severely injured victims, most of them severely burned, to the hospital and started treatment for burns and injuries consisting of bone fractures, cuts from pieces of glass, and embedding of debris and pieces of glass fragments deep in the skin. This number was very small compared to the total number of victims who suffered severe injuries, estimated to be approximately 30,000 in Nagasaki. A few hundred victims out of 700 were able to survive, thanks to intensive care at Omura Navy Hospital. They were indeed lucky people.

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Initial Difficulty in Recognizing Radiation Effects:

In the early days after the atomic bombings, many doctors had difficulty in identifying the symptoms of radiation-related ailments. There was no information about the nature of this new type of bomb. They did not even know that the bombs were nuclear and that radiation was dangerous to human beings. This difficulty was resolved after several weeks by autopsy studies by US and Japanese pathologists, but it was too late for the early victims. As mentioned above, short-distance victims suffered various combinations of three major physical effects of the detonations. After doctors gained information about the radiation hazards associated with the atomic bomb, they began to use Japanese medical terms genbaku-shou (atomic-bomb symptoms), or genshi-byou (atomic disease), as a diagnosis for the severest condition seen among victims. This vague diagnosis limited efficient medical treatment for survivors with multiple clinical problems, as mentioned above. However, medical and pathological research done by academic groups gradually separated several symptoms and signs into different categories of disorders. It became apparent that the result of radiation-induced cellular damage in several organs was responsible for the major symptoms and signs; the most severely affected organs were bone marrow and intestinal mucosa as shown in Figure below. Normal bone marrow is full of blood-forming cells as black-stained cells (above right), while heavily irradiated bone marrow is characterized by the eradication of blood forming cells replaced with fat and white-stained cells (above left). Normal colon is with many folds (below right), while colon exposed to radiation is flattened with some bleeding (below left). These pathological findings led to a clear recognition of acute radiation sickness or acute radiation syndrome (ARS), which is now used formally as a diagnosis for radiation victims in the field of nuclear or radiation accidents such as the Chernobyl accident.

Figure below shows Pathological findings of acute radiation sickness (ARS) in atomic bomb survivors.

Although most doctors did not clearly recognize that hair loss was the result of profound radiation effects, all doctors and even the victims themselves began to recognize that the beginning of hair loss was the most peculiar common symptom recognized by hibakusha themselves and, importantly, the earliest sign indicating that death would soon follow (Figure below). Therefore, appearance of hair loss became the most horrifying sign for hibakusha. Every morning, they tried to pull their hair to confirm it was intact.

Figure above shows people of Hiroshima affected by gamma rays, all bald within 10 days after the explosion of the atomic bomb.

Other than hair loss, major symptoms and signs are as described below.

Purpura (Skin Blood Spot):

Many survivors who became seriously ill after a few days and weeks began to suffer skin problems (bleeding known as “purpura”). In addition, mucosal bleeding from the oral cavity and gingiva and intestine caused bloody saliva and bloody diarrhoea.

High Fever:

A fever of 39–42°C was quite frequently observed. This symptom, which started within a week in many survivors, was accompanied by shivering and marked sweating. This sign made doctors think of bacterial infections, such as typhoid fever, pneumonia, and sepsis in the severest cases. Later, high fever was recognized as a consequence of radiation-induced bone-marrow damage causing bone-marrow failure. This appeared as a rapid decline of the white-blood-cell count, which directly led to bacterial invasion through damaged wounds. The most important protection against bacterial invasions is white blood cells. (“neutrophils” is the medical term for the cells.) The disappearance of neutrophils from the blood allowed bacterial infections to become severe and subsequent death. A great number of people died because of infections. In such victims with high fever, the white-blood-cell sometimes fell below1,000/mm3, which is only 20% or less of normal counts.

Most victims of high-grade ARS suffer simultaneously from bacterial infections. Thus, the early diagnostic difficulty was clearly explained within a few months based on the concept of ARS. However, doctors were not yet able to use antibiotics, except a few samples of penicillin supply by Allied medical doctors for selected cases such as severe and wide-area skin burn.

Bloody Diarrhoea:

This symptom first started as simple diarrhoea as early as a week after the bombing but soon was exacerbated by bloody stool. This symptom persisted for several weeks, leading to a rapid deterioration in general condition, especially emaciation due to nutritional deficiency, dehydration, and anaemia. This condition made doctors think of typhoid fever or other intestinal bacterial infections, which were seen fairly frequently among citizens living in poor sanitary conditions during wartime. Lack of antibiotics often led to lethal consequence among diarrhoea cases.

Combined Manifestations as ARS:

Diarrhoea with bloody stool, skin burn with peeling and bleeding, high fever, and tissue necrosis often appearing in the oral cavity and throat were usually seen in various degrees of severity and combinations. Skin also showed bloody spots with a purple color (purpura). Survivors were severely dehydrated and thus felt a strong thirst, but they never were able to relieve it by drinking water because their intestinal-wall mucosa was destroyed by ARS and could not absorb water at all.

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Radiation Dosimetry by the Atomic Bomb Casualty Commission:

US Army Manhattan Engineer District did not provide the US joint research team with radiation-dose data that would allow radiation-related medical consequences such as hair loss, bone marrow damage, and colon damage to be analyzed on the basis of the victims’ distance from ground zero. It was hypothesized that radiation dose is inversely proportional to distance: the shorter the distance from ground zero, the larger the radiation dose to each hibakusha.

Later, in 1965, the first formal dosimetry system, named DS65 was developed by the Atomic Bomb Casualty Commission (ABCC), which had been established in 1947 by President Truman for studying the long-term influence of atomic-bomb radiation on humans. DS65 was further improved and revised in 1985, named DS85. The most recent dosimetry system is DS02, which was revised in 2002 (Young and Kerr Citation2005).

Presently, all statistical analysis of delayed effects of the atomic bombing is based on DS02, which is believed to be the most precise one, although there is still some ambiguity in the radiation dose, such as uncertainties due to radioactive fallout and internal exposure by inhaled radionuclides. The DS02 dose by distance from ground zero to 2,500 meter is shown in Table below. Dose of gamma rays and neutron rays is shown separately.

Exposure dose by distance from ground zero: gamma rays and neutron rays estimated by DS02.

distance from hypocenter (m)	slant distance from epicenter (m)		Gamma Rays (Gy)	Neutrons (Gy)
0	Hiroshima	590	120	34.5
0	Nagasaki	502	328	18.8
500	Hiroshima	780	35.7	6.48
500	Nagasaki	709	83.0	2.97
1,000	Hiroshima	1,166	4.2200	0.26
1,000	Nagasaki	1,119	8.6200	0.125
1,500	Hiroshima	1,615	0.5270	0.00904
1,500	Nagasaki	1,582	0.9830	0.00511
2,000	Hiroshima	2,088	0.0764	0.00039
2,000	Nagasaki	2,062	0.1380	0.00024
2,500	Hiroshima	2,571	0.0125	0.00002
2,500	Nagasaki	2,550	0.0228	0.00001

Based on these dosimetry systems, it became possible to estimate an exposure dose for each hibakusha based on the distance from ground zero, and to correct it further by shielding effect obtained from intensive interview on how he or she was exposed to radiation. For example, the shielding effect from thick concrete walls was fairly large. These individualized dose estimates are considered the most precise to date.

There is also another dosimetry system, called biological dosimetry. One example of this is the electron-spin resonance method applied to survivors’ extracted teeth. This allows direct measurement of the dose at the enamel layer of a tooth, which represents the dose of a given hibakusha at the time of bombings. Data from this electron-spin resonance method have been compared with DS02 data. The two sets of data matched fairly well. Therefore, it is considered scientifically reasonable to statistically analyze all observed disease incidences according to the DS02 although there still remains some small statistical ambiguity, as described above.

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Residual radiation = fallout + induced radiation + internal radiation

The most important factor that affects bodily injury by radiation is the distance from ground zero. The radiation emitted within one minute of nuclear fission constitutes over 90% of the total dose emitted. This hits hibakusha bodies directly as external exposure. However, there also exists residual radiation from the fallout of radionuclides as fission products that have fallen from the sky after an atomic explosion more than 500 meters above the ground. These radionuclides include cesium-134, strontium-90, plutonium-239, and many others. The fallout emitted gamma rays, beta rays, and/or alpha rays on the ground. The effects of residual radiation on the human body are still ill-defined, and it remains difficult to reproduce measurements scientifically. So this is the reason for some ambiguity in the total understanding of atomic-bombing effects.

An additional factor in radiation exposure by nuclear fission is induced radiation by neutrons. The total amount of neutron emitted from the atomic bombs was fairly large. Therefore, the total dose of neutrons to each hibakusha was carefully estimated in DS65, DS86, and DS02. Induced radiation from various materials, mainly metals and stones by neutron exposure, is another component of radiation exposure to human bodies, especially in the first 24 hours after the explosion. This component has not been officially estimated, especially in individual hibakusha and those people who entered areas near ground zero soon after the bombing for rescue activities or searches for family members. It is hypothesized at this moment that the magnitude of this component is so small that each DS can ignore its human effects.

The final radiation-exposure pattern is internal radiation due to radionuclides such as plutonium in the case of Nagasaki bomb. As one element of the fallout, un-fissioned plutonium fell and was spread over soil by wind currents and remained there for a long time. The half-life of plutonium is amazingly long, 24,100 years in case of Pu-239. Subsequently, an intensive survey of plutonium in the soil was conducted in the 1970s in the suburbs of Nagasaki City. Plutonium particles were found in areas from 10 to 50 kilometers east of Nagasaki City, but the effect of these particles on the human body is thought to be very small and health effect is thought to be negligible.

There is a possibility that plutonium fallout could have been inhaled by some hibakusha in the first few hours after detonations. Plutonium is known to reside in the lungs for a long time. Therefore, there is a possibility that such residual plutonium particles continue to emit alpha rays intermittently and injure lung cells nearby, finally causing lung cancer. This possibility has not been formally confirmed scientifically although a group of Nagasaki University pathologists recently found evidence of plutonium particles remaining in the autopsied lungs and bones obtained from hibakusha who died very soon after the bombing (Shichijo et al. Citation2018). Epidemiological study is not performed yet on the health effect, such as lung cancer, induced by the residual radiation emitted from plutonium.

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Late Effects of Atomic Bombings: 1948–2018:

About 270,000 victims of Hiroshima and Nagasaki finally recovered their health. They had to start their new daily life with a serious shortage of food and other necessities. After spending three years of recovery with relatively good health, hibakusha encountered the first malignant disease: leukemia. It is classified as the earliest occurring malignant disease due to atomic-bomb radiation because it was clearly distinguished from the disorders caused by ARS. Therefore, leukemia was the first malignant disease derived from cells injured by initial radiation exposure; the cells then transformed to malignant leukemia cells. This earliest delayed, or “late”, effect was followed by many kinds of cancer of various organs. Thus, the late effect spans an extremely long period.

Figure below shows Time Trend of the late effect of atomic bomb radiation.

Dose was clearly very important:

Among those who were within about 900 meters of the hypocenter and received more than 2 grays of radiation, 124 have died of cancer. (That dose is about 1000 times the average annual radiation dose from natural, medical, and occupational sources combined.) In its latest LSS update, RERF scientists conclude—based on comparisons of cancer deaths between the exposed group and unexposed controls—that radiation was responsible for 70 of those deaths. Scientists call this number, 56.5%, the attributable fraction. The numbers of deaths are low because few who were close to ground zero survived the blast. But among these people, “Most of the cancers are due to the radiation.

Figure below shows the percentage of cancer deaths due to radiation—the attributable fraction—increased with dose.

At 1 gray of exposure, the dose roughly 1100 meters from the hypocenter, the attributable fraction is 34.8%, and it decreases linearly for lower doses.

Women were at higher risk of developing radiation-associated cancer, largely because of additional cases of breast cancer as seen in the figure below:

Both men and women exposed at a younger age were more at risk as they aged. It’s thought that actively dividing cells are more susceptible to radiation effects, so younger people are more sensitive. The younger an individual was at the time of the bombings, the greater their risk of developing cancer as seen in the figure below. But the risk decreased over a survivor’s lifetime.

Radiation most increased the risk of leukemia among survivors, followed by cancer of the stomach, lung, liver, and breast. There was little impact on cancers of the rectum, prostate, and kidney.

Exposure also heightened the risk of heart failure and stroke, asthma, bronchitis, and gastrointestinal conditions, but less so; for those with a 2-gray exposure, 16% of noncancer deaths were deemed attributable to radiation.

Leukemias:

In 1949, doctors in Hiroshima and Nagasaki began to recognize a gradual increase in the number of hibakusha patients, including children, suffering from leukemia. The excess annual rate of leukemia continued to rise until 1955 and then continued at an elevated level for more than 10 years. Acute and chronic types of leukemia both were observed. These leukemias were later analyzed in detail when the first dosimetry system (DS65) became available. A clear radiation-dose dependency was revealed as a curve that elevated exponentially (called quadratic) from 100 millisieverts (mSv) at around 2.0 km from ground zero to more than 4 Gy at around 1.0 km. Dose is thus inversely proportional to the square of the distance. Total leukemia incidence was four to five times higher than the control group of Nagasaki citizens not exposed to the bombing (Preston et al. Citation1996). From around 1955 to 1970, the excess rate of leukemia gradually declined. However, even around 2003, the number of leukemia case was still slightly higher among proximally exposed survivors (2 km or less) than distant survivors (2–8 km). During the post-bombing period of 60 years, the statistics showed that about 300 victims actually died of leukemia out of the LSS cohort group of 100,000.

Moreover, recent epidemiological studies clearly showed that the risk of a specific type of leukemia that typically occurs among the elderly, called myelodysplastic syndromes (MDS), is three times higher among people who were at a short distance from the bombing and therefore received a high dose of radiation. MDS, a disease that was identified in the mid-1980s, is characterized by anaemia and a reduced number of neutrophils and platelets without the massive growth of immature blood cells typical of acute leukemia. The disease generally occurs in elderly population.

Cancers:

Around 1960, the incidence of solid cancers began to rise gradually. The elevated cancer incidence lasted for a long time. It peaked around the year 2000 and remained at that level until now. The types of cancer that appeared include lung, breast, thyroid, stomach, colon, liver, skin, and bladder. Cancers of the pancreas, gall bladder, and uterus, which are all deep-seated organs, have not yet been confirmed as radiation induced. The excess of these cancers was also clearly dependent on the total dose (gamma + neutron) of radiation that the survivors received. As noted above, 100 mGy is considered to be the lowest dose that produces a significant increase in cancer incidence. The risk is statistically significant between the range from 100 mGy to 3 Gy. Even in 2018, when the average age of hibakusha reached 82, the increased risk of all the types of cancer listed above still did not show a decline. In other words, the data show a continuing plateau.

Multiple Cancers:

Recent epidemiological studies also show a distance-dependent increase in multiple cancers in individual survivors who were within 2 km of the hypocenter. The multiple cancers, namely second and third cancer, are independent of the primary cancer – that is, they are not a result of metastasis of the primary cancer to other organs. Some survivors suffered from three or more cancers, maximally five. Since atomic-bomb victims were usually exposed to radiation in their whole body, development of multiple cancers seems a reasonable consequence.

In-utero Radiation Exposure:

Microcephaly:

In both Hiroshima and Nagasaki, many pregnant women were exposed to various doses of radiation. Miscarriages and malformation of newborn babies were frequently observed, but there were no good statistics showing radiation-dose effect. Some mothers who were in the early prenatal period at the time of the bombing sometimes bore babies who had a small head. The babies later became mentally disabled. There were 62 such babies recorded among 1,470. The larger the dose to the mother’s uterus was, the higher the incidence of microcephalic babies, suggesting high-dose radiation interrupted brain development. This is the most obvious phenomenon observed among foetuses exposed to radiation in utero.

Cancers:

In-utero exposed babies were later found to have an increased risk of cancer development during their early adulthood.

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Ill-defined Second-generation Effect:

The children of atomic-bomb survivors have been intensively investigated to document any increase in the rate of malformation, leukemia, and cancers. So far, such investigations have not shown elevated rates for these disorders. The most recent study of transmission of gene abnormality from three cases of fathers exposed to higher doses of atomic bomb radiation to their three children was conducted by a Nagasaki University Atomic Bomb Disease Institute group at the DNA level by using a sophisticated new technology for DNA (genome) analysis. Their result again showed no positive results (Horai et al. Citation2017). However, many studies using animal experiments by irradiating parent mice and observing malformation and cancers in F1 mice (second generation) have not infrequently revealed positive results. These findings in animals have added to the considerable anxiety among the second generation of survivors. The second-generation population, comprising more than 200,000 people, is now entering the cancer-prone age of fifties to sixties. If positive results with regard to the increased risk of leukemia and cancers are confirmed in the future, it can be concluded that atomic bomb is a weapon that targets human genes and induces hereditary transmission of malignant diseases.

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Frequently Asked Questions:

Is there still radiation in Hiroshima?

No, Hiroshima does not have dangerous levels of radiation today. The radiation levels are comparable to natural background radiation found elsewhere on Earth, posing no threat to human health. This is because the radiation from the bomb dissipated quickly, with residual radiation decreasing significantly within weeks of the explosion. Hiroshima is not radioactive today primarily because the atomic bomb exploded above ground, which caused most of the radioactive material to disperse into the atmosphere and decay rapidly. The initial intense radiation had a short half-life and diminished quickly, reducing the long-term radiation impact on the environment.

Is Nagasaki still radioactive?

Like Hiroshima, Nagasaki is also safe from dangerous radiation levels. The radiation levels have returned to normal background levels that are safe for human habitation. Most of the residual radiation from the bombings decayed rapidly shortly after the explosions.

Who is the man who survived both atomic bombs?

Tsutomu Yamaguchi is known as the man who survived both atomic bombings. He was in Hiroshima on a business trip during the first bombing and returned to his home in Nagasaki just in time to experience the second bombing. Despite being exposed to both bombings, he lived to the age of 93, becoming a symbol of resilience and the devastating impact of nuclear warfare.

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Section-10

Probability and risk of nuclear holocaust:

Probability is simply a measure of how likely an event is to occur, expressed as a percentage between 0% (impossible) to 100% (guaranteed). It does not guarantee an outcome but quantifies the likelihood. Risk refers to the possibility of an undesirable outcome and is often evaluated using probability data. Risk is traditionally defined as a function of probability and impact. The impact of a risk is the consequences of the event, such as the extent to which a project is affected. Risk is generally quantified as the probability of some adverse event occurring, multiplied by the severity of the event if it occurs. Common risks can be quantified using past event data. For example, to quantify the risk of you dying in a car crash, one can use abundant data on past car crashes and segment them according to various criteria such as where you live and how old you are. You personally have never died in a car crash, but many other people have, and those data make for reliable risk quantification. Without this and similar data, the insurance industry couldn’t operate their business.

The risk of you dying in a nuclear war cannot be calculated in the same way. There has only been one previous nuclear war – World War Two – and one data point is not enough. Furthermore, the atomic bombings of Hiroshima and Nagasaki occurred 79 years ago, under circumstances that no longer apply. When WW2 began, nuclear weapons had not yet been invented, and when the bombings in Japan occurred, the US was the only country with nuclear weapons. There was no nuclear deterrence, no threat of mutual assured destruction. There was also no taboo against the use of nuclear weapons, nor were there any international treaties governing their use.

If WW2 was all we had to go on for evaluating nuclear war risk, our understanding would be very limited. However, while there may be only one piece of data to rely on, there is also a lot of relevant information – sources of insight that can help us understand the risk. One example is events that went partway to nuclear war, such as the Cuban missile crisis. The ongoing Russian invasion of Ukraine will hopefully turn out to be another – the only way that it won’t is if it turns into an actual nuclear war. Another important source of information is a conceptual mapping of the various scenarios in which nuclear war could occur. Broadly speaking, there are two types of scenarios: intentional nuclear war, in which one side decides to launch a first-strike nuclear attack, such as WW2. And inadvertent nuclear war, in which one side mistakenly believes it is under nuclear attack and launches nuclear weapons. Examples include the 1983 Able Archer incident, when the USSR initially misinterpreted Nato military exercises, and the 1995 Norwegian rocket incident, when a scientific launch was briefly mistaken for a missile. Finally, there is information about specific events that may provide a guide. For example, in the ongoing Russian invasion of Ukraine, an important parameter is Vladimir Putin’s mental state. Nuclear war is more likely if he is angry, temperamental, humiliated, or even suicidal. Other factors include whether Ukraine succeeds in fighting off the Russian military, whether Nato gets more involved in direct military operations, and whether any major false alarms occur. These sorts of details – to the extent that we are able to learn about them – are valuable for informing our understanding of the probability of this particular event resulting in nuclear war.

All of the above pertains to the probability of nuclear war. To evaluate risk, we also need the severity. This has two parts. First are the details of the war itself. How many nuclear weapons are detonated? With what explosive yield? At which locations and altitudes? What other, non-nuclear attacks also occurred during the conduct of the war? These details determine the initial harm. The second part is what happens next. Are survivors able to maintain basic needs – food, clothing, shelter? How severe are secondary effects such as nuclear winter? Given all the various stressors, are survivors able to maintain any semblance of modern civilisation, or does civilisation collapse? If collapse does happen, do survivors or their descendants ever rebuild it? These factors determine the total, long-term harm caused by the nuclear war.

Any nuclear war, however “small”, would be catastrophic for the affected areas. However, what makes nuclear weapons so worrisome is not the damage that can be caused by a single explosion. That can be large in its own right, but it’s still comparable to the damage that can be caused by conventional, non-nuclear explosives. WW2 is illustrative: of the roughly 75 million people who died in this conflict, only around 200,000 were killed by nuclear weapons. Comparable amounts of destruction were caused by the carpet bombing of cities such as Berlin, Hamburg, and Dresden. Nuclear weapons are terrible, but so are conventional weapons used in sufficient quantity.

What makes nuclear weapons so worrisome is that they make it so easy to cause so much devastation. With a single launch order, a country can cause many times more harm than occurred in all of WW2, and they can do it without sending a single soldier overseas, by instead delivering nuclear warheads with intercontinental ballistic missiles. Mass destruction has long been possible, but it has never been so easy. This is why the taboo against the use of nuclear weapons is so important. The taboo serves to help countries resist any temptation they may have to use nuclear weapons. If it’s OK to use one nuclear weapon, then maybe it’s also OK to use two, or three, or four, and so on until there has been massive global destruction.

John F. Kennedy estimated the probability of the Cuban Missile Crisis escalating to nuclear conflict as between 33% and 50%. In a poll of experts at the Global Catastrophic Risk Conference in Oxford (17–20 July 2008), the Future of Humanity Institute estimated the probability of complete human extinction by nuclear weapons at 1% within the century, the probability of 1 billion dead at 10% and the probability of 1 million dead at 30%. These results reflect the median opinions of a group of experts, rather than a probabilistic model; the actual values may be much lower or higher. Scientists have argued that even a small-scale nuclear war between two countries, such as India and Pakistan, could have devastating global consequences and such local conflicts are more likely than full-scale nuclear war.

Those advocating the abolition of nuclear weapons often note that if you flip a coin once, the chance of getting heads is 50%; but if you flip it ten times, the chance of getting heads at least once rises to 99.9%. A 1% chance of nuclear war in the next 40 years becomes 99% after 8,000 years. Sooner or later, the odds will turn against us. Even if we cut the risks by half every year, we can never get to zero.

But the coin-flip metaphor is misleading where nuclear weapons are concerned, because it assumes independent probabilities, whereas human interactions are more like loaded dice. What happens on one flip can change the odds on the next flip. There was a lower probability of nuclear war in 1963, just after the Cuban Missile Crisis, precisely because there had been a higher probability in 1962. The simple form of the law of averages does not necessarily apply to complex human interactions. In principle, the right human choices can reduce probabilities.

The likelihood of nuclear war rests on both independent and interdependent probabilities. A purely accidental war might fit the model of the coin flip, but such wars are rare, and any accidents might turn out to be limited. Moreover, if an accidental conflict remains limited, it may trigger future actions that would further limit the probability of a larger war. And the longer the period, the greater the chance that things may have changed. In 8,000 years, humans may have much more pressing concerns than nuclear war.

We simply do not know what the interdependent probabilities are. But if we base our analysis on post-World War II history, we can assume that the annual probability is not in the higher range of the distribution.

Nuclear scholar and Russian forces expert Pavel Podvig argued that nuclear strikes are so rare, it is impossible to calculate their frequency and therefore meaningless to translate that frequency into a probability. Director of the Global Catastrophic Risk Institute Seth Baum noted that Podvig was critiquing frequentist approaches to calculating, which infer how likely an event is to happen based on a sampling of past similar events. He argued that instead, Bayesian approaches – which rely on subjective probabilities that get updated when new information is presented – could be a more helpful way of thinking across multiple different nuclear scenarios, as Baum himself has done in a working paper. Superforecasting, when ordinary people cultivate their intuitive sense for prediction, and which relies in part on good Bayesian updating, is one such approach to nuclear scenarios; Baum’s co-author and superforecaster Robert de Neufville argued in March that there was a 4% chance of at least one fatality from nuclear use by July 1, 2022. Podvig and Baum are correct that frequentist approaches are definitely not useful here. Estimating the likelihood of a future nuclear war based on how often past nuclear wars occurred is not appropriate, given how rare past nuclear weapons use is. Bayesian approaches are useful for thinking about adjusting one’s own subjective estimate of probability, but not for informing the actual probability of Putin deciding to use a nuclear weapon. What’s more, there is no way of adjudicating between subjective estimates, and consequently no way of coming up with a combined estimate overall. Even people with the same information may have wildly different guesses: Former U.S. President John Kennedy estimated the odds of nuclear war during the Cuban Missile Crisis to be between one in three and one half, but former U.S. National Security Advisor McGeorge Bundy thought it was one in 100.

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The risk of the use of nuclear weapons:

Evidence of the foreseeable impacts of a nuclear detonation is an integral part of a nuclear weapons risk assessment. Although nuclear weapons have not been used in armed conflict since 1945, there has been a disturbingly high number of close calls in which nuclear weapons were nearly used inadvertently as a result of miscalculation or error. During the three conferences on the humanitarian impacts of nuclear weapons in 2013 and 2014, it was demonstrated that the risks of a nuclear weapon detonation, whether by accident, miscalculation or design, stem notably from:

the vulnerability of nuclear weapon command-and-control networks to human error and cyberattacks
the maintaining of nuclear arsenals on high levels of alert, with thousands of weapons ready to be launched within minutes
the dangers of access to nuclear weapons and related materials by non-state actors.

The conferences furthermore observed that international and regional tensions between nuclear-armed states, coupled with existing military doctrines and security policies that give a prominent role to nuclear weapons, increase the risk of nuclear weapons being used, and concluded that, given the catastrophic consequences of a nuclear weapon detonation, the risk of nuclear weapons being used is unacceptable, even if the probability of such an event were considered low.

It is possible to conceptualize the increasing risk of nuclear weapons being used according to the following four risk-of-use scenarios:

-a) doctrinal use of nuclear weapons, i.e. the use of nuclear weapons as outlined and envisaged in declared policies, doctrines, strategies and concepts

-b) escalatory use, i.e. the use of nuclear weapons in an ongoing situation of tension or conflict

-c) unauthorized use, i.e. the non-sanctioned use of nuclear weapons by a non-state actor

-d) accidental use, i.e. the use of nuclear weapons through error, including technical malfunction and human error.

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The probability of a nuclear war:

Let us look at historical evidence, the views of experts, and predictions made by forecasters. Surveys of experts and superforecasters are one way we can try to put a number on the chances of some kind of nuclear war.

-1. Historical evidence:

We can establish a base rate for the probability of nuclear war by looking at the number of times nuclear weapons have been used during a war: one time since they were developed 79 years ago. This could be interpreted to mean that the likelihood of nuclear war is around 1.26% per year. But there are several reasons not to put much stock in this probability (Baum, de Neufville, & Barrett, 2018). The most important reason is the fact that the one time that nuclear weapons were used during a war — by the US, during World War II — the US was the only country who had nuclear weapons. Because of this, they weren’t deterred by the threat of nuclear retaliation. Today, because countries considering using nuclear weapons risk a nuclear second strike, the threshold for using nuclear weapons is likely higher than it was when the US used nuclear bombs during WWII, thereby decreasing the probability of nuclear war somewhat.

Baum et al. (2018) also point out that a number of other historical circumstances have changed: the political leaders, the number of countries with nuclear weapons, and the relationships between countries with nuclear weapons, among other things. And again, they note that the probability might be somewhat higher than the base rate would suggest, given that there have been a number of geopolitical crises that almost escalated to the point of nuclear war but didn’t (near misses in grey box in the figure below):

Source: Adapted from Baum, de Neufville, and Barrett (2018)

To take these close calls into account, researchers Barrett, Baum and Hostetler (2013) took an alternative approach to estimating the baseline probability of nuclear war using historical frequencies (though they focus only on the risk of accidental nuclear war between the US and Russia). Rather than looking only at the instances where nuclear war actually happened, they looked back at the frequency of accidents that nearly led to nuclear war. They argued that, if one assumes that those near misses could have also ended in disaster, one can make inferences about the probability of nuclear war that are more informative than just looking at the base rate of nuclear war. Based on this reasoning, Barrett et al. (2013) concluded that the median annual probability of inadvertent nuclear war between the US and Russia is about 0.9% (90% CI: 0.02% — 7%).

But there’s controversy over how to interpret those close calls. Should we consider them evidence that a nuclear war could easily have happened multiple times since WWII — that we’re just lucky they didn’t? Or should we think of them as evidence that, while near-misses are relatively common, it’s actually really hard for a close call to escalate to the point of a nuclear exchange? Even though human and technological error may lead to more close calls that we’d hope, the systems in place to identify mistakes before they escalate might just work well enough to keep nuclear war from happening by accident. But this is only very weak evidence, and there’s a lot of reason to be uncertain. Given this uncertainty, it’s useful to look to other forms of evidence for how likely a nuclear exchange — intentional or otherwise — might be.

-2. Evidence from expert surveys:

The 2008 Global Catastrophic Risk (GCR) survey asked experts to make predictions about nuclear war scenarios through to 2100. Specifically, the experts were asked to estimate the likelihood that nuclear wars kill a) at least one million people, b) at least one billion people, and c) enough people that humans become extinct (Sandberg & Bostrom, 2008). From this we can glean that experts see the probability of nuclear war killing at least 1 million or 1 billion people by 2100 as reasonably small, but not insignificant — about 0.39% and 0.12% per year, respectively. They see the risk of extinction caused by nuclear war as much smaller, but again, it’s not insignificant at about 0.011% per year.

Another expert survey, the Lugar Survey On Proliferation Threats and Responses, asked experts all over the world to estimate the probability of nuclear attack, but over a shorter time span (Lugar, 2005). The median view of experts estimating the probability of a nuclear attack within 5 years (from 2004-2009) was 10%, or 2.09% per year, and 20% over 10 years (from 2004-2014), or 2.21% per year.

The Project for the Study of the 21st Century (PS21) Great Power Conflict Report, released for publication in 2015, asked 50 national security experts from all over the world to estimate the probability of a variety of conflict scenarios that could plausibly occur in the next 20 years (Apps, 2015). The median view of the experts was that the probability of a nuclear exchange between the US and Russia in the next 20 years is around 4.72%, or 0.24% per year.

-3. Evidence from Superforecasters:

In 2018, Good Judgment Inc. (GJI) had its superforecasters make a set of predictions about the probability of a nuclear exchange by the year 2021. The GJI forecasts are likely to be less susceptible to the biases that lead experts to make somewhat worse predictions (AI Impacts, 2019). The forecasters predicted that there is a 1% chance of a nuclear attack by a state actor causing at least one fatality before 1 January 2021 — equivalent to about 0.40% per year.

Here’s a table of every estimate found since 2000:

Definition	Annualised probability	Source
Nuclear weapon kills > 1,000 people	0.54%	Existential Persuasion Tournament (2022), superforecasters
Nuclear weapon kills > 1,000 people	0.61%	Existential Persuasion Tournament (2022), domain experts
Nuclear attack	2.21%	Lugar expert survey (2005)
Nuclear war	1.00%	Applied Physics Laboratory (2021), Chapter 4
Nuclear detonation by a state actor causing at least 1 fatality	0.40%	Good Judgement Inc (2018)
Nuclear detonation as an act of war	0.92%	Metaculus (2024)
Nuclear exchange	0.28%	Metaculus (2024)
Nuclear war killing at least 1 million people	0.39%	Global Catastrophic Risks Survey (2008)

Depending on who you ask — and the exact definition of nuclear war you use — the typical annual probability of some kind of nuclear war is around 0.28% to 2.21%. If we aggregate historical evidence, the views of experts and predictions made by forecasters, we can start to get a rough picture of how probable a nuclear war might be. We shouldn’t put too much weight on these estimates, as each of the data points feeding into those estimates come with serious limitations. The first thing to note is that these estimates are generally looking at a nuclear conflict of any size, not just extremely large ones. But even given that, the numbers are surprisingly high. After all:

There hasn’t been a nuclear strike since 1945.
Nuclear states are very aware that the use of strategic nuclear weapons would very likely result in nuclear retaliation.
Since a retaliatory strike could have devastating consequences for a nuclear state, there’s a strong deterrence effect.
Nuclear weapons are complex and expensive enough to build that non-state actors seem unlikely to get access to nuclear weapons unless they’re intentionally supplied by a state actor.

Ultimately, the exact numbers aren’t particularly important. The takeaway is that experts think that some kind of nuclear attack could very plausibly happen this century — and some even think it’s more likely than not.

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Nuclear Proliferation and the Probability of War:

An important question that has been the subject of controversy is the influence of additional nuclear weapons states on the probability of nuclear war. While the usual argument is that proliferation will increase the probability of nuclear war, some have argued that proliferation may reduce rather than increase this probability, as in Gallois (1961), Wentz (1968), and Waltz (1981). Gallois argued that additional nuclear weapon states, such as France at the time he was writing, would so raise the stakes of a potential conflict that such proliferation would make nations more cautious and thus reduce the probability of nuclear war. Wentz argued that it might be in US interest to promote selective nuclear proliferation. Waltz argued that proliferation was, in general, stabilizing. As additional nations acquire nuclear weapons, it becomes more likely that there will be other nuclear powers prepared to exploit any postwar weakness of the initiating power, further reinforcing general deterrence and thus enhancing stability against war outbreak. The probability of a deliberate initiation of a war thus decreases as the acquisition of nuclear weapons restrains the existing nuclear nations. Increasing the number of nuclear nations implies that a nation that initiates a war would be relatively worse off in the post-war environment, both in the case where the other nuclear nations are belligerents and in the case where they remain neutral. Increasing the number of nuclear nations also increases the uncertainty as to how other nuclear powers will react during and after a war. As the number of nuclear nations increases, however, there is a rapid increase in the number of potential nations or counter coalitions with which any initiating nuclear power would have to contend both during and after a war. As a result, the probability of a calculated attack may fall.

While proliferation of nuclear weapons may either increase or decrease the probability of war, control over accidental or irrational war must reduce the chance of nuclear war. In fact, policies and actions, both technical and political, which would reduce the chance of accidental or inadvertent war, could overcome many of the problems associated with nuclear proliferation. The nuclear nations as a group should probably be as concerned about accidental or inadvertent war as about nuclear proliferation. This policy conclusion is further strengthened when considering the relative numbers of weapons involved. There can be considerably more value in controlling the accidental or inadvertent detonation of even a few of the thousands of warheads in the current nuclear nations than in preventing the acquisition of a small number of weapons in a new nuclear nation. There may be, for example, merit in sharing technology to control nuclear weapons with the other nuclear nations or even with all potential nuclear weapons nations. Such policies, which would have the effect of lowering the probability of accidental war, can significantly offset the potentially destabilizing effects of nuclear proliferation.

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Nuclear war is unlikely to happen:

First, let’s look at the reasons why a nuclear war is unlikely to happen. One of the main deterrents against a nuclear war is the concept of mutually assured destruction (MAD). This means that if one country launches a nuclear attack on another, the other country will retaliate with equal or greater force, resulting in the destruction of both sides. This creates a situation where no one wins and everyone loses, which makes it irrational for any country to start a nuclear war.

Another reason why a nuclear war is unlikely to happen is the existence of international treaties and organizations that aim to prevent the proliferation and use of nuclear weapons. For example, the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) is a global agreement that limits the number of countries that can possess nuclear weapons and promotes peaceful uses of nuclear energy. The International Atomic Energy Agency (IAEA) is an organization that monitors and inspects nuclear facilities and activities around the world to ensure compliance with the NPT and other agreements. The United Nations Security Council (UNSC) is a body that can impose sanctions and resolutions on countries that violate international norms and threaten peace and security. These treaties and organizations have been effective in reducing the number of nuclear weapons in the world and preventing their use in conflicts. For example, since the end of the Cold War, the United States and Russia have reduced their nuclear arsenals by more than 80%. The only time nuclear weapons were used in war was in 1945, when the United States dropped atomic bombs on Hiroshima and Nagasaki in Japan. Since then, no country has used nuclear weapons in combat, despite several crises and wars involving nuclear-armed states.

Of course, these treaties and organizations are not perfect and do not guarantee that a nuclear war will never happen. There are still some countries that are not part of the NPT or do not comply with its obligations, such as North Korea and Iran. There are also some non-state actors that may try to acquire or use nuclear weapons, such as terrorist groups or rogue regimes. There are also some scenarios that could trigger a nuclear war by accident or miscalculation, such as cyberattacks, false alarms, human errors or miscommunication. However, these risks can be minimized by strengthening international cooperation and dialogue, enhancing transparency and verification measures, improving crisis management and communication systems, and reducing the role and salience of nuclear weapons in national security strategies. These are some of the steps that many countries and organizations are taking to prevent a nuclear war from happening.

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Likelihood of complete human extinction:

Many scholars have posited that a global thermonuclear war with Cold War-era stockpiles, or even with the current smaller stockpiles, may lead to human extinction. This position was bolstered when nuclear winter was first conceptualized and modelled in 1983. However, models from the past decade consider total extinction very unlikely, and suggest parts of the world would remain habitable. Technically the risk may not be zero, as the climatic effects of nuclear war are uncertain and could theoretically be larger, but also smaller, than current models suggest. There could also be indirect risks, such as a societal collapse following nuclear war that can make humanity much more vulnerable to other existential threats.

While a nuclear war would cause immense damage and suffering, it would not necessarily result in the extinction of humanity. This depends on several factors, such as the number, type, size, and target of the nuclear weapons used, the weather conditions, the population density, the level of preparedness and response, and the resilience and adaptation of human societies. The idea that global nuclear war could kill most or all of the world’s population is critically examined and found to have little or no scientific basis.

The available evidence suggests that a major global nuclear war, one involving the explosion of most of the nuclear bombs that exist, would kill 400 to 450 million people, mostly in the US, Europe and Soviet Union, and to a lesser extent China and Japan, directly from blast, heat and radiation effects, and up to 1 billion people indirectly from environmental consequences such as firestorms, nuclear winter, fallout; in particular starvation or epidemics following agricultural failure or economic breakdown. This would be a catastrophic loss of life, but it would not wipe out all humans from the face of the earth. There would still be billions of people who would survive in other parts of the world, especially in regions that are less affected by nuclear explosions or fallout.

Moreover, humans have shown remarkable ability to survive and recover from disasters throughout history. Humans have endured natural disasters such as earthquakes, volcanoes, floods, droughts, famines, plagues, and pandemics. Humans have also survived man-made disasters such as wars, genocides, atrocities, and holocausts. Humans have also demonstrated creativity and innovation in finding ways to cope with adversity and rebuild their lives. Therefore, even if a nuclear war does happen, it does not mean that humanity will go extinct. It means that humanity will face enormous challenges and hardships, but also opportunities for learning and transformation. It means that humanity will have to rethink its values and priorities, its relationships with each other and with nature, its systems of governance and cooperation, its modes of production and consumption, its sources of energy and resources, and its visions of the future.

Many people, perhaps especially in the peace movement, believe that global nuclear war will lead to the death of most or all of the world’s population. Yet the available scientific evidence provides no basis for this belief. Furthermore, there seem to be no convincing scientific arguments that nuclear war could cause human extinction. In particular, the idea of ‘overkill’, if taken to imply the capacity to kill everyone on earth, is highly misleading. In the absence of any positive evidence, statements that nuclear war will lead to the death of all or most people on earth should be considered exaggerations. In most cases the exaggeration is unintended, since people holding or stating a belief in nuclear extinction are quite sincere.

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Section-11

Nuclear proliferation:

Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as “Nuclear Weapon States” by the Non-Proliferation Treaty or NPT. Nuclear proliferation most commonly refers to the spread of nuclear weapons to additional countries and increases the risks of nuclear war arising from regional conflicts. The diffusion of nuclear technologies — especially the nuclear fuel cycle technologies for producing weapons-usable nuclear materials such as highly enriched uranium and plutonium — contributes to the risk of nuclear proliferation. These forms of proliferation are sometimes referred to as horizontal proliferation to distinguish them from vertical proliferation, the expansion of nuclear stockpiles of established nuclear powers. Nuclear proliferation is greatly enhancing the likelihood of nuclear war. It dramatically increases the number of scenarios for small-scale nuclear wars or nuclear terrorism, that could escalate to nuclear war between the superpowers. Deterrence, the cornerstone of national security in present strategies, fails against nuclear terrorism simply because there are no well-defined targets against which to retaliate.

Four countries besides the five recognized Nuclear Weapon States have acquired, or are presumed to have acquired, nuclear weapons: India, Pakistan, North Korea, and Israel. None of these four are a party to the NPT, although North Korea acceded to the NPT in 1985, then withdrew in 2003 and conducted its first nuclear test in 2006. One critique of the NPT is that the treaty is discriminatory in the sense that only those countries that tested nuclear weapons before 1968 are recognized as nuclear weapon states while all other states are treated as non-nuclear-weapon states who can only join the treaty if they forswear nuclear weapons. Despite flaws in the NPT, implementation of the NPT continues to provide important security benefits — by providing assurance that, in the great majority of non-nuclear-weapon States, nuclear energy is not being misused for weapon purposes. Although the NPT is sometimes perceived as a project of the industrialized world, its benefits extend across any geopolitical divide. Proliferation has been opposed by many nations with and without nuclear weapons, as governments fear that more countries with nuclear weapons will increase the possibility of nuclear warfare (up to and including the so-called countervalue targeting of civilians with nuclear weapons), de-stabilize international or regional relations, or infringe upon the national sovereignty of nation states.

Nuclear proliferation – be it among nations or terrorists – greatly increases the chance of nuclear violence on a scale that would be intolerable. Proliferation increases the chance that nuclear weapons will fall into the hands of irrational people, either suicidal or with no concern for the fate of the world. Irrational or outright psychotic leaders of military factions or terrorist groups might decide to use a few nuclear weapons under their control to stimulate a global nuclear war, as an act of vengeance against humanity as a whole. Countless scenarios of this type can be constructed. Limited nuclear wars between countries with small numbers of nuclear weapons could escalate into major nuclear wars between superpowers. For example, a nation in an advanced stage of “latent proliferation,” finding itself losing a nonnuclear war, might complete the transition to deliverable nuclear weapons and, in desperation, use them. If that should happen in a region, such as the Middle East, where major superpower interests are at stake, the small nuclear war could easily escalate into a global nuclear war.

Security guarantees:

In their article, “The Correlates of Nuclear Proliferation,” Sonali Singh and Christopher R. Way argue that states protected by a security guarantee from a great power, particularly if backed by the “nuclear umbrella” of extended deterrence, have less of an incentive to acquire their own nuclear weapons. States that lack such guarantees are more likely to feel their security threatened and so have greater incentives to bolster or assemble nuclear arsenals. As a result, it is then argued that bipolarity may prevent proliferation whereas multipolarity may actually influence proliferation.

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Limitations of technical barriers and safeguards against proliferation of nuclear weapons:

Any determined nation could develop and start stockpiling reasonably efficient and reliable nuclear weapons within ten years and, in many cases, in a much shorter time. The knowledge, nonnuclear materials, and components needed for the production of nuclear weapons are accessible worldwide. The main technical barrier is obtaining the required nuclear material (highly enriched uranium or plutonium), but even that is not much of a barrier today. Detailed information needed to design facilities for producing nuclear weapon materials is public. Key components of such facilities can be purchased through international markets. Using plutonium extracted from spent fuel from nuclear reactors is also open to any country that has a civilian reactor or high-power research reactor. Another alternative, applicable to at least a dozen nations, is the diversion of highly enriched uranium or plutonium from other types of research facilities. These often contain enough material for at least several nuclear weapons.

There are several ways that present safeguards against diversion of nuclear material from nonmilitary reactors and their supporting facilities could be defeated. These facilities produce nuclear material suitable for use in weapons and many, allegedly used for peaceful purposes, are not subject to proliferation safeguards of the International Atomic Energy Agency (IAEA). Further, even where IAEA safeguards do apply, they cannot detect diversion of small amounts of nuclear material and, at many facilities, the annual threshold of detection is significantly greater than the amount of material needed for a nuclear explosive. In addition, even nations currently adhering to international safeguards can break the agreement at a later date if the nation decides its vital interests so dictate, for example if the nation is losing a conventional war.

Even where there is no current diversion of nuclear materials, the worldwide spread of plutonium produced in civilian nuclear power reactors has produced “latent proliferation” — the ability to produce nuclear weapons in short order — in every country with a nuclear power plant. Nuclear explosives can be made with less than 6 kilograms of plutonium, in size about enough to fill a coffee cup. The plutonium produced in a reactor must be separated before it can be used in a weapon. While commercial facilities are more complex, a separation plant suitable for military purposes can be built for less than $50 million in several months’ time. Every nation with a commercial nuclear power plant has such resources, since they are small compared with those needed for acquiring the power plant itself. Each year, the reprocessing plant can extract approximately 250 kilograms of plutonium from a single commercial reactor, enough for forty nuclear weapons at the very least.

To summarize the point: The most difficult technical barrier for the production of nuclear weapons is access to the required nuclear material. But thirty-six countries with nuclear power plants produce at least enough plutonium for forty nuclear weapons per year from each such plant. It is also possible that international illegal markets in nuclear weapon materials or, conceivably, in complete nuclear weapons, may develop in the future, as they have for a wide variety of other weapons in the past. As with other weapons, the illegal suppliers of such materials could be criminals who steal the materials or act as middlemen between illegal suppliers and the buyer.

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Clandestine enrichment facility:

Natural uranium (NU), LEU or slightly enriched uranium (SEU) separated at the reprocessing plant can be diverted to a clandestine enrichment facility where HEU is produced. These pathways appear in figure below:

Figure above shows Diversion Pathways to HEU from a clandestine enrichment plant. The relative attractiveness of the different pathways shown in figure above depends on the enrichment of the source material and increases in the following order: NU, SEU, LEU. Another parameter is the purity of the source material. LEU entering the uranium fuel fabrication plant is naturally more attractive than the LEU contained in the fabricated fuel assemblies. If one compares the pathways of figure above to the misuse of an existing commercial enrichment plant, it is evident that the construction of a clandestine plant would be motivated in the countries where the nuclear power programme is too small for a commercial plant.

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Enriched uranium versus plutonium as proliferator’s choice:

A recurrent question in discussions of nuclear proliferation is which fissile material, enriched uranium or plutonium, states prefer for their weapons programs? An answer would shed light on the development of nuclear weapons programs in the past, and also serve as a predictive mechanism to help understand how future programs may develop. Both enriched uranium and plutonium were produced for the first time in the early 1940s by researchers in the United States. Uranium, a naturally occurring element, has a number of isotopes. The preferred isotope for weapons— U235— comprises only 0.7 percent of natural ore. Typically, the concentration of U235 must be increased to about 90 percent before uranium is suitable for weapons, though lower concentrations can be used. Increasing the concentration of U235 relative to the more plentiful isotope U238 is a laborious process known as “enrichment.” Plutonium is not a naturally occurring element and therefore must be produced, typically by bombarding U238 with neutrons in a nuclear reactor. The chemical extraction of plutonium from spent reactor fuel is known as “reprocessing.” Considerably less plutonium than uranium is needed to make a simple fission weapon.

It would be difficult to generate dollar/kiloton of yield figures for the two metals, and plots of cost versus production time would be even more elusive. The necessary production facilities are complex and technically demanding and so defy easy estimations of cost. Many types of enrichment techniques, reactors, and reprocessing facilities exist, and even a single label, say “centrifugation,” in reality describes a wide range of technologies. Any assessment of a state’s likely choice of fissile material must take into account its motivation in seeking such materials. While technological accessibility also influences the choice of materials, accessibility is in part determined by such intangible and country-specific factors as the willingness of other states to supply equipment, the willingness and ability of the acquiring state to procure equipment clandestinely, and the material and intellectual resources of the acquiring state.

The choice of fissile material must be preceded by the more basic decision to produce fissile material at all. An examination of the historical record amply demonstrates that a state’s rationale for seeking fissile material has often played an important role in determining the material chosen. Mastery of the nuclear fuel cycle can yield new sources of electricity, commercial revenue, and naval propulsion. Programs that yielded nuclear weapons have been undertaken with a mix of military and non-military applications in mind, and the benefits listed in table below, among others, have often played a significant role in the choice of fissile material. Foreign assistance and the urgency of production have also been important influences.

The Proliferator’s Initial Choice of Fissile Materials is depicted in table below:

	Enriched Uranium	Plutonium	Motivation for Materials Choices
United States	X	X	urgency of production, technological uncertainty, extensive resources
Soviet Union	X	X**	urgency of production, technological uncertainty, extensive resources, **preference for Pu
United Kingdom		X	technological accessibility, non-explosive applications (very minor)
France		X	technological accessibility, non-explosive applications (far more so than in the United Kingdom)
China	X	**	critical equipment transferred from Soviet Union, **were to have received reactor as well
Israel		X	critical equipment transferred from France
India		X	critical equipment transferred from Canada and the United States, non-explosive applications
South Africa	X*		non-explosive applications, *substantial (?) foreign orders
Pakistan	X*	**	technological accessibility, historical accident, substantial foreign orders, *sought Pu first
Brazil	X		non-explosive applications, institutional factors
Argentina	X	X	urgency of production (?), non-explosive applications/technological mastery
Iraq	X*	**	technological accessibility, substantial foreign orders, *sought Pu first
North Korea		X	technological accessibility

Some general conclusions can be drawn about the nature of proliferation: first, and most obviously, the preferred method for producing fissile materials is through the purchase of complete systems for doing so. This has not been uncommon. India, Israel, and China acquired a weapons capability in this manner, and Iraq and Pakistan tried unsuccessfully to do so. More interestingly, in four of the five cases the equipment in question was for plutonium. In the odd case, China, both uranium and plutonium producing equipment were to be transferred, but by happenstance the uranium plant was completed first.

Some further conclusions concerning the relative accessibility of plutonium and uranium can be drawn based strictly on the historical record. For early proliferators working in isolation like the United Kingdom and France, plutonium was the preferred choice. The Soviets also suspected this to be the case. More recently, the proliferation of companies familiar with enrichment technology has meant that bomb builders no longer work in isolation. Parts, designs, and expertise can all be acquired without the assistance of another government. Having failed to procure plutonium production facilities, both Pakistan and Iraq elected to pursue enrichment programs for which components could be purchased piecemeal from a number of suppliers, rather than to develop a reactor program indigenously. South Africa and Brazil also found enrichment feasible using some foreign parts.

While it would be bravado to claim that the present state of the North Korean program was predictable, it is at least explainable in light of these conclusions. Frigid foreign relations and intense notions of self-reliance have combined to reproduce in North Korea an isolation similar to that faced by the earliest weapons programs. Furthermore, North Korea possesses a modest industrial capability, suggesting the adoption of technologies that can be developed without significant foreign purchases. The result has been an indigenous plutonium program based on a reactor design well-suited to the North’s industrial capabilities. Current concern is focused on an unsafeguarded five megawatt reactor and reprocessing facility at Yongbyon. Thought to have been built without significant foreign assistance, this gas-cooled graphite moderated reactor requires neither heavy water nor enriched uranium fuel, obviating the need for revealing foreign purchases. The North Koreans overcame by themselves the most difficult hurdle remaining, purification of the moderating graphite. Strikingly, the North Korean’s choices of coolant and moderator are the same as those in the French G reactors at Marcoule and an early British station at Calder Hall.

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Strategies of Nuclear Proliferation:

What are the strategies of nuclear proliferation available to states? There are four broad strategies of proliferation: hedging, sprinting, hiding, and sheltered pursuit.

Typology for Strategies of Nuclear Proliferation:

Strategy	Intended Outcome
Hedging	Develop the option for a weapon
Sprinting	Weaponize as quickly as possible
Hiding	Weaponize without being discovered
Sheltered pursuit	Weaponize before patron abandons client

Table above illustrates the goals of the four strategies of nuclear proliferation. Except for the sprinting strategy, states pursuing nuclear weapons do not consider speed of paramount importance. For example, hedgers intentionally slow down or even stall the acquisition process, whereas hiders sacrifice speed to maintain secrecy. Sheltered pursuers are in a unique category that balances the desire for speed and secrecy, while their patron state protects them from external efforts to stop them.

Hedging:

A hedger is distinguished from other proliferators by its intent to develop a bomb option, deferring a decision on actual weaponization. It refrains from actively developing nuclear weapons but has not explicitly forsworn the option, putting the pieces in place for a future nuclear weapons program. Hedgers develop capabilities that are consistent with both the pursuit of nuclear weapons and a peaceful nuclear energy program, preserving a “breakout option” if their desire for nuclear weapons shifts from “maybe” to “yes.” Hedgers include states with civilian energy programs that have—or are in a position to achieve—control of the fuel cycle and those that seek to develop indigenous uranium enrichment capabilities that could provide weapons-grade uranium or reprocessing capabilities for plutonium weapons. Importantly, however, hedging is not simply a technological condition or a state of so-called nuclear latency, which is largely related to enrichment and reprocessing technologies. Rather, this strategy focuses on how, where, and why states might consciously choose to hedge on a nuclear weapons program as opposed to acquiring such weapons. There are three varieties of hedging; technical hedging, insurance hedging and hard hedging.

Sprinting:

The first active weapons acquisition strategy is sprinting. States selecting this strategy seek to develop nuclear weapons as quickly as possible. The state must be relatively unconcerned with external powers knowing its intent and capabilities. There are almost always efforts at tactical obfuscation to protect the integrity of research and production facilities and activity, but there is little attempt to mask either the intent or capability to develop nuclear weapons. The state is free to openly develop uranium enrichment or reprocess plutonium for expressly military purposes, as well as build delivery vehicles and create organizational routines to manage a nuclear weapons arsenal. Sprinting is a strategy that is likely to lead to a nuclear weapons capability. It may take some states longer than others for technical or organizational reasons, but if a state devotes the necessary resources and is immune from economic or military preventive action, its prospects for acquiring nuclear weapons are good.

Hiding:

A hider seeks to acquire nuclear weapons, but does so in a fashion that privileges secrecy over speed. Hiders fear prevention or coercion if their activities and capabilities are discovered by other states. They may also fear reactive proliferation by their rivals if their efforts become known. The ideal outcome for a hider is to present the fait accompli of a nuclear weapons capability before it is discovered or to achieve at least sufficient progress to deter prevention. Hiders tend to prefer pathways to nuclear weapons that are easier to conceal, and they are willing to sacrifice efficiency to maximize secrecy. Although uranium enrichment technologies are often presumed to be easier to conceal than plutonium reprocessing technologies, there have been hiders, such as Taiwan, that attempted to conceal their plutonium reprocessing capabilities.

Hiding is a high-risk, high-reward strategy. If a state is able to hide and present its development of nuclear weapons as a fait accompli, it is able to reap all the benefits of a nuclear deterrent while avoiding the external duress of the proliferation process. Once presented with a fait accompli, the international community may have little choice but to accept the state’s nuclear weapons capability, given that nuclear weapons, at least theoretically, provide protection against existential threats. But if a hider is caught, diplomatic or military mobilization against it may be more likely because of the perceived illegitimacy of hiding a nuclear capability. Hiding has rarely been successful, however, because maintaining complete secrecy against a global intelligence apparatus designed to detect hidden nuclear weapons programs is difficult. Nevertheless, some states, such as South Africa and North Korea, did achieve a nuclear weapons capability using a hiding strategy. Thus, even a small prospect of success may tempt states to pursue this strategy because of the huge upside.

Sheltered pursuit:

Sheltered pursuit involves actively cultivating or opportunistically taking advantage of major power protection against external threats to pursue nuclear weapons. The state offering shelter is often a superpower, but may also include other major powers such as China. The major power is not usually a formal ally, given that major powers often prefer their formal allies not to possess nuclear weapons so that they can alone control nuclear use and escalation within their alliance blocs. Instead, the state may find itself in a transactional client-patron relationship with a major power that is complicit in, or at least tolerant of, its nuclear weapons pursuit and offers immunity against external coercion. The immunity given to the sheltered pursuer often has nothing to do with its nuclear program. The United States, for example, has never wanted another state to acquire nuclear weapons. Instead, shelter may be extended because the state has found itself useful to the major power for other domestic or geopolitical reasons that override nonproliferation objectives. This strategy therefore allows the pursuer to opportunistically acquire nuclear weapons. It opens a window of protection against the major power patron, during which the client can attempt to acquire nuclear weapons, while the patron’s diplomatic and military protection provides the client cover against other external powers. The aim of the sheltered pursuit strategy is to develop a nuclear weapons capability before the major power patron abandons the client.

The sheltered pursuit strategy is appealing because it allows a state to proliferate under an umbrella of protection. Israel and Pakistan are the quintessential sheltered pursuers, having taken advantage of protection from the United States to develop nuclear weapons while claiming to other states that its facilities were only for nonmilitary purposes—textile factories or goat sheds, respectively.

Which proliferation strategies have states selected and when?

Why do states select one strategy of proliferation over others?

In deciding how to pursue nuclear weapons, states must consider three sets of variables: (1) their immediate security environment, (2) their internal domestic context, and (3) their international nonproliferation constraints and opportunities.

The reasons for nuclear pursuit did not correlate with the ultimate choice of proliferation strategy (e.g., all states that pursued nuclear weapons for security motivations did not choose a sprinting strategy, or the advent of a stronger nonproliferation regime did not force all states into hiding). So, the correlation between why states pursue nuclear weapons and how they go about doing so is weak. Therefore, it is reasonable to treat the selection of a strategy of proliferation as a sui generis decision once states decide to embark on it. Furthermore, although fewer states have pursued nuclear weapons over time—both because many that thought about pursuing them have already done so, and because the increasingly robust U.S.-led nonproliferation regime has deterred many states from even exploring nuclear weapons options —a significant number of states have continued to attempt to acquire nuclear weapons. Twenty-nine states have explored or pursued nuclear weapons and some states have shifted strategies over time, providing additional observations (forty seven in total). No theory can explain all forty-seven strategies coded in figure below, given that most theories are probabilistic and proliferation is an extremely complex process.

Figure above shows observed strategies of Nuclear Proliferation.

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Nuclear latency:

Nuclear latency or a nuclear threshold state is the condition of a country possessing all the technology, expertise and infrastructure needed to quickly develop nuclear weapons, without having actually yet done so. Japan is considered a “paranuclear” state, with complete technical prowess to develop a nuclear weapon quickly, and is sometimes called being ‘one screwdriver’s turn” from the bomb, as it is considered to have the materials and technical capacity to make a nuclear weapon at will. Alongside Japan, Iran is also considered a nuclear threshold state, and has been described being “a hop, skip, and a jump away” from developing nuclear weapons, with its advanced nuclear program capable of producing fissile material for a bomb in a matter of days if weaponized. Other most notable nuclear threshold states are Canada, Germany, the Netherlands and Australia.

Nuclear latency, hedging and arms race:

Nuclear latency can be achieved with solely peaceful intentions, but in some cases nuclear latency is achieved in order to be able to create nuclear arms in the future, which is known as “nuclear hedging”. While states engaging in nuclear hedging do not directly violate the NPT, they do run the risk of potentially encouraging their neighboring states, particularly those they have had conflicts with, to do the same, spawning a “virtual” arms race to ensure the potential of future nuclear capability. Such a situation could rapidly escalate into an actual arms race, drastically raising tensions in the region and increasing the risk of a potential nuclear exchange.

Other nuclear-threshold states:

South Africa has successfully developed its own nuclear weapons, but dismantled them in 1989. Taiwan and South Korea have both been identified as “insecure” nuclear threshold states—states with the technical capability to develop nuclear weapons. South Korea had been involved in nuclear energy technology since the end of the Korean War, and possessed an active nuclear weapons program that was terminated in the mid-1970s with its signing of the Nuclear Non-Proliferation Treaty, while still engaging in some clandestine nuclear weapons research into the late 1980s, and the security motivations to seriously contemplate such an option—since the publishing of a Mitre Corporation report in 1977. US intelligence also believes Taiwan has designed devices suitable for nuclear testing.

The number of states that are technically nuclear-latent has steadily increased as nuclear energy and its requisite technologies have become more available, but the number of states that are actually at the threshold status are limited. Nuclear latency does not presume any particular intentions on the part of a state recognized as being nuclear-latent.

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Nuclear hedging and Iran:

The international community has been in pursuit of a lasting solution to the Iranian nuclear challenge. From the Tehran Declaration of 2003 to attempts to secure a Joint Comprehensive Plan of Action (JCPOA), diplomatic efforts have been driven by fears that Iran is seeking nuclear weapons. These fears have been fuelled by Tehran’s insistence on pursuing an expansive enrichment programme that far surpasses current civil requirements, the inability of the International Atomic Energy Agency (IAEA) to confirm the peaceful nature of that programme, and evidence hinting at possible military dimensions to Iran’s nuclear activities. Iran has vigorously repudiated claims that its nuclear programme aims at covertly advancing an aspiration to develop nuclear weapons. For Iran, diplomacy on the nuclear issue has long been used as a means of dissipating pressure and buying time for the nuclear programme to advance. Iran could make enough fissile material for a nuclear bomb in “less than two weeks” and could produce a nuclear weapon in “several more months,” according to the top U.S. military officer.

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Determining peacefulness of a nuclear program:

In a paper written following the establishment of the JCPOA, a Counsellor of the Nuclear Threat Initiative, John Carlson, outlined several criteria for use in helping to determine whether a state’s nuclear program was run solely with peaceful intentions, or if the state was engaging in nuclear hedging:

-1. Production of nuclear materials significantly beyond what could feasibly be needed in order to maintain a state’s current nuclear reactors. This includes both the processes of the enrichment of uranium and the reprocessing of plutonium.

-2. Retaining stores of nuclear materials which can be used in weapons construction beyond the amount that could reasonably be slated for use in civilian purposes, such as research or power generation.

-3. Noncompliance or lack of proper cooperation with the IAEA, or grievous disregard for reasonable safeguards.

-4. Construction of facilities and infrastructure which is more reasonably oriented toward the production of nuclear weapons than for civil purposes, such as reactors that produce extremely large quantities of plutonium.

-5. Production of technologies which are primarily oriented toward the creation of nuclear weapons, such as the explosive lenses required to build an implosion-type weapon.

-6. Production or development of systems designed to allow for the deliverance of nuclear payloads, such as long-range ballistic missiles.

-7. A supposedly civilian nuclear energy program having heavy involvement with the state’s military, an indication that the state’s military is likely seeking to obtain nuclear materials.

-8. Making use of black-market sources in order to obtain nuclear materials, technology used for reprocessing or enrichment, technology used in the production of nuclear arms or delivery systems, or the purchase of nuclear delivery systems outright.

-9. The state being in a location in which it has a history of severe conflicts in its relationships with several neighboring states. This gives the state a reason to desire nuclear arms as a potential deterrence of its neighboring adversaries.

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Arguments for nuclear proliferation:

There has been much debate in the academic study of international security as to the advisability of proliferation. In the late 1950s and early 1960s, Gen. Pierre Marie Gallois of France, an adviser to Charles DeGaulle, argued in books like The Balance of Terror: Strategy for the Nuclear Age (1961) that mere possession of a nuclear arsenal, what the French called the Force de frappe, was enough to ensure deterrence, and thus concluded that the spread of nuclear weapons could increase international stability. Some very prominent neo-realist scholars, such as Kenneth Waltz, Emeritus Professor of Political Science at the University of California, Berkeley and Adjunct Senior Research Scholar at Columbia University, and John Mearsheimer, R. Wendell Harrison Distinguished Service Professor of Political Science at the University of Chicago, continue to argue along the lines of Gallois in a separate development. Specifically, these scholars advocate some forms of nuclear proliferation, arguing that it will decrease the likelihood of war, especially in troubled regions of the world. Aside from the majority opinion which opposes proliferation in any form, there are two schools of thought on the matter: those, like Mearsheimer, who favor selective proliferation, and those such as Waltz, who advocate a laissez-faire attitude to programs like North Korea’s.

There are two opposing theories regarding the question of proliferation and non-proliferation of nuclear weapons. After the advent of the nuclear age, nuclear weapons have been a central topic for debate within academia, foreign-policy communities and think tanks. Kenneth Waltz and Scott Sagan, two prominent scholars of International Relations have proposed two different opposing theories to address the problem.

Kenneth Waltz was an advocate of nuclear proliferation. He was a strong supporter of “Rational Deterrence Theory”. He believed the world would be safer if more countries had nuclear weapons.

According to Waltz, proliferation would bring more peace for the following reasons:

Nuclear weapons make war less likely because nuclear weapons encourage both defense and deterrence. The possibility of total annihilation in a nuclear war makes states more careful and miscalculation more difficult. Nuclear weapons dissuade attack both on home territory and on vital strategic interests.
Weak and small countries will not use nuclear weapons irresponsibly. There is a good chance that they will be defeated in a conventional war. Nukes are their last resort, so they will save their nukes for final battles. They will only use those nukes if survival is at stake, certainly not for reckless invasion.
It is not possible to completely stop the proliferation of nuclear weapons because states will continuously attempt to improve their security environment.
In a nuclear war both parties will be destroyed, so no one will be tempted to use nuclear weapons in a war.
Nuclear weapons act as a deterrent force; meaning, if you have nuclear bombs other countries will be discouraged to initiate a war in the first place for the fear of nuclear annihilation.
A state calculates the costs and benefits before going to war. If costs outweigh benefit then there will be no incentives to start a war. In a nuclear war, there are no benefits; it will only increase your costs, so nuclear weapons can prevent wars.
The acquisition of nuclear weapons makes states “exceedingly cautious” and they will not fight if they can’t win much and stand to lose everything. Prominent realist thinker John Mearsheimer supports Kenneth Waltz by stating that “nuclear weapons are a superb deterrent” (New York Times 1998).

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Nuclear non-proliferation amount to nuclear apartheid:

Iran:

Former Iranian President Mahmoud Ahmadinejad has been a frequent critic of the concept of “nuclear apartheid” as it has been put into practice by several countries, particularly the United States. In an interview with CNN’s Christiane Amanpour, Ahmadinejad said that Iran was “against ‘nuclear apartheid,’ which means some have the right to possess it, use the fuel, and then sell it to another country for 10 times its value. We’re against that. We say clean energy is the right of all countries. But also it is the duty and the responsibility of all countries, including ours, to set up frameworks to stop the proliferation of it.” Hours after that interview, he spoke passionately in favor of Iran’s right to develop nuclear technology, claiming the nation should have the same liberties.

India:

India has also been discussed in the context of “nuclear apartheid”. India has consistently attempted to pass measures that would call for full international disarmament, however, they have not succeeded due to protests from those states that already have nuclear weapons. In light of this, India viewed nuclear weapons as a necessary right for all nations as long as certain states were still in possession of nuclear weapons. India stated that nuclear issues were directly related to national security.

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Arguments against nuclear proliferation:

Proliferation begets proliferation:

‘Proliferation begets proliferation’ is a concept described by professor of political science Scott Sagan in his article, “Why Do States Build Nuclear Weapons?”. This concept can be described as a strategic chain reaction. If one state produces a nuclear weapon it creates almost a domino effect within the region. States in the region will seek to acquire nuclear weapons to balance or eliminate the security threat. Sagan describes this reaction in his article where he states, “Every time one state develops nuclear weapons to balance against its main rival, it also creates a nuclear threat to another region, which then has to initiate its own nuclear weapons program to maintain its national security”. Going back through history we can see how this has taken place. When the United States demonstrated that it had nuclear power capabilities after the bombing of Hiroshima and Nagasaki, the Russians started to develop their program in preparation for the Cold War. With the Russian military buildup, France and the United Kingdom perceived this as a security threat and therefore they pursued nuclear weapons. Even though proliferation causes proliferation, this does not guarantee that other states will successfully develop nuclear weapons because the economic stability of a state plays an important role in whether the state will successfully be able to acquire nuclear weapons. The article written by Dong-Jong Joo and Erik Gartzke discusses how the economy of a country determines whether they will successfully acquire nuclear weapons.

Scott Sagan’s arguments against the proliferation of nuclear weapons:

Sagan used “Organizational Theory” to make his points against the spread of nuclear weapons. He observes that behavior of military and state are not same. States go to war to achieve broader political gains; but military is solely focused on victory, which means defeating the enemy in a narrow margin may still be considered a victory for the military. So, the military will be tempted to use nukes if they are not effectively controlled by the state.
States do not manage their nuclear arsenal themselves. Organizations under the supervision of states control nuclear weapons. Organizations have biases and parochial interests. If states do not strongly control them then it may result in deterrence failure.
Certain institutions maintain and supervise nuclear weapons. Institutions have inherent organizational weaknesses, so the proliferation of nuclear weapons is a risky business.
A state or group of states will pre-emptively attack a proliferating state to destroy or hinder its nuclear program. For example, Israel pre-emptively attacked Syrian nuclear facilities in 2007 to destroy its nuclear program. An action of this kind will jeopardize regional stability and security.
The accidental launch of nuclear weapons may lead to unnecessary nuclear war.
Electronic errors, misinformation, panic, or enormous pressure on leadership during a war can lead to an inadvertent nuclear exchange.

Experts and scholars both from realist and liberal camps, in general, discourage nuclear proliferation. They support a strong NPT and reduction of existing nuclear stockpiles. International organizations, the international community, and most of the states are opposed to nuclear proliferation. After weighing pros and cons, it seems to me that non-proliferation, as well as the elimination of all nuclear weapons, is the best choice to ensure global peace and security. In my view, accidental launch, electronic or human error, false alarm, misinformation, cyberattack, irrational leaders and nuclear materials falling in hands of wrong guys; are strong points for nuclear non-proliferation and disarmament. We ought to eliminate nuclear weapons.

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Section-12

Nuclear terrorism:

Nuclear terrorism refers to any person or persons detonating a nuclear weapon as an act of terrorism. Some definitions of nuclear terrorism include the sabotage of a nuclear facility and/or the detonation of a radiological device, colloquially termed a dirty bomb, but consensus is lacking. In legal terms, nuclear terrorism is an offense committed if a person unlawfully and intentionally “uses in any way radioactive material … with the intent to cause death or serious bodily injury; or with the intent to cause substantial damage to property or to the environment; or with the intent to compel a natural or legal person, an international organization or a State to do or refrain from doing an act”, according to the 2005 United Nations International Convention for the Suppression of Acts of Nuclear Terrorism. It is considered plausible that terrorists could acquire a nuclear weapon. Nonetheless, despite thefts and trafficking of small amounts of fissile material, there is no credible evidence that any terrorist group has ever obtained or produced nuclear materials of sufficient quantity or purity to produce a viable nuclear weapon. Nuclear terrorism is rare, with only 91 incidents in the last 50 years. None of these attacks resulted in environmental contamination or radioactive fallout.

Nuclear terrorism could include:

Acquiring or fabricating a nuclear weapon
Fabricating a dirty bomb
Attacking a nuclear reactor, e.g., by disrupting critical inputs (e.g. water supply)
Attacking or taking over a nuclear-armed submarine, plane, or base.

Former U.S. President Barack Obama called nuclear terrorism “the single most important national security threat that we face”. In his first speech to the U.N. Security Council, President Obama stated that “Just one nuclear weapon exploded in a city—be it New York or Moscow, Tokyo or Beijing, London or Paris— could kill hundreds of thousands of people”, and warned such an attack could “destabilize our security, our economies, and our very way of life”.

Threat Scenarios:

Dirty Bomb:

The most accessible nuclear device for any terrorist would be a radiological dispersion bomb. This so-called ‘dirty bomb’ would consist of waste by-products from nuclear reactors wrapped in conventional explosives, which upon detonation would spew deadly radioactive particles into the environment. This is an expedient weapon, in that radioactive waste material is relatively easy to obtain. Radioactive waste is widely found throughout the world, and in general is not as well guarded as actual nuclear weapons.

In the United States, radioactive waste is located at more than 70 commercial nuclear power sites, in 31 states. Enormous quantities also exist overseas — in Europe and Japan in particular. Tons of wastes are transported long distances, including between continents (Japan to Europe and back). In Russia, security for nuclear waste is especially poor, and the potential for diversion and actual use by Islamic radicals has been shown to be very real indeed. In 1996, Islamic rebels from the break-away province of Chechnya planted, but did not detonate, such a device in Moscow’s Izmailovo park to demonstrate Russia’s vulnerability. This dirty bomb consisted of a deadly brew of dynamite and one of the highly radioactive by-products of nuclear fission — Cesium 137.

Extreme versions of such gamma-ray emitting bombs, such as a dynamite-laden casket of spent fuel from a nuclear power plant, would not kill quite as many people as died on Sept. 11. A worst-case calculation for an explosion in downtown Manhattan during noontime: more than 2,000 deaths and many thousands more suffering from radiation poisoning.

Attack on Nuclear Power Plants:

A terrorist attack on a commercial nuclear power plant with a commercial jet or heavy munitions could have a similar affect to a radiological bomb, and cause for greater casualties. If such an attack were to cause either a meltdown of the reactor core (similar to the Chernobyl disaster), or a dispersal of the spent fuel waste on the site, extensive casualties could be expected. In such an instance, the power plant would be the source of the radiological contamination, and the plane or armament would be the explosive mechanism for spreading lethal radiation over large areas.

Diversion of Nuclear Material or Weapons:

The threat from radiological dispersion dims in comparison to the possibility that terrorists could build or obtain an actual atomic bomb. An explosion of even low yield could kill hundreds of thousands of people. A relatively small bomb, say 15-kilotons, detonated in Manhattan could immediately kill upwards of 100,000 inhabitants, followed by a comparable number of deaths in the lingering aftermath.

Fortunately, bomb-grade nuclear fissile material (highly enriched uranium or plutonium) is relatively heavily guarded in most, if not all, nuclear weapon states. Nonetheless, the possibility of diversion remains. Massive quantities of fissile material exist around the world. Sophisticated terrorists could fairly readily design and fabricate a workable atomic bomb once they manage to acquire the precious deadly ingredients (the Hiroshima bomb which used a simple gun-barrel design is the prime example).

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Building a terrorist bomb:

The most difficult part of constructing a nuclear weapon is obtaining the fissile material required – either highly enriched uranium (HEU, enriched to 20% or more of the isotope U-235) or plutonium (Pu). There is an important distinction between the skills needed to build reliable, efficient, compact, sophisticated nuclear weapons with predictable yield, able to be delivered by a missile or fighter plane; and building one or a few crude nuclear weapons which may be bulky, unsafe, of uncertain yield, and require delivery by boat or truck; but nevertheless, have a high probability of exploding. Designs for reliable nuclear weapons are openly available and building them repeatedly proven to be well within the capacity of competent undergraduate physics students.

The weak radioactivity of uranium means it can be handled by hand and is easily smuggled. A further possible advantage for terrorists is that the simplest gun-type bomb design can be used, in which one subcritical mass is fired (or even dropped) down a cylinder into another subcritical mass, the combined mass being supercritical i.e. able to sustain an explosive chain reaction. The bomb dropped on Hiroshima, and South Africa’s now dismantled nuclear weapons, were of this type. However, enrichment of uranium is technically demanding and current centrifuge methods involve large, expensive industrial scale facilities. Laser enrichment, such as being developed at Lucas Heights in Sydney by Silex Systems, now in partnership with General Electric Corporation, if further developed, could pose a significant proliferation risk by making uranium enrichment simpler, cheaper, more compact, modular and concealable.

Plutonium isotopes are inevitably produced when U-238 (the main isotope in natural uranium) absorbs neutrons in a nuclear reactor. All plutonium isotopes (Pu-238, 239, 240, 241, 242) are fissionable and though weapons are typically made with weapons-grade plutonium enriched to more than 90% Pu-239, any combination of plutonium isotopes containing less than 80% Pu-238 is usable for making a nuclear weapon, including so-called reactor-grade plutonium. Spent nuclear fuel must be chemically reprocessed to extract the plutonium before the latter can be used in weapons; this process is relatively straightforward but is made much more difficult by the intense radioactivity produced by the other fission products in spent reactor fuel. Plutonium is more radioactive, easier to detect and somewhat harder to handle than uranium; but terrorists could handle it with simple equipment such as rubber gloves and polyethylene sheeting.

Nuclear weapons using plutonium must use an implosion design, with a series of shaped explosive lenses arranged in a sphere, fired simultaneously to compress a less than critical mass of plutonium (or HEU) at the centre. While this is technically more demanding than construction of a gun-type bomb, it is certainly within the capacity of a sophisticated terrorist group, particularly if they obtained knowledgeable help.

The critical mass of fissile material is not fixed, but decreases with the square of the density i.e. if squeezed to twice its normal density, only a quarter as much material is needed. If a sphere of plutonium metal is surrounded by a shell of neutron reflecting material such as beryllium or uranium, which reduces the number of neutrons escaping without causing a fission event, the critical mass can be reduced further. A thick reflector will reduce the critical mass by a factor of 2 or more. Thus, whereas the critical mass of a bare sphere of weapons grade plutonium metal is about 11 kg, modern nuclear weapons contain less than 4 kg of plutonium. Six kg of weapons-grade plutonium, the amount used in the bomb dropped on Nagasaki, would occupy less than 400 mL, about the size of an ordinary drink can or a grapefruit. Both HEU and plutonium are best suited to bombs in pure metal form. In the nuclear industry, material is often in oxide form, however these can be converted to metal through chemical processes which have been widely published. Terrorists would need to buy or steal HEU or Pu, or a ready-made nuclear weapon. There have been numerous instances of nuclear smuggling. The IAEA Illicit Trafficking Database has documented more than 650 instances of intercepted smuggling of radioactive materials in the 1990s decade.

Effects of a nuclear terrorist attack:

A 10-kiloton nuclear bomb set off at Times Square on a typical workday could kill half a million people and spread deadly fallout many miles downwind. A study by the RAND Corporation estimated that the early, direct economic costs of a nuclear terrorist attack on a US port would exceed $1 trillion, about ten times the cost of 9/11. There would be immediate pressure to close all US ports to prevent another attack. Given that US ports carry out 7.5% of all global trade activity, the consequences for the world economy would be catastrophic. Former UN Secretary-General Kofi Annan has argued that a nuclear terrorist attack “would stagger the world economy and thrust tens of millions of people into dire poverty,” creating “a second death toll throughout the developing world.”

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Prevention of nuclear terrorism:

Unlike state-level use of nuclear weapons, retaliation is not likely to deter terrorist groups from the use of nuclear weapons, so the doctrine of mutually assured destruction does not apply.

The most important single step to prevent nuclear terrorism is to secure all nuclear weapons and fissile material, so they can’t be stolen and fall into terrorist hands. No fissile material available to terrorists – no nuclear terrorism. Denial of access to nuclear materials is thus the approach taken by interested nations. Techniques include import and export restrictions, physical security at nuclear facilities to prevent theft, and consolidation or elimination of stockpiles to reduce the security perimeter. The United States subsidizes security for nuclear materials and dismantlement of nuclear weapons through the Cooperative Threat Reduction and Global Threat Reduction Initiative programs.

Efforts to secure nuclear materials are also made by threatening to punish any country that uses, sells, or gives away nuclear weapons or materials. One example of this is when U.S. President George W. Bush threatened North Korea with consequences if they were to engage in such behavior.

Pakistan nuclear weapons at risk of theft by terrorists, US report warns in 2010:

A report by Harvard University’s Belfer Centre for Science and International Affairs, titled Securing the Bomb 2010, said Pakistan’s stockpile “faces a greater threat from Islamic extremists seeking nuclear weapons than any other nuclear stockpile on earth”. Experts said the danger was growing because of the arms race between Pakistan and India. Pakistan came under increased pressure over its nuclear arsenal when this study warned of “a very real possibility” that its warheads could be stolen by terrorists.

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Section-13

False alarms and close calls:

Ever since the two adversaries in the Cold War, the U.S.A. an the U.S.S.R., realized that their nuclear arsenals were sufficient to do disastrous damage to both countries at short notice, the leaders and the military commanders have thought about the possibility of a nuclear war starting without their intention or as a result of a false alarm. Increasingly elaborate accessories have been incorporated in nuclear weapons and their delivery systems to minimize the risk of unauthorized or accidental launch or detonation. A most innovative action was the establishment of the “hot line” between Washington and Moscow in 1963 to reduce the risk of misunderstanding between the supreme commanders. Despite all precautions, the possibility of an inadvertent war due to an unpredicted sequence of events remained as a deadly threat to both countries and to the world.

Although the Cold War standoff that gave rise to massive U.S. and Russian nuclear arsenals ended decades ago, the nuclear strategies that could lead to the firing of hundreds of nuclear weapons remain susceptible to false alarms. Today, each side deploys some 1,400 strategic nuclear warheads on hundreds of sea- and land-based missiles and long-range bombers—far greater than is necessary to deter an attack and more than enough to produce catastrophic devastation. Each side maintains hundreds of warheads that can be fired within minutes of a launch order from the president, and both leaders retain the option to retaliate before they confirm that nuclear weapons have been detonated on their territory. These dangerous launch-under-attack postures perpetuate the risk that false alarms could trigger a massive nuclear exchange.

A nuclear close call is an incident that might have led to at least one unintended nuclear detonation or explosion, but did not. False alarm may lead to close call but close call may occur accidently and inadvertently. These incidents typically involve a perceived imminent threat to a nuclear-armed country which could lead to retaliatory strikes against the perceived aggressor. The damage caused by international nuclear exchange is not necessarily limited to the participating countries, as the hypothesized rapid climate change associated with even small-scale regional nuclear war could threaten food production worldwide—a scenario known as nuclear famine.

There have also been a number of accidents involving nuclear weapons, such as crashes of nuclear armed aircraft. Since nuclear weapons were developed, there have been a number of accidents, equipment malfunctions, and human mistakes that brought the world close to nuclear war. Some of these close calls were closer than others.

For example, in 1961, a B-52 bomber carrying two nuclear warheads broke apart in mid-air over Goldsboro, North Carolina. The breakup of the plane triggered the mechanism (a simple pulley system) meant to be used by the pilot to drop the bomb over a target, which started the arming process for both bombs. One of the bombs landed safely on the ground, fail-safe intact, after the successful deployment of its parachute. The other plummeted to the ground after its parachute failed and completed three of its four arming steps. Had it detonated, the bomb — which had over 250 times the explosive yield of the nuclear bomb dropped on Hiroshima — could have killed millions of people across the East Coast (Mosher, 2017; Paoletti, 2017). According to a now-declassified report on the event, now known as the Goldsboro incident, “one simple, dynamo-technology, low voltage switch stood between the United States and a major catastrophe”. The report later says that the “bomb did not possess adequate safety for the airborne alert role in the B-52″. In another recently declassified report, Secretary of Defense McNamara is quoted as saying that only “by the slightest margin of chance, literally the failure of two wires to cross, a nuclear explosion was averted”.

Other incidents like this are similarly alarming. In 1960, early warning systems reported that long-range Russian missiles had been launched with “99.9% certainty” (Baum, de Neufville, & Barrett, 2018). It turned out it was just the moonrise, which officers eventually figured out after no other warning systems were sounding alarms. Two decades later, a technological glitch caused early warning systems to go off at the US Strategic Air Command, alerting officials of an incoming attack — mistakenly (Baum, de Neufville, & Barrett, 2018). Strategic bomber pilots prepared to take off from their air bases, but the alert was found to be a false alarm when no other warning systems detected incoming missiles. A list of eighteen close calls caused by accidents like this is available in Baum, de Neufville, and Barrett, (2018). Given this history of near-miss events, it’s not hard to imagine that human or technological errors could lead us to nuclear war.

It’s tempting to imagine that the risk of accidental nuclear war has decreased as the technologies that have failed in the past, like early warning radar and fail-safes have likely improved. For example, the US’s early warning systems that detect incoming missiles (which have been partially responsible for near-miss events in the past) have been upgraded with technology that is better at classifying and tracking projectiles (Owens, 2017). This likely reduces the risk that the US or Russia would mis-identify meteorological events or non-nuclear projectiles as an impending nuclear attack. But the expanded use of technology in nuclear weapons systems may introduce new risks. Unal and Lewis warn that, because nuclear weapons now rely more heavily on digital technology, they’ve become more vulnerable to cyber-attack (Unal & Lewis, 2018).

We know of a few very close calls when the world really was on the brink of nuclear war. For example:

During the Cuban Missile Crisis in October 1962, Valentin Savitsky, the captain of a nuclear submarine which had been cut off from radio traffic, decided that a war might have already started and wanted to launch a nuclear torpedo. Vasili Arkhipov, the 36-year-old second captain and brigade chief of staff, refused to give his assent. He convinced the sub’s top officers that launching the nuclear torpedo would be a fatal mistake. The sub returned to the surface, headed away from Cuba, and steamed back toward the Soviet Union.
On Nov. 9, 1979, the U.S. Defense Department detected an imminent nuclear attack against the United States through the early-warning system of the North American Aerospace Defense Command (NORAD). U.S. bomber and missile forces went on full alert, and the emergency command post, known as the “doomsday plane,” took to the air. The 1979 incident was one of the most dangerous false alarms of the nuclear age, but it was not the first or the last.
On January 25, 1995, Boris Yeltsin decided not to launch a retaliatory strike against the US on detecting a rocket that radar operators thought was a Trident missile. The rocket was actually studying the aurora over Svalbard and Russia had been notified of the launch, but this information hadn’t filtered down to the nuclear operators.
On September 26, 1983, Stanislav Petrov refused to report five incoming US missiles that had been detected by the USSR’s early warning system, suspecting a false alarm.

Cuban Missile Crisis:

For thirteen days in October 1962 the world waited—seemingly on the brink of nuclear war—and hoped for a peaceful resolution to the Cuban Missile Crisis. In October 1962, an American U-2 spy plane secretly photographed nuclear missile sites being built by the Soviet Union on the island of Cuba. President Kennedy did not want the Soviet Union and Cuba to know that he had discovered the missiles. He met in secret with his advisors for several days to discuss the problem. After many long and difficult meetings, Kennedy decided to place a naval blockade, or a ring of ships, around Cuba. The aim of this “quarantine,” as he called it, was to prevent the Soviets from bringing in more military supplies. He demanded the removal of the missiles already there and the destruction of the sites. On October 22, President Kennedy spoke to the nation about the crisis in a televised address. No one was sure how Soviet leader Nikita Khrushchev would respond to the naval blockade and US demands. But the leaders of both superpowers recognized the devastating possibility of a nuclear war and publicly agreed to a deal in which the Soviets would dismantle the weapon sites in exchange for a pledge from the United States not to invade Cuba. In a separate deal, which remained secret for more than twenty-five years, the United States also agreed to remove its nuclear missiles from Turkey.

According to Martin Sherwin, co-author of the Pulitzer Prize-winning biography of Oppenheimer that the recent movie was based on, “The extraordinary (and surely disconcerting) conclusion has to be that on October 27, 1962, a nuclear war was averted not because President Kennedy and Premier Khrushchev were doing their best to avoid war (they were), but because Capt. Vasily Arkhipov (vide supra) had been randomly assigned to submarine B-59.”

This is but one of countless examples where global and military history has been dramatically altered by chance and luck. On Oct. 27, 1962, the world was extremely lucky. The question that Robert Oppenheimer would surely ask is, will we be so lucky the next time?

No one is perfect. Mistakes happen, even when it comes to nuclear weapons. No matter how many fail-safes and back-ups are put into place, machines malfunction, animals cause radar confusion, and routine occurrences get mistaken for incoming missile attacks, prompting alarms to ring and urgent decisions to be made. We’ve come close – dangerously close – to a nuclear war. Machines fail, animals get in the way, and, at the end of the day, humans are fallible. Exacerbating the risk of nuclear use is the fact that roughly 1,400 nuclear weapons in the U.S. and Russia are kept on hair-trigger alert, ready to launch at a moment’s notice. Launch on warning strategies give leaders minutes to decide whether to order the launch of nuclear missiles or risk losing them to an incoming nuclear attack. With decision time under such constraints – sometimes as little as 4 minutes – the risk of accidental launch due to false alarm is unnecessarily high. The U.S. and Russia need to take steps to reduce the risk of nuclear use such as negotiating a bilateral agreement to stand down their nuclear weapons on hair-trigger alert. The decision of whether or not to launch a nuclear weapon should not be confined to mere minutes. We were lucky the false alarms of the Cold War did not trigger nuclear war. Because we may not be so lucky in the future, our leaders must act now to take the steps necessary to reduce and eliminate the nuclear danger.

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Section-14

Nuclear weapon tests and its harms:

The Trinity Nuclear Test on 16 July 1945 is a key incident in the blockbuster Oppenheimer movie and in the history of humankind. Many scientists think it marks the beginning of the Anthropocene, a new geological era characterized by humanity’s influence on the Earth. That’s because Trinity’s radioactive fallout will forever appear in the geological record, creating a unique signature of human activity that can be precisely dated. Since then, over 2,000 nuclear tests have been conducted in over a dozen different sites around the world.

Venn diagram above displays the historical proliferation among declared (solid circles) and undeclared nuclear weapon states (dashed circles). Numbers in parentheses are the explosive nuclear tests conducted by a particular nation. The overlap between Russia and U.S. reflects the purchase by the U.S. Defense Special Weapons Agency.

Nuclear weapons tests are experiments carried out to determine the performance, yield, and effects of nuclear weapons. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by different conditions, and how personnel, structures, and equipment are affected when subjected to nuclear explosions. However, nuclear testing has often been used as an indicator of scientific and military strength. Many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status through a nuclear test.

Four major types of nuclear testing are: (1. atmospheric, (2. underground, (3. exoatmospheric, and (4. Underwater.

With the advent of nuclear technology and its increasing impact an anti-nuclear movement formed and in 1963, three (UK, US, Soviet Union) of the then four nuclear states and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. The treaty permitted underground nuclear testing. France continued atmospheric testing until 1974, and China continued until 1980. Neither has signed the treaty. Underground tests conducted by the Soviet Union continued until 1990, the United Kingdom until 1991, the United States until 1992, and both China and France until 1996. In signing the Comprehensive Nuclear-Test-Ban Treaty in 1996, these countries pledged to discontinue all nuclear testing; CTBT will formally enter into force after 44 designated “nuclear-capable states” (as listed in Annex 2 of the treaty) have deposited their instruments of ratification with the UN secretary-general. To date, 187 states have signed and 178 have ratified the treaty. Non-signatories India and Pakistan last tested nuclear weapons in 1998. North Korea conducted nuclear tests in 2006, 2009, 2013, January 2016, September 2016 and 2017. The most recent confirmed nuclear test occurred in September 2017 in North Korea.

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Detecting nuclear tests:

Nuclear explosions are pretty obvious, and the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) already runs a commission to monitor the atmosphere, oceans and subsurface for any testing. Infrasound monitors are capable of detecting aboveground explosions, and underwater microphones can detect undersea testing (both of which were banned under the Partial Nuclear Test Ban Treaty of 1963). Underground nuclear tests show up on seismometers that are designed to detect earthquakes. There are many such arrays, run by research organizations, governments and even private entities, and quite a few of those upload all their data online. That means that anyone with an internet connection can detect an underground nuclear test, as long as they know what to look for. Scientists ordinarily have fairly good ideas about where nuclear testing is going on. So any kind of tremor near a nuclear test site attracts a lot of attention. Nuclear tests create a lot of what geophysicists call “p-waves,” which are compressional waves created by the big blast pushing everything outward, all at once. These waves look quite different from the signals created by earthquakes. Earthquakes are caused by faults sliding side-by-side, so their seismic signals are dominated by shear-wave energy. Thanks to remote seismic monitoring, the international community can tell within seconds to minutes if any regime has detonated something at its underground testing site. By triangulating the source of waves detected at different seismic stations, scientists can even tell exactly where at the site the explosions occurred, even if they were as close as a kilometer apart from one another. North Korea detonated bombs at Punggye-ri in 2006, 2009, 2013, 2016 and 2017. The first two tests are widely considered to be failures. The 2013 and 2016 tests were indicative of a first-generation plutonium fission bomb, not unlike the bomb dropped on Nagasaki in 1945. North Korea claims that the 2016 and 2017 bombs were both thermonuclear, or hydrogen bombs, which generate explosions via nuclear fusion rather than fission. Some experts think the North Korean government really does have a thermonuclear bomb, though others, are sceptical. For the purpose of gaining recognition on the world stage, Pyongyang would like everyone to believe its nuclear program is strong but it’s not clear that the testing done so far indicates the existence of a thermonuclear bomb.

Note:

Underground nuclear explosion can cause an earthquake and even an aftershock sequence. However, earthquakes induced by explosions have been much smaller than the explosion, and the aftershock sequence produces fewer and smaller aftershocks than a similar size earthquake. Not all explosions have caused earthquakes.

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Harms of nuclear tests:

Over 500 atmospheric nuclear weapons tests were conducted at various sites around the world from 1945 to 1980. Radioactive fallout from nuclear weapons testing was first drawn to public attention in 1954 when the Castle Bravo hydrogen bomb test at the Pacific Proving Grounds contaminated the crew and catch of the Japanese fishing boat Lucky Dragon. One of the fishermen died in Japan seven months later, and the fear of contaminated tuna led to a temporary boycotting of the popular staple in Japan. The incident caused widespread concern around the world, especially regarding the effects of nuclear fallout and atmospheric nuclear testing, and “provided a decisive impetus for the emergence of the anti-nuclear weapons movement in many countries”. Nuclear tests usually took place at remote locations at least 100 kilometers from human populations. In terms of distance from the detonation site, “local fallout” is within 50 to 500 kilometers from ground zero, “regional fallout” 500-3,000 kilometers and global fallout more than 3,000 kilometers.

Figure above shows atmospheric nuclear weapon tests almost doubled the concentration of radioactive 14C in the Northern Hemisphere called the Bomb pulse, before levels slowly declined following the Partial Test Ban Treaty.

As public awareness and concern mounted over the possible health hazards associated with exposure to the nuclear fallout, various studies were done to assess the extent of the hazard. A Centers for Disease Control and Prevention/ National Cancer Institute study claims that fallout from atmospheric nuclear tests would lead to perhaps 11,000 excess deaths among people alive during atmospheric testing in the United States from all forms of cancer, including leukemia, from 1951 to well into the 21st century. As of March 2009, the U.S. is the only nation that compensates nuclear test victims. Since the Radiation Exposure Compensation Act of 1990, more than $1.38 billion in compensation has been approved. The money is going to people who took part in the tests, notably at the Nevada Test Site, and to others exposed to the radiation. In addition, leakage of byproducts of nuclear weapon production into groundwater has been an ongoing issue, particularly at the Hanford site.

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Nuclear testing can cause long-term harm to human health and the environment in many ways, including:

Cancer:

The most significant long-term risk of exposure to nuclear radiation is cancer. For example, physicians estimate that 2.4 million people will die from cancer caused by atmospheric nuclear tests between 1945 and 1980.

Genetic damage:

Nuclear radiation can cause genetic damage.

Radioactive contamination:

Nuclear testing can contaminate the soil, air, and water with radioactive particles. This can make areas uninhabitable or cut off access to resources like fishing grounds.

Birth defects:

Nuclear testing can cause birth defects, miscarriages, stillbirths, and reproductive problems.

Acute radiation sickness:

Nuclear radiation can cause acute radiation sickness, which can be fatal. Children are especially vulnerable to the effects of radiation because their bodies are still growing and developing.

Psychological stress:

Nuclear testing can cause psychosocial stress, stigma, and loss of wealth and opportunity.

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Radioactive Fallout from Nuclear Weapons Testing:

Detonating nuclear weapons aboveground sends radioactive materials as high as 50 miles into the atmosphere. Large particles fall to the ground near the explosion site, but lighter particles and gases travel into the upper atmosphere. The particles that are swept up into the atmosphere and fall back down to Earth are called fallout. The highest particles can circulate around the world for years until they gradually fall to Earth or are brought back to the surface by precipitation. The path of the locations of the fallout depends on wind and weather patterns.

Fallout typically contains hundreds of different radionuclides. Some stay in the environment for a long time because they have long half-lives, like cesium-137, which has a half-life of about 30 years. Most have very short half-lives, so decay away in a few minutes or a few days, for examples iodine-131, has a half-life of 8 days. Very little radioactivity from weapons testing in the 1950s and 1960s can still be detected in the environment now.

The United States conducted the first aboveground nuclear weapon test in southeastern New Mexico on July 16, 1945. Between 1945 and 1963, hundreds of aboveground tests took place around the world. Over time the number and size (or yield) of these weapons increased, especially in the late 1950s and early 1960s. After the Limited Test Ban Treaty of 1963 was signed by the United States, the Soviet Union and Great Britain, most aboveground tests ceased. Some aboveground weapons testing by other countries continued until 1980. Since the end of aboveground nuclear weapons testing, the day-to-day radiation in air readings from monitoring sites has fallen. For many years, analysis of air samples has shown risk levels far below regulatory limits. In fact, results are now generally below levels that instruments can detect.

Even though there is very little fallout that still exists in the environment, it is important to remember that recent fallout, within about 10 to 20 miles downwind of the detonation, can be very dangerous. There are different ways we can be exposed to radiation if a nuclear detonation occurs.

When a nuclear detonation occurs, people, plants, and animals can be exposed to the fallout in several ways. Livestock may eat contaminated plants or drink contaminated water. People who then eat this livestock will then still experience internal contamination, in which radioactive material ends up inside of our bodies, despite not consuming contaminated plants or water directly.

Radionuclides that are inhaled or ingested are not blocked by an external shield. These radionuclides interact with internal cells and tissues, which increases the risk of harmful health effects. When radionuclides can ingested, they can change the structure of cells, which is one of the ways people can develop cancer. The health risks from fallout have been described in many studies. One example is the Federal Radiation Council’s 1962 report, Health Implications of Fallout from Nuclear Weapons Testing through 1961. This is one of the reasons why radiation protection professionals work hard to protect people from unnecessary exposure to radiation.

The radioactive dust that settles on the environment around us is an example of potential external exposure. Radionuclides that emit alpha and beta particles would pose a lower external exposure threat because they do not travel very far in the atmosphere and are not as penetrating as more energetic radiation. Shielding, one of the three principles of radiation protection, prevents some external exposure because alpha particles are blocked by the dead skin cells that sit on the surface of our bodies. Gamma rays, however, travel much farther in the atmosphere, and are higher energy rays that can only be blocked by heavy shielding, like a concrete wall or a lead apron. These rays pose a higher external exposure risk.

The Castle Bravo test of the Teller–Ulam design for a thermonuclear weapon was the first of many. The explosive yield of this bomb was 15 Megatons (Mt), which is 1000 times the explosive yield of the bomb dropped over Hiroshima, Japan. The explosive yield of this test was greater than twice that expected, causing radioactive fallout beyond the areas of the Marshall Islands that were previously evacuated. The effects of the radioactive fallout of this thermonuclear weapon test were described by Dr. S. Sevitt, Pathology Department, Birmingham Accident Hospital (Sevitt, 1955), who was a member of the international medical commission that visited Japan to investigate the effects of the atom bomb and the experimental hydrogen bomb explosions in the Marshall Islands. His assessment following the H-bomb explosion at Bikini in 1954 in the journal The Lancet are the following, with the author’s comments in brackets:

Perhaps even more important to the future of mankind than the terrible A-bombs in Japan have been the effects of the experimental H-bomb explosions at Bikini, the first of which took place in March, 1954. The experience of the ill-fated fishing-boat, Fukuryu Maru, which was heavily showered with radioactive dust for 4 hours whilst steaming 80–100 miles outside the “calculated danger zone” was merely an incident in the radioactive contamination of the Pacific Ocean and of the atmosphere. Radioactive rain fell all over Japan for months [3,600 km or 2,200 miles from ground zero of the Castle Bravo thermonuclear test on Bikini Atoll], particularly along the Pacific Coast and in the southern and central areas. In May, the radioactivity varied from 0.1 to 1.0 μCi per litre [3700 to 37,000 disintegration per second per liter]. This was associated with contamination of the atmosphere by radioactive dust which was falling to the ground and contaminating the soil. Radiochemical analysis of the rain at different institutions has shown that the radioactivity was due to a mixture of fission products similar to those detected in the Bikini ash collected from the deck of the Fukuryu Maru … In various parts of Japan radioactive rain and dust resulted in the contamination of many kinds of crops, all or most of which have been freely sold in the markets. Crop contamination was not only due to surface contamination of the leaves but also to absorption of radioactivity through the roots. In this way barley, wheat, rice, vegetables, and tea were contaminated—all the main crops in Japan. The degree of radioactivity was not high, but there was a definite or considerable excess of radioactivity in the tea, barley, rice, and wheat as compared with the 1952 and 1953 crops. In many places the rice crop, for example, was found to be 10–20 times more radioactive than in the preceding years … Thus, the whole Japanese people were eating radioactive fish, bread, rice, and vegetables, drinking radioactive tea, and inhaling radioactive dust in the air for months after the Bikini explosion. The dose per head of population was probably insufficient to cause acute radiation disease (except to the Marshall Islanders who have suffered the bloody diarrhoea, epilation, and leukopenia of radiation disease) but the cumulative action of continuous small doses of radiation upon the whole Japanese people (and no doubt upon the populations of other countries) will have unfavourable…effects.

Authors of a study published in 1990 in the Journal of the American Medical Association found nearly eight times more leukemia in children under 19 who lived in southwestern Utah during the aboveground testing. Later that decade, a National Cancer Institute study concluded that aboveground testing in Nevada may have produced as many as 212,000 “excess lifetime cases” of thyroid cancer, although some experts suggested that might be an undercount. Yet another study, conducted jointly in 2005 by the Centers for Disease Control and Prevention and the National Cancer Institute, found that any person living in the contiguous United States since 1951 has been exposed to radioactive fallout from testing. The United States conducted 1,054 atomic tests—costing more than $100 billion and taking an incalculable toll on humans and the environment. Potassium iodide pills are often given out during nuclear emergencies, actual or imminent. For example, the European Union pledged to pre-emptively donate more than five million anti-radiation tablets to Ukraine, amid fears of a Chernobyl-level catastrophe at the Russian-occupied, embattled Zaporizhzhia nuclear power plant.

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Section-15

Nuclear accidents:

A nuclear meltdown occurs when the core of a nuclear reactor melts due to an uncontrolled chain reaction, releasing a large amount of radiation and thermal energy. A meltdown can happen when the cooling system fails or is defective, causing the fuel rods to overheat and melt. The melting fuel, called corium, is highly radioactive and can remain hazardous for centuries. A nuclear and radiation accident is defined by the International Atomic Energy Agency (IAEA) as “an event that has led to significant consequences to people, the environment or the facility.” Examples include lethal effects to individuals, large radioactivity release to the environment, or a reactor core melt. The prime example of a “major nuclear accident” is one in which a reactor core is damaged and significant amounts of radioactive isotopes are released, such as in the Chernobyl disaster in 1986 and Fukushima nuclear disaster in 2011. Technical measures to reduce the risk of accidents or to minimize the amount of radioactivity released to the environment have been adopted, however human error remains, and “there have been many accidents with varying impacts as well near misses and incidents”. As of 2014, there have been more than 100 serious nuclear accidents and incidents from the use of nuclear power. Fifty-seven accidents or severe incidents have occurred since the Chernobyl disaster, and about 60% of all nuclear-related accidents/severe incidents have occurred in the USA. Stuart Arm states, “apart from Chernobyl, no nuclear workers or members of the public have ever died as a result of exposure to radiation due to a commercial nuclear reactor incident.” Nuclear submarine accidents include the K-19 (1961), K-11 (1965), K-27 (1968), K-140 (1968), K-429 (1970), K-222 (1980), and K-431 (1985) accidents. Serious radiation incidents/accidents include the Kyshtym disaster, Three Mile Island accident, the Windscale fire, the radiotherapy accident in Costa Rica, the radiotherapy accident in Zaragoza, the radiation accident in Morocco, the Goiania accident, the radiation accident in Mexico City, the Samut Prakan radiation accident, and the Mayapuri radiological accident in India. The IAEA maintains a website reporting recent nuclear accidents.

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Chernobyl Nuclear Disaster:

26th of April 1986 witnessed one of the world’s worst Nuclear Disaster ever in Chernobyl. Chernobyl is approximately 80 miles (which is 120 kilometers) north of the capital city of the Ukraine, Kiev. The accident took lives of 30 people immediately and vast evacuation of 135000 people within 20 mile radius of the power plant was carried out after the accident. Some 150,000 square kilometres in Belarus, Russia and Ukraine are contaminated and stretch northward of the plant site as far as 500 kilometres. An area spanning 30 kilometres around the plant is considered the “exclusion zone” and is essentially uninhabited. Radioactive fallout scattered over much of the northern hemisphere via wind and storm patterns, but the amounts dispersed were in many instances insignificant.

On April 26, 1986, the Number Four RBMK reactor at the nuclear power plant at Chernobyl, Ukraine, went out of control during a test at low-power, leading to an explosion and fire that demolished the reactor building and released large amounts of radiation into the atmosphere. Safety measures were ignored, the uranium fuel in the reactor overheated and melted through the protective barriers. RBMK reactors do not have what is known as a containment structure, a concrete and steel dome over the reactor itself designed to keep radiation inside the plant in the event of such an accident. Consequently, radioactive elements including plutonium, iodine, strontium and caesium were scattered over a wide area. In addition, the graphite blocks used as a moderating material in the RBMK caught fire at high temperature as air entered the reactor core, which contributed to emission of radioactive materials into the environment.

Radiation exposure:

Dose rates in the regions surrounding Reactor IV were highly variable due to distinct plumes of radioactive fallout released subsequent to the explosion. The first plume, designated the Western Trace, yielded doses in excess of 6 Gy/hour in some areas, resulting in the death of over 400 ha of pine (Pinus sylvestris) forest. Radiation doses to firemen and reactor personnel exposed shortly after the explosion reached as high as 15 Gy, leading to the deaths of 29 persons (two died as a direct result of the explosion) within 4 months. Exposure of children and adolescents to Chernobyl fallout has contributed to elevated cases of thyroid cancers in northern Ukraine and southern Belarus. Dose rates rapidly declined subsequent to the Chernobyl accident and ensuing fire. Most of the isotopes released had short half-lives, so their energy rapidly generated absorbed radiation doses. Ninety-eight percent of the isotopes released at Chernobyl has now dissipated. The predominant radionuclides remaining are 137Cs and 90Sr, each having half-lives of ∼30 years. These isotopes, however, have high biological affinities and are readily incorporated into living tissues. Because of this affinity, the animals living in the regions near the reactor (Red Forest) are the most radioactive organisms living in otherwise natural environments. Some rodents, for example, are receiving up to 0.1 Gy/day from caesium and strontium in their muscle and bone.

Major health effects for exposed populations:

There have been at least 1800 documented cases of thyroid cancer children who were between 0 and 14 years of age when the accident occurred., which is far higher than normal. The thyroid gland of young children is particularly susceptible to the uptake of radioactive iodine, which can trigger cancers, treatable both by surgery and medication. Health studies of the registered cleanup workers called in (so-called “liquidators”) have failed to show any direct correlation between their radiation exposure and an increase in other forms of cancer or disease. The psychological effects of Chernobyl were and remain widespread and profound, and have resulted for instance in suicides, drinking problems and apathy.

Radioactive elements emitted into the environment:

There were over 100 radioactive elements released into the atmosphere when Chernobyl’s fourth reactor exploded. Most of these were short lived and decayed (reduced in radioactivity) very quickly. Iodine, strontium and caesium were the most dangerous of the elements released, and have half-lives of 8 days, 29 years, and 30 years respectively. The isotopes Strontium-90 and Caesium-137 are therefore still present in the area to this day. While iodine is linked to thyroid cancer, Strontium can lead to leukaemia. Caesium is the element that travelled the farthest and lasts the longest. This element affects the entire body and especially can harm the liver and spleen.

What was done to ensure the safety of other RBMK reactors, so that this scenario will not present itself again?

Lessons learned from the accident were a significant driving force behind a decade of IAEA assistance to the countries of Central and Eastern Europe and the former Soviet Union. Much of this work focused on identifying the weaknesses in and improving the design safety of VVR and RBMK reactors. Upgrading was performed on all RBMK units to eliminate the design deficiencies which contributed to the Chernobyl accident, to improve shutdown mechanisms and heighten general safety awareness among staff. Just as important as the design safety work has been the focus on operational safety and on systems of regulatory oversight.

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Fukushima Daiichi Nuclear Disaster:

The Fukushima Daiichi nuclear disaster was a series of equipment failures, nuclear meltdowns, and releases of radioactive materials at the Fukushima I Nuclear Power Plant, following the Tohoku earthquake and tsunami on 11 March, 2011. It is the largest nuclear disaster since the Chernobyl disaster of 1986. The plant comprises six separate boiling water reactors originally designed by General Electric (GE), and maintained by the Tokyo Electric Power Company (TEPCO). At the time of the quake, Reactor 4 had been de-fuelled while 5 and 6 were in cold shutdown for planned maintenance. The remaining reactors shut down automatically after the earthquake, and emergency generators came online to control electronics and coolant systems. The tsunami resulted in flooding of the rooms containing the emergency generators. Consequently, those generators ceased working, causing eventual power loss to the pumps that circulate coolant water in the reactor. The pumps then stopped working, causing the reactors to overheat due to the high decay heat that normally continues for a short time, even after a nuclear reactor shut down. The flooding and earthquake damage hindered external assistance. In the hours and days that followed. Reactors 1, 2 and 3 experienced full meltdown. As workers struggled to cool and shut down the reactors, several hydrogen- air chemical explosions occurred. The hydrogen gas was produced by high heat in the reactors causing a hydrogen-producing reaction between the nuclear fuel metal cladding and the water surrounding them. An estimated 538.1 petabecquerels (PBq) of iodine-131, caesium-134 and caesium-137 was released. Fears of radioactivity releases led to a 20 km (12 mi)-radius evacuation around the plant. During the early days of the accident workers were temporarily evacuated at various times for radiation safety reasons. Electrical power was slowly restored for some of the reactors, allowing for automated cooling. There was one suspected death due to radiation, as one person died 4 years later of a lung cancer possibly triggered by it. Radiation exposure of those living in proximity to the accident site was estimated at 12–25 mSV in the year following the accident. Residents of Fukushima City were estimated to have received 4 mSv in the same time period. In comparison, the dosage of background radiation received over a lifetime is 170 mSv. Very few or no detectable cancers are expected as a result of accumulated radiation exposures.

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Hiroshima & Nagasaki versus Chernobyl & Fukushima:

Hiroshima and Nagasaki were rehabilitated after the atomic bomb attacks while Chernobyl and parts of Fukushima still remain uninhabitable to this day. Where do the ‎differences stem from?‎ What could be the possible reasons for this?

First, the bombs were exploded in the air to achieve maximum damage due to huge shock waves, so the products of the explosion were mainly pushed up into the atomic mushroom cloud. Both bombs were detonated more than 500 meters above street level so as to wreak maximum destruction (surrounding buildings would have blocked much of the force of ground-level explosions). That limited surface contamination, since most of the radioactive debris was carried off in the mushroom cloud instead of being embedded in the earth. There was plenty of lethal fallout in the form of “ashes of death” and “black rain,” but it was spread over a fairly wide area.

Second, the amount of radioactive material loaded onto the bombs was relatively small – seventy kilograms of uranium on the “Little Boy” and seven kilograms of plutonium on the “Fat Man”. By comparison, nuclear reactors contain several tons of radioactive material.

Finally, nuclear bombs are a one-time source of radiation, while the melting reactors continue to release large amounts of radiation even today, years after the disaster. Most of the radionuclides had brief half-lives — some lasting just minutes. The bomb sites were intensely radioactive for the first few hours after the explosions, but thereafter the danger diminished rapidly. Therefore, although we cannot compare the loss of life and property during disasters themselves, Hiroshima and Nagasaki were easy to rehabilitate and rebuild, while the Chernobyl and parts of Fukushima areas will remain abandoned and dangerous to live in for many years to come. Thanks to decontamination efforts and a gradual decline in airborne radiation dose rates, among other factors, the area of Fukushima under evacuation orders was reduced from 12% of the prefecture in 2011 to 2.2% in 2024. The 1986 disaster at the Chernobyl Nuclear Power Plant transformed the surrounding region into the most radioactive landscape known on the planet. It will not be habitable for humans for at least 20,000 years.

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Section-16

Nuclear power plant attack:

Vulnerability of nuclear plants to attack:

The vulnerability of nuclear plants to deliberate attack is of concern in the area of nuclear safety and security. Nuclear power plants, civilian research reactors, certain naval fuel facilities, uranium enrichment plants, fuel fabrication plants, and even potentially uranium mines are vulnerable to attacks which could lead to widespread radioactive contamination. The attack threat is of several general types: commando-like ground-based attacks on equipment which if disabled could lead to a reactor core meltdown or widespread dispersal of radioactivity; external attacks such as an aircraft crash into a reactor complex, or cyber attacks. If terrorist groups could sufficiently damage safety systems to cause a core meltdown at a nuclear power plant, and/or sufficiently damage spent fuel pools, such an attack could lead to widespread radioactive contamination. The Federation of American Scientists have said that if nuclear power use is to expand significantly, nuclear facilities will have to be made extremely safe from attacks that could release massive quantities of radioactivity into the community.

Population surrounding plants:

Population density is one critical lens through which risks have to be assessed. The KANUPP plant in Karachi, Pakistan, has the most people—8.2 million—living within 30 kilometres, although it has just one relatively small reactor with an output of 125 megawatts. Next in the league, however, are much larger plants—Taiwan’s 1,933-megawatt Kuosheng plant with 5.5 million people within a 30-kilometre radius and the 1,208-megawatt Chin Shan plant with 4.7 million; both zones include the capital city of Taipei.

172,000 people living within a 30 kilometre radius of the Fukushima Daiichi nuclear power plant had been forced or advised to evacuate the area. More generally, a 2011 analysis by Nature and Columbia University shows that some 21 nuclear plants have populations larger than 1 million within a 30-km radius, and six plants have populations larger than 3 million within that radius.

Various ways by which nuclear plants are attacked:

-1. Military attacks:

Nuclear reactors become preferred targets during military conflict and, over the past three decades, have been repeatedly attacked during military air strikes, occupations, invasions and campaigns.

-2. Vulnerabilities of nuclear reactors and waste-sites within war-zones:

Risks of nuclear energy systems aren’t limited to deliberate bombing/shelling of or near nuclear energy plants – nuclear energy systems within war-zones in general have various additional vulnerabilities. Deliberate or unintentional bombing/shelling of or near radioactive waste-sites is a further concern. These risks have become clearer during the 2022 Russian invasion of Ukraine.

-3. Nuclear terrorism:

Nuclear plants were designed to withstand earthquakes, hurricanes, and other extreme natural events. But deliberate attacks involving large airliners loaded with fuel, such as those that crashed into the World Trade Center and the Pentagon, were not considered when design requirements for today’s fleet of reactors were determined. The EU Commission’s research center (JRC) investigated in spring 2021 in a report and concluded that the terrorist risk of nuclear power plants is vanishingly small, and that even successful terrorism will have relatively insignificant consequences. JRC, finds that hydropower/dams and oil and gas infrastructure pose a significantly greater terrorist risk.

-4. Sabotage by insiders:

Insider sabotage regularly occurs, because insiders can observe and work around security measures. A deliberate fire caused between $5m and $10m worth of damage to New York’s Indian Point Energy Center in 1971. The arsonist turned out to be a plant maintenance worker. Sabotage by workers has been reported at many other reactors in the United States: at Zion Nuclear Power Station (1974), Quad Cities Nuclear Generating Station, Peach Bottom Nuclear Generating Station, Fort St. Vrain Generating Station, Trojan Nuclear Power Plant (1974), Browns Ferry Nuclear Power Plant (1980), and Beaver Valley Nuclear Generating Station (1981). Many reactors overseas have also reported sabotage by workers. Suspected arson has occurred in the United States and overseas.

-5. Civil disobedience:

Non-proliferation policy experts are concerned about the relative ease with which unarmed, unsophisticated protesters could cut through a fence and walk into the center of the facility. On December 5, 2011, two anti-nuclear campaigners breached the perimeter of the Cruas Nuclear Power Plant in France, escaping detection for more than 14 hours, while posting videos of their sit-in on the internet.

-6. Cyber-attacks:

Stuxnet is a computer worm discovered in June 2010 that is believed to have been created by the United States and Israel to attack Iran’s nuclear facilities. It switched off safety devices, causing centrifuges to spin out of control. The number and sophistication of cyber-attacks is on the rise. The computers of South Korea’s nuclear plant operator (KHNP) were hacked in December 2014.

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Military attack on nuclear power plant by nuclear weapon:

A gigawatt nuclear power plant may be a valuable industrial target in a nuclear war. If a targeting rationale is proposed that the largest possible amount of gross national product be destroyed in an attack on a nation’s industry (one measure of the worth of a target to a nation), then large (~1000 MW(e)) nuclear power plants could become priority targets for relatively small (kt) strategic weapons (Chester and Chester, 1976). In the United States there are about 100 such targets, and worldwide there are about 300. There are also military nuclear reactors and weapons facilities that could be targeted. Since these facilities may be targeted, reactor-generated radioactivity should be considered as part of the potential postattack radiological problem.

Whether the radioactivity contained in a reactor vessel can be dispersed in a manner similar to a weapon’s radioactivity is debatable. Nuclear reactor cores are typically surrounded by a 1-m-thick reinforced concrete building that has about a 1-cm-thick inner steel lining, many heavy steel structural elements inside the containment building, and an approximately 10-cm-thick reactor vessel. Inside the reactor vessel are fuel rods and cladding capable of withstanding high temperatures and pressures. For the core radioactivity to be dispersed in the same way’ as the weapon’s radioactivity, all of these barriers must be breached. The core itself must be at least fragmented, and possibly vaporized, and then entrained into the rising nuclear cloud column along with possibly hundreds of kilotons of fragmented and vaporized dirt and other materials from the crater and nearby structures, including the thick concrete slab that supports the reactor building. Under certain conditions of damage, there is a possibility of a reactor core meltdown resulting in the release of some of the more volatile radionuclides to the local environment. If this were to occur, however, the area of contamination would be relatively small compared to the contamination by a reactor core if it were to be pulverized and lofted by a nuclear explosion.

The primary contributor to the long-term radiation dose at a nuclear power plant would not be the core. The most hazardous radioactivity, when assessing long-term effects (year after attack), is that held in the spent-fuel ponds, if the reactor has been operating at full power for a few years. Since the spent-fuel storage usually has no containment building nor reactor vessel to be breached, it is much more vulnerable to being lofted by a nuclear weapon than are the core materials. Unless spent fuel is located at sufficient distance from a reactor, it could potentially become part of the local fallout problem.

Other nuclear fuel cycle radioactivity may also be significant. Reprocessing plants, although not as immediately important economically as power plants, contain a great deal of radioactivity that could significantly contribute to the long-term radiation doses. Also, military nuclear reactors developing fissile material and their reprocessing plants might be important wartime targets. They also hold significant amounts of radioactivity in their waste ponds and reactor cores.

A study found that using some worst-case assumptions for a speculative nuclear war scenario wherein 100 GW(e) of the nuclear power industry is included in the target list, the 50-year global fallout dose is estimated to increase by a factor of 3 over similar estimates wherein nuclear power facilities are not attacked.

If one adds the internal doses necessarily accompanying the external doses (perhaps doubling or tripling the latter) and considers that localized hotspots can be formed with up to 10 times the average dose, it seems that moderate to heavy attacks on civilian and military nuclear facilities could result in significant long-term radiological problems for humans and ecosystems. Many of these problems involving the radiological assessments associated with nuclear facilities are unresolved and uncertain but deserve more thorough attention.

Nobel laureate nuclear physicist Joseph Rotblat demonstrated the dangers posed by nuclear attack on nuclear reactors. The decay of radioactivity of a nuclear reactor is much slower than that following a nuclear explosion, because of a greater inventory of long-lived isotopes. An attack on a nuclear power plant or fuel storage tank would result in greater and longer-lived radioactivity release than following an attack alone (Table below).

Areas affected by detonation of nuclear weapons alone and on nuclear power facilities:

Radiation dose between 1 month and 1 year after detonation (Gray)	Area (square km) 1 Mt bomb	1 Mt bomb on a 1000 MW reactor	1 Mt bomb on a spent fuel storage tank
1	2000	34,000	61,000
0.1	25,000	122,000	164,000

Mt –million tons TNT equivalent explosive power; MW – million watts electricity output; 1 Gray is a substantial radiation dose, often resulting in acute radiation sickness; 0.1 Gy (100 mGy) is equivalent to 100 times the recommended annual dose limit for a member of the public, about 1000 chest X-rays, or about 40 years of natural background radiation.

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Section-17

Physical effects of nuclear weapon explosion:

Note:

Please read glossary about nuclear weapon & nuclear explosion; and glossary and measurement for Radiation Exposure in section 1 to get acquainted with very basics and terminology.

Nuclear weapons are fundamentally different from conventional weapons because of the vast amounts of explosive energy they can release and the kinds of effects they produce, such as high temperatures and radiation. The prompt effects of a nuclear explosion and fallout are well known through data gathered from the attacks on Hiroshima and Nagasaki in Japan; from more than 500 atmospheric and more than 1,500 underground nuclear tests conducted worldwide; and from extensive calculations and computer modeling. Longer-term effects on human health and the environment are less certain but have been extensively studied. The impacts of a nuclear explosion depend on many factors, including the design of the weapon (fission or fusion) and its yield; whether the detonation takes place in the air (and at what altitude), on the surface, underground, or underwater; the meteorological and environmental conditions; and whether the target is urban, rural, or military.

Nuclear vs. Conventional explosion:

In general terms, an explosion is a rapid release of a large amount of energy within a limited space.

There are five basic differences between nuclear and conventional explosion:

-Nuclear explosions are caused by an unrestrained fission reaction (or fission plus fusion) whereas conventional explosions are caused by chemical reactions.

-Nuclear explosions can be millions of times more powerful than the largest conventional explosions.

-Nuclear explosions create much higher temperatures and much brighter light flashes than conventional explosions, to the extent that skin burns and fires can occur at considerable distances.

-Nuclear explosions are accompanied by highly penetrating and harmful radiation.

-Radioactive debris is spread by a nuclear blast, to the extent that lethal exposures can be received long after the explosion occurs.

Main types of effects from nuclear weapons detonation:

Fireball: x-rays instantly create large sphere tens of millions of degrees hot
EMP: instantaneously creates electromagnetic pulse that can destroy or disrupt electronic equipment
Heat and light wave: causes fires and burns in seconds (fires can significantly add to effects)
Prompt nuclear radiation: harmful to life and damaging to electronic equipment
Air blast wave (lower atmosphere): hundreds of miles per hour winds
Shock wave (surface or near-surface burst): causes damage to underground structures
Residual nuclear radiation: emitted over extended period of time
Electronic: extended interference of communications equipment

The energy of a nuclear explosion is released in a number of different ways:

-an explosive blast, which is qualitatively similar to the blast from ordinary chemical explosions, but which has somewhat different effects because it is typically so much larger;

-direct nuclear radiation;

-direct thermal radiation, most of which takes the form of infrared and visible light;

-pulses of electrical and magnetic energy, called electromagnetic pulse (EM P); and

-the creation of a variety of radioactive particles, which are thrown up into the air by the force of the blast, and are called radioactive fallout when they return to Earth.

The distribution of the bomb’s energy among these effects depends on its size and on the details of its design, but a general description is possible as seen in the figure below:

Nuclear explosions produce both immediate and delayed destructive effects. Immediate effects (blast, thermal radiation, prompt ionizing radiation) are produced and cause significant destruction within seconds or minutes of a nuclear detonation. The delayed effects (radioactive fallout and other possible environmental effects) inflict damage over an extended period ranging from hours to centuries, and can cause adverse effects in locations very distant from the site of the detonation.

When a nuclear weapon detonates, a fireball occurs with temperatures higher than those at the center of the Sun. The energy emitted takes several forms. Approximately 85 percent of the explosive energy produces air blast (and shock) and thermal radiation (heat). The remaining 15 percent is released as initial radiation, produced within the first minute or so, and residual (or delayed) radiation, emitted over a period of time, some of which can be in the form of local fallout. Despite the fact that several nuclear weapon designs exist, the effects of nuclear explosions are essentially the same for all types. In particular, the intensity of nuclear weapon effects depends almost entirely on the bomb’s yield. However, the effects vary depending on the environment in which the explosion occurs (outer space, the atmosphere, underwater, or underground). Most discussions of nuclear weapon effects refer to weapons that detonate within the atmosphere because, if nuclear war ever did occur, this would be the most common type of explosion.

When a nuclear weapon explodes, the kinetic energy from the fission fragments, neutrons, and helium (for fusion reactions) heat the weapon debris to approximately 100 million degrees centigrade within a few microseconds. This hot core radiates energy like the coals in one’s fireplace. However, because the temperature is so high the radiation is in the x-ray band of the electromagnetic spectrum. As the hot core expands, it begins to cool. The result is a huge sphere of very hot air or fireball (approximately 1 mile in diameter for a 1-MT explosion) that begins to rise, eventually creating the mushroom cloud so often associated with nuclear explosions.

The most immediate effect of a nuclear explosion is an intense burst of nuclear radiation, primarily gamma rays and neutrons. This direct radiation is produced in the weapon’s nuclear reactions themselves, and lasts well under a second. Lethal direct radiation extends nearly a mile from a 10-kiloton explosion. With most weapons, though, direct radiation is of little significance because other lethal effects generally encompass greater distances. An important exception is the enhanced-radiation weapon, or neutron bomb, which maximizes direct radiation and minimizes other destructive effects.

An exploding nuclear weapon instantly vaporizes itself. What was cold, solid material microseconds earlier becomes a gas hotter than the Sun’s 15-million-degree core. This hot gas radiates its energy in the form of X-rays, which heat the surrounding air. A fireball of superheated air forms and grows rapidly; 10 seconds after a 1-megaton explosion, the fireball is a mile in diameter. The fireball glows visibly from its own heat — so visibly that the early stages of a 1-megaton fireball are many times brighter than the Sun even at a distance of 50 miles. Besides light, the glowing fireball radiates heat. This thermal flash lasts many seconds and accounts for more than one-third of the weapon’s explosive energy. The intense heat can ignite fires and cause severe burns on exposed flesh as far as 20 miles from a large thermonuclear explosion. Two-thirds of injured Hiroshima survivors showed evidence of such flash burns. You can think of the incendiary effect of thermal flash as analogous to starting a fire using a magnifying glass to concentrate the Sun’s rays. The difference is that rays from a nuclear explosion are so intense that they don’t need concentration to ignite flammable materials. The intense heat can ignite fires and cause severe burns on exposed flesh as far as 20 miles from a large thermonuclear explosion.

A fraction of a second after a nuclear explosion, the heat from the fireball causes a high-pressure wave to develop and move outward producing the blast effect. The front of the blast wave, i.e., the shock front, travels rapidly away from the fireball, a moving wall of highly compressed air. The air immediately behind the shock front is accelerated to high velocities and creates a powerful wind. These winds in turn create dynamic pressure against the objects facing the blast. Shock waves cause a virtually instantaneous jump in pressure at the shock front. The combination of the pressure jump (called the overpressure) and the dynamic pressure causes blast damage.

Ultimately, the energy from a nuclear explosion appears as five weapon effects: blast, thermal radiation, prompt nuclear radiation, fallout, and an electromagnetic pulse.

Surface targets are destroyed by combination of heat and blast wave as seen in the figure below.

Thermal radiation and blast are inevitable consequences of the near instantaneous release of an immense amount of energy in a very small volume, and are thus characteristic to all nuclear weapons regardless of type or design details. The release of ionizing radiation, both at the instant of explosion and delayed radiation from fallout, is governed by the physics of the nuclear reactions involved and how the weapon is constructed, and is thus very dependent on both weapon type and design.

For an explosion in the atmosphere, the fireball quickly expands to maximum size and then begins to cool as it rises like a balloon through buoyancy in the surrounding air. As it does so, it takes on the flow pattern of a vortex ring with incandescent material in the vortex core. Heat rises, and the incredible blast of heat and energy from an explosive fireball quickly ascends through the atmosphere, creating a vacuum in its wake. This vacuum is immediately filled with smoke and debris, forming the visible central column of what will become the mushroom cloud. Mushroom cloud height depending on yield for ground bursts as seen in the figure below:

The heat and airborne debris created by a nuclear explosion can cause rain; the debris is thought to do this by acting as cloud condensation nuclei. During the city firestorm which followed the Hiroshima explosion, drops of water were recorded to have been about the size of marbles. This was termed black rain and has served as the source of a book and film by the same name. Black rain is not unusual following large fires and is commonly produced by pyrocumulus clouds during large forest fires. The rain directly over Hiroshima on that day is said to have begun around 9 a.m. with it covering a wide area from the hypocenter to the northwest, raining heavily for one hour or more in some areas. The rain directly over the city may have carried neutron activated building material combustion products, but it did not carry any appreciable nuclear weapon debris or fallout, although this is generally to the contrary to what other less technical sources state. The “oily” black soot particles, are a characteristic of incomplete combustion in the city firestorm.

The description of nuclear weapon effects given in the preceding paragraphs is for a single nuclear explosion. However, nuclear Armageddon results not from a single explosion, devastating as that might be, but from the effects of hundreds or thousands of explosions. A single nuclear bomb can certainly destroy a large military facility or a small city; however, it can take tens of nuclear bombs to destroy a large city, around 500 300-KT nuclear weapons to promptly kill half the US urban population, and more to destroy the military facilities within a large country like the United States or Russia.

Other effects must be considered if a large number of explosions occur. Global fallout and ‘nuclear winter’ – the hypothesis that dust carried aloft by hundreds or thousands of mushroom clouds would cause global freezing temperatures, which upon re-analysis appears to be more like ‘nuclear fall’ with temperatures dropping by 5–15° C over large portions of the northern hemisphere for several months or more – are probably not more serious than the direct effects of a large number of nuclear explosions. However, widespread social and economic collapse may cause severe problems. Medical support, food, and energy supplies may disappear because the transportation infrastructure could be severely disrupted and political and financial institutions may collapse. This could lead to widespread starvation, epidemics, and political instability or civil war. Obviously, the magnitude of such effects is difficult to determine and will depend on the size and scope of a large-scale nuclear war.

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Types of nuclear explosions:

The immediate phenomena associated with a nuclear explosion, as well as the effects of shock and blast and of thermal and nuclear radiations, vary with the location of the point of burst in relation to the surface of the earth. For descriptive purposes five types of bursts are distinguished, although many variations and intermediate situations can arise in practice. The main types are (l) air burst, (2) high-altitude burst, (3) underwater burst, (4) underground burst, and (5) surface burst.

It might seem logical that the most destructive way of using a nuclear weapon would be to explode it right in the middle of its target – i.e. ground level. But for most uses this is not true. Generally nuclear weapons are designed to explode above the ground – as air bursts (the point directly below the burst point is called the hypocenter). Surface (and sub-surface) bursts can be used for special purposes.

Air Bursts:

Provided the nuclear explosion takes place at an altitude where there is still an appreciable atmosphere, e.g., below about 100,000 feet, the weapon residues almost immediately incorporate material from the surrounding medium and form an intensely hot and luminous mass, roughly spherical in shape, called the “fireball.” An “air burst” is defined as one in which the weapon is exploded in the air at an altitude below 100,000 feet, but at such a height that the fireball (at roughly maximum brilliance in its later stages) does not touch the surface of the earth. For example, in the explosion of a I-megaton weapon the fireball may grow until it is nearly 5,700 feet (1.1 mile) across at maximum brilliance. This means that, in this particular case, the explosion must occur at least 5,700 feet above the earth’s surface if it is to be called an air burst.

When an explosion occurs it sends out a shock wave like an expanding soap bubble. If the explosion occurs above the ground the bubble expands and when it reaches the ground it is reflected – i.e. the shock front bounces off the ground to form a second shock wave travelling behind the first. This second shock wave travels faster than the first or direct shock wave since it is travelling through air already moving at high speed due to the passage of the direct wave. The reflected shock wave tends to overtake the direct shock wave and when it does they combine to form a single reinforced wave. The reflected blast wave merges with the incident shock wave to form a single wave, known as the Mach Stem. The overpressure at the front of the Mach wave is generally about twice as great as that at the direct blast wave front. Because of this, air blast is maximized with a low air burst rather than a surface burst.

Figure below shows the development of a 1-Mt airburst detonated at an altitude of 6,500 feet (about 2 km) at five distinct points of time during the process.

The sequence of events for a 1-Mt airburst detonated at 6,500 feet (about 2 km) altitude are shown in A through E. This altitude maximizes the range from ground zero at which the primary and secondary shock waves coalesce to give a 15-psi peak overpressure on the ground. By adjusting the detonation altitude to 11,000 feet (about 3,353 m), the 5-psi distance could be increased from 3.8 to 4.3 miles (about 6 to 7 km), but the 15-psi range would shrink to near zero.

The higher the burst altitude, the weaker the shock wave is when it first reaches the ground. On the other hand, the shock wave will also affect a larger area. Air bursts therefore reduce the peak intensity of the shock wave, but increase the area over which the blast is felt. For a given explosion yield, and a given blast pressure, there is a unique burst altitude at which the area subjected to that pressure is maximized. This is called the optimum burst height for that yield and pressure.

All targets have some level of vulnerability to blast effects. When some threshold of blast pressure is reached the target is completely destroyed. Subjecting the target to pressures higher than that accomplishes nothing. By selecting an appropriate burst height, an air burst can destroy a much larger area for most targets than can surface bursts. The Mach Effect enhances shock waves with pressures below 50 psi. At or above this pressure the effect provides very little enhancement, so air bursts have little advantage if very high blast pressures are desired.

An additional effect of air bursts is that thermal radiation is also distributed in a more damaging fashion. Since the fireball is formed above the earth, the radiation arrives at a steeper angle and is less likely to be blocked by intervening obstacles and low altitude haze.

High altitude blast:

A “high-altitude burst” is defined as one in which the explosion takes place at an altitude in excess of 100,000 feet. Above this level, the air density is so low that the interaction of the weapon energy with the surroundings is markedly different from that at lower altitudes and, moreover, varies with the altitude. The absence of relatively dense air causes the fireball characteristics in a high-altitude explosion to differ from those of an air burst. For example, the fraction of the energy converted into blast and shock is less and decreases with increasing altitude. Two factors affect the thermal energy radiated at high altitude. First, since a shock wave does not form so readily in the less dense air, the fireball is able to radiate thermal energy that would, at lower altitudes, have been used in the production of air blast. Second, the less dense air allows energy from the exploding weapon to travel much farther than at lower altitudes. Some of this energy simply warms the air at a distance from the fireball and it does not contribute to the energy that can be radiated within a short time. In general, the first of these factors is effective between 100,000 and 140,000 feet, and a larger proportion of the explosion energy is released in the form of thermal radiation than at lower altitudes. For explosions above about 140,000 feet, the second factor becomes the more important, and the fraction of the energy that appears as thermal radiation at the time of the explosion becomes smaller.

When the bomb is exploded outside the atmosphere, generally any altitude above about 100 kilometres (330,000 ft), the lack of interaction with the air changes the nature of the fireball formation. In this case, the various subatomic particles can travel arbitrary distances, and continue to outpace the expanding bomb debris. The lack of atmosphere also means that no shockwave forms, and it is only the glowing bomb debris themselves that forms the fireball. In these sorts of explosions, the fireball itself is not a significant radar issue, but the particles’ interactions with the atmosphere below them causes a number of secondary effects that are just as effective at blocking radar as a fireball at low altitude.

A nuclear bomb detonated on the ground:

A ground-level explosion would create a gigantic crater ––a major difference from an explosion in the urban sky. Rocks, dirt, and masonry would turn into radioactive dust and debris. Larger particulates would settle rapidly and finer ones more slowly, primarily downwind from the explosion. Compared to an airburst, the blast would probably cause damage to an area half the size. Extra structural damage would affect buildings as if there had been an earthquake. Although immediate deaths would probably number half those from an airburst, many would die of radiation sickness, especially survivors who had no shelter from fallout. An explosion at a harbor would also create a crater –and a tidal wave. Most harbor water would turn radioactive, spray into the sky, and cause radioactive downpour. Thus, severe radioactive fallout would probably render the city, along with affected downwind regions up to 10 km, uninhabitable for years.

Destruction of underground facilities require ground- or shallow sub-surface bursts to ensure shock wave causes an underground fracture or “damage zone”. In a sub-surface burst the shock wave moving upward is trapped by the surface material and reflected downward where it reinforces the original chock wave. This “coupling” effect enables an earth-penetrator to destroy underground targets 2-5 times deeper than ground burst weapons.

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Fireball:

The fireball, an extremely hot and highly luminous spherical mass of air and gaseous weapon residues, occurs within less than one millionth of one second of the weapon’s detonation as the result of the absorption by the surrounding medium of the thermal X rays emitted by the extremely hot (several tens of million degrees) weapon residues. Initially, the fireball contains a highly ionized plasma consisting only of atoms of the weapon, its fission products, and atmospheric gases of adjacent air. As the plasma cools, the atoms react, forming fine droplets and then solid particles of oxides.

Figure below shows trinity test fireball:

As this incandescent ball of hot gas expands, it radiates part of its energy away as thermal radiation (including visible and ultraviolet light), part of its energy also goes into creating a shock wave or blast wave in the surrounding environment. The generation of these two destructive effects are thus closely linked by the physics of the fireball.

Immediately after its formation, the fireball begins to grow in size, engulfing the surrounding air. This growth is accompanied by a decrease in temperature because of the accompanying increase in mass. At the same time the fireball rises, like a hot-air balloon. Within seven-tenths of one millisecond from the detonation, the fireball from a 1-megaton weapon is about 440 feet across, and this increases to a maximum value of about 5,700 feet in 10 seconds. It is then rising at a rate of 250 to 350 feet per second. After a minute, the fireball has cooled to such an extent that it no longer emits visible radiation. It has then risen roughly 4.5 miles from the point of burst.

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The Energy from a Nuclear Weapon:

One of the fundamental differences between a nuclear and a conventional explosion is that nuclear explosions can be many thousands (or millions) of times more powerful than the largest conventional detonations. Both types of weapons rely on the destructive force of the blast or shock wave. However, the temperatures reached in a nuclear explosion are very much higher than in a conventional explosion, and a large proportion of the energy in a nuclear explosion is emitted in the form of light and heat, generally referred to as thermal energy. This energy is capable of causing skin burns and of starting fires at considerable distances. Nuclear explosions are also accompanied by various forms of radiation, lasting a few seconds to remaining dangerous over an extended period of time.

Depending on the design of the weapon and the location in which it is detonated, the energy distributed to any one of these categories may be significantly higher or lower. The physical blast effect is created by the coupling of immense amounts of energy, spanning the electromagnetic spectrum, with the surroundings. The environment of the explosion (e.g. submarine, ground burst, air burst, or exo-atmospheric) determines how much energy is distributed to the blast and how much to radiation. In general, surrounding a bomb with denser media, such as water, absorbs more energy and creates more powerful shock waves while at the same time limiting the area of its effect. When a nuclear weapon is surrounded only by air, lethal blast and thermal effects proportionally scale much more rapidly than lethal radiation effects as explosive yield increases. This bubble is faster than the speed of sound. The physical damage mechanisms of a nuclear weapon (blast and thermal radiation) are identical to those of conventional explosives, but the energy produced by a nuclear explosion is usually millions of times more powerful per unit mass, and temperatures may briefly reach the tens of millions of degrees.

The energy breakdown from a nuclear explosion is depicted in figure below:

Approximately 85 percent of the energy of a nuclear weapon produces air blast (and shock), thermal energy (thermal radiation). The remaining 15 percent of the energy is released as various type of nuclear radiation. Of this, 5 percent constitutes the initial nuclear radiation, defined as that produced within a minute or so of the explosion, are mostly gamma rays and neutrons. The final 10 percent of the total fission energy represents that of the residual (or delayed) nuclear radiation, which is emitted over a period of time. This is largely due to the radioactivity of the fission products present in the weapon residues, or debris, and fallout after the explosion.

The three categories of immediate effects are: blast, thermal radiation, and prompt ionizing or nuclear radiation. Their relative importance varies with the yield of the bomb. At low yields, all three can be significant sources of injury. With an explosive yield of about 2.5 kt, the three effects are roughly equal. All are capable of inflicting fatal injuries at a range of 1 km. This is based on thermal radiation just sufficient to cause 3rd degree burns (8 calories/cm^2); a 4.6 psi blast overpressure (and optimum burst height); and a 500 rem radiation dose.

A convenient rule of thumb for estimating the short-term fatalities from all causes due to a nuclear attack is to count everyone inside the 5 psi blast overpressure contour around the hypocenter as a fatality. In reality, substantial numbers of people inside the contour will survive and substantial numbers outside the contour will die, but the assumption is that these two groups will be roughly equal in size and balance out. This completely ignores any possible fallout effects.

The Area Affected:

The area affected depends on the yield of the nuclear device, the topography at the explosion site (buildings and geological structures), the altitude of the explosion, and weather conditions. The general pattern of damage for a 10-kT bomb, is as follows:

Initial effects (or prompt effects) of the nuclear explosion—the shockwave, thermal (heat) energy, and initial radiation—cover an approximately circular area of devastation. Effects decrease with distance from ground zero. For nuclear devices with a higher yield, heat damage becomes the primary initial effect of concern, eclipsing both the damage from the shockwave and the initial radiation.
Radioactive fallout spreads in an irregular elliptical pattern in the direction the wind blows. The most dangerous fallout would occur near the explosion site within minutes of the explosion, but fallout carrying lethal radiation doses could be deposited several miles away. Fallout could potentially travel hundreds of miles, but its concentration and radiation dose decrease as it spreads and as time passes.

Figure above represents the general patterns of damage from a 10-kT nuclear explosion on the ground. The destruction from the initial effects— shockwave, thermal (heat) energy, and initial radiation—expands in a circular pattern. Severe shockwave damage could extend to about a half a mile. Severe thermal damage would extend out about a mile. Flying debris could extend up to a few miles. Initial (prompt) nuclear radiation for a 10-kT blast could expose unprotected people within about 3/4 mile of the explosion site to a lethal radiation dose. Radioactive fallout occurs in an irregular elliptical pattern in the direction the wind is blowing; lethal radiation could extend up to 6 miles.

Scaling laws for the destructive radius:

The underlying principles behind these scaling laws are easy to explain. The fraction of a bomb’s yield emitted as thermal radiation, blast, and ionizing radiation are essentially constant for all yields, but the way the different forms of energy interact with air and targets vary dramatically.

Air is essentially transparent to thermal radiation. The thermal radiation affects exposed surfaces, producing damage by rapid heating. A bomb that is 100 times larger can produce equal thermal radiation intensities over areas 100 times larger. The area of an (imaginary) sphere centered on the explosion increases with the square of the radius. A = 4 π r^2 Thus the destructive radius increases with the square root of the yield (this is the familiar inverse square law of electromagnetic radiation). Actually the rate of increase is somewhat less, partly due to the fact that larger bombs emit heat more slowly which reduces the damage produced by each calorie of heat. It is important to note that the area subjected to damage by thermal radiation increases almost linearly with yield.

Blast effect is a volume effect. The blast wave deposits energy in the material it passes through, including air. When the blast wave passes through solid material, the energy left behind causes damage. When it passes through air it simply grows weaker. The more matter the energy travels through, the smaller the effect. The amount of matter increases with the volume of the imaginary sphere centered on the explosion. Blast effects thus scale with the inverse cube law which relates radius to volume. V = 4/3 π r^3

The intensity of nuclear radiation decreases with the inverse square law like thermal radiation. However nuclear radiation is also strongly absorbed by the air it travels through, which causes the intensity to drop off much more rapidly.

These scaling laws show that the effects of thermal radiation grow rapidly with yield (relative to blast), while those of nuclear radiation rapidly decline due to absorption by air.

With bombs bigger than 10-100 kilotons (kt), the radiation lethal area may be smaller than the blast and heat lethal areas, as can be seen in table below.

Table below shows areas of Lethal Damage from various effects (km2) correlation with explosive yield:

Type of Damage	1 kt	10 kt	100 kt	1 Mt	10 Mt
Blast	1.5	4.9	22	104	480
Heat	1.1	10.5	60	350	1,300
Initial radiation	2.9	5.7	11	22	54

If the blast and heat lethal zones extend beyond the radiation lethal zone, the mean radiation dose to the survivors will be relatively smaller.

How far do a weapon’s destructive effects (blast damage) extend?

That distance — the radius of destruction — depends on the explosive yield. The volume encompassing a given level of destruction depends directly on the weapon’s yield. Because volume is proportional to the radius cubed, that means the destructive radius grows approximately as the cube root of the yield. A 10-fold increase in yield then increases the radius of destruction by a factor of only a little over two.

Figure below shows destructive radii of 100-kiloton, 1-megaton, and 10-megaton weapons superimposed on a map of the New York City area. The destructive radius is defined as the distance within which blast overpressure exceeds 5 pounds per square inch, and it measures 2 miles, 4.4 miles, and 9.4 miles for the weapon yields shown. These values assume air-burst explosions at optimum altitudes over Central Park.

In the Hiroshima attack (bomb yield approx. 15 kt) casualties (including fatalities) were seen from all three causes. Burns (including those caused by the ensuing fire storm) were the most prevalent serious injury (two thirds of those who died the first day were burned), and occurred at the greatest range. Blast and burn injuries were both found in 60-70% of all survivors. People close enough to suffer significant radiation illness were well inside the lethal effects radius for blast and flash burns, as a result only 30% of injured survivors showed radiation illness. Many of these people were sheltered from burns and blast and thus escaped their main effects. Even so, most victims with radiation illness also had blast injuries or burns as well.

With yields in the range of hundreds of kilotons or greater (typical for strategic warheads) immediate radiation injury becomes insignificant. Dangerous radiation levels only exist so close to the explosion that surviving the blast is impossible. On the other hand, fatal burns can be inflicted well beyond the range of substantial blast damage. A 20 megaton bomb can cause potentially fatal third degree burns at a range of 40 km, where the blast can do little more than break windows and cause superficial cuts.

Equivalent megaton (EMT):

EMT is a measure of destructive power in area rather than radius of destruction. When a bomb explodes it will destroy things in all directions including up and down, but for the purposes of destroying cities, the metric that matters is how much surface area on the earth is destroyed, and this is what EMT is meant to quantify. If we model the destruction zone as a sphere and suppose that the volume of the region of space which is destroyed by a bomb is directly proportional to its yield, then mathematically the volume of destruction is related to the yield as seen in equation below:

4/3πR^3 ∝ Y

From this we can see that the radius of destruction R is related to yield as R ∝ Y^1/3

The surface area of a sphere is the total area of its outer surface, and is calculated using the formula SA = 4πR^2 so everything on the surface of the earth within that radius will be destroyed. Therefore the surface area of destruction is proportional to square of radius which in turn is proportional to cube root of yield. So surface area of destruction is proportional to yield (cube root x cube root) as A∝ Y^2/3

So we see that the surface cleaning power of the bomb is related to yield to the power of 2/3. EMT is defined as this quantity Y^2/3 as to quantify the power of a bomb in this context. Intuitively, if the EMT of a bomb is doubled then the size of area which it destroys is doubled.

In evaluating the destructive power of a weapons system, it is customary to use the concept of equivalent megatons (EMT). Equivalent megatonnage is defined as the actual megatonnage raised to the two-thirds power as calculated above:

EMT = Y^2/3 where Y is in megatons or kilotons.

This relation arises from the fact that the destructive power of a bomb does not vary linearly with the yield. The area of destruction grows faster but still not in direct proportion to the yield. That relatively slow increase in destruction with increasing yield is one reason why multiple smaller weapons are more effective than a single larger one. Thus 1 bomb with a yield of 1 megaton would destroy 80 square miles. While 8 bombs, each with a yield of 125 kilotons, would destroy 160 square miles. This relationship is one reason for the development of delivery systems that could carry multiple warheads (MIRVs).

Note:

The blast destructive radius grows approximately as the cube root of the yield while the blast destructive area grows approximately as the 2/3 root of the yield.

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Blast wave (shock wave):

An explosion, in general, results from the very rapid release of a large amount of energy within a limited space. This is true for a conventional high explosive such as TNT, as well as for a nuclear (or atomic) explosion, although the energy is produced in quite different ways. The sudden liberation of energy causes a considerable increase of temperature and pressure, so that all the materials present are converted into hot, compressed gases. Since these gases are at very high temperatures and pressures, they expand rapidly and thus initiate a pressure wave, called a “shock wave,” in the surrounding medium—air, water, or earth. The characteristic of a shock wave is that there is (ideally) a sudden increase of pressure at the front, with a gradual decrease behind it, as shown in figure below. A shock wave in air is generally referred to as a “blast wave” because it resembles and is accompanied by a very strong wind. In water or in the ground, however, the term “shock” is used, because the effect is like that of a sudden impact.

Figure below shows variation of pressure (in excess of ambient) with distance in an ideal shock wave:

As the blast wave travels in the air away from its source, the overpressure at the front steadily decreases, and the pressure behind the front falls off in a regular manner. After a short time, when the shock front has travelled a certain distance from the fireball, the pressure behind the front drops below that of the surrounding atmosphere and a so-called “negative phase” of the blast wave forms. In this region the air pressure is below that of the original (or ambient) atmosphere, so that an “underpressure” rather than an overpressure exists. During the negative (rarefaction or suction) phase, a partial vacuum is produced and the air is sucked in, instead of being pushed away from the explosion as it is when the overpressure is positive. At the end of the negative phase, which is somewhat longer than the positive phase, the pressure has essentially returned to ambient.

Most of the material damage caused by a nuclear explosion at the surface or at a low or moderate altitude in the air is due—directly or indirectly—to the shock (or blast) wave which accompanies the explosion. Many structures will suffer some damage from air blast when the overpressure in the blast wave, i.e., the excess over the atmospheric pressure (14.7 pounds per square inch at standard sea level conditions), is about one-half pound per square inch or more. The distance to which this overpressure level will extend depends primarily on the energy yield of the explosion, and on the height of the burst.

As the rapidly expanding fireball pushes into the surrounding air, it creates a blast wave consisting of an abrupt jump in air pressure. The blast wave moves outward initially at thousands of miles per hour but slows as it spreads. It carries about half the bomb’s explosive energy and is responsible for most of the physical destruction. Normal air pressure is about 15 pounds per square inch (psi). That means every square inch of your body or your house experiences a force of 15 pounds. You don’t usually feel that force, because air pressure is normally exerted equally in all directions, so the 15 pounds pushing a square inch of your body one way is counterbalanced by 15 pounds pushing the other way. If you’ve ever tried to open a door against a strong wind, you’ve experienced overpressure. An overpressure of even 1/100 psi could make a door almost impossible to open. That’s because a door has lots of square inches — about 3,000 or more. So 1/100 psi adds up to a lot of pounds. The blast wave of a nuclear explosion may create overpressures of several psi many miles from the explosion site. Think about that! There are about 50,000 square inches in the front wall of a modest house — and that means 50,000 pounds or 25 tons of force even at 1 psi overpressure. Overpressures of 5 psi are enough to destroy most residential buildings. An overpressure of 10 psi collapses most factories and commercial buildings, and 20 psi will level even reinforced concrete structures.

People, remarkably, are relatively immune to overpressure itself. But they aren’t immune to collapsing buildings or to pieces of glass hurtling through the air at hundreds of miles per hour or to having themselves hurled into concrete walls — all of which are direct consequences of a blast wave’s overpressure. Blast effects therefore cause a great many fatalities. Blast effects depend in part on where a weapon is detonated. The most widespread damage to buildings occurs in an air burst, a detonation thousands of feet above the target. The blast wave from an air burst reflects off the ground, which enhances its destructive power. A ground burst, in contrast, digs a huge crater and pulverizes everything in the immediate vicinity, but its blast effects don’t extend as far. Nuclear attacks on cities would probably employ air bursts, whereas ground bursts would be used on hardened military targets such as underground missile silos.

The expansion of intensely hot gases at extremely high pressures in a nuclear fireball generates a shock wave that expands outward at high velocity. The “overpressure,” or crushing pressure, at the front of the shock wave can be measured in pascals (or kilopascals; kPa) or in pounds per square inch (psi). The greater the overpressure, the more likely that a given structure will be damaged by the sudden impact of the wave front. A related destructive effect comes from the “dynamic pressure,” or high-velocity wind, that accompanies the shock wave. An ordinary two-story, wood-frame house will collapse at an overpressure of 34.5 kPa (5 psi). A one-megaton weapon exploded at an altitude of 3,000 meters (10,000 feet) will generate overpressure of this magnitude out to 7 km (about 4 miles) from the point of detonation. The winds that follow will hurl a standing person against a wall with several times the force of gravity. Within 8 km (5 miles) few people in the open or in ordinary buildings will likely be able to survive such a blast. Enormous amounts of masonry, glass, wood, metal, and other debris created by the initial shock wave will fly at velocities above 160 km (100 miles) per hour, causing further destruction.

There are two aspects to blast – the shock wave and winds. The shock wave (so-called peak overpressure) is a wall of compressed air traveling outward from the explosion at speeds above the speed of sound, dissipating as it goes. It crushes objects in its path. The wind (so-called dynamic overpressure) follows behind the shock wave, blowing over objects in its path. Houses can withstand peak overpressures of approximately 5 pounds per square inch (psi) whereas hardened military structures can withstand peak overpressures above 1000 psi. Blast waves are lethal to humans primarily because the wind picks up objects that become lethal projectiles. The lethal range for winds against humans is roughly equivalent to the range of the 5 psi shock wave.

The magnitude of the blast effect (generally measured in pounds per square inch) diminishes with distance from the center of the explosion. It is related in a more complicated way to the height of the burst above ground level. For any given distance from the center of the explosion, there is an optimum burst height that will produce the greatest overpressure, and the greater the distance the greater the optimum burst height. As a result, a burst on the surface produces the greatest overpressure at very close ranges (which is why surface bursts are used to attack very hard, very small targets such as missile silos), but less overpressure than an air burst at somewhat longer ranges. Raising the height of the burst reduces the overpressure directly under the bomb, but widens the area at which a given smaller overpressure is produced. Thus, an attack on factories with a l-Mt weapon might use an air burst at an altitude of 8,000 feet [2,400 m], which would maximize the area (about 28 mi2 [7,200 hectares]) that would receive 10 psi or more of overpressure.

Table below shows the ranges of overpressures and effects from such a blast.

When a nuclear weapon is detonated on or near the surface of the Earth, the blast digs out a large crater. Some of the material that used be in the crater is deposited on the rim of the crater; the rest is carried up into the air and returns to earth as fallout. An explosion that is farther above the Earth’s surface than the radius of the fireball does not dig a crater and produces negligible immediate fallout. For the most part, blast kills people by indirect means rather than by direct pressure. While a human body can withstand up to 30 psi of simple overpressure, the winds associated with as little as 2 to 3 psi could be expected to blow people out of typical modern office buildings. Most blast deaths result from the collapse of occupied buildings, from people being blown into objects, or from buildings or smaller objects being blown onto or into people. Clearly, then, it is impossible to calculate with any precision how many people would be killed by a given blast—the effects would vary from building to building.

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Thermal radiation:

The primary method by which the Sun transfers heat to the Earth is thermal radiation. Thermal radiation is one of the fundamental mechanisms of heat transfer, along with conduction and convection. Thermal radiation is emitted by all matter. The dominant frequency range of the emitted radiation shifts to higher frequencies as the temperature of the emitter increases. The intensity of thermal radiation increases very rapidly – as the fourth power of the temperature. Thus at the 60-100 million degrees C of a nuclear explosion, which is some 10,000 times hotter than the surface of the sun, the brightness (per unit area) is some 10 quadrillion (10^16) times greater! Consequently about 80% of the energy in a nuclear explosion exists as photons.

A primary form of energy from a nuclear explosion is thermal radiation. Initially, most of this energy goes into heating the bomb materials and the air in the vicinity of the blast. The center of a nuclear explosion can reach temperatures of around 100 million degrees Celsius, which is four to five times hotter than the center of the sun, and produce a brilliant fireball.

Two pulses of thermal radiation emerge from the fireball. The first pulse, which lasts about a tenth of a second, consists of radiation in the ultraviolet region. The second pulse (visible light and infrared) which may last for several seconds, carries about 99 percent of the total thermal radiation energy. It is this radiation that is the main cause of skin burns and eye injuries suffered by exposed individuals and causes combustible materials to break into flames. Its intensity can exceed 1000 watts/cm^2 (the maximum intensity of direct sunlight is 0.14 watts/cm^2). Thermal radiation can ignite combustible materials like vegetation and wood frame buildings, even at a distance from the blast. The intensity of this radiation drops off faster than the square of the distance from the explosion and is affected by the weather and the presence of clouds, smoke, or haze.

As a rule of thumb, approximately 35 percent of the total energy yield of an airburst is emitted as thermal radiation— light and heat capable of causing skin burns and eye injuries and starting fires of combustible material at considerable distances. The shock wave, arriving later, may spread fires further. Nuclear weapons are extremely efficient at igniting vast numbers of simultaneous fires over large areas. These would consume all flammable materials and coalesce into massive confluent fires within which no one could survive the > 800 °C heat, intense smoke, and oxygen depletion. Atmospheric scientists estimated that even the relatively small tactical size nuclear weapon exploded on Hiroshima (15 kilotons of high explosive equivalent) released about 1000 times as much energy in the fires it ignited as in the explosion itself. In Hiroshima approximately 13 km2 of the city burned completely. Detonation of the large currently deployed nuclear weapons, up to five megatons in size, would result in a confluent megafire more than 45 km in diameter, 1600 km2 in area.

If the individual fires are extensive enough, they can coalesce into a mass fire known as a firestorm, generating a single convective column of rising hot gases that sucks in fresh air from the periphery. The inward-rushing winds and the extremely high temperatures generated in a firestorm consume virtually everything combustible. At Hiroshima the incendiary effects were quite different from those at Nagasaki, in part because of differences in terrain. The firestorm that raged over the level terrain of Hiroshima left 11.4 square km (4.4 square miles) severely damaged—roughly four times the area burned in the hilly terrain of Nagasaki. Approximately 20–30% of the casualties at Hiroshima have been attributed to thermal radiation.

The visible light will produce “flashblindness” in people who are looking in the direction of the explosion. Flashblindness can last for several minutes, after which recovery is total. A l-Mt explosion could cause flashblindness at distances as great as 13 miles [21 km] on a clear day, or 53 miles [85 km] on a clear night. If the flash is focused through the lens of the eye, a permanent retinal burn will result. At Hiroshima and Nagasaki, there were many cases of flashblindness, but only one case of retinal burn, among the survivors. On the other hand, anyone flashblinded while driving a car could easily cause permanent injury to himself and to others.

Skin burns result from higher intensities of light, and therefore take place closer to the point of explosion. A 1-Mt explosion can cause first-degree burns (equivalent to a bad sunburn) at distances of about 7 miles [11 km], second-degree burns (producing blisters that lead to infection if untreated, and permanent scars) at distances of about 6 miles [10 km], and third-degree burns (which destroy skin tissue) at distances of up to 5 miles [8 km]. Third-degree burns over 24 percent of the body, or second-degree burns over 30 percent of the body, will result in serious shock, and will probably prove fatal unless prompt, specialized medical care is available. The entire United States has facilities to treat 1,000 or 2,000 severe burn cases; a single nuclear weapon could produce more than 10,000.

It is possible that individual fires, whether caused by thermal radiation or by blast damage to utilities, furnaces, etc., would coalesce into a mass fire that would consume all structures over a large area. This possibility has been intensely studied, but there remains no basis for estimating its probability. Mass fires could be of two kinds: a “firestorm,” in which violent inrushing winds create extremely high temperatures but prevent the fire from spreading radially outwards, and a “conflagration,” in which a fire spreads along a front. Hamburg, Tokyo, and Hiroshima experienced firestorms in World War 11; the Great Chicago Fire and the San Francisco Earthquake Fire were conflagrations. A firestorm is likely to kill a high proportion of the people in the area of the fire, through heat and through asphyxiation of those in shelters. A conflagration spreads slowly enough so that people in its path can escape, though a conflagration caused by a nuclear attack might take a heavy toll of those too injured to walk. Some believe that firestorms in U.S. or Soviet cities are unlikely because the density of flammable materials (“fuel loading”) is too low–the ignition of a firestorm is thought to require a fuel loading of at least 8 lbs/ft2 (Hamburg had 32), compared to fuel loading of 2 lbs/ft2 in a typical U.S. suburb and 5 lbs/ft2 in a neighborhood of two-story brick rowhouses. The likelihood of a conflagration depends on the geography of the area, the speed and direction of the wind, and details of building construction. Another variable is whether people and equipment are available to fight fires before they can coalesce and spread.

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Ionizing radiation from a nuclear bomb:

Ionizing radiation release refers to a unique phenomenon in nuclear explosions. It is a type of energy released by atoms in the form of electromagnetic waves or particles that could travel unseen and pass through materials. Nuclear air bursts form ionizing radiation, such as γ-rays and neutrons. The ionizing activity can alter molecules within the cells of our bodies, causing cancer and death. Ionizing radiation from explosion of atomic bombs consists of initial and residual radiation. Initial radiation can result directly from nuclear fission and fission products of fireballs, causing exposure over ground to γ-rays and neutrons. An initial nuclear radiation level drops quickly based on the distance from a fireball; less than 1 roentgen (0.008695652 Gray) reaches 8 km from ground zero. The roentgen is a legacy unit to measure radiation exposure by a person over a period of time. Residual radiation results from neutron-caused radioactive materials in the environment as well as fission products in fallout (Delayed Radiation). As fission products cool after rising to high atmospheric layers, the fallout usually drops to ground after a nuclear bomb blast. More than 300 fission products may be generated from a fission reaction, and multiple fission products are radioactive with great differences in half-lives –from a second to months or years.

Figure above shows ionizing radiation released from atomic bombs.

Beside shock, blast, and heat a nuclear bomb generates high intensity flux of radiation in form of γ-rays, x-rays, and neutrons as well as large abundances of short and long-lived radioactive nuclei which contaminate the entire area of the explosion and is distributed by atmospheric winds worldwide.

Initial nuclear radiation:

A special feature of a nuclear explosion is the emission of nuclear radiation, which may be separated into initial radiation and residual radiation. Initial radiation, also known as prompt radiation, consists of gamma rays and neutrons produced within a minute of the detonation. Beta particles (free electrons) and a small proportion of alpha particles (helium nuclei, i.e., two protons and two neutrons bound together) are also produced, but these particles have short ranges and typically will not reach Earth’s surface if the weapon is detonated high enough above ground. Gamma rays and neutrons can produce harmful effects in living organisms, a hazard that persists over considerable distances because of their ability to penetrate most structures. If sufficiently intense, prompt nuclear radiation can kill or incapacitate humans or other living organisms, and destroy or upset electronic circuitry. The lethal dose for humans is approximately is in the range from 400 to 450 rem (4 to 5 sieverts) received over a very short period. Prompt nuclear radiation accounts for about 5% of the energy released in a nuclear explosion and its intensity falls off quickly with distance. Hence, it is not a principal cause of damage, especially for high-yield nuclear weapons (>20 kT) although it can be significant for lower-yield weapons (<20 kT). The ‘neutron bomb’ is a low-yield weapon with enhanced neutron output, thereby making prompt nuclear radiation the principal lethal effect against humans while reducing the blast and thermal effects.

The neutron burst itself can be a significant source of radiation, depending on weapon design. As the neutrons travel through the air they are slowed by collisions with air atoms, and are eventually captured. Even this process of neutron attenuation generates hazardous radiation. Part of the kinetic energy lost by fast neutrons as they slow is converted into gamma rays, some with very high energies (for the 14.1 MeV fusion neutrons). The duration of production for these neutron scattering gammas is about 10 microseconds. The capture of neutrons by nitrogen-14 also produces gammas, a process completed by 100 milliseconds.

Immediately after the explosion, there are substantial amounts of fission products with very short half-lives (milliseconds to minutes). The decay of these isotopes generates correspondingly intense gamma radiation that is emitted directly from the fireball. This process is essentially complete within 10 seconds.

The explosion itself emits a very brief burst (about 100 nanoseconds) of gamma rays and neutrons, before the bomb has blown itself apart. The intensity of these emissions depends very heavily on the type of weapon and the specific design. In most designs the initial gamma ray burst is almost entirely absorbed by the bomb (tamper, casing, explosives, etc.) so it contributes little to the radiation hazard. The neutrons, being more penetrating, may escape. Both fission and fusion reactions produce neutrons. Fusion produces many more of them per kiloton of yield, and they are generally more energetic than fission neutrons. Some weapons (neutron bombs) are designed specifically to emit as much energy in the form as neutrons as possible. In heavily tamped fission bombs few if any neutrons escape. It is estimated that no significant neutron exposure occurred from Fat Man, and only 2% of the total radiation dose from Little Boy was due to neutrons.

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Residual radiation and fallout:

Fallout is the radioactive debris that falls to the ground after a nuclear explosion. Residual radiation is defined as radiation emitted more than one minute after the detonation. If the fission explosion is an airburst, the residual radiation will come mainly from the weapon debris. If the explosion is on or near the surface, the soil, water, and other materials in the vicinity will be sucked upward by the rising cloud, causing early (local) and delayed (worldwide) fallout. Early (local) fallout settles to the ground during the first 24 hours; it may contaminate large areas and be an immediate and extreme biological hazard. Delayed (global) fallout, which arrives after the first day, consists of microscopic particles that are dispersed by prevailing winds and settle in low concentrations over possibly extensive portions of Earth’s surface. Global fallout occurs when a nuclear explosion happens high in the atmosphere, causing radioactive material to rise into the stratosphere and be dispersed by winds. Global fallout can settle in low concentrations over large portions of the Earth’s surface. The main difference between local and global fallout is the size of the radioactive particles involved. Local fallout consists of larger particles that are deposited close to the explosion site. Global fallout consists of smaller particles that are dispersed over large areas and extended periods of time. The particles are dispersed by the wind and settle in low concentrations.

Figure above shows dangerous fallout zone for a 10-kiloton detonation. The pattern will vary depending on wind speed and direction, and the zone will shrink substantially over a day or so. Radioactive decay is the sole source of beta and alpha particles. They are also emitted during the immediate decay, but their range is too short to make any prompt radiation contribution. Betas and alphas become important when fallout begins settling out. Gammas remain very important at this stage as well.

A nuclear explosion produces a complex mix of more than 300 different isotopes of dozens of elements, with half-life from fractions of a second to millions of years. The total radioactivity of the fission products is extremely large at first, but it falls off at a fairly rapid rate as a result of radioactive decay. Seven hours after a nuclear explosion, residual radioactivity will have decreased to about 10 percent of its amount at 1 hour, and after another 48 hours it will have decreased to 1 percent. (The rule of thumb is that for every sevenfold increase in time after the explosion, the radiation dose rate decreases by a factor of 10.)

Among some there is the unfounded fear that Hiroshima and Nagasaki are still radioactive; in reality, this is not true. Following a nuclear explosion, there are two forms of residual radioactivity. The first is the fallout of the nuclear material and fission products. Most of this was dispersed in the atmosphere or blown away by the wind. Though some did fall onto the city as black rain, the level of radioactivity today is so low it can be barely distinguished from the trace amounts presents throughout the world as a result of atmospheric tests in the 1950s and 1960s. The other form of radiation is neutron activation. Neutrons can cause non-radioactive materials to become radioactive when caught by atomic nuclei. However, since the bombs were detonated so far above the ground, there was very little contamination—especially in contrast to nuclear test sites such as those in Nevada. In fact, nearly all the induced radioactivity decayed within a few days of the explosions.

Fallout is radioactive material, mostly fission fragments, that attaches to small pieces of dust or dirt entrained in the mushroom cloud of a nuclear explosion. Approximately 10% of the energy from a nuclear explosion is contained in these fission fragments. Fallout is a serious problem only when the explosion occurs so close to the ground that the fireball touches the surface of the earth and, hence, entrains a large amount of material in the mushroom cloud. The radioactive dust then settles back to earth over a period of hours to months depending on the particle size. The lethal effects are the same as for prompt nuclear radiation although they can occur much further from the site of the explosion (e.g., tens to hundreds of miles) depending on the wind speed and weather. Fission fragments have relatively short radioactive half-lives so the radiation intensity from fallout decays rapidly with time. For example, after 2 weeks the radiation intensity is 1 one-thousandth that which occurs 1 hour after the explosion.

The fallout produced in a nuclear explosion depends greatly on the type of weapon, its explosive yield, and where it’s exploded. The neutron bomb, although it produces intense direct radiation, is primarily a fusion device and generates only slight fallout from its fission trigger. Small fission weapons like those used at Hiroshima and Nagasaki produce locally significant fallout. But the fission-fusion-fission design used in today’s thermonuclear weapons introduces the new phenomenon of global fallout. Most of this fallout comes from fission of the U-238 jacket that surrounds the fusion fuel. The global effect of these huge weapons comes partly from the sheer quantity of radioactive material and partly from the fact that the radioactive cloud rises well into the stratosphere, where it may take months or even years to reach the ground. Even though we’ve had no nuclear war since the bombings of Hiroshima and Nagasaki, fallout is one weapons effect with which we have experience. Atmospheric nuclear testing before the 1963 Partial Test Ban Treaty resulted in detectable levels of radioactive fission products across the globe, and some of that radiation is still with us.

Fallout differs greatly depending on whether a weapon is exploded at ground level or high in the atmosphere. In an air burst, the fireball never touches the ground, and radioactivity rises into the stratosphere. This reduces local fallout but enhances global fallout. In a ground burst, the explosion digs a huge crater and entrains tons of soil, rock, and other pulverized material into its rising cloud. Radioactive materials cling to these heavier particles, which drop back the ground in a relatively short time. Rain may wash down particularly large amounts of radioactive material, producing local hot spots of especially intense radioactivity. A hot spot in Albany, New York, thousands of miles from the 1953 Nevada test that produced it, exposed area residents to some 10 times their annual background radiation dose. The exact distribution of fallout depends crucially on wind speed and direction; under some conditions, lethal fallout may extend several hundred miles downwind of an explosion. However, it’s important to recognize that the lethality of fallout quickly decreases as short-lived isotopes decay.

Fallout is a complex mixture of different radioactive isotopes, the composition of which continually changes as each isotope decays into other isotopes. Many isotopes make significant contributions to the overall radiation level. Radiation from short lived isotopes dominates initially, and the general trend is for the intensity to continually decline as they disappear. Over time the longer lived isotopes become increasingly important, and a small number of isotopes emerge as particular long-term hazards.

Radioactive isotopes are usually measured in terms of curies. A curie is the quantity of radioactive material that undergoes 3.7×10^10 decays/sec (equal to 1 g of radium-226). More recently the SI unit becquerel has become common in scientific literature, one becquerel is 1 decay/sec. The fission of 57 grams of material produces 3×10^23 atoms of fission products (two for each atom of fissionable material). One minute after the explosion this mass is undergoing decays at a rate of 10^21 disintegrations/sec (3×10^10 curies). It is estimated that if these products were spread over 1 km^2, then at a height of 1 m above the ground one hour after the explosion the radiation intensity would be 7500 rads/hr.

Isotopes of special importance include iodine-131, strontium-90 and 89, and cesium-137. This is due to both their relative abundance in fallout, and to their special biological affinity. Isotopes that are readily absorbed by the body, and concentrated and stored in particular tissues can cause harm out of proportion to their abundance.

Iodine-131 is a beta and gamma emitter with a half-life of 8.07 days (specific activity 124,000 curies/g) Its decay energy is 970 KeV; usually divided between 606 KeV beta, 364 KeV gamma. Due to its short half-life it is most dangerous in the weeks immediately after the explosion, but hazardous amounts can persist for a few months. It constitutes some 2% of fission-produced isotopes – 1.6×10^5 curies/kt. Iodine is readily absorbed by the body and concentrated in thyroid gland.

Strontium-90 is a beta emitter (546 KeV, no gammas) with a half-life of 28.1 years (specific activity 141 curies/g), Sr-89 is a beta emitter (1.463 MeV, gammas very rarely) with a half-life of 52 days (specific activity 28,200 Ci/g). Each of these isotopes constitutes about 3% of total fission isotopes: 190 curies of Sr-90 and 3.8×10^4 curies of Sr-89 per kiloton. Due to their chemical resemblance to calcium these isotopes are absorbed fairly well, and stored in bones. Sr-89 is an important hazard for a year or two after an explosion, but Sr-90 remains a hazard for centuries. Actually most of the injury from Sr-90 is due to its daughter isotope yttrium-90. Y-90 has a half-life of only 64.2 hours, so it decays as fast as it is formed, and emits 2.27 MeV beta particles.

Cesium-137 is a beta and gamma emitter with a half-life of 30.0 years (specific activity 87 Ci/g). Its decay energy is 1.176 MeV; usually divided by 514 KeV beta, 662 KeV gamma. It comprises some 3-3.5% of total fission products – 200 curies/kt. It is the primary long-term gamma emitter hazard from fallout, and remains a hazard for centuries.

Although not important for acute radiation effects, the isotopes carbon-14 and tritium are also of interest because of possible genetic injury. These are not direct fission products. They are produced by the interaction of fission and fusion neutrons with the atmosphere and, in the case of tritium, as a direct product of fusion reactions. Most of the tritium generated by fusion is consumed in the explosion but significant amounts survive. Tritium is also formed by the capture of fast neutrons by nitrogen atoms in the air: N-14 + n -> T + C-12. Carbon-14 in also formed by neutron-nitrogen reactions: N-14 + n -> C-14 + p. Tritium is a very weak beta emitter (18.6 KeV, no gamma) with a half-life of 12.3 years (9700 Ci/g). Carbon-14 is also a weak beta emitter (156 KeV, no gamma), with a half-life of 5730 years (4.46 Ci/g). Atmospheric testing during the fifties and early sixties produced about 3.4 g of C-14 per kiloton (15.2 curies) for a total release of 1.75 tonnes (7.75×10^6 curies). For comparison, only about 1.2 tonnes of C-14 naturally exists, divided between the atmosphere (1 tonne) and living matter (0.2 tonne). Another 50-80 tonnes is dissolved in the oceans. Due to carbon exchange between the atmosphere and oceans, the half-life of C-14 residing in the atmosphere is only about 6 years. By now the atmospheric concentration has returned to within 1% or so of normal. High levels of C-14 remain in organic material formed during the sixties (in wood, say, or DNA).

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Electromagnetic pulse:

A nuclear electromagnetic pulse (EMP) is the time-varying electromagnetic radiation resulting from a nuclear explosion. The development of the EMP is shaped by the initial nuclear radiation from the explosion—specifically, the gamma radiation. High-energy electrons are produced in the environment of the explosion when gamma rays collide with air molecules (a process called the Compton effect). Positive and negative charges in the atmosphere are separated as the lighter, negatively charged electrons are swept away from the explosion point and the heavier, positively charged ionized air molecules are left behind. This charge separation produces a large electric field. Asymmetries in the electric field are caused by factors such as the variation in air density with altitude and the proximity of the explosion to Earth’s surface. These asymmetries result in time-varying electrical currents that produce the EMP. The characteristics of the EMP depend strongly on the height of the explosion above the surface.

Only a symmetric radial electron field is produced if the ionized deposition region is spherically symmetric; there is no net electron current as seen in figure a above.

Disturbance of symmetry results in a net electron current; a pulse of electromagnetic radiation is emitted which is strongest in directions perpendicular to the net current as seen in figure b above.

In a crude sense, the EMP radiations are somewhat similar to the familiar radio waves, although there are some important differences. Radio transmitters are designed to produce electromagnetic waves of a particular frequency (or wavelength), but the waves in the EMP have a wide range of frequencies and amplitudes. Furthermore, the strength of the electric fields associated with the EMP can be millions of times greater than in ordinary radio waves. Nevertheless, in each case, the energy of electromagnetic waves is collected by a suitable antenna (or conductor) and transferred to attached or adjacent equipment. The energy from the EMP is received in such a very short time, however, that it produces a strong electric current which could damage the equipment. An equal amount of energy spread over a long period of time, as in conventional radio reception, would have no harmful effect.

EMP was first noticed in the United States in the 1950s when electronic equipment failed because of induced currents and voltages during some nuclear tests. In 1960 the potential vulnerability of American military equipment and weapons systems to EMP was officially recognized. EMP can damage unprotected electronic equipment, such as radios, radars, televisions, telephones, computers, and other communication equipment and systems. EMP damage can occur at distances of tens, hundreds, or thousands of kilometers from a nuclear explosion, depending on the weapon yield and the altitude of the detonation. For example, in 1962 a failure of electronic components in street lights in Hawaii and activation of numerous automobile burglar alarms in Honolulu were attributed to a high-altitude U.S. nuclear test at Johnston Atoll, some 1,300 km (800 miles) to the southwest. For a high-yield explosion of approximately 10 megatons detonated 320 km (200 miles) above the center of the continental United States, almost the entire country, as well as parts of Mexico and Canada, would be affected by EMP. Procedures to improve the ability of networks, especially military command and control systems, to withstand EMP are known as “hardening.”

Since the Partial Test Ban Treaty of 1963, it has been virtually impossible to study EMP effects directly, although elaborate devices have been developed to mimic the electronic impact of nuclear weapons. Increasingly, crucial electronic systems are “hardened” to minimize the impact of EMP. Nevertheless, the use of EMP in a war could wreak havoc with systems for communication and control of military forces.

Many countries are around the world are developing high-powered microwave weapons which, although not nuclear devices, are designed to produce EMPs. These directed-energy weapons, also called e-bombs, emit large pulses of microwaves to destroy electronics on missiles, to stop cars, to detonate explosives remotely, and to down swarms of drones. Despite these EMP weapons being nonlethal in the sense that there’s no bang or blast wave, an enemy may be unable to distinguish their effects from those of nuclear weapons.

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Radio and Radar effects:

The transmission of electromagnetic waves with wavelengths of I millimeter or more, which are used for radio communications and for radar, is often dependent upon the electrical properties, i.e., the ionization, of the atmosphere. The radiations from the fireball of a nuclear explosion and from the radioactive debris can produce marked changes in the atmospheric ionization. The explosion can, therefore, disturb the propagation of the electromagnetic waves mentioned before. Apart from the energy yield of the explosion, the effects are dependent on the altitudes of the burst and of the debris and on the wavelength (or frequency) of the electromagnetic waves. In certain circumstances, e.g., short-wave (high frequency) communications after the explosion of a nuclear weapon at an altitude above about 40 miles, the electromagnetic signals may be completely disrupted, i.e., “blacked out,” for several hours. Shortwave radio uses electromagnetic waves with wavelengths of 10–80 meters (33–262 feet). The name comes from the shorter wavelengths of shortwave radio compared to the longer wavelengths used in early radio communications.

Ionization, that is, the formation of ion pairs consisting of separated electrons and positive ions, can be produced, either directly or indirectly, by the gamma rays and neutrons of the prompt nuclear radiation, by the beta particles and gamma rays of the residual nuclear radiation, by the X rays and the ultraviolet light present in the primary thermal radiation, and by positive ions in the weapon debris. Hence, after a nuclear explosion, the density of electrons in the atmosphere in the vicinity is greatly increased. These electrons can affect electromagnetic (radio and radar) signals in at least two ways. First, under suitable conditions, they can remove energy from the wave and thus attenuate the signal; second, a wave front traveling from one region into another in which the electron density is different will be refracted, i.e., its direction of propagation will be changed. It is evident, therefore, that the ionized regions of the atmosphere created by a nuclear explosion can influence the behavior of communications or radar signals whose transmission paths encounter these regions.

When an electromagnetic wave l interacts with free electrons, some of the energy of the wave is transferred to the electrons as energy of vibration. If the electrons do not lose this energy as the result of collisions with other particles (atoms, molecules, or ions) in the air, they will reradiate electromagnetic energy of the same frequency, but with a slight time delay. Thus, the energy is restored to the wave without loss, but with a change in phase. If, however, the air density is appreciable, e.g., more than about one ten-thousandth (10^-4) of the sea-level value, as it is below about 40 miles altitude, collisions of electrons with neutral particles will take place at a significant rate. Even above 40 miles, collisions between electrons and ions are significant if the electron density is abnormally high. In such collisions, most of the excess (coherent) energy of the electron is transformed into kinetic energy of random motion and cannot be reradiated. The result is that energy is absorbed from the wave and the electromagnetic signal is attenuated.

Radar blackout:

The heat of the explosion causes air in the vicinity to become ionized, creating the fireball. The free electrons in the fireball affect radio waves, especially at lower frequencies. This causes a large area of the sky to become opaque to radar, especially those operating in the VHF and UHF frequencies, which is common for long-range early warning radars. The effect is less for higher frequencies in the microwave region, as well as lasting a shorter time – the effect falls off both in strength and the affected frequencies as the fireball cools and the electrons begin to re-form onto free nuclei.

A second blackout effect is caused by the emission of beta particles from the fission products. These can travel long distances, following the Earth’s magnetic field lines. When they reach the upper atmosphere they cause ionization similar to the fireball but over a wider area. Calculations demonstrate that a two-megaton H-bomb, will create enough beta radiation to blackout an area 400 kilometres (250 mi) across for five minutes. Careful selection of the burst altitudes and locations can produce an extremely effective radar-blanking effect. The physical effects of nuclear explosion giving rise to blackouts also cause EMP, which can also cause power blackouts. The two effects are otherwise unrelated, and the similar naming can be confusing.

Blackout is a particular concern for anti-ballistic missile (ABM) systems. By exploding a warhead in the upper atmosphere just beyond the range of defensive missiles, an attacker can blanket a wide area of the sky beyond which additional approaching warheads cannot be seen. When those warheads emerge from the blackout area there may not be enough time for the defensive system to develop tracking information and attack them. This was a serious concern for the LIM-49 Nike Zeus program of the late 1950s, and one of the reasons it was ultimately canceled. A key discovery revealed in testing was that the effect cleared more quickly for higher frequencies. Later missile defense designs used radars operating at higher frequencies in the UHF and microwave region to mitigate the effect.

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Summary:

The following table summarizes the most important effects of single nuclear explosions under ideal, clear skies, weather conditions. Tables like these are calculated from nuclear weapons effects scaling laws. Advanced computer modelling of real-world conditions and how they impact on the damage to modern urban areas has found that most scaling laws are too simplistic and tend to overestimate nuclear explosion effects. The scaling laws that were used to produce the table below assume (among other things) a perfectly level target area, no attenuating effects from urban terrain masking (e.g. skyscraper shadowing), and no enhancement effects from reflections and tunneling by city streets. As a point of comparison in the chart below, the most likely nuclear weapons to be used against countervalue city targets in a global nuclear war are in the sub-megaton range. Weapons of yields from 100 to 475 kilotons have become the most numerous in the US and Russian nuclear arsenals; for example, the warheads equipping the Russian Bulava submarine-launched ballistic missile (SLBM) have a yield of 150 kilotons. US examples are the W76 and W88 warheads, with the lower yield W76 being over twice as numerous as the W88 in the US nuclear arsenal.

Effects	Explosive yield / height of burst
Effects	1 kt / 200 m	20 kt / 540 m	1 Mt / 2.0 km	20 Mt / 5.4 km
Blast—effective ground range in km
Urban areas completely levelled (20 psi or 140 kPa)	0.2	0.6	2.4	6.4
Destruction of most civilian buildings (5 psi or 34 kPa)	0.6	1.7	6.2	17
Moderate damage to civilian buildings (1 psi or 6.9 kPa)	1.7	4.7	17	47
Railway cars thrown from tracks and crushed (62 kPa; values for other than 20 kt are extrapolated using the cube-root scaling)	≈0.4	1.0	≈4	≈10
Thermal radiation—effective ground range in km
Fourth degree burns, Conflagration	0.5	2.0	10	30
Third degree burns	0.6	2.5	12	38
Second degree burns	0.8	3.2	15	44
First degree burns	1.1	4.2	19	53
Effects of instant nuclear radiation—effective slant range¹ in km
Lethal² total dose (neutrons and gamma rays)	0.8	1.4	2.3	4.7
Total dose for acute radiation syndrome²	1.2	1.8	2.9	5.4

1 For the direct radiation effects the slant range instead of the ground range is shown here because some effects are not given even at ground zero for some burst heights. If the effect occurs at ground zero the ground range can be derived from slant range and burst altitude (Pythagorean theorem).

2 “Acute radiation syndrome” corresponds here to a total dose of one gray, “lethal” to ten grays. This is only a rough estimate since biological conditions are neglected here.

Further complicating matters, under global nuclear war scenarios with conditions similar to that during the Cold War, major strategically important cities like Moscow and Washington are likely to be hit numerous times from sub-megaton multiple independently targetable re-entry vehicles, in a cluster bomb or “cookie-cutter” configuration. It has been reported that during the height of the Cold War in the 1970s Moscow was targeted by up to 60 warheads.

The reason that the cluster bomb concept is preferable in the targeting of cities is twofold: the first is that large singular warheads are much easier to neutralize as both tracking and successful interception by anti-ballistic missile systems than it is when several smaller incoming warheads are approaching. This strength in numbers advantage to lower yield warheads is further compounded by such warheads tending to move at higher incoming speeds, due to their smaller, more slender physics package size, assuming both nuclear weapon designs are the same (a design exception being the advanced W88). The second reason for this cluster bomb, or ‘layering’ (using repeated hits by accurate low yield weapons) is that this tactic along with limiting the risk of failure reduces individual bomb yields, and therefore reduces the possibility of any serious collateral damage to non-targeted nearby civilian areas, including that of neighboring countries.

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Section-18

Deaths and injuries caused by nuclear explosion:

Historically, it has been difficult to estimate the total number of deaths resulting from a global nuclear exchange because scientists are continually discovering new effects of nuclear weapons, and also revising existing models. Early reports considered direct effects from nuclear blast, heat and radiation; and indirect effects from economic, social, and political disruption. In a 1979 report for the U.S. Senate, the Office of Technology Assessment estimated casualties under different scenarios. For a full-scale countervalue/ counterforce nuclear exchange between the U.S. and the Soviet Union, they predicted U.S. deaths from 35 to 77 percent (70 million to 160 million dead at the time), and Soviet deaths from 20 to 40 percent of the population. Although this report was made when nuclear stockpiles were at much higher levels than they are today, it also was made before the risk of nuclear winter was first theorized in the early 1980s. Additionally, it did not consider other secondary effects, such as electromagnetic pulses (EMP), and the ramifications they would have on modern technology and industry.

The Hiroshima bomb is estimated to have killed 90,000–140,000 people and the Nagasaki bomb, 60,000–80,000 not including cancer deaths caused by radiation decades later. The combined power of Little Boy and Fat Man was (190 TJ). For perspective consider a US thermonuclear weapon, (H-bomb; Castle Bravo; 63,000 TJ) 1000 times more powerful compared with the Hiroshima bomb. Russia has a thermonuclear weapon 3000 times more powerful (Tsar Bomba; 210,000 TJ). You can estimate the potential death toll from these enormous modern nuclear weapons.

For perspective it’s important to compare causalities from the Japan A-bombs with other bombings during WWII. For example, in February, 1945 the UK and US fire bombed Dresden. The bombing and the resulting firestorm destroyed more than 2.5 square miles of the city centre killing an estimated 25,000 civilians. In March, 1945 the US fire bombed Tokyo, the single most destructive bombing in human history; 16 square miles of central Tokyo were destroyed, with an estimated 100,000 civilian deaths. But these actions required thousands of bombs, not 1 bomb.

Major Injuries:

Burn Wounds:

In the immediate post attack period, burns would constitute the most common and serious medical problem. Hundreds of thousands of people would have sustained major second and third degree burns, some from the direct effects of the heat flash on exposed skin, others injured in the thousands of fires that would rage on the periphery of the great firestorm.

Other Types of Injuries:

In addition to these burn patients there would be many thousands of other injuries. People blinded by the blast flash or deafened when the pressure wave ruptured their ear drums. People with lungs collapsed by the tremendous pressures. People with stab wounds of the head chest and abdomen who had been struck by flying debris. People with bones broken when they had been hurled through the air by the hurricane force winds or trapped under collapsing buildings.

The Effects of Radiation Sickness:

Shortly after the explosion, another addition to this list of suffering includes a unique form of injury: radiation sickness. The precise extent of radiation injuries would depend to a great deal on weather conditions; particularly the direction and speed of the wind at the time of the explosion. Bone marrow death is caused by a dose of radiation between 2 and 10 Gray. Gastrointestinal death is caused by a dose of radiation between 10 and 50 Gray. Central nervous system death is the main cause of death in 24–48 hours among those exposed to 50 Gray. Erythema of skin lasting more than 10 days occurs in 50% of people exposed to 5-6 Gray and 2–3 Gray exposure leads temporary hair loss.

People who were exposed to very high doses of radiation, 40 to 50 grays, would suffer what is known as the central nervous system syndrome. Their brain tissue, damaged by the radiation, would swell, causing nausea, vomiting, explosive diarrhea, and progressive difficulty walking talking and thinking clearly. They would develop convulsions and pass into a coma and die, usually within the first day or two after the bomb. Once someone had been exposed to doses in this range, there would be no effective treatment.

People exposed to lesser doses of radiation, down to about 4 to 6 grays, would suffer a gastrointestinal form of radiation sickness. They would experience nausea, vomiting and diarrhea soon after exposure which would last for several days and then seem to improve. But, after a few days to a week, the symptoms would return and become worse. The diarrhea and vomit would become bloody as the lining of their stomachs and intestines, damaged by the radiation, began to shed. The majority of these patients would also die, despite the most intensive medical therapy.

People with even smaller radiation exposure, in the 1 to 3 gray range, would suffer from the hematologic radiation syndrome. They also would suffer nausea, vomiting and diarrhea for a few days, but these symptoms would resolve. About three weeks after exposure, their bone marrow would stop producing normal numbers of blood cells. As their white blood cell count fell, they would become prey to infection. Sores would form in their mouths. Burns and other wounds suffered in the initial attack would become infected and fail to heal. They would also have a fall in the number of platelets, the cell fragments that help blood to clot. They would hemorrhage into their skin, and new bleeding would begin in the intestines and stomach.

Combined Injuries (Synergism):

So far, the discussion of each major effect (blast, nuclear radiation, and thermal radiation) has explained how this effect in isolation causes deaths and injuries to humans. But it is obvious that combined injuries are possible. Some of the obvious possibilities are:

Nuclear Radiation Combined with Thermal Radiation:

Severe burns place considerable stress on the blood system, and often cause anemia. It is clear from experiments with laboratory animals that exposure of a burn victim to more than 100 rems of radiation will impair the blood’s ability to support recovery from the thermal burns. Hence a sublethal radiation dose could make it impossible to recover from a burn that, without the radiation, would not cause death.

Nuclear Radiation Combined with Mechanical Injuries:

Mechanical injuries, the indirect results of blast, take many forms. Flying glass and wood will cause puncture wounds. Winds may blow people into obstructions, causing broken bones, concussions, and internal injuries. Persons caught in a collapsing building can suffer many similar mechanical injuries. There is evidence that all of these types of injuries are more serious if the person has been exposed to 300 rems, particularly if treatment is delayed. Blood damage will clearly make a victim more susceptible to blood loss and infection. This has been confirmed in laboratory animals in which a borderline lethal radiation dose was followed a week later by a blast overpressure that alone would have produced a low level of prompt lethality. The number of prompt and delayed (from radiation) deaths both increased over what would be expected from the single effect alone.

Thermal Radiation and Mechanical injuries:

There is no information available about the effects of this combination, beyond the common sense observation that since each can place a great stress on a healthy body, the combination of injuries that are individually tolerable may subject the body to a total stress that it cannot tolerate. Mechanical injuries should be prevalent at about the distance from a nuclear explosion that produces sublethal burns, so this synergism could be an important one.

In general, synergistic effects are most likely to produce death when each of the injuries alone is quite severe. Because the uncertainties of nuclear effects are compounded when one tries to estimate the likelihood of two or more serious but (individually) nonfatal injuries, there really is no way to estimate the number of victims.

A further dimension of the problem is the possible synergy between injuries and environmental damage. To take one obvious example, poor sanitation (due to the loss of electrical power and water pressure) can clearly compound the effects of any kind of serious injury. Another possibility is that an injury would so immobilize the victim that he would be unable to escape from a fire.

Cancer induction:

Cancer induction is the most significant long-term risk of exposure to a nuclear bomb. Approximately 1 out of every 80 people exposed to 1 Gray will die from cancer, in addition to the normal rate of 20 out of 80. About 1 in 40 people will get cancer, in addition to the typical rates of 16-20 out of 40. Different types of cancer take different times for them to appear:

2 years for leukemia to appear
20 or more years for skin cancer or lung cancer

In utero effects on human development:

Depending on the stage of fetal development, the health consequences of exposure at doses greater than 0.5 Gy can be severe, even if such a dose is too low to cause an immediate effect for the mother. The health consequences can include growth restriction, malformations, impaired brain function, and cancer. A 1 Gy dose of radiation will cause between 0 and 20 extra cases of perinatal mortality per 1,000 births and 0-20 cases per 1000 births of severe mental sub-normality. The data shows a probability of occurrence of mental retardation of 40% per Gray in children exposed in utero to the atomic bombs in Hiroshima and Nagasaki.

Transgenerational genetic damage:

Exposure to even relatively low doses of radiation generates genetic damage in the progeny of irradiated rodents. This damage can accumulate over several generations. No statistically demonstrable increase of congenital malformations was found among the later conceived children born to survivors of the Nuclear weapons at Hiroshima and Nagasaki. The surviving women of Hiroshima and Nagasaki, that could conceive, who were exposed to substantial amounts of radiation, went on and had children with no higher incidence of abnormalities than the Japanese average.

Immune suppression and Infectious diseases resulting from nuclear attack:

Survivors of a nuclear attack would suffer from injuries caused by ionizing and UV radiation, physical trauma, burns, malnutrition, and psychosocial stress. Several independent lines of research have indicated that these separate agents converge on the T lymphocyte component of the immune system, generally causing a reduction in T lymphocytes and a decrease in the ratio of helper-to-suppressor T lymphocytes. A striking similarity exists between acquired immunodeficiency syndrome (AIDS) and the anticipated immunosuppressed condition of survivors of a nuclear war: both are characterized by absolute depression of the helper T lymphocyte population, reduced helper-to-suppressor T lymphocyte ratios, reduced lymphocytic response to mitogens and antigens, and reduced to absent antibody response following immunization. Additionally, in persons receiving heavy doses of A-bomb radiation, both mature lymphocytes and bone marrow stem cells were severely damaged, causing profound depletion of granulocytes and natural killer cells, which together defend against microbial (or bacterial and viral) invasion. On the top of it, there would be a massive increase in infectious diseases caused by faecal matter contaminated water from untreated sewage, crowded living conditions, poor standard of living, and lack of vaccines in the aftermath of a nuclear war.

In a medical context it’s important to acknowledge there is no effective response to the use of a strategic nuclear weapon on a civilian population. Consider this scenario: detonation of a nuclear weapon over Detroit, 75 times more powerful compared with the Hiroshima bomb. About 470,000 people of a population of 4.3 million would be killed and 630,000 injured. Blast and burn effects would dominate amongst the injured. There would be 440,000 blast injuries, 409,000 thermal injuries and 157,000 persons exposed to moderate or marked radiation. These numbers emphasises that although these are nuclear weapons their damage and destruction is mostly percussive and thermal. Treating the survivors would require 352,000 hospital beds or one-third of all US hospital beds including 42,000 burn unit beds and 142,000 ICU beds. About 13,000 physicians and 130,000 nurses would be needed to care for the injured. More than 1 million units of whole blood and the same number of RBC units would be needed along with more than 15 million units of platelets. Because physicians and nurses are concentrated in urban centres like Detroit many or most would be killed or injured by the blast and unavailable to treat the injured. Now increase the scale to a 250 nuclear weapon exchange and it becomes obvious that there would be no effective medical response.

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Section-19

Environmental harms of nuclear explosion:

The only atomic bombs to ever be used outside of testing were those used by the United States in Hiroshima and Nagasaki to end the Second World War. These blasts exploded with the force of about 15 kilotons and 21 kilotons of TNT respectively (World Nuclear Association, 2016). The total nuclear arsenal in the world today includes more than 12,000 nuclear weapons, many of which are even more deadly than those. This could destroy the world multiple times over and yet we never really consider what would happen in the long run if these weapons were to be used. Politicians and policy-makers like to talk about the size of a nuclear blast and the initial consequences that would result from their use, such as severe radiation poisoning and black snow, but they do not consider that nuclear war could have lasting consequences on the environment far beyond the area directly affected by the blast.

In the eighties, a lot of research was done that looked into the lasting effects of nuclear war on the environment and people of the world. However, with the Cold War underway, the government did work to undermine scientists and research that implied that nuclear weapons would cause huge problems for the environment beyond the initial blast, coining the term “nuclear autumn” to combat the research that described the possibility of a “nuclear winter” following a nuclear war (Starr, 2009). This slowed research and it also helped to keep the public away from information that could lead to unrest if widely known.

Unfortunately, the short-term effects of nuclear warfare have been observed through the survivors of the bombs that were dropped on Hiroshima and Nagasaki. The radiation poisoning, cancer, intense burns, and all the other horrors of nuclear war were enough to keep the United States and the Union of Soviet Socialist Republics (USSR) away from actual conflict during the Cold War, but still today policy-makers often overlook the true, long-term, climate, and environmental horrors that would become reality in the event of an extended nuclear war be it in that politician’s country of origin or not.

It is generally thought that a smaller nuclear force would target the largest cities possible as that would be most likely to do the most damage. This tactic would lead to huge firestorms spreading across urban and industrial spaces. A firestorm is when multiple fires within an area that contains a lot of fuel coalesce into one massive fire which heats the air and can cause heavy winds, further spreading the fire. This would kick an astronomical amount of soot into the air all at the same time on the scale of a couple million tons (Robock & Toon, 2012). All this soot would be able to make it into the upper stratosphere where it would reflect and absorb sunlight, keeping that light from reaching the surface of the Earth (Robock & Toon, 2012). This could block sunlight on a regional level, produce a regional state of cooling temperatures, and potentially decrease the average yearly rainfall amounts. However, this would not be certain to affect the rest of the world in any large way. This is because the soot clouds would not be large enough to cover areas outside of the region of the war.

Newer, more accurate models have found that the original estimates of global cooling as a result of nuclear war were actually quite low. The old models predicted that the global average temperatures would decrease quite a bit initially and that the soot would remain in the upper atmosphere for a couple years at most. The newer simulations utilize the NASA Goddard Institute for Space Studies climate model of the entire troposphere, stratosphere, and mesosphere, and they predict that the Earth’s average temperature would actually decrease further than initially estimated and that the soot would remain in the upper stratosphere for significantly longer than predicted. The new estimates are that the average global temperature would decrease by about 1.25 degrees Celsius on average for the first few years and that the soot would hang around in the upper stratosphere for at least a decade, with temperatures still about 0.5 degrees Celsius below average at the end of that decade. These decrease temperatures would be most noticeable in the areas directly affected by the nuclear war, but they would be significant enough to affect the global averages. While the global temperature does not appear to decrease very drastically, most of the cooling would be regional and would affect the Northern hemisphere in particular, shortening the growing season for some crops by up to thirty days. This would cause crops to fail to reach maturity and many of the world’s food producing crops, such as grains and fruits, would not yield enough if any at all (Harwell & Harwell, 1986). Not only this, but the average global precipitation could be reduced by approximately 10% (Starr, 2009) further harming crops and food production. The effects of these changes in global climate, and particularly in the climate of the northern hemisphere, are simple to see from this data. Many crops would fail in the first few years and food would become very scarce; without even considering the other issues, the food shortages alone would cause many deaths after the end of the war.

If, however, a larger catastrophe was to occur, a strategic war between two or more very large nuclear arsenals, the effects could be even more devastating for the entire world, not just for the regions directly impacted. Another simulation was done by Robock, Oman, and Stenchikov (2007) to test what would happen if approximately one third of the world’s nuclear weapons, about 4,000 weapons, were to be detonated in this type of conflict. Once again using the NASA Goddard Institute for Space Studies climate model, it was estimated that this kind of war would produce 180 million tons of soot and would result in 70% of the sunlight being blocked from the surface of the northern hemisphere and 35% from the southern hemisphere. So much of the sunlight would be blocked out that many people would experience multiple days of darkness in which even midday appears as dark as a moonlit night (Robock & Toon, 2012). This could cause the average global temperatures to decrease rapidly by up to eight degrees Celsius and after a decade the temperatures could still be four degrees below the normal as the soot layer would still linger in the upper stratosphere. The cooling caused by the soot would be potentially worse than the cooling in the worst part of the last Ice Age (Robock et al., 2007).

In addition to the global cooling, regional cooling in this larger war would be even more intense than just eight degrees Celsius. The central part of the United States, if attacked by a large number of nuclear weapons, could see decreased temperatures around twenty degrees and parts of Eurasia could see decreases around thirty or even thirty-five degrees Celsius (Robock et al., 2007). This cooling, in particular, is what would kill almost anyone who survived the initial nuclear blasts. Nightly temperatures could drop below freezing fairly consistently during the first one to three crop growing seasons and cause almost no fields in these areas to produce anything useful. Without these crops, many people in Europe, Asia, and North America will starve to death and other food producing livestock would die due to a lack of food. This would only further the overall food shortages.

Not only would crops fail due to the decreased temperatures and the shortened growing season, but, the crops would likely not get enough sunlight or rain, due to the soot in the stratosphere. The upper stratosphere is above where our usual weather occurs. This means that when the sun is blocked out, less evaporation will occur, and rainfall will decrease significantly. In the moderate to large war simulations, global rainfall is predicted to decrease by 45% (Starr, 2009). Without this rainfall and sunlight, regardless of freezing temperatures, crops would undoubtedly fail and livestock and humans alike would die due to a lack of access to food.

The global climate and the health of any survivors of either regional or global nuclear conflicts would depend on another factor, as well, and that is the ozone layer. The soot lofted into the upper parts of the atmosphere would carry particles that would rapidly destroy the ozone layer. The soot is heated to near water’s boiling point and chemical reactions causes bonds in the ozone to break. With the ozone layer significantly weakened, the Earth would be exposed to more ultraviolet radiation than most life would be able to handle. Plants have been shown to have reduced height and shoot mass when exposed to increased UV light, further reducing the survivors’ access to food. Additionally, higher levels of UV-B light have been shown to inhibit phytoplankton activity which would cause the ocean’s total food production to decrease drastically (Smith et al., 1992). This ozone depletion, and therefore the increased exposure to UV light, would last for around five years and then there would remain lesser issues for another five years. During those first five years, the UV index could reach nearly double what is considered the standard safe maximum (Mills et al., 2014). Since the ozone layer protects Earth’s surface from harmful UV radiation, such impacts would be devastating to humans and the environment. High levels of UV radiation have been linked to certain types of skin cancer, cataracts, and immunological disorders. The ozone layer also protects terrestrial and aquatic ecosystems, as well as agriculture.

Throughout the years, research into the full effects of nuclear war has been done, suppressed, and done again. Nuclear war, even on a small scale, would cause death beyond those initially injured in the blast due to regional cooling and soot kicked up into the atmosphere. A larger war could cause world-wide famine for a decade due to nuclear winter, decreased sunlight, and decreased rainfall. Additionally, a large war could also break down large parts of the ozone layer that protects the Earth from harmful ultraviolet radiation leading to significantly decreased ocean life, less healthy plant life, and lasting issues due to the loss of that ozone. Any nuclear war would kill many more people than just those caught in the initial blast and a larger war could change life on Earth into the distant future. Even a single nuclear blast is harmful, but an all-out war would be devastating for the environment.

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Toxic Chemicals:

A multitude of toxic pollutants would be produced by the pyrolysis and partial combustion of chemicals, petroleum products, and synthetic materials stored in strategic, industrial, and urban areas. Military installations, chemical plants, gas and oil refineries, and urban centers contain vast stores of chemical and petroleum products, as well as the waste products of defense, industry, and everyday life. The tragedy of Bhopal, India, where a ruptured storage tank released methyl isocyanate, killing 3500 people in few days, is a small indication of what might happen following a nuclear war as the result of explosions near chemical plants. Clearly, in heavily industrialized regions, the kill area for nuclear explosions could be greatly increased by the release of poisonous chemicals into the atmosphere.

The first question that one might logically ask is whether chemical releases would make the atmosphere lethally toxic on a global or semi-global basis. The answer is no. Even if an entire year’s production of organic chemicals were released and uniformly mixed over half of the Northern Hemisphere, the total concentration of all chemical compounds would still be a factor of 5,000 times less than the 50 percent lethal dose (LD50) of hydrogen cyanide gas. Of course, most compounds are not nearly so toxic, and probably only 5-10 percent of a year’s chemical production is in storage at any one time. Similarly, it is also true that toxic compounds such as carbon monoxide, acrolein, hydrogen chloride, hydrogen cyanide, sulfur dioxide, phosgene, and the oxides of nitrogen produced in urban fires could be significant causes of death only on a local basis. Thus, for the long-term survivors of a nuclear war, the concern with chemical releases would be similar to concern with delayed radioactive fallout, namely, mutations leading to cancers and birth defects. In this sense, we might, by analogy, refer to these effects as arising from the chemical fallout. An important difference between chemical toxins and radionuclides is that radioactive contamination is readily detected by relatively inexpensive Geiger counters, while the compound 2,3,7,8-tetrachlorodibenzodioxin (TCDD) isomer of dioxin, like many other toxic compounds, can only be determined by use of a gas chromatograph coupled to a mass spectrometer; the cost of the latter instruments are in the range of $100,000 to $500,000. Thus, an important characteristic of chemical fallout is that living environments, food, and water could not be readily surveyed in order to determine their safety.

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Nuclear winter:

The direct effects of nuclear war would be horrific, with blasts, fires, and radiation killing and injuring many people. But in 1983, United States and Soviet Union scientists showed that a nuclear war could also produce a nuclear winter, with catastrophic consequences for global food supplies for people far removed from the conflict. Smoke from fires ignited by nuclear weapons exploded on cities and industrial targets would block out sunlight, causing dark, cold, and dry surface conditions, producing a nuclear winter, with surface temperatures below freezing even in summer for years. Nuclear winter theory helped to end the nuclear arms race in the 1980s and helped to produce the Treaty on the Prohibition of Nuclear Weapons in 2017, for which the International Campaign to Abolish Nuclear Weapons received the 2017 Nobel Peace Prize. Because awareness of nuclear winter is now widespread, nuclear nations have so far not used nuclear weapons. But the mere existence of nuclear weapons means that they can be used, by unstable leaders, accidently from technical malfunctions, such as in computers and sensors, due to human error, or by terrorists. Because they cannot be used without the danger of escalation (resulting in a global humanitarian catastrophe), because of recent threats to use them by Russia, and because nuclear deterrence doctrines of all nuclear-armed states are based on the capability and readiness to use nuclear weapons, it is even more urgent for scientists to study these issues, to broadly communicate their results, and to work for the elimination of nuclear weapons.

In the 1970s, several studies posited that the layer of ozone in the stratosphere that shields living things from much of the Sun’s harmful ultraviolet radiation might be depleted by the large amounts of nitrogen oxides produced by nuclear explosions. Further studies speculated that large amounts of dust kicked up into the atmosphere by nuclear explosions might block sunlight from reaching the Earth’s surface, leading to a temporary cooling of the air. Scientists then began to take into account the smoke produced by vast forests set ablaze by nuclear fireballs, and in 1983 an ambitious study, known as the TTAPS study (from the initials of the last names of its authors, R.P. Turco, O.B. Toon, T.P. Ackerman, J.B. Pollack, and Carl Sagan), took into consideration the crucial factor of smoke and soot arising from the burning petroleum fuels and plastics in nuclear-devastated cities. (Smoke from such materials absorbs sunlight much more effectively than smoke from burning wood.) The TTAPS study coined the term “nuclear winter,” and its ominous hypotheses about the environmental effects of a nuclear war came under intensive study by both the American and Soviet scientific communities.

The basic cause of nuclear winter, as hypothesized by researchers, would be the numerous and immense fireballs caused by exploding nuclear warheads. These fireballs would ignite huge uncontrolled fires (firestorms) over any and all cities and forests that were within range of them. Great plumes of smoke, soot, and dust would be sent aloft from these fires, lifted by their own heating to high altitudes where they could drift for weeks before dropping back or being washed out of the atmosphere onto the ground. Several hundred million tons of this smoke and soot would be shepherded by strong west-to-east winds until they would form a uniform belt of particles encircling the Northern Hemisphere from 30° to 60° latitude. These thick black clouds could block out all but a fraction of the Sun’s light for a period as long as several weeks. Surface temperatures would plunge for a few weeks as a consequence, perhaps by as much as 11° to 22° C (20° to 40° F). The conditions of semidarkness, killing frosts, and subfreezing temperatures, combined with high doses of radiation from nuclear fallout, would interrupt plant photosynthesis and could thus destroy much of the Earth’s vegetation and animal life. The extreme cold, high radiation levels, and the widespread destruction of industrial, medical, and transportation infrastructures along with food supplies and crops would trigger a massive death toll from starvation, exposure, and disease. A nuclear war could thus reduce the Earth’s human population to a fraction of its previous numbers. A number of scientists have disputed the results of the original calculations, and, though such a nuclear war would undoubtedly be devastating, the degree of damage to life on Earth remains controversial.

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Alan Robock, an environmental sciences professor at Rutgers University, has spent decades trying to understand what a nuclear war would do to the planet. The sum of his work, along with other colleagues’, is based on economic, scientific, and agricultural models. Here’s what he found: The most devastating long-term effects of a nuclear war actually come down to the black smoke, along with the dust and particulates in the air, that attacks produce. In a nuclear war, cities and industrial areas would be targeted, thereby producing tons of smoke as they burn. Some of that smoke would make it into the stratosphere — above the weather — where it would stay for years because there’s no rain to wash it out. That smoke would expand around the world as it heats up, blocking out sunlight over much of Earth. As a result, the world would experience colder temperatures and less precipitation, depleting much of the globe’s agricultural output. That, potentially, would lead to widespread famine in a matter of years.

The impact on the world, however, depends on the amount of rising smoke. While scientists’ models and estimates vary, it’s believed that around 5 million to 50 million tons of black smoke could lead to a so-called “nuclear autumn,” while 50 million to 150 million tons of black smoke might plunge the world into a “nuclear winter.”

-1) “Nuclear autumn”

A nuclear fight between New Delhi and Islamabad could cause a “nuclear autumn.” “Even a ‘small’ nuclear war between India and Pakistan, with each country detonating 50 Hiroshima-size atom bombs,” Robock and Toon, the University of Colorado Boulder professor, wrote in 2016, “could produce so much smoke that temperatures would fall below those of the Little Ice Age of the fourteenth to nineteenth centuries, shortening the growing season around the world and threatening the global food supply.”

Here’s why: an India-Pakistan nuclear fight of that size could emit at least 5 million to 6 million tons of black smoke into the stratosphere. At that point, American and Chinese agricultural production, particularly in corn and wheat, would drop by about 20 to 40 percent in the first five years. It’s possible that the cooling would last at least a decade, plunging temperatures to levels “colder than any experienced on Earth in the past 1,000 years,” Robock and Toon wrote. Ira Helfand, a board director at the anti-nuclear war Physicians for Social Responsibility, calls this scenario a “nuclear autumn.” As many as 2 billion people would be at risk of starvation even in that “limited” range, he estimates, most of them in Southeast Asia, Latin America, North America, and Europe. The death of 2 billion people wouldn’t be the end of the human race but it would be the end of modern civilization as we know it. The effects could get worse. The lack of food would drive up prices for what sustenance remains. Surely there would be worldwide skirmishes — and perhaps wars — over remaining resources. The situation could get so bad that we might see another nuclear war as states try to seize control of more food and water, Helfand fears.

-2) “Nuclear winter”

The absolute doomsday scenario is a “nuclear winter.” For that to happen, the US and Russia would have to use about 2,000 nukes each and destroy major cities and targets, Toon said. Each country would effectively take out the other — and likely bring down most of humanity as well. According to Robock and others, the roughly 150 million tons of black smoke rising from burning cities and other areas would spread around to most of the planet over a period of weeks. That would plunge surface temperatures by about 17 to 20 degrees Fahrenheit for the first few years, and then come back up just by 5 degrees Fahrenheit for the following decade. The Northern Hemisphere would suffer the coldest temperatures, but the world would feel the impact. “[T]his would be a climate change unprecedented in speed and amplitude in the history of the human race,” they wrote. Global precipitation would also drop by around 45 percent. Between that and the cold, almost nothing would grow, ensuring those who didn’t die in the nuclear firefight soon would of starvation. And if that didn’t do it, the depleted ozone layer — a side effect of a major nuclear war — would allow large amounts of ultraviolet light to make it to the surface. That would harm nearly every ecosystem and make it harder for some humans to go outside. “A Caucasian person couldn’t go outside for a few minutes before getting a sunburn,” Toon said.

Figure below show effects on climate after nuclear war as discussed above:

Some experts, however, disagree with the conclusions of Robock and his colleagues’ work. In 1990, five scientists who coined the term “nuclear winter” said their original findings were overblown and that a large-scale nuclear war wouldn’t extinguish humanity. And in February 2018, Jon Reisner and others in a government-backed study wrote that the impact of smoke in the atmosphere would be bad, but not as dire as Robock’s crew have predicted.

Still, the point remains the same: A nuclear war would almost certainly affect hundreds of millions or billions of people not directly caught in the fighting. Its effects would reverberate, sometimes literally, around the planet. That’s why we don’t ever want to run the risk of a nuclear conflict — and are trying to do something about it.

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Ozone loss:

The sun emits light or radiation at a large range of energies or frequencies. Much of this radiation is absorbed by the earth’s atmosphere and does not reach the surface. Human eyes have evolved to be highly receptive to radiation in the so-called visual spectrum which is not absorbed very much at all by the atmosphere. At the violet, high-energy end of this band of transmitted light lies what is called ultraviolet light or UV. Ultraviolet light with high energies is strongly absorbed by molecular oxygen – the oxygen we breathe – in the upper atmosphere. This absorption can cause the molecular oxygen to break into two oxygen atoms each of which in turn can react with other molecular oxygen to form ozone, a compound made up of three oxygen atoms. In turn, ozone strongly absorbs ultraviolet light itself, including UV with energies lower than that absorbed by molecular oxygen. Small amounts of UV can be beneficial, especially in forming vitamin D in the skin. But large amounts can be harmful, especially of the more energetic UV, causing sunburn and skin cancer in humans and adversely affecting the growth of many plants. Many scientists believe that much of biological evolution took place under the protective UV shield of upper atmospheric ozone.

Nitric oxide is produced essentially by the ‘burning’ of nitrogen in the atmosphere, and this occurs whenever air temperatures are sufficiently hot: in automobile engines, in aircraft engines and in nuclear explosions. It was first recognized in 1972 that oxides of nitrogen produced in nuclear fireballs and lofted to the stratosphere could result in severe ozone depletion (Foley and Ruderman, 1973; Johnston et al., 1973). Ozone in the stratosphere serves as a protective shield against ultraviolet radiation. Particularly significant to the biosphere is radiation in the ultraviolet-B (UV-B) region (280-320 nm). This finding that nuclear explosions could affect stratospheric ozone came as a result of the earlier recognition by Crutzen (1971) and Johnston (1971) that oxides of nitrogen serve as catalysts for ozone destruction according to the now well-known cycle of reactions:

NO + O3 → NO2 + O2

NO2 + O → NO + O2

O3 + hv → O2 + O

Net: 2O3 → 3O2

Note that nitric oxide (NO) initiates the ozone destruction process, but is regenerated, so that no net consumption of nitrogen oxides occurs. In fact, each NO molecule introduced into the stratosphere can destroy about 10^12 to 10^13 ozone molecules during its residence time in the stratosphere (Brasseur and Solomon, 1984).

In 1975 the National Academy of Sciences evaluated the effect of a 10,000-megaton (Mt) nuclear war on the stratospheric ozone shield (NRC, 1975). That study estimated a 30 to 70 percent reduction in the ozone column over the Northern Hemisphere and a 20 to 40 percent depletion for the Southern Hemisphere. Since that time, there has been a modernization of the nuclear arsenals; large multimegaton warheads have been replaced by more numerous warheads (due to MIRV—Multiple, Independently Targetable, Reentry Vehicles), typically having individual yields of 100 to 500 kilotons (kt). The degree of ozone depletion is highly dependent on the height of injection of oxides of nitrogen, and these smaller warheads produce bomb clouds that stabilize at much lower altitudes. The altitude distributions of the nitric oxide injections for the two scenarios were evaluated in the 1985 study of the National Academy of Sciences. The NRC baseline scenario utilizes exactly half of the strategic warheads of every type in both the U.S. and Soviet arsenals, except for any weapons with yields greater than 1.5 Mt. For this scenario oxides of nitrogen would only be carried to altitudes as high as 18 km, and the maximal ozone depletion in the Northern Hemisphere would be 17 percent. An excursion scenario considers that an additional 100 bombs with yields of 20 Mt each would be detonated. For this scenario, oxides of nitrogen would reach an altitude of 37 km, and the maximal ozone depletion would be 43 percent. Note that the maximum in ozone depletion would occur after a period of 8 to 12 months, and it would take on the order of 10 years for ozone concentrations to return to normal. Thus, once most of the smoke and dust was removed from the atmosphere and sunlight began to break through, the biosphere would not receive normal sunlight but, rather, sunlight highly enriched in ultraviolet radiation.

No estimates of ozone depletion have yet taken into account the large perturbations in atmospheric physics and chemistry resulting from the dust and smoke emissions. The recent finding by Malone that the solar-heated smoke clouds would rise into the stratosphere is extremely important in this regard. The introduction of smoke aerosol to the stratosphere would be expected to add to ozone destruction in at least three ways: (1) The absorption of short-wavelength radiation by the smoke would reduce the rate of oxygen photolysis, thereby decreasing the rate at which ozone would be produced in the stratosphere. (2) The absorption of solar radiation by the smoke particles would heat the stratosphere and increase the rates of reactions that catalyze ozone destruction (e.g., the NO + O3 reaction given in the cycle above). (3) Reaction of ozone at the particle surfaces would directly destroy ozone. The particle surface could catalyze the conversion of ozone to oxygen 2O3 → 3O2 or be oxidized by ozone to form products such as carbon monoxide O3 + C (solid) → O2 + CO (gas). The latter reaction would act to consume the particles and thereby shorten the duration of the nuclear winter. Although ozone would be destroyed in either case, UV-B radiation would also be strongly absorbed by soot particles, so that the effects on the biosphere would not be felt until most of the soot was either destroyed by ozone or removed from the stratosphere. This is a very important problem that should be treated by model calculations in the future.

An increase in UV-B radiation would affect the already stressed ecosystems of our planet in several ways (Ehrlich et al., 1983). UV-B wavelengths of light are absorbed strongly by peptide bonds and by nucleic and amino acids (National Research Council, 1982), and these energetic photons can cause chemical changes which affect biological structure and function. Productivity of terrestrial plants and marine plankton is known to decrease with even small increases in UV-B levels (Caldwell, 1981; National Research Council, 1982). Immune system suppression (National Research Council, 1982), blindness (Pitts, 1983), and other physiological stress factors caused by UV-B increases would lead to increased incidence of disease in humans and other mammals. Even normal processes of DNA repair in bacteria are suppressed by increased UV-B exposure (National Research Council, 1982).

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Extreme Ozone Loss Following Nuclear War Results in Enhanced Surface Ultraviolet Radiation, a 2021 study:

For the first time, authors use a modern climate model with interactive chemistry including the effects of aerosols on photolysis rates to simulate the consequences of regional and global scale nuclear wars (injecting 5 and 150 Tg of soot respectively) for the ozone layer and surface ultraviolet (UV) light. For a global nuclear war, heating in the stratosphere, reduced photolysis, and an increase in catalytic loss from the HOx cycle cause a 15 year-long reduction in the ozone column, with a peak loss of 75% globally and 65% in the tropics. This is larger than predictions from the 1980s, which assumed large injections of nitrogen oxides (NOx), but did not include the effects of smoke. NOx from the fireball and the fires provides a small (5%) increase to the global average ozone loss for the first few years. Initially, soot would shield the surface from UV-B, but UV Index values would become extreme: greater than 35 in the tropics for 4 years, and greater than 45 during the summer in the southern polar regions for 3 years. For a regional war, global column ozone would be reduced by 25% with recovery taking 12 years. This is similar to previous simulations, but with a faster recovery time due to a shorter lifetime for soot in authors’ simulations.

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Ocean effects:

Cold ocean and cold land:

A new study [A New Ocean State After Nuclear War] published in AGU Advances in 2022 shows how a full-scale nuclear war would cool the planet and disrupt the planet’s oceans, with dire consequences for humanity. The study’s lead author LSU Department of Oceanography & Coastal Sciences Assistant Professor Cheryl Harrison and coauthors ran multiple computer simulations to study the impacts of regional and larger scale nuclear warfare on the Earth’s systems given today’s nuclear warfare capabilities. The researchers simulated what would happen to the Earth’s systems in a full-scale global war, with the U.S. and Russia using 4,400 100-kiloton nuclear weapons to bomb cities and industrial areas. They also simulated what would happen in a regional nuclear conflict, like India and Pakistan detonating about 500 100-kiloton nuclear weapons on the Asian continent.

In all of the researchers’ simulated scenarios, nuclear firestorms would release soot and smoke into the upper atmosphere that would block out the Sun resulting in crop failure around the world. In the first month following nuclear war, average global temperatures would plunge by about 13 degrees, a larger temperature change than in the last Ice Age. “It doesn’t matter who is bombing whom. It can be India and Pakistan or NATO and Russia. Once the smoke is released into the upper atmosphere, it spreads globally and affects everyone,” explains Harrison. About 100 million people would die from the blasts in the first hours of the war. Weeks later, lower temperatures would reduce the growing season of plants and shift weather patterns, with disastrous effects on global crop production. An estimated 1 to 2 billion people could face starvation.

Ocean temperatures would drop quickly and would not return to their pre-war state even after the smoke clears. As the planet gets colder, sea ice expands blocking major ports in the Northern Hemisphere, including Beijing, Copenhagen and St. Petersburg. The sea ice would spread into normally ice-free coastal regions blocking shipping across the world’s oceans making it difficult to get food and supplies into some areas. The sudden drop in light and ocean temperatures, especially from the Arctic to the North Atlantic and North Pacific oceans, would kill the marine algae, which is the foundation of the marine food web, essentially creating a famine in the ocean. This would halt most fishing and aquaculture.

Oceans take longer to recover than land. In the largest U.S.-Russia scenario, ocean recovery is likely to take decades at the surface and hundreds of years at depth, while changes to Arctic sea ice will likely last thousands of years and effectively be a “Nuclear Little Ice Age.” Marine ecosystems would be highly disrupted by both the initial perturbation and in the new ocean state, resulting in long-term, global impacts to ecosystem services such as fisheries, write the authors.

The authors note that volcanic eruptions can show at a smaller scale what could happen after a nuclear war. Throughout history, large eruptions and the clouds of particles they erupted into Earth’s atmosphere have had similar negative impacts on the planet and civilization. “We can avoid nuclear war, but volcanic eruptions are definitely going to happen again. There’s nothing we can do about it, so it’s important when we’re talking about resilience and how to design our society, that we consider what we need to do to prepare for unavoidable climate shocks,” Harrison said. “We can and must however, do everything we can to avoid nuclear war. The effects are too likely to be globally catastrophic.”

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Counter study:

Warm ocean and cold land:

Nuclear Niño response observed in simulations of nuclear war scenarios, a 2021 study:

In the case of a nuclear conflict between the world’s superpowers, millions of tons of soot aerosols could be released into the atmosphere, reducing the amount of sunlight reaching the Earth’s surface. This would lead to global surface cooling, a phenomenon called “nuclear winter.” In the case of such a catastrophic event, vast crop failure could follow, leading to widespread food scarcity. Unable to feed the world’s population using land-based farming, people would likely turn to the oceans, but how will marine life fare in such a scenario? This is the question Joshua Coupe of Rutgers University and colleagues set out to answer in their article published in Nature Communications Earth & Environment.

The climate impacts of smoke from fires ignited by nuclear war would include global cooling and crop failure. Facing increased reliance on ocean-based food sources, it is critical to understand the physical and biological state of the post-war oceans. Here authors use an Earth system model to simulate six nuclear war scenarios. Authors show that global cooling can generate a large, sustained response in the equatorial Pacific, resembling an El Niño but persisting for up to seven years. Researchers showed that in the aftermath of a nuclear conflict, tropical regions of the Pacific Ocean would experience a “Nuclear Niño,” a term coined due to the event’s similarity to an El Niño. Nuclear Niño would be characterized by westerly trade wind anomalies and a shutdown of equatorial Pacific upwelling, caused primarily by cooling of the Maritime Continent and tropical Africa. The Pacific Ocean naturally warms up and cools down around every three to seven years, cycling between El Niño (warm) and La Niña (cool) periods. This oscillation in temperature is sensitive to atmospheric events and has tremendous impacts on seafood availability. Specifically, strong El Niño events lead to significant reductions in fisheries production due to reduced availability of nutrients in the marine ecosystem. The researchers argued that a Nuclear Niño would be stronger and longer-lasting than an El Niño, leading to anomalously high sea surface temperatures in the equatorial Pacific lasting seven years. This warming would result in a 40% reduction in algae biomass, which would in turn cause the population of fish dependent on algae for nutrients to decline. Thus, seafood production of the equatorial Pacific region, a major player in the global seafood trade, would plummet. This means that in a post-nuclear war world, humanity will suffer from world-wide food insecurity caused by catastrophic multi-year global climate change that will affect not only land, but also the world’s oceans. These results indicate nuclear war could trigger extreme climate change and compromise food security beyond the impacts of crop failure.

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Nuclear famine:

It is difficult to estimate the number of casualties that would result from nuclear winter, but it is likely that the primary effect would be global famine (known as nuclear famine), wherein mass starvation occurs due to disrupted agricultural production and distribution. A landmark report, Nuclear Famine (2022), published by the International Physicians for the Prevention of Nuclear War (IPPNW) summarizes the latest scientific work which shows that a so-called “limited” or “regional” nuclear war would be neither limited nor regional. A war that detonated less than 1/20th of the world’s nuclear weapons would still crash the climate, the global food supply chains, and likely public order. Famines and unrest would kill hundreds of millions, perhaps even billions. Several independent studies show corroborated conclusions that agricultural outputs would be significantly reduced for years by climatic changes driven by nuclear wars. Reduction of food supply would be further exacerbated by rising food prices, affecting hundreds of millions of vulnerable people, especially in the poorest nations of the world.

Extraordinary events such as large volcanic eruptions or nuclear war could cause sudden global climate disruptions and affect food security. Global volcanic cooling caused by sulfuric acid aerosols in the stratosphere has resulted in severe famines and political instability, for example, after the 1783 Laki eruption in Iceland1 or the 1815 Tambora eruption in Indonesia. For a nuclear war, the global cooling would depend on the yields of the weapons, the number of weapons and the targets, among other atmospheric and geographic factors. In a nuclear war, bombs targeted on cities and industrial areas would start firestorms, injecting large amounts of soot into the upper atmosphere, which would spread globally and rapidly cool the planet. Such soot loadings would cause decadal disruptions in Earth’s climate which would impact food production systems on land and in the oceans. In the 1980s, there were investigations of nuclear winter impacts on global agricultural production and food availability for 15 nations, but new information now allows us to update those estimates. Several studies have recently analysed changes of major grain crops and marine wild catch fisheries for different scenarios of regional nuclear war using climate, crop and fishery models. A war between India and Pakistan, which recently are accumulating more nuclear weapons with higher yield, could produce a stratospheric loading of 5–47 Tg of soot. A war between the United States, its allies and Russia—who possess more than 90% of the global nuclear arsenal—could produce more than 150 Tg of soot and a nuclear winter. While amounts of soot injection into the stratosphere from the use of fewer nuclear weapons would have smaller global impacts, once a nuclear war starts, it may be very difficult to limit escalation.

Global food insecurity and famine from reduced crop, marine fishery and livestock production due to climate disruption from nuclear war soot injection, a 2022 study:

Atmospheric soot loadings from nuclear weapon detonation would cause disruptions to the Earth’s climate, limiting terrestrial and aquatic food production. Here, authors use climate, crop and fishery models to estimate the impacts arising from six scenarios of stratospheric soot injection, predicting the total food calories available in each nation post-war after stored food is consumed. In quantifying impacts away from target areas, authors demonstrate that soot injections larger than 5 Tg would lead to mass food shortages, and livestock and aquatic food production would be unable to compensate for reduced crop output, in almost all countries. Adaptation measures such as food waste reduction would have limited impact on increasing available calories. Authors estimate more than 2 billion people could die from nuclear war between India and Pakistan, and more than 5 billion could die from a war between the United States and Russia—underlining the importance of global cooperation in preventing nuclear war.

The scenarios authors studied are listed in Table below. Each scenario assumes a nuclear war lasting one week, resulting in the number and yield of nuclear weapons shown in the table and producing different amounts of soot in the stratosphere. There are many war scenarios that could result in similar amounts of smoke and thus similar climate shocks, including wars involving the other nuclear-armed nations (China, France, United Kingdom, North Korea and Israel).

Number of weapons on urban targets, yields, direct fatalities from the bomb blasts and resulting number of people in danger of death due to famine for the different scenarios authors studied are depicted in table below:

Soot (Tg)	Number of weapons detonated	Yield (kt)	Number of direct fatalities	Number of people without food at the end of Year 2
5	100	15	27,000,000	255,000,000
16	250	15	52,000,000	926,000,000
27	250	50	97,000,000	1,426,000,000
37	250	100	127,000,000	2,081,000,000
47	500	100	164,000,000	2,512,000,000
150	4,400	100	360,000,000	5,341,000,000

Tg teragram = 10^12 grams = million ton

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Seaweed as a Resilient Food Solution after a Nuclear War, a 2024 study:

An abrupt sunlight reduction scenario like nuclear winter could reduce sunlight and harm agriculture. According to the authors, if nuclear war broke out and thousands of warheads were exchanged between nuclear powers, an estimated 150 Teragram (Tg) of soot emissions could be ejected into the atmosphere, blocking the sunlight for years. But they found that there would still be enough sunlight for seaweeds to photosynthesize and grow, even with black carbon in the atmosphere. Some seaweed species’ light requirement to saturate photosynthesis could be as low as 50–100 µmol photons. Sunlight in the tropics during the noon time of a cloudless day can reach almost 2,000 µmol photons. Seaweed is a promising food source for such events because it can grow quickly in many conditions. Seaweed is rich in nutrients and provides livelihoods for coastal communities in many lower-income countries. Seaweeds, often eaten in salads or as dried food wraps, are rich in proteins, minerals, vitamins, essential amino acids and fatty acids. Authors studied the growth of seaweed globally using a model based on one type of seaweed (kelp), and found that it could provide an equivalent of up to 45% of the world’s food in 9–14 months. The main challenge is building new seaweed farms quickly enough. The growth of seaweed actually increases after a nuclear war, because more nutrients become available in the ocean. This means seaweed has the potential to be a reliable food source in case of abrupt sunlight reduction. While a pure seaweed diet is not possible, this intervention could have an expected value of averting up to ∼1.2 billion deaths from starvation. At their fullest extent, the seaweed farms would replace 15% of the food currently consumed by humans, while also providing 50% of current biofuel production and 10% of animal feed. The main bottleneck to produce enough seaweed to make a significant contribution to global food security is the speed at which the construction of new seaweed farms can be scaled up. Therefore, investments into increasing such capacity could help to avoid a global famine in an abrupt sunlight reduction scenario. In addition, global carbon sequestration with seaweed has a similar demand in inputs as the scale proposed here to use seaweed as a resilient food after a nuclear war (DeAngelo et al., 2022). This means that seaweed farming at a much larger scale than today could combat climate change, while also making the food system much more resilient in abrupt sunlight reduction scenarios.

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Section-20

What to do after a nuclear attack to survive:

How to survive nuclear blast:

A nuclear blast comes in six stages. There’s a flash of light, a wave of heat, a release of nuclear radiation, a fireball, a blast of air, and finally the radioactive fallout. This all happens very quickly—within just a few seconds—but modern early warning systems will likely give you some time to react as ballistic missile take 15 to 30 minutes from enemy country to reach target. Survivability is highly dependent on factors such as if one is indoors or out, the size of the explosion, the proximity to the explosion, and to a lesser degree the direction of the wind carrying fallout. Death is highly likely and radiation poisoning is almost certain if one is caught in the open with no terrain or building masking effects within a radius of 0–3 kilometres (0.0–1.9 mi) from a 1 megaton airburst, and the 50% chance of death from the blast extends out to ~8 kilometres (5.0 mi) from the same 1 megaton atmospheric explosion.

Get inside, stay inside:

A single nuclear weapon could result in tens of thousands, if not hundreds of thousands, of immediate deaths in a major city like New York or Washington. The number of casualties depends on the size of the weapon, where it’s detonated, and how many people are upwind of the blast. The blast zone of a nuclear explosion breaks down into three areas: the severe damage zone, the moderate damage zone, and the light damage zone. If you’re in the severe damage zone (the area consumed by the fireball) your chances of surviving are low, but you may live through it if you have the right shelter. People did survive in Hiroshima and Nagasaki in that zone. And they weren’t in any kind of bunker, they just happened to be in a strong concrete building. One woman survived in a bank just 300 meters from the epicenter. Not in the vault, just the bank. But around the edges of the blast, in the moderate and light damage zones, there is even more room for survival. Your first instinct might be to hit the road, but that could be a deadly mistake. No matter which damage zone you’re in, the safest place to be during a nuclear blast is in a large, secure building. If you do have some warning, find the nearest large, commercial, well-built building. If it’s got a basement, go in there. If it doesn’t, move to the center of the building. Sit tight. Nothing is guaranteed, and you don’t know where the weapon will likely go off, but these kinds of structures do much better against blast, heat, and radiation than anything else. The most important thing to do was to “Get inside and stay inside.” That’s the core message. It does not matter if the explosion came from a small suitcase detonated by a terrorist or an ICBM launched by a rival country, the message to the public is the same: “Get inside and stay inside.”

If done before the detonation (in an attack-warning scenario), seeking shelter can significantly mitigate blast, thermal, and radiation effects. After the detonation, sheltering-in- place can provide protection from exposure to radioactive fallout. This simple protective measure could save hundreds of thousands of lives in a major city. When possible, emergency messaging and pre-incident awareness campaigns should emphasize that the best shelter location is in the center of a large building of heavy construction (e.g., concrete, reinforced brick, cement), away from windows and doors, or in basements and other underground areas (e.g., parking garages, subways). Sheltering in a subterranean basement or the center of a large building provides better protection. In figure below, the numbers in the various rooms represent a “dose reduction factor.” For example, a dose reduction factor of 200 indicates that a person in that area would receive 1/200th of the dose of a person out in the open.

Figure above shows protection factors for a variety of building types.

If a nuke were ever detonated in a modern city, some people in the surrounding areas would make it. They might have about five to 10 seconds after the initial flash to get to safety. If they happened to be in a thick concrete structure with few openings, like in a bank or a subway, they might survive if they used that limited time to run into the corner of a back room with few openings. Being in an enclosed space matters because, the researchers find, the blast winds following the initial fireball can be even more dangerous and deadly than the blast itself. These winds push outward behind the shock wave, and anyone facing the brunt of them could be slammed against a wall at high speed. The winds are especially dangerous if a person is near a door or window or in a corridor or an opening to a room. Winds quickly funnel through such areas, throwing people and furniture around—it’s like a storm let loose in a building. If multiple buildings happen to lie between the structure you’re in and the incoming blast wave, that shadowing effect can lessen the airspeed and forces involved. Those in a basement might avoid the worst blast effects too.

Avert your eyes:

It’s also important to not to look at the bright flash of light emitted as the bomb detonates; it will blind anyone looking at it. This blindness is temporary, only lasting for a few seconds or few minutes, but for that brief time it could make people more vulnerable to hazards such as rubble. The best course of action is simply to avert your eyes. When a nuclear bomb strikes, it sets off a flash of light and a giant orange fireball. A 1-megaton bomb (about 80 times larger than the “Little Boy” atomic bomb dropped on Hiroshima, Japan) could temporarily blind people up to 13 miles away on a clear day and up to 53 miles away on a clear night.

The Centers for Disease Control and Prevention recommends dropping to the ground with your face down and your hands tucked under your body to protect from flying debris or sweltering heat that could burn your skin. If you have a scarf or handkerchief, cover your nose and mouth.

But make sure to keep your mouth open, so your eardrums don’t burst from pressure. Research also suggests that if you’re in an above-ground building, avoid narrow hallways and doorways, which can act like a wind tunnel, accelerating the detonation’s shockwaves to dangerous, bone-crushing pressures. Instead, seek shelter along walls in large, open spaces and avoid rooms with windows, if you can.

How to survive after the early fallout:

Survivors of a nuclear attack would have about 15 minutes before sand-like radioactive particles, known as nuclear fallout, reached the ground. Exposure to fallout can result in radiation poisoning, which can damage the body’s cells and prove fatal. Surviving the initial blast requires some luck even inside a building, but staying safe after the initial detonation requires patience. The nuclear blast will suck up thousands of pounds of dirt and debris, coat that dirt and debris with the fission products produced during the explosion, and after it stabilizes miles up in the air the heavier particles will come down. They will be radioactive. Protecting yourself from exposure to that is something you can do after the blast occurs. Around 15 minutes after the initial blast, this fallout will begin to move through the atmosphere and pepper the ground. Being as far away from that material as possible is what’s going to change your outcomes. Get inside, stay inside, and stay tuned. If you can get into a basement, that’s even better. Cover your mouth and nose with a face mask or other material (such as a scarf or handkerchief) until the fallout cloud has passed. Radioactive iodine will be released by nuclear blast; it can be inhaled or absorbed in food and water. Thus, exposed person should take a KI (potassium iodide) pill immediately after a nuclear blast to prevent the thyroid gland from absorbing radiated particles. KI protects you from I-131 exposure by simply flooding your thyroid with safe potassium iodide until no more can be absorbed. Each dose offers twenty-four hours of protection (per dose) to help reach safety.

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Blast Shelters:

Some structures, particularly those designed for the purpose, offer substantial protection against direct nuclear effects (blast, thermal radiation, ionizing radiation, and related effects such as induced fires). Since blast is usually the most difficult effect to protect against, such shelters are generally evaluated on blast resistance, and protection against other direct effects is assumed. Since most urban targets can be destroyed by an overpressure of 5 to 10 psi, a shelter providing protection against an overpressure of about 10 psi is called a blast shelter, although many blast shelters offer greater protection. Other shelters provide good protection against fallout, but little resistance to blast–are called “fallout shelters”. Blast shelters generally protect against fallout, but best meet this purpose when they contain adequate Life-support systems. (For example, a subway station without special provisions for water and ventilation would make a good blast shelter but a poor fallout shelter.)

Nuclear explosions produce “rings” of various overpressures. If the overpressure at a given spot is very low, a blast shelter is unnecessary; if the overpressure is very high (e. g., a direct hit with a surface burst), even the best blast shelters will fail. The “harder” the blast shelter (that is, the greater the overpressure it can resist), the greater the area in which it could save its occupants’ lives. Moreover, if the weapon height of burst (HOB) is chosen to maximize the area receiving 5 to 10 psi, only a very small area (or no area at all) receives more than 40 to 50 psi. Hence, to attack blast shelters of 40 to 50 psi (which is a reasonably attainable hardness), weapons must be detonated at a lower altitude, reducing the area over which buildings, factories, etc., are destroyed.

Another problem is protection against fallout. If a sheltered population is to survive fallout, two things must be done. First, fallout must be prevented from infiltrating shelters through doors, ventilation, and other conduits. Other measures to prevent fallout from being tracked or carried into a shelter must also be taken. More important, the shelter must enable its occupants to stay inside as long as outside radiation remains dangerous; radiation doses are cumulative and a few brief exposures to outside fallout may be far more hazardous than constant exposure to a low level of radiation that might penetrate into a shelter.

Since radiation may remain dangerous for periods from a few days to several weeks, each shelter must be equipped to support its occupants for at least this time. Requirements include adequate stocks of food, water, and necessary medical supplies, sanitary facilities, and other appliances. Equipment for controlling temperature, humidity, and “air quality” standards is also critical. With many people enclosed in an airtight shelter, temperatures, humidity, and carbon dioxide content increase, oxygen availability decreases, and fetid materials accumulate. Surface fires, naturally hot or humid weather, or crowded conditions may make things worse. If unregulated, slight increases in heat and humidity quickly lead to discomfort; substantial rises in temperature, humidity, and carbon dioxide over time could even cause death. Fires are also a threat to shelterers because of extreme temperatures (possibly exceeding 2,000” F) and carbon monoxide and other noxious gases. A large fire might draw oxygen out of a shelter, suffocating shelterers. World War II experience indicates that rubble heated by a firestorm may remain intolerably hot for several days after the fire is put out.

Fallout shelter:

A fallout shelter is an enclosed space specially designated to protect occupants from radioactive debris or fallout resulting from a nuclear explosion. Many such shelters were constructed as civil defense measures during the Cold War. Fallout protection is relatively easy to achieve. Any shielding material reduces the radiation intensity. Different materials reduce the intensity by differing amounts. For example, the thickness (in inches) of various substances needed to reduce gamma radiation by a factor of 10 is: steel, 3.7; concrete, 12; earth, 18; water, 26; wood, 50. Consider an average home basement that provides a protection factor (PF) of 10 (reduces the inside level of radiational protection, a family sheltered here could still be exposed to dangerous levels of radiation over time. For example, after 7 days an accumulated dose of almost 400 rems inside the basement would occur if the radiation outside totalled 4,000 roentgens. This could be attenuated to a relatively safe accumulation of 40 rems, if about 18 inches of dirt could be piled against windows and exposed walls before the fallout begins. Thirty-six inches of dirt would reduce the dose to a negligible level of 4 rems. Thus, fallout protection is as cheap as dirt. Moving dry, unfrozen earth to increase the protection in a fallout shelter requires considerable time and effort, if done by hand. A cubic foot of earth weighs about 100 lbs; a cubic yard about 2,700 Ibs. Given time, adequate instructions, and the required materials, unskilled people can convert home basements into effective fallout shelters.

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Is it true that cockroaches could survive a nuclear holocaust?

No.

Their reputation for radiation resistance is greatly exaggerated. Granted, they are tougher than humans, but that’s true of virtually all insects. Their simpler bodies and much shorter lifespans inherently make them less vulnerable, but a cockroach can only survive between six and 15 times the lethal radiation dose for humans. The exception being the parasitic wasp Habrobracon, which can cope with over 180 times our lethal exposure.

Researchers conducted a small study on German cockroach. They exposed the cockroaches to three radiation doses from cobalt-60 for a month: 1000 rads, 10,000 rads, and 100,000 rads. To put this in perspective, the gamma rays released by the Hiroshima bomb were about 10,000 rads. After 30 days, half of the roaches exposed to 1000 rads remained alive, 10% of the roaches in the 10,000 rad group were alive, but none of the insects in the 100,000 rad group survived. The results showed some cockroaches can survive the radiation from a nuclear explosion, but that they eventually succumb if the radiation lasts too long or the dose is too high.

While humans, cockroaches, and other creatures may survive the initial detonation of an atomic bomb, they don’t survive at Ground Zero and they might not live for long. At ground zero, cockroaches and humans get blasted by heat to the tune of 10 million degrees Celsius. Even 50 meters away, temperatures hit 10,000 degrees. Only creatures far enough away from the blast have a chance of survival.

Many microbes can handle amazingly high amounts of radiation, particularly those that live in deserts. The extreme stress of living in such a harsh environment, where desiccation and higher levels of ultraviolet radiation are a constant threat, would seem to give these microbes an advantage in surviving a nuclear war. The same goes for certain large desert animals, such as scorpions. In general, the smaller you are, the better. Possibly the most radiation-resistant organism yet discovered is Deinococcus radiodurans, which is famous for its ability to quickly repair damage due to radiation. These hardy microbes can easily take 1,000 times the radiation dose that would kill a human. A type of wheel-shaped microscopic animal called bdelloid rotifers also have been found to be extremely resistant to radiation. So have tardigrades, also known as water bears or moss piglets. Some fish, like goldfish or the mummichog, are quite hardy when it comes to withstanding radiation. When trying to predict what types of species would survive a nuclear war, we need to consider not only radiation resistance but lifestyle. Tardigrades, for example, could survive nearly any type of radiation fallout in their dormant stage. But that wouldn’t help them much if all their food was gone when they woke up. Survival also will depend on where you live. Birds would be particularly vulnerable, as would any surface dwellers. But animals that live below ground, including the naked mole rat would have a better chance of pulling through. As far as nuclear famine is concerned, there will be starvation over much of the globe, not only for humans but for many animals.

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Australia and New Zealand are best placed to survive nuclear apocalypse, a study finds:

The lucky country can count on one more piece of good fortune, with researchers finding Australia – followed by neighbour New Zealand – best placed to survive a nuclear winter and help reboot a collapsed human civilisation. The study ‘Island refuges for surviving nuclear winter and other abrupt sunlight-reducing catastrophes’ published in the journal Risk Analysis in 2022 describes Australia, New Zealand, Iceland, Solomon Islands and Vanuatu as the island countries most capable of producing enough food for their populations after an “abrupt sunlight‐reducing catastrophe” such as a nuclear war, super volcano or asteroid strike. There would “likely be pockets of survivors around the planet in even the most severe” scenario, the researchers write – with those in the most resilient nations standing the best chance of avoiding a pre-industrial collapse.

The authors compared 38 island countries on 13 factors they said could predict success as a post-apocalyptic survival state, including food production, energy self-sufficiency, manufacturing and the disaster’s effect on climate. Australia and New Zealand – both robust agricultural producers and tucked away from the likely sites of northern hemisphere nuclear fallout – topped the tables, with Australia performing best overall. “Australia’s food supply buffer is gigantic,” the study concludes, “with potential to feed many tens of millions of extra people.” Australia’s relatively good infrastructure, vast energy surplus, high health security and defence budget all aided in pushing it to the top of the table. Australia did have one major factor working against it, however: its relatively close military ties with the UK and US made it more likely to become a target in a nuclear war.

In this area, New Zealand displayed some advantages, the authors said, with its longstanding nuclear-free status. Its resilience in the event of an abrupt drop in global temperature prompted by a period of darkness (everywhere in New Zealand is relatively close to the ocean, cushioning it from extreme temperature plunges) would also help. “We have this super efficient food export economy that could feed New Zealanders multiple times over just from exports,” said one of the study’s authors, Prof Nick Wilson from the University of Otago, Wellington. Even in the worst-case scenario – a 61% reduction in crops during a prolonged nuclear winter – New Zealanders would still have enough to eat, he added. Despite New Zealand’s abundance of food and its high ranking on social cohesion metrics, a shutdown of global trade could precipitate social collapse by degrees, Wilson added.

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Section-21

Measures to prevent nuclear holocaust:

Although nuclear weapons have only been used twice in warfare, about 12,500 reportedly remain in our world today and there have been over 2,000 nuclear tests conducted to date. Disarmament is the best protection against such dangers but achieving this goal has been a tremendously difficult challenge. The UN has sought to eliminate such weapons ever since its establishment. The first resolution adopted by the UN General Assembly in 1946 established a Commission to deal with problems related to the discovery of atomic energy among others. The Commission was to make proposals for, inter alia, the control of atomic energy to the extent necessary to ensure its use only for peaceful purposes. Several multilateral treaties have since been established with the aim of preventing nuclear proliferation and testing, while promoting progress in nuclear disarmament. These include the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), the Treaty Banning Nuclear Weapon Tests In The Atmosphere, In Outer Space And Under Water, also known as the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which was signed in 1996 but has yet to enter into force, and the Treaty on the Prohibition of Nuclear Weapons (TPNW). The International Day for the Total Elimination of Nuclear Weapons is celebrated on September 26th every year to raise awareness about the threat of nuclear weapons and to promote their elimination. It was declared by the UN General Assembly in 2013.

Missiles continue to be a focus of increased international attention, discussion, and activity. Their potential to carry and deliver weapons of mass destruction (WMD) payload quickly and accurately makes missiles a qualitatively significant political and military issue. In addition, the diversity of international views on matters related to missiles poses a particular challenge for efforts to address the issue in multilateral fora. Currently, there is no legally binding multilateral instrument dealing with the issue of missiles. Pursuant to General Assembly resolutions, three Panels of Government Experts devoted to the issue of missiles have been established within the United Nations. Presently, several other multilateral regimes exist which seek to prevent the proliferation of missiles and related technology. These include, notably, the Hague Code of Conduct (HCOC) and the Missile Technology Control Regime (MTCR).

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Why Countries Acquire and Abandon Nuclear Bombs:

The decision to build a nuclear program is often shaped by a range of domestic and international economic and political factors as seen in the figure below:

The decisions to acquire and give up nuclear weapons are not simple: they are informed by domestic and international issues and threats, both real and perceived. The decision to build or destroy a nuclear weapons program can have life altering ramifications for citizens of one’s country and those living around the world.

South Africa is the only country in the world to have developed and then dismantled its nuclear program. The South African case offers insights into why leaders of a country would seek to acquire nuclear weapons and why they would give them up. Of course, South Africa armed and disarmed in secret, so its exact motivations can be difficult to determine. But declassified documents and official accounts help historians understand what drove the country’s leaders to pursue a nuclear program and then abandon it less than two decades later.

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Safeguards to Prevent Nuclear Proliferation:

The initial development of nuclear technology was military, during World War II. Two nuclear bombs made from uranium-235 and plutonium-239 were dropped on Japan’s Hiroshima and Nagasaki respectively in August 1945 and these brought the long war to a sudden end. The immense and previously unimaginable power of the atom had been demonstrated. Then attention turned to civil applications. In the course of half a century nuclear technology has enabled access to significant source of energy at a time when constraints are arising on the use of fossil fuels. The question is: To what extent and in what ways does nuclear power generation contribute to or alleviate the risk from nuclear weapons?

In the 1960s it was widely assumed that there would be 30-35 nuclear weapons states by the turn of the century. In fact there were eight – a tremendous testimony to the effectiveness of the Nuclear Non-Proliferation Treaty (NPT) and its incentives both against weapons and for civil nuclear power, despite the baleful influence of the Cold War (1950s to 80s) which saw a massive build-up of nuclear weapons particularly by the USA and the Soviet Union. Possession of nuclear weapons is evidently for military deterrence, but the proposition that more of them in more countries would diminish warfare is not widely accepted, and is rejected as a basis for international policy. The nuclear non-proliferation regime is much more than the NPT, although this is the pre-eminent international treaty on the subject. The regime includes treaties, conventions and common (multilateral and bilateral) arrangements covering security and physical protection, export controls, nuclear test-bans and, potentially, fissile material production cut-offs. The international community can apply pressure to states outside the NPT to make every possible effort to conform to the full range of international norms on nuclear non-proliferation that make up this regime.

The International Atomic Energy Agency (IAEA):

The IAEA was set up by unanimous resolution of the United Nations in 1957 to help nations develop nuclear energy for peaceful purposes. Allied to this role since 1970 is the administration of safeguards arrangements. This provides assurance to the international community that individual countries are honouring their treaty commitments to use nuclear materials and facilities exclusively for peaceful purposes. The IAEA therefore undertakes regular inspections of civil nuclear facilities to verify the accuracy of documentation supplied to it. The agency checks inventories and undertakes sampling and analysis of materials. Safeguards are designed to deter diversion of nuclear material by increasing the risk of early detection. They are complemented by controls on the export of sensitive technology from countries such as UK and USA through voluntary bodies such as the Nuclear Suppliers’ Group. The international safeguards system has since 1970 successfully prevented the diversion of fissile materials into weapons. Its scope has been widened to address undeclared nuclear activities. Safeguards are backed by diplomatic and economic measures including international sanctions.

Safeguards in countries with nuclear weapons:

In Nuclear Weapons States, IAEA safeguards apply under a “voluntary offer agreement”. Where offered, facilities are put on each state’s “list of facilities that are eligible for IAEA safeguards” and it is up to the IAEA to decide which (if any) to inspect. However, all these facilities must maintain IAEA-standard accounting.

	First weapons test	Safeguards situation for nuclear power
USA	1945	All civil nuclear facilities are subject to IAEA safeguards. The National Nuclear Safety Administration (NNSA) applies some materials accounting to all fuel cycle facilities and communicates with the IAEA.
UK	1952	All civil nuclear facilities are subject to IAEA safeguards.
Russia	1949	IAEA safeguards not generally applied, though this is changing*.
France	1960	All civil nuclear facilities are under Euratom safeguards, all civil facilities containing safeguards-obligated nuclear material are subject to IAEA safeguards.
China	1964	All imported nuclear power plants are under IAEA safeguards, as is the Russian-supplied Shaanxi centrifuge enrichment plant.
India	1974	14 civil power reactors are under IAEA safeguards, along with all future civil facilities, pursuant to 2008 US-India agreement and 2014 Additional Protocol.
Pakistan	1998	Civil power reactors under item-specific IAEA safeguards.
Israel	nil	No nuclear power plant
North Korea	2006	No nuclear power plant

* To date civil facilities have not been made subject to IAEA safeguards unless they are of value to IAEA, e.g. for training or experience. However, Angarsk international fuel cycle centre is subject to IAEA safeguards, and an increasing number of civil facilities are expected to be made subject to IAEA safeguards in the future due to increasing commerce.

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Reducing risk of nuclear war:

The only way to completely eliminate nuclear risks is to eliminate nuclear weapons from the planet. Roughly 9,500 nuclear weapons are hidden away in bunkers and missile siloes, stored in warehouses, at airfields and naval bases, and carried by dozens of submarines across the world. A single warhead can demolish a city center. A full-fledged nuclear war would threaten life as we know it. But with the right policies and safeguards, we can help protect against mistakes, accidents, and poor decision-making—and we can work toward a world free from the nuclear threat.

-1. No-first-use:

Nuclear weapons are meant to deter nuclear attacks from other countries. However, current policy allows the United States to begin a nuclear war by being the first to use nuclear weapons in a conflict—in response to a non-nuclear attack by North Korea, Russia, or China. A “no-first-use” policy would take this option off the table. The United States and other nuclear powers could pledge that it will never be the first to use a nuclear weapon, regardless of the circumstances. Doing so would reduce the risk of miscalculation during a crisis, and limit the possibility of a smaller, non-nuclear conflict escalating into a nuclear one. Without no-first-use, the US public is at greater risk of a devastating attack, either because another country—fearing the US will use nuclear weapons— decides to escalate first, or the United States chooses to start a nuclear war, leading to cataclysmic retaliation. India and China have no first use policy and other nuclear powers must endorse it.

-2. Sole authority:

In the United States, the president is singlehandedly responsible for the decision to launch a nuclear weapon. They are not required to consult with anyone, and no one carries the authority to stop a legal launch order once given. This system of control (known as “sole authority”) isn’t the only way to handle launch decisions. Other officials could securely be included in the decision, providing checks and balances and a basic defense against mistakes, accidents, miscalculations, and recklessness. In my view, no one person can be so wise that he/she alone can take decision to launch nuclear weapon. We need unanimous decision of three people; president (or prime minister), leader of opposition (or speaker of parliament) and chief justice of supreme court.

-3. De-alerting (Off hair-trigger alert):

Hair-Trigger Alert means nuclear warheads are kept ready to launch within minutes—making us less safe, not safer. Currently, 800 nuclear-tipped missiles in the US heartland are kept on “hair-trigger alert.” If sensors show an incoming nuclear attack that threatens these missiles, it’s US policy to alert the president, who would need to order their almost immediate launch to prevent them from being destroyed—before the attack is confirmed as real. Once such a counterstrike, which could kill millions, is launched, it is impossible to recall the missiles. But sensors can be wrong. A long list of nuclear close calls—which include technical malfunctions, miscommunications, and plain bad luck—shows how close we’ve come to mistakenly starting nuclear war. Taking these missiles off hair-trigger alert (or “de-alerting”) would immediately remove the risk of a mistaken or accidental launch, while preserving ability to retaliate with missiles on submarines hidden at sea. The United States and Russia should work together to take these weapons off hair-trigger alert. United States and Russia would both be much more secure if the risk of an accidental, mistaken, or unauthorized launch of a nuclear ballistic missile were further reduced.

-4. International agreements and treaties:

A total of nine countries possesses nuclear weapons. Reducing the risk of nuclear war will require domestic policy changes in all those countries, as well as cooperation and verified agreements between them. Several non-proliferation treaties have been key in achieving the large reduction of nuclear stockpiles. Diplomacy has a strong track record. Multiple treaties and agreements—and decades of dialogue and cooperation—helped reduce US and Soviet arsenals from a high of 64,000 warheads in the 1980s to a total of around 8,000 today.

For over 50 years, but especially since the end of the cold war, the United States and the Russian Federation (formerly the Soviet Union) have engaged in a series of bilateral arms control measures that have drastically reduced their strategic nuclear arsenals as seen in the figure below.

Key treaties:

Partial Test Ban Treaty (PTBT) 1963: Prohibited all testing of nuclear weapons except underground.
Nuclear Non-Proliferation Treaty (NPT)—signed 1968, came into force 1970: An international treaty (currently with 189 member states) to limit the spread of nuclear weapons. The treaty has three main pillars: nonproliferation, disarmament, and the right to peacefully use nuclear technology.
Interim Agreement on Offensive Arms (SALT I) 1972: The Soviet Union and the United States agreed to a freeze in the number of intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) that they would deploy.
Anti-Ballistic Missile Treaty (ABM) 1972: The United States and Soviet Union could deploy ABM interceptors at two sites, each with up to 100 ground-based launchers for ABM interceptor missiles. In a 1974 Protocol, the US and Soviet Union agreed to only deploy an ABM system to one site.
Strategic Arms Limitation Treaty (SALT II) 1979: Replacing SALT I, SALT II limited both the Soviet Union and the United States to an equal number of ICBM launchers, SLBM launchers, and heavy bombers. Also placed limits on Multiple Independent Reentry Vehicles (MIRVS).
Intermediate-Range Nuclear Forces Treaty (INF) 1987: Banned US and Soviet Union land-based ballistic missiles, cruise missiles, and missile launchers with ranges of 500–1,000 kilometers (310–620 mi) (short medium-range) and 1,000–5,500 km (620–3,420 mi) (intermediate-range).
Strategic Arms Reduction Treaty (START I)—signed 1991, ratified 1994: Limited long-range nuclear forces in the United States and the newly independent states of the former Soviet Union to 6,000 attributed warheads on 1,600 ballistic missiles and bombers.
Strategic Arms Reduction Treaty II (START II)—signed 1993, never put into force: START II was a bilateral agreement between the US and Russia which attempted to commit each side to deploy no more than 3,000 to 3,500 warheads by December 2007 and also included a prohibition against deploying multiple independent reentry vehicles (MIRVs) on intercontinental ballistic missiles (ICBMs)
Strategic Offensive Reductions Treaty (SORT or Moscow Treaty)—signed 2002, into force 2003: A very loose treaty that is often criticized by arms control advocates for its ambiguity and lack of depth, Russia and the United States agreed to reduce their “strategic nuclear warheads” (a term that remained undefined in the treaty) to between 1,700 and 2,200 by 2012. Was superseded by New Start Treaty in 2010.
Comprehensive Nuclear-Test-Ban Treaty (CTBT)—signed 1996, not yet in force: The CTBT is an international treaty (currently with 181 state signatures and 148 state ratifications) that bans all nuclear explosions in all environments. While the treaty is not in force, Russia has not tested a nuclear weapon since 1990 and the United States has not since 1992.
New START Treaty— signed 2010, into force in 2011: replaces SORT treaty, reduces deployed nuclear warheads by about half, will remain into force until 2026.
Treaty on the Prohibition of Nuclear Weapons— signed 2017, entered into force on January 22, 2021: prohibits possession, manufacture, development, and testing of nuclear weapons, or assistance in such activities, by its parties.

Only one country (South Africa) has been known to ever dismantle an indigenously developed nuclear arsenal completely. The apartheid government of South Africa produced half a dozen crude fission weapons during the 1980s, but they were dismantled in the early 1990s.

Figure below offers a high-level summary of the status and scope of current and historical nuclear disarmament treaties as of 2012.

Figure above shows Strategic Nuclear Arms Control Agreements

Figure below shows how various treaties reduced weapons:

Unfortunately, today international nuclear arms control is in trouble. The Biden administration’s 5-year extension of the New Strategic Arms Reduction Treaty (New START) with Russia, is the last remaining bilateral arms control agreement between the two countries. In 2023 Russian President Vladimir Putin announced his decision to suspend the New Strategic Arms Reduction Treaty (New START), further weakening the last remaining treaty limiting U.S. and Russian strategic nuclear arsenals. To resume treaty activities, the United States would need to cut off support for Ukraine and bring France and the United Kingdom into arms control talks, he said. Negotiation of a new agreement, or renewal of the current agreement would reduce nuclear risk but will be difficult to achieve. Separately, China strongly prefers international approaches to arms control rather than bilateral agreements. It is willing to work with the US government to bring the Comprehensive Nuclear Test Ban Treaty into force and negotiate a Fissile Material Cutoff Treaty. Both agreements would make the United States and the world more secure.

Smaller nuclear stockpiles:

Reducing the stockpiles further is seen as an important and achievable goal by experts. It is considered achievable because smaller stockpiles would still provide the deterrence benefits from nuclear weapons. And it is important as it reduces the risk of accidents and the chance that a possible nuclear war would end civilization.

Better monitoring, better control:

The risk can be further reduced by efforts to better control nuclear weapons – so that close calls occur less frequently. Similarly better monitoring systems would reduce the chance of false alarms. Taking nuclear weapons off ‘hair-trigger alert’ would reduce the risk that any accident that does occur can rapidly spiral out of control. And a well-resourced International Atomic Energy Agency can verify that the agreements in the treaties are met.

Better public understanding, global relations, and culture:

It will help to see clearly that billions of us share the same goal. None of us wants to live through a nuclear war, none of us wants to die in one. As Reagan said, a nuclear war cannot be won and it would be better to do away with these weapons entirely. A generation ago, a broad and highly visible societal movement pursued the goal of nuclear disarmament. These efforts were to a good extent successful. But since then, this goal has unfortunately lost much of the attention it once received – and this is despite the fact that things have not fundamentally changed: the world still possesses weapons that could kill billions. It is time more young people would set themselves the goal to make the world safe from nuclear weapons.

Nuclear disarmament:

Nuclear disarmament refers both to the act of reducing or eliminating nuclear weapons and to the end state of a nuclear-free world. Proponents of disarmament typically condemn a priori the threat or use of nuclear weapons as immoral and argue that only total disarmament can eliminate the possibility of nuclear war. Critics of nuclear disarmament say that it would undermine deterrence and make conventional wars more likely, more destructive, or both. The debate becomes considerably complex when considering various scenarios for example, total vs partial or unilateral vs multilateral disarmament.

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Pro and Cons of the Policy to assassinate nuclear scientists to retard nuclear weapon program:

Targeting atomic scientists to retard a potential nuclear weapons program predates the existence of nuclear weapons. Alarmed by the possibility that the giant of German physics, Werner Heisenberg, was working on an atomic bomb for Adolf Hitler, noted theoretical physicist Victor Weisskopf consulted with Hans Bethe, a renowned colleague working in the Manhattan Project, in the autumn of 1942; Weisskopf subsequently corresponded with Robert Oppenheimer, then newly appointed to lead theoretical work for the Manhattan Project. According to Thomas Powers’s account in Heisenberg’s War, Weisskopf wrote, “I believe that by far the best thing to do in this situation would be to organize a kidnapping of Heisenberg in Switzerland” (Weisskopf, 1942). Over time, within the Manhattan Project and the Office of Strategic Services (OSS), Weisskopf’s proposal mutated into a plot to kill Heisenberg—a plot that very nearly came to pass.

Since 2007, international media have reported the violent deaths of four scientists and engineers connected with Iran’s nuclear program and an attempt on the life of a fifth. Responsibility for the killings and attempted killings of the Iranian nuclear scientists remains an unsolved mystery. Iran has accused several countries, but all have denied involvement. It is therefore impossible to know, with certainty, the thinking of those who sponsored the assassination plots. Nonetheless, assassinations would not go forward if the country sponsoring them did not believe there was some possibility of achieving positive results.

History suggests that when nations contemplate the extreme step of targeting nuclear scientists in another country, they are focused on the existential imperative that a hostile nuclear weapons program can raise. When the potential negative consequences of inaction are perceived to be infinite, otherwise reasonable doubts—about the quality of intelligence, or the negative consequences associated with unsavoury action—may seem irrelevant. The spectre of annihilation dramatically changes risk–benefit analyses. Under such circumstances, doing something will nearly always appear better than doing nothing.

A nation that made the fateful decision to proceed with assassinating nuclear scientists could hope, at most, to delay, but not halt, a hostile nuclear weapons program. Assassination might produce an effect beyond the individual scientists who are killed, perhaps deterring other scientists from joining or continuing to work in a nuclear program. Nonetheless, the empirical evidence is clear: Nuclear weapons programs are large, complex undertakings, involving hundreds of key people. Killing a few workers, even if they are talented and working on important projects, will not halt the undertaking. It is difficult to imagine a country having a scientific infrastructure large enough to support a nuclear weapons program, but too small to sustain a viable effort after the loss of even several individuals. Targeting scientists would probably be less effective than military strikes on nuclear facilities in terms of lasting programmatic setbacks. Because of its deniability, however, assassination might be seen as less provocative than an overt military operation. As a result, it might also carry a lower risk—in terms of both likelihood and severity of retaliation. These are modest advantages, even from the perspective of a nation that fears a failure to act will lead to its own destruction.

The disadvantages of targeting nuclear scientists are, of course, many:

First, even in theory, it is very difficult to target effectively those scientists and engineers most critical to a program’s success. Such precise targeting would require intimate and detailed knowledge of a program’s day-to-day operations and problem solving—a difficult matter, given that nuclear proliferation programs are shrouded in secrecy. Moreover, it is not enough simply to target those who have made significant past contributions to a program. Rather, it would be necessary to predict whose skills will be necessary to solve future technological problems. Neither is seniority necessarily a useful gauge; depending on the maturity of a program, engineers may be more valuable than scientists, and technicians, who actually operate machinery, may be most indispensable of all. At least with respect to crude but still-devastating nuclear weapons, manufacture is now more about engineering than science.

Second, targeted killings can be counterproductive, providing the country with a covert nuclear program a reason to diminish cooperation with the IAEA.

Third, and related to the previous disadvantage, targeted killings would inevitably increase operational security within a nuclear proliferation program. If secrecy is a matter of life and death, security breaches are likely to be fewer and farther between. Given that lack of information about the progress of nuclear programs is a huge barrier to effective export control and diplomatic or military action, this is a significant problem.

Fourth, killing nuclear personnel may well have a strong negative effect on any chance of a negotiated solution to a nuclear proliferation issue. Such action understandably raises levels of hostility and mistrust within the targeted program. Given the covert origins of Iran’s enrichment program and its longstanding refusal to abide by IAEA Board of Governors and UN Security Council resolutions, it is not clear that a negotiated solution to the nuclear crisis is or ever was possible, but the violent deaths of several Iranian nuclear personnel are likely to harden Tehran’s position.

Finally, targeted killings of nuclear scientists may provoke retaliation, either in-kind or asymmetrical.

Can targeted killings of nuclear scientists be justified?

Nuclear scientists are different from terrorists. They do not pose an immediate threat of violence against another nation. Presumably, they are acting within the laws of their country. They are working under instructions of their political and military leadership. Unless their nation is at war, they are not obviously legitimate military targets.

Prudent nations will contemplate assassinations only in the gravest of circumstances. These circumstances would seem to have to include at least several components: There must be solid and substantial evidence of a covert nuclear weapons program. That program must be in the hands of a hostile power that has such fundamental differences with another country as to pose an existential threat to it, attempts to deter notwithstanding. There must be no credible possibility of a diplomatic solution. In short, the circumstances are those that would make an act of desperation seem reasonable. Given the obviously limited advantages and serious disadvantages of targeted killing of nuclear scientists, a state that undertakes such action must calculate that it has essentially no other choice: that all other options (short of military operations) to halt a hostile nuclear weapons program have failed and will fail, that time is running short, and that knowledge about the status and development of the program is less important than slowing it down immediately.

My view:

I condemn assassination of nuclear scientists to retard nuclear weapon program. Let me give one example. How about a Japanese assassinating Oppenheimer for Hiroshima and Nagasaki. The decision to bomb was taken by political and military leaders of America, and Oppenheimer was only doing his job. If America and Japan were not at war, even if Oppenheimer designed a fission bomb, it would not be used. Don’t blame scientist for faulty leadership. The same fission reaction is generating electricity thanks to scientists. It is the political and military leaders of world that are pursuing nuclear weapon program and they have to be held accountable for the mess we are in.

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Anti-nuclear movement:

Antinuclear movement is a social movement opposed to the production of nuclear weapons and the generation of electricity by nuclear power plants. The goals and ideologies of the antinuclear movement range from an emphasis on peace and environmentalism to intellectual social activism based on knowledge of nuclear technology and to political and moral activism based on conflicts between nuclear power applications and policies and personal values. Antinuclear organizations tend to emphasize alternative energy sources, the dangers of the proliferation of nuclear weapons, possible environmental hazards, and the safety of nuclear-industry workers. Many seek a complete moratorium on nuclear development and research. Arguing that nuclear-related terrorist attacks and nuclear accidents are probable and that radioactive waste is difficult to adequately dispose of, antinuclear activists push for alternative energy technologies to meet the needs of the human race prior to the depletion of fossil fuels.

The anti-nuclear movement is a social movement that opposes various nuclear technologies. Some direct action groups, environmental movements, and professional organisations have identified themselves with the movement at the local, national, or international level. Major anti-nuclear groups include Campaign for Nuclear Disarmament, Friends of the Earth, Greenpeace, International Physicians for the Prevention of Nuclear War, Peace Action, Seneca Women’s Encampment for a Future of Peace and Justice and the Nuclear Information and Resource Service. The initial objective of the movement was nuclear disarmament, though since the late 1960s opposition has included the use of nuclear power. Many anti-nuclear groups oppose both nuclear power and nuclear weapons. The formation of green parties in the 1970s and 1980s was often a direct result of anti-nuclear politics.

Many studies have shown that the public “perceives nuclear power as a very risky technology” and, around the world, nuclear energy declined in popularity in the aftermath of the Fukushima Daiichi nuclear disaster, but it has recently rebounded in response to the climate crisis. Anti-nuclear critics see nuclear power as a dangerous, expensive way to boil water to generate electricity. Opponents of nuclear power have raised a number of related concerns:

Nuclear accidents: a safety concern that the core of a nuclear power plant could overheat and melt down, releasing radioactivity.
Nuclear Fuel Mining: mining of nuclear fuels like uranium and thorium causes radium pollution and radon pollution in environment and ultimately affects public health.
Radioactive waste disposal: a concern that nuclear power results in large amounts of radioactive waste, some of which remains dangerous for very long periods.
Nuclear proliferation: a concern that some types of nuclear reactor designs use and/or produce fissile material which could be used in nuclear weapons.
High cost: a concern that nuclear power plants are very expensive to build, and that clean up from nuclear accidents are highly expensive and can take decades.
Attacks on nuclear plants: a concern that nuclear facilities could be targeted by terrorists or criminals.
Curtailed civil liberties: a concern that the risk of nuclear accidents, proliferation and terrorism may be used to justify restraints on citizen rights.

Of these concerns, nuclear accidents and disposal of long-lived radioactive waste have probably had the greatest public impact worldwide. Anti-nuclear campaigners point to the 2011 Fukushima nuclear emergency as proof that nuclear power can never be 100% safe. Costs resulting from the Fukushima Daiichi nuclear disaster are likely to exceed 12 trillion yen ($100 billion) and the clean up effort to decontaminate affected areas and decommission the plant is estimated to take 30 to 40 years.

Anti-nuclear organizations:

The anti-nuclear movement is a social movement which operates at the local, national, and international level. Various types of groups have identified themselves with the movement:

direct action groups, such as the Clamshell Alliance and Shad Alliance
environmental groups, such as Friends of the Earth and Greenpeace
consumer protection groups, such as Ralph Nader’s Critical Mass
professional organisations, such as International Physicians for the Prevention of Nuclear War
political parties such as European Free Alliance

Anti-nuclear organizations may oppose uranium mining, nuclear power, and/or nuclear weapons. Anti-nuclear groups have undertaken public protests and acts of civil disobedience which have included occupations of nuclear plant sites. Other salient strategies have included lobbying, petitioning government authorities, influencing public policy through referendum campaigns and involvement in elections. Anti-nuclear groups have also tried to influence policy implementation through litigation and by participating in licensing proceedings.

Anti-nuclear power organisations have emerged in every country that has had a nuclear power programme. Protest movements against nuclear power first emerged in the United States, at the local level, and spread quickly to Europe and the rest of the world. National nuclear campaigns emerged in the late 1970s. Fuelled by the Three Mile Island accident and the Chernobyl disaster, the anti-nuclear power movement mobilised political and economic forces which for some years “made nuclear energy untenable in many countries”. In the 1970s and 1980s, the formation of green parties was often a direct result of anti-nuclear politics (e.g., in Germany and Sweden).

Some of these anti-nuclear power organisations are reported to have developed considerable expertise on nuclear power and energy issues. In 1992, the chairman of the Nuclear Regulatory Commission said that “his agency had been pushed in the right direction on safety issues because of the pleas and protests of nuclear watchdog groups”.

ICAN:

The International Campaign to Abolish Nuclear Weapons (ICAN) is a broad, inclusive campaign, focused on mobilizing civil society around the world to support the specific objective of prohibiting and eliminating nuclear weapons. ICAN was launched in 2007. In 2022, it counted 661 partner organizations in 110 countries. It is working to promote adherence to and full implementation of the Treaty on the Prohibition of Nuclear Weapons. The campaign helped bring about this treaty. The Treaty on the Prohibition of Nuclear Weapons (TPNW) prohibits States Parties from developing, testing, producing, manufacturing, acquiring, possessing, or stockpiling nuclear weapons or other nuclear explosive devices. The Treaty on the Prohibition of Nuclear Weapons (TPNW) now has 73 states parties while 25 further states have signed but not yet ratified. This means that a total of 98 states (or 49.75% of all states) have accepted binding obligations in international law under the TPNW. Only one more signature or accession is needed to pass the 50% mark of the 197 states that can adhere to the treaties in the legal architecture for weapons of mass destruction (WMD). The campaign received the 2017 Nobel Peace Prize “for its work to draw attention to the catastrophic humanitarian consequences of any use of nuclear weapons and for its ground-breaking efforts to achieve a treaty-based prohibition of such weapons.”

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Moral of the story:

-1. The most important fissile materials for nuclear energy and nuclear weapons are an isotope of plutonium, plutonium-239, and an isotope of uranium, uranium-235. In nuclear reactors, the fission process is controlled and the energy is harnessed to produce electricity. In nuclear weapons, the fission energy is released all at once to produce a violent explosion. Inside a warhead, trillions of fissions occur inside a small space within a fraction of a second, resulting in a massive explosion. Inside a nuclear reactor, the fissions are slower and more spread out, and the resulting heat is used to boil water, to make steam, to turn turbines which generate electricity. The fission of 1 kg of uranium or plutonium produces about 17.5 kilotons of TNT-equivalent explosive energy. The energy from a nuclear explosion appears as five weapon effects: blast, thermal radiation, prompt nuclear radiation, fallout, and an electromagnetic pulse. In a conventional nuclear reactor, one kilogram of Pu-239 can produce sufficient heat to generate nearly 8 million kilowatt-hours of electricity and fission of 1 kg of U-235 generates approximately 24 million kWh of electricity. Uranium isotope is better fuel in thermal reactors because around 85 per cent of the neutrons absorbed by 235U cause fission, while the proportion for 239Pu is 74 per cent; and generated 240Pu and 241Pu have high capture cross-sections, as a result, a larger amount of fissile plutonium than fissile uranium is required for a given energy output in thermal reactors. Note that reactor grade and weapon grade uranium/plutonium are different.

-2. Plutonium is not a naturally occurring element and therefore must be produced typically by bombarding U238 with neutrons in a nuclear reactor. The chemical extraction of plutonium from spent reactor fuel is known as “reprocessing.” Considerably less plutonium than uranium is needed to make a simple fission weapon. Plutonium-239 is more frequently used in nuclear weapons than uranium-235 as it is easier to obtain in a quantity of critical mass. Both plutonium-239 and uranium-235 are obtained from natural uranium, which primarily consists of uranium-238 but contains traces of other isotopes of uranium such as uranium-235. The process of enriching uranium, i.e. increasing the ratio of 235U to 238U to weapons grade, is generally a more lengthy and costly process than the production of plutonium-239 from 238U and subsequent reprocessing.

-3. A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. It has become more-or-less customary, although not strictly accurate, to refer to weapons in which all the energy results from fission as A-bombs or atomic bombs. Hydrogen (thermonuclear) bombs use a series of fission-fusion-fission reactions to produce a much greater yield than fission weapons. There are many ways of categorising nuclear weapons (by fission/fusion, by delivery mechanism, by yield, etc.). One common distinction is between ‘strategic’ and ‘tactical’ (or ‘non-strategic’) weapons. A nuclear device no larger than a conventional bomb can devastate an entire city by blast, fire, and radiation. Since they are weapons of mass destruction, nuclear non-proliferation and disarmament are focus of international policy.

-4. Since the atomic bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated over 2,000 times for testing and demonstration. Only a few nations possess such weapons or are suspected of seeking them. At present there are 9 countries in the world that possess nuclear weapons. They are: • Russia • United States • China • France • United Kingdom • Pakistan • India • Israel • North Korea.

These states have roughly 12,121 nuclear warheads with the average size 200 kt, with over 9,585 in active military stockpiles for use by missiles, aircraft, ships and submarines. Of the 9,585 warheads in the military stockpiles, some 3,904 are deployed with operational forces (on missiles or bomber bases). Of those, approximately 2,100 US, Russian, British and French warheads are on high alert, ready for use on short notice. The U.S. and Russia keep 900 nuclear weapons on prompt alert, meaning they could be ready to launch in under 15 minutes. Other countries keep their nuclear weapons in central storage or in de-targeted mode and would require days to be brought to launch-ready status.

-5. Were Russia to launch a nuclear-armed intercontinental ballistic missile at the US, residents would have roughly 30 minutes, or less, to find shelter, assuming they were immediately warned of the attack. In theory you could park a submarine closer to North America, thereby lessening the warning and flight time. If Russia launched a weapon from international waters just off the East Coast, people in cities like New York, Boston, and Washington, DC, might have just 10 to 15 minutes to prepare.

-6. Why use nuclear over conventional weapon:

(1. What makes nuclear weapons so worrisome is not the damage that can be caused by a single explosion. That can be large in its own right, but it’s still comparable to the damage that can be caused by conventional, non-nuclear explosives. WW2 is illustrative: of the roughly 75 million people who died in this conflict, only around 200,000 were killed by nuclear weapons. Comparable amounts of destruction were caused by the carpet bombing of cities such as Berlin, Hamburg, and Dresden. Nuclear weapons are terrible, but so are conventional weapons used in sufficient quantity. What makes nuclear weapons so worrisome is that they make it so easy to cause so much devastation. With a single launch order, a country can cause many times more harm than occurred in all of WW2, and they can do it without sending a single soldier overseas, by instead delivering nuclear warheads with intercontinental ballistic missiles. Mass destruction has long been possible, but it has never been so easy.

(2. The destructive effect of nuclear weapons is unlike any other created by human beings. The most powerful U.S. conventional bomb – MOAB – has an explosive yield of approximately 0.011 kt TNT, roughly 30 times less than the lowest yield setting (0.3 kt) on the B61 thermonuclear gravity bomb. The B61-12 weighs 850 lbs (385 kg), nearly thirty times less that the MOAB’s 22,600 lbs (10,300 kg).

(3. Nuclear bombs put a much larger fraction of their output into thermal energy than do conventional bombs, which tend to concentrate the energy in blast. Another difference is the immediate and residual nuclear radiation energy from nuclear weapons. The energy distribution of a conventional chemical bomb is ten percent thermal and ninety percent blast. The energy distribution of conventional nuclear bomb is fifty percent blast, thirty five percent thermal, ten percent delayed radiation, and five percent prompt radiation.

(4. The development of nuclear weapons has been justified by arguing that they are cheaper than equivalent conventional weapons. In terms of destructive power, this is true, they yield ‘more bang for the buck’ or ‘more rubble for the rouble’. The initial investment cost to produce fission weapons is around $2 to $10 billion for indigenous programs; however, the marginal cost thereafter can be as low as $1–2 million per nuclear bomb for large programs.

(5. Certain capabilities would provide a significant advantage over conventional alternatives in some circumstances.

-First, some military targets, such as hardened, deep targets, will resist all but nuclear weapons.

-Second, nuclear weapons compensate for inaccuracy, delivering greater explosive yield and farther lethality.

-Third, nuclear forces can compensate for lack of available firepower.

-7. The critical mass for any material is the smallest amount needed for a sustained nuclear chain reaction. The shape with minimal critical mass and the smallest physical dimensions is a sphere. Bare-sphere critical masses at normal density of U-235 is 52 kg with diameter 17 cm and of Pu-239 is 10 kg with diameter 9.9 cm. But the amounts of fissile material required for a single nuclear device depends on the skills and technical capability of the producer. Neutron reflectors, compressing the fissile core via implosion, triggers, fusion boosting, and tampering which slows the expansion of the fissioning core with inertia, allow nuclear weapon designs that use less than what would be one bare-sphere critical mass at normal density.

The critical mass of fissile material is not fixed, but decreases with the square of the density i.e. if squeezed to twice its normal density, only a quarter as much material is needed. Compressing the fissile core by implosion reduces critical mass because at higher densities, emitted neutrons are more likely to strike a fissionable nucleus before escaping. If a sphere of plutonium metal is surrounded by a shell of neutron reflecting material such as beryllium or uranium, which reduces the number of neutrons escaping without causing a fission event, the critical mass can be reduced further. A thick reflector will reduce the critical mass by a factor of 2 or more. By using a neutron reflector, only about 11 pounds (5 kilograms) of nearly pure or weapon’s grade plutonium 239 or about 33 pounds (15 kilograms) uranium 235 is needed to achieve critical mass. 239Pu is a key fissile component in nuclear weapons, due to its ease of fission and availability. Typically in a modern weapon, the weapon’s pit contains 3.5 to 4.5 kilograms (7.7 to 9.9 lb) of plutonium and at detonation produces approximately 5 to 10 kilotons of TNT (21 to 42 TJ) yield, representing the fissioning of approximately 0.5 kilograms (1.1 lb) of plutonium.

-8. Virtually all thermonuclear weapons deployed today use the “two-stage” design of fission and fusion, but it is possible to add additional fusion stages—each stage igniting a larger amount of fusion fuel in the next stage. This technique can be used to construct thermonuclear weapons of arbitrarily large yield. The practical maximum yield-to-weight ratio for fusion weapons (thermonuclear weapons) has been estimated to six kilotons of TNT per kg of bomb mass (25 TJ/kg). Hydrogen bombs of more than 50 megatons have been detonated, but the explosive power of the weapons mounted on strategic missiles usually ranges from 100 kilotons to 1.5 megatons.

This is in contrast to fission bombs, which are limited in their explosive power due to criticality danger (premature nuclear chain reaction caused by too-large amounts of pre-assembled fissile fuel). Eventually all fission-based weapons have an upper yield limit due to the difficulties of dealing with large critical masses. The largest pure-fission bomb ever constructed had a 500 kiloton yield, which is probably in the range of the upper limit on such designs. Fusion boosting could likely raise the efficiency of such a weapon significantly.

-9. Advanced boosted fissile nuclear weapons usually use plutonium-239 in the primary stage, but the jacket or tamper secondary stage, which is compressed by the primary nuclear explosion often uses HEU with enrichment between 40% and 80% along with the fusion fuel lithium deuteride. This multi-stage design enhances the efficiency and effectiveness of nuclear weapons, allowing for greater control over the release of energy during detonation. For the secondary of a large nuclear weapon, the higher critical mass of less-enriched uranium can be an advantage as it allows the core at explosion time to contain a larger amount of fuel. This design strategy optimizes the explosive yield and performance of advanced nuclear weapons systems. The 238U is not said to be fissile but still is fissionable by fast neutrons (>2 MeV) such as the ones produced during D-T fusion. Fusion boosted fission weapons are more efficient than other designs because they are immune to neutron radiation from nearby explosions, which can cause other weapons to predetonate. Most modern nuclear weapons are fusion-boosted. Typically no more than about 20% of the material in an average size pure fission bomb will split before the reaction ends (it can be much lower: the Hiroshima bomb was 1.4% efficient). By accelerating the fission process a boosted fission bomb increase the fission yield 100%. The yield of a boosted fission bomb is limited by practical concerns like mass and diameter, and is typically less than one megaton of TNT.

-10. Uranium’s most common isotope, 238U, is fissionable but not fissile, meaning that it cannot sustain a chain reaction because its daughter fission neutrons are not (on average) energetic enough to cause follow-on 238U fissions. However, the neutrons released by fusion of the heavy hydrogen isotopes deuterium and tritium will fission 238U. This 238U fission reaction in the outer jacket of the secondary assembly of a two-stage thermonuclear bomb produces by far the greatest fraction of the bomb’s energy yield, as well as most of its radioactive debris. In large, megaton-range hydrogen bombs, about half of the yield comes from the final fissioning of depleted uranium. This fact of 238U’s ability to fast-fission from thermonuclear neutron bombardment is of central importance. The plenitude and cheapness of both bulk dry fusion fuel (lithium deuteride) and 238U (depleted uranium, a byproduct of uranium enrichment) permit the economical production of very large thermonuclear arsenals, in comparison to pure fission weapons requiring the expensive 235U or 239Pu fuels. Thermonuclear weapons are considered much more difficult to successfully design and execute than primitive fission weapons. Almost all of the nuclear weapons deployed today use the thermonuclear design because it results in an explosion hundreds of times stronger than that of a fission bomb of similar weight.

-11. Vast stocks of fissile materials, the highly enriched uranium and plutonium from which nuclear weapons can be built, persist in civilian and military stockpiles in tens of countries. There are no effective international constraints on the production of these materials. Every state with a civilian nuclear industry is also capable of producing fissile materials; and any state that can enrich uranium to reactor grade can enrich it to weapons grade. Nuclear reactors inevitably convert some of the uranium in the fuel into plutonium. The average modern nuclear weapon contains around 4 kg of plutonium and/or 15 kg of highly enriched uranium (HEU). With the global fissile material stockpile at the start of 2020 estimated by the International Panel on Fissile Materials to contain 1330 tonnes of HEU and 540 tonnes of separated plutonium, this equates to more than 225,000 nuclear weapon equivalents of material.

-12. Uranium is among the more common elements in the earth’s crust — about 500 times more common than gold. There are three natural isotopes of uranium — uranium-234 (U-234), uranium-235 (U-235) and uranium-238 (U-238). U-238 is the most common one, accounting for around 99 per cent of natural uranium found on earth while natural uranium typically contains only 0.72 per cent of U-235. U-235 is the only fissile isotope that exists in nature as a primordial nuclide. Uranium enrichment is the process of concentrating or increasing the fraction of the 235U isotope, compared with the 238U isotope. In order to use uranium in nuclear weapons or a fuel in nuclear reactors it is necessary to increase the concentration of uranium 235. The 1.27% difference in mass between U-235 and U-238 allows the isotopes to be separated and makes it possible to increase or “enrich” the percentage of U-235. All present and historic enrichment processes, directly or indirectly, make use of this small mass difference.

-13. Numerous technologies have been developed to enrich uranium, such as gaseous-diffusion, centrifuges, and electromagnetic separation. All of these technologies require a large initial investment and large amounts of energy to operate. Enriching uranium is both technically difficult and expensive, as it requires separating isotopes that have very similar chemical and physical properties. The enrichment process is thus the main barrier to producing uranium suitable for use in nuclear weapons. One tonne of natural uranium feed might end up: as 120-130 kg of uranium for power reactor fuel (5 % U-235), as 26 kg of typical research reactor fuel (20% U-235), or conceivably as 5.6 kg of weapons-grade material (90% U-235).

-14. The Separative Work Unit (SWU) is a unit that defines the effort required in the uranium enrichment process, in which uranium-235 and -238 are separated. Separative work performed to enrich uranium is defined by a mathematical formula, but in essence it is a measure of work performed by a process to take a quantity of feed material at a certain 235U concentration and convert it into a quantity of enriched product with a higher 235U concentration and a balancing quantity of depleted “tails” with a lower 235U concentration. The isotope-separation work required to produce an enriched product depends on the tails assay of the depleted uranium streams but is independent of the method of separation used. It takes approximately 225 SWU to make 1 kg of weapon grade uranium (uranium enriched to 90 per cent) using natural uranium feed of 180 kg and a tails assay of 0.2 per cent.

As the number of SWUs required during enrichment increases, the levels of 235U in the depleted stream decreases and the amount of NU needed also decrease. Because the amount of NU required and the number of SWUs required during enrichment change in opposite directions, if NU is cheap and enrichment services are more expensive, then the operators will typically choose to allow more 235U to be left in the DU stream whereas if NU is more expensive and enrichment is less so, then they would choose the opposite.

-15. Plutonium-239 (usually referred as plutonium) is a heavy element consisting of 94 protons and 145 neutrons. Nuclear weapons use plutonium metal. Plutonium dioxide is used as a component of some nuclear fuels. Two key facilities are needed to obtain plutonium. First, in a nuclear reactor, uranium-238 absorbs a neutron. This leads to nuclear reactions which convert it to plutonium. The plutonium ends up in the spent nuclear fuel along with unused uranium and highly radioactive fission products. Essentially all nuclear reactors in the world produce plutonium in this way, but plutonium in spent fuel is not usable for nuclear energy or nuclear weapons. To get plutonium into a usable form, a second key facility, a reprocessing plant, is needed to chemically separate out the plutonium from the other materials in spent fuel. Plutonium separation is easier than uranium enrichment because it involves separating different elements rather than different isotopes of the same element, and it uses well known chemical separation techniques. In modern reprocessing plants, less than 1 percent of the plutonium contained in spent fuel may end up in wastes.

-16. A 1000 MWe light water reactor gives rise to about 25 tonnes of used fuel a year, containing up to 290 kilograms of plutonium. If the plutonium is extracted from used reactor fuel it can be used as a direct substitute for U-235 in the usual fuel, the Pu-239 being the main fissile part, but Pu-241 also contributing. In order to extract it for recycle, the used fuel is reprocessed and the recovered plutonium oxide is mixed with depleted uranium oxide to produce mixed oxide (MOX) fuel, with about 8% Pu-239 (this corresponds with uranium enriched to 5% U-235). MOX fuel is used in light water reactors and consists of 60 kg of plutonium per tonne of fuel. MOX fuel is not generally cost competitive with uranium fuels when used in thermal reactors, unless uranium prices rise steeply and offset the higher costs associated with their manufacture and usage. Plutonium, both that routinely made in power reactors and that from dismantled nuclear weapons, is a valuable energy source when integrated into the nuclear fuel cycle.

-17. All plutonium explosive!

Plutonium isotopes are inevitably produced when U-238 (the main isotope in natural uranium) absorbs neutrons in a nuclear reactor. All plutonium isotopes (Pu-238, 239, 240, 241, 242) are fissionable, and plutonium-239 and plutonium-241 are fissile, and though weapons are typically made with weapons-grade plutonium enriched to more than 90% Pu-239, any combination of plutonium isotopes containing less than 80% Pu-238 is usable for making a nuclear weapon, including so-called reactor-grade plutonium.

Plutonium-240 is the second most common isotope, formed by neutron capture by Pu-239 in about one-third of impacts. Its concentration in nuclear fuel builds up steadily, since it does not undergo fission by slow neutrons to produce energy in the same way as Pu-239. Pu240 is not fissile but Pu-240 has a relatively high rate of spontaneous fission with consequent neutron emissions which can provoke predetonation (or a fizzle), in which the nuclear weapon blows itself apart before the intended explosion occurs. This makes reactor grade plutonium unsuitable for use in a bomb. Reactor grade plutonium is defined as that with 19% or more of Pu-240. This is also called ‘civil plutonium’. Relatively large amounts of plutonium-240, as would be contained in reactor grade plutonium, can cause a weapon to detonate early and “fizzle,” causing a smaller explosion than intended. However, even a weapon that fizzles would cause an explosion roughly equivalent to 1,000 tons (1 kiloton) of TNT. A weapon of this size could kill tens of thousands of people if detonated in a city, which clearly demonstrates that even reactor grade plutonium would present a potent danger. The International Atomic Energy Agency (IAEA) is conservative on this matter so that, for the purpose of applying IAEA safeguards measures, all plutonium (other than plutonium comprising 80% or more of the isotope Pu-238) is defined by the IAEA as a ‘direct-use’ material, that is, “nuclear material that can be used for the manufacture of nuclear explosives components without transmutation or further enrichment”. The ‘direct use’ definition also applies to plutonium which has been incorporated into commercial MOX fuel, which as such certainly could not be made to explode.

-18. As distinct from the production of uranium with high concentrations of uranium 235, the technique of isotopic enrichment has not been used to produce weapon-grade plutonium from lower-grade material. Instead, the nuclear weapons producers have achieved the desired isotopic content of plutonium mainly by controlling the extent to which uranium fuel elements are irradiated with neutrons in nuclear reactors. This is known as the fuel burn-up, whose unit of measurement is megawatt-days per ton (MWd/t) of uranium fuel.

In order to minimise the amount of Pu-240, fuel rods in a plutonium production reactor should be irradiated for a relatively short period: long enough to transmute around 1% of the U-238 into Pu-239, but not so long that too much Pu-239 is converted into Pu-240. Hence ‘weapons-grade’ plutonium is made in special production reactors by burning natural uranium fuel to the extent of only about 100 MWd/t (effectively three months), instead of the 45,000 MWd/t typical of LWR power reactors. Allowing the fuel to stay longer in the reactor increases the concentration of the higher isotopes of plutonium, in particular the Pu-240 isotope. Plutonium with less than 7% of Pu-240 is considered “weapons grade”. In a power reactor, fuel elements are left in the reactor much longer, and plutonium extracted from their fuel rods may have 19% or more Pu-240—this is called “reactor grade” plutonium. This doesn’t mean you can’t make a bomb from reactor grade plutonium: in 1962, the U.S. conducted a nuclear test of a bomb using plutonium with a high Pu-240 fraction.

-19. Technology for Nuclear Proliferation:

(1. The LEU cannot be used for weapons but the use of even LEU raises two proliferation concerns: The enrichment facilities used to produce the low-enriched fuel can be used to produce HEU, and if the low-enriched fuel is used as input to an enrichment cascade, the quantity of work required to produce HEU would be much reduced. Centrifuges pose a unique proliferation challenge because detecting covert facilities in a timely manner is very difficult and existing centrifuges can be quickly reconfigured to produce HEU.

(2. There are many metric tons of plutonium in spent nuclear fuel stored around the world. To be usable, plutonium would need to be separated from the other products in spent fuel. This process, known as reprocessing, uses chemicals to separate plutonium from uranium and other fission products. Once separated, plutonium oxide can be mixed with uranium oxide to produce mixed oxide or MOX fuel. MOX fuel can be used in power reactors. Reprocessing is controversial internationally, because the plutonium can also be used to make nuclear weapons.

(3. While MOX fuel itself is unlikely to be used to make nuclear weapons, the plutonium can be separated from the uranium by a straightforward chemical process. Moreover, MOX does not contain the highly radioactive components that make spent fuel difficult and dangerous to reprocess. As a result, MOX is as a proliferation concern as plutonium itself.

(4. A nuclear reactor that is used to produce plutonium for weapons has means, for exposing 238U to neutron radiation and for frequently replacing the irradiated 238U with new 238U. Most commercial nuclear power reactor designs require the entire reactor to shut down, often for weeks, in order to change the fuel elements. Any commercial power reactor designs that do permit refueling without shutdowns may pose a proliferation risk.

(5. A nuclear reactor produces abundant neutrons, with enough left over from the fissioning of U-235 to irradiate U-238 and start the sequence of reactions which will yield Pu-239. Furthermore, by using a neutron moderator of graphite or heavy water, it is possible to build a nuclear reactor which will sustain fission using natural uranium, eliminating the need for uranium enrichment. (For reasons of cost and efficiency, most nuclear power stations use regular light water as moderator and coolant, but this requires enriched fuel.) In principle, you build a graphite or heavy water moderated reactor, fuel it with natural uranium refined from uranium ore, start it up, let it run for a while, then remove the fuel elements, which will now contain Pu-239 bred from the U-238 in the natural uranium you started with, and chemically separate the plutonium and hand it off to the bomb builders.

-20. Link between civilian and military use of nuclear technology:

Initial nuclear development in the United States, Great Britain, France, and the former Soviet Union was influenced by the technological and nuclear expertise gained from strategic and military activities and the global civilian nuclear industry was established to legitimatize the development of nuclear weapons. The civil nuclear power industry grew out of the atomic bomb programme in the 1940s and the 1950s. Many nations used civil nuclear power programme as a cover for military activities. The prime use of plutonium-239 and uranium-235, and the reason they were produced in the first place, is to make nuclear weapons.

Nuclear fuel is the fuel that is used in a nuclear reactor to sustain a nuclear chain reaction. These fuels are fissile, and the most common nuclear fuels are the radioactive metals uranium-235 and plutonium-239. The various activities associated with the production of electricity from nuclear reactions are referred to collectively as the nuclear fuel cycle. The nuclear fuel cycle starts with the mining of uranium and ends with the disposal of nuclear waste, and includes enrichment and reprocessing.

It is important to remember that nuclear technologies are dual-use and offer opportunities for energy production and weapons development. Reprocessing is generally regarded as one of the key links between civilian nuclear power capability and nuclear weapons production capability; and the other is uranium enrichment.

(1. Neutron absorption by uranium-238 in a nuclear reactor produces plutonium (typically isotope Pu-239). Reprocessing spent reactor fuel can recover unused plutonium to serve as fissile material for nuclear weapons. Irradiating uranium fuel elements in nuclear reactors either results in plutonium for power reactors or weapons-grade plutonium. The outcome depends on the type of reactor, used fuel and length of irradiation. When irradiated fuel elements are reprocessed, the plutonium generated in that process can be chemically isolated and used for weapons construction. Technically, it is even possible to build a nuclear weapon with plutonium from power reactors. Although civilian plutonium has a different isotopic composition from plutonium that has been produced for weapons, it can be used to make a nuclear explosive.

(2. All the processes at the front of the nuclear fuel cycle, i.e. uranium ore mining, uranium ore milling, uranium ore refining, and U-235 enrichment are used for both power and military purposes. The process of enriching uranium to make it into fuel for nuclear power stations is also used to make nuclear weapons. Whoever needs fuel elements for nuclear reactors, research reactors or nuclear propulsion for vessels has to enrich uranium. The same goes for whoever wants to build nuclear weapons with a uranium core. These differences are more gradual than fundamental. Light water reactors, for instance, require two- to five per cent enriched uranium while research or ship reactors more often than not use much more highly enriched uranium, or even uranium that is just as highly enriched as weapons-grade uranium (20 to over 90 per cent). Uranium enrichment poses a nuclear proliferation risk because the same technology that can produce LEU for reactor fuel can also be used to produce HEU for nuclear weapons. There are no technical barriers to prevent countries with enrichment capabilities from using them to enrich uranium to the higher levels required for nuclear weapons.

(3. Factory that makes nuclear fuel for reactors also makes nuclear fuel for nuclear submarines.

(4. Nuclear reactors are used to create tritium (the radioactive isotope of hydrogen) necessary for nuclear weapons.

The civilian and military use of nuclear technology can be compared to Siamese Twins. They are so closely connected that one can hardly separate them. The civilian use of nuclear technology can create knowledge, materials and technology that can also be used for a military nuclear programme. Comprehensive nuclear programmes – even if they are purely civilian by nature – therefore often create concern that the real intention is the desire to possess nuclear weapons.

Without civil nuclear power, no military nuclear power, and, without military nuclear, no civil nuclear. This is largely why nuclear-armed France is pressing the European Union to support nuclear power. This is why non-nuclear-armed Germany has phased out the nuclear technologies it once led the world in. This is why other nuclear-armed states are so disproportionately fixated by nuclear power. It is the military interests of some nations that are pushing for new nuclear power plants.

Building more nuclear reactors unavoidably increases nuclear proliferation risks. Civilian nuclear energy technologies are potential facilitators of nuclear weapons proliferation to new states. Nuclear power programs can be instrumental in the accumulation of technical knowledge and diversion of fissile materials for use in parallel military nuclear weapons programs. Indeed, beyond the nine nuclear-armed states, an additional 26 have explored development of nuclear weapons. Recent scholarship has shown that these countries may leverage civilian nuclear programs as a threat to build nuclear weapons. Having research nuclear reactors and having experiences with them could contribute to the decision to “explore” or “pursue” nuclear weapons. A fundamental goal for global security is to minimize the proliferation risks associated with the expansion of nuclear power.

The crux of the nuclear proliferation problem, as with all proliferation problems involving dual-use technologies (i.e., ones with civilian and military applications), is to devise arms control regimes that allow states to develop nuclear power while at the same time restrict the development of nuclear weapons. This is the central challenge of everybody involved in nuclear non-proliferation. The International Atomic Energy Agency (IAEA) has promoted two contradictory missions: on the one hand, the Agency seeks to promote and spread internationally the use of civilian nuclear energy; on the other hand, it seeks to prevent, or at least detect, the diversion of civilian nuclear energy to nuclear weapons, nuclear explosive devices or purposes unknown. There is inherent contradiction in the work of IAEA because you cannot separate civilian and military nuclear program. Nuclear weapons and nuclear power share several common features and there is a danger that having more nuclear power stations in the world could mean more nuclear weapons. If the world wants to avoid nuclear war, we have to abandon even civil nuclear program.

-21. Three processes for nuclear bomb:

(1. Enrichment of uranium—uranium bomb

(2. Nuclear reactor-irradiation of nuclear fuel-low burnup-weapon grade plutonium

(3. Reprocessing spent fuel—plutonium bomb

You may have a country that just enriches natural uranium and make uranium bomb without any nuclear reactor at all. For plutonium bomb, you need natural uranium, nuclear reactor and reprocessing facility; with enrichment facility or even without enrichment facility e.g. CANDU reactor.

So, you can make nuclear bomb without any enrichment facility (plutonium bomb) and you can make nuclear bomb without any nuclear reactor (uranium bomb). You can use gun-type uranium bomb without any test.

Any determined nation could develop and start stockpiling reasonably efficient and reliable nuclear weapons within ten years and, in many cases, in a much shorter time. The main technical barrier is obtaining the required nuclear material (highly enriched uranium or plutonium), but even that is not much of a barrier today.

A clandestine uranium enrichment plant would be motivated in the countries where the nuclear power programme is too small for a commercial enrichment plant and clandestine enrichment plant would generate HEU for nuclear weapons.

Each year, the reprocessing plant can extract approximately 250 kilograms of plutonium from a single commercial reactor, enough for forty nuclear weapons at the very least.

Six countries are found to have violated their NPT obligations with illicit nuclear activities did so by maintaining covert facilities (Iran, Iraq, North Korea, Libya, Romania, and Syria).

-22. Downblending:

The opposite of enriching is downblending; surplus HEU can be downblended to LEU to make it suitable for use in commercial nuclear fuel. Downblending is a key process in nuclear non-proliferation efforts, as it reduces the amount of highly enriched uranium available for potential weaponization while repurposing it for peaceful purposes. The main weapons material is highly enriched uranium (HEU) usually about 90% U-235. HEU can be blended down with uranium containing low levels of U-235 to produce low-enriched uranium (LEU), less than 5% U-235 as fuel for power reactors. It is blended with depleted uranium (mostly U-238), natural uranium (0.7% U-235), or partially-enriched uranium.

Weapons-grade plutonium entering the civil fuel cycle needs to be kept under very tight security, and there are some technical measures needed to achieve this. Military plutonium can blended with depleted uranium oxide to form mixed oxide (MOX) fuel.

After LEU or MOX is burned in power reactors, the spent fuel is not suitable for weapons manufacture without reprocessing plant. Thus HEU and Pu-239 from dismantled nuclear weapons can be recycled as LEU and MOX respectively and burned to generate electricity with spent fuel unsuitable for weapons manufacture. Note that United States does not currently recycle spent nuclear fuel but countries, such as France, do. Commitments by the USA and Russia to convert nuclear weapons into fuel for electricity production was known as the Megatons to Megawatts program. It’s time for the whole world to commit to ‘Megaton to Megawatt’ program.

-23. Nuclear peace theory says the presence of nuclear weapons decreases the risk of crisis escalation, since parties will seek to avoid situations that could lead to the use of nuclear weapons. The strategy is a form of Nash equilibrium in which, once armed, neither side has any incentive to initiate a conflict nor to disarm. Proponents of nuclear peace theory therefore believe that controlled nuclear proliferation may be beneficial for global stability. Critics argue that nuclear proliferation increases the chance of nuclear war through either deliberate or inadvertent use of nuclear weapons, as well as the likelihood of nuclear material falling into the hands of violent non-state actors. Proliferation has been opposed by many nations with and without nuclear weapons, as governments fear that more countries with nuclear weapons will increase the possibility of nuclear warfare (up to and including the so-called countervalue targeting of civilians with nuclear weapons), de-stabilize international or regional relations, or infringe upon the national sovereignty of nation states. Proliferation increases the chance that nuclear weapons will fall into the hands of irrational people, either suicidal or with no concern for the fate of the world.

-24. Deterrence is widely defined as any use of threats (implicit or explicit) or limited force intended to dissuade an actor from taking an action (i.e. maintain the status quo). Deterrence is most likely to be successful when a prospective attacker believes that the probability of success is low and the costs of attack are high. Regardless of the weapons employed or the strategy adopted, capability and credibility are the key ingredients of deterrence success. Opponents must believe that the side issuing deterrent threats has the capability to make good on those threats and will actually execute them in the wake of deterrence failure.

Deterrence theory stipulates that adversaries are deterred from launching a nuclear attack against the United States — or more than 30 of its treaty-covered allies — because by doing so they risk an overwhelming counterattack. Possessing nuclear weapons isn’t about winning a nuclear war, the theory goes; it’s about preventing one. Nuclear deterrence theory states that nations with nuclear weapons will not be subject to attack, especially nuclear attack, because the prospect of a retaliatory nuclear strike is too terrible to contemplate. The second-strike capabilities are essential to nuclear deterrence.

Why nuclear deterrence will fail:

(1. Deterrence relies on the possibility of a retaliatory strike strong enough to destroy a nuclear state. But there are ways this could fail.

(2. As long as rational actors remain in control of nuclear weapons (and do not make mistakes,) it seems the current status quo can persist indefinitely. Unfortunately, there exists no guarantee that nuclear powers will always act rationally or not make mistakes.

(3. Nuclear deterrence makes nuclear use more likely because the threat of use of nuclear weapons must be credible, and so the nuclear armed states are always poised to launch nuclear weapons.

(4. Nuclear weapons don’t keep the peace. History shows that the existence of nuclear weapons has done nothing to prevent the many terrible conflicts since 1945, including acts of aggression against countries with nuclear weapons. In reality, nuclear weapons haven’t been used due solely to good luck – which cannot be expected to last forever.

(5. Deterrence fails against nuclear terrorism simply because there are no well-defined targets against which to retaliate.

-25. Some have argued that nuclear weapons have helped prevent war. But in fact, since 1945 the eight countries possessing nuclear weapons have been involved in over eight times as many wars, on average, as all the non-nuclear countries. Some credit nuclear weapons with having prevented nuclear war, which is preposterous: without nuclear weapons, there could be no nuclear war. Nuclear arms race entailed a waste of resources, damaged political relations, increased the probability of war, and hindered states in accomplishing their goals. Even if the probability of nuclear war is low, the risk and consequences are so high that only zero probability will work, that is total nuclear disarmament.

-26. Mirage of nuclear superiority:

Any use of nuclear weapons carries with it a high and inescapable risk of escalation into the general nuclear war which would bring ruin to all and victory to none. If this is correct, then even nuclear superiority cannot allow states to meaningfully win a nuclear war. In turn, superior states should have few advantages over their inferior opponents, so long as those inferior opponents can credibly demonstrate that they are willing to risk nuclear escalation. In fact, the positive association between nuclear superiority and crisis victory decreases as the disparity between competing states’ arsenals increases. United States boasts a far superior nuclear arsenal than all remaining nuclear states. Yet, despite its immense nuclear capabilities, the United States is struggling to curb North Korean, Chinese and Iranian threats. Nuclear superiority provides few benefits in these settings.

-27. According to 2018 study, National Pragmatic Safety Limit for Nuclear Weapon; there is a fundamental upper limit for the number of nuclear weapons needed by any country. This fundamental limit, defined as the pragmatic limit, is based on the direct physical negative consequences of a large number of nuclear weapons being used anywhere on the globe. The nuclear pragmatic limit means the direct physical negative consequences of nuclear weapons use are counter to national interests. Stated simply: no country should have more nuclear weapons than the number necessary for unacceptable levels of environmental blow-back on the nuclear power’s own country if they were used. 100 nuclear warheads is adequate for nuclear deterrence in the worst case scenario, but using more than 100 nuclear weapons by any aggressor nation would cause unacceptable damage to their own society. Thus, 100 nuclear warheads are the pragmatic limit and use of government funds to maintain more than 100 nuclear weapons does not appear to be rational.

-28. The impacts of a nuclear explosion depend on many factors, including the design of the weapon (fission or fusion) and its yield; whether the detonation takes place in the air (and at what altitude), on the surface, underground, or underwater; the terrain & topography; the meteorological and environmental conditions; and whether the target is urban, rural, or military.

-29. Nuclear explosions produce both immediate and delayed destructive effects. Immediate effects (blast, thermal radiation, prompt ionizing radiation, EMP) are produced and cause significant destruction within seconds or minutes of a nuclear detonation. Thermal radiation and blast are inevitable consequences of the near instantaneous release of an immense amount of energy in a very small volume, and are thus characteristic to all nuclear weapons regardless of type or design details. Electromagnetic Pulse is a short burst of electromagnetic energy that disrupts and damages electronics and other infrastructure.

The delayed effects (radioactive fallout and other possible environmental effects) inflict damage over an extended period ranging from hours to centuries, and can cause adverse effects in locations very distant from the site of the detonation. Residual radiation would include fallout plus induced radiation (metals and stones by neutron exposure) plus internal radiation (inhalation of un-fissioned plutonium).

-30. The explosive yield of a nuclear weapon is the amount of energy released such as blast, thermal, and nuclear radiation, when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would produce the same energy discharge), either in kilotons (kt—thousands of tonnes of TNT), in megatons (Mt—millions of tonnes of TNT), or sometimes in terajoules (TJ). An explosive yield of one terajoule is equal to 0.239 kilotons of TNT. The two nuclear weapons dropped on Hiroshima and Nagasaki, had an explosive yield of the equivalent of about 15 kilotons of TNT and 20 kilotons of TNT respectively. In modern nuclear arsenals, those devastating weapons are considered “low-yield.” Many of the modern nuclear weapons in Russian and U.S. nuclear weapons are thermonuclear weapons and have explosive yields of the equivalent at least 100 kilotons of TNT and some are much higher. One 100-kiloton nuclear weapon dropped on New York City could lead to roughly 583,160 fatalities.

-31. The three categories of immediate effects are: blast, thermal radiation, and prompt ionizing nuclear radiation. Fatal injuries are caused by thermal radiation just sufficient to cause 3rd degree burns is 8 calories/cm2; a 4.6 psi blast overpressure; and a 500 rem (5 sievert) radiation dose at once. A convenient rule of thumb for estimating the immediate fatalities from all causes due to a nuclear attack is to count everyone inside the 5 psi blast overpressure contour around the hypocenter as a fatality. While a human body can withstand up to 30 psi of simple overpressure, the winds associated with as little as 2 to 3 psi could be expected to blow people out of typical modern office buildings. After all-out nuclear war, unsheltered persons would receive weekly radiation doses in excess of 1 Sv (1,000 mSv or 100 rem), some 400 times annual background; 60 percent would receive fatal doses in excess of 10 Sv. Thermal flash burns extend well beyond the 5-psi radius of destruction. A single nuclear explosion might produce 10,000 cases of severe burns requiring specialized medical treatment; in an all-out war there could be several million such cases.

Note that average background radiation level worldwide is 2.4 millisieverts (mSv) per year and radiation dose limit for radiation workers for whole-body is 20 mSv/year.

-32. Why air burst (explosion) at optimum height:

(1. When an explosion occurs, it sends out a shock (blast) wave like an expanding soap bubble. If the explosion occurs above the ground the bubble expands and when it reaches the ground it is reflected – i.e. the shock front bounces off the ground to form a second shock wave travelling behind the first. This second shock wave travels faster than the first or direct shock wave since it is travelling through air already moving at high speed due to the passage of the direct wave. The reflected shock wave tends to overtake the direct shock wave and when it does, they combine to form a single reinforced wave. The reflected blast wave merges with the incident shock wave to form a single wave, known as the Mach Stem. The overpressure at the front of the Mach wave is generally about twice as great as that at the direct blast wave front. Because of this, air blast is maximized with a low air burst rather than a surface burst.

(2. The higher the burst altitude, the weaker the shock wave is when it first reaches the ground. On the other hand, the shock wave will also affect a larger area. Air bursts therefore reduce the peak intensity of the shock wave, but increase the area over which the blast is felt.

(3. All targets have some level of vulnerability to blast effects. When some threshold of blast pressure is reached the target is completely destroyed. Subjecting the target to pressures higher than that accomplishes nothing. By selecting an optimum burst height, an air burst can destroy a much larger area for most targets than can surface bursts.

(4. An additional effect of air bursts is that thermal radiation is also distributed in a more damaging fashion. Since the fireball is formed above the earth, the thermal radiation arrives at a steeper angle and is less likely to be blocked by intervening obstacles and low altitude haze.

(5. The blast wave from an air burst reflects off the ground, which enhances its destructive power. A ground burst, in contrast, digs a huge crater and pulverizes everything in the immediate vicinity, but its blast effects don’t extend as far. Compared to an airburst, the ground blast would probably cause damage to an area half the size and immediate deaths would probably number half those from an airburst. Nuclear attacks on cities would probably employ air bursts, whereas ground bursts would be used on hardened military targets such as underground missile silos. Hiroshima and Nagasaki bombs were detonated more than 500 meters above street level so as to wreak maximum destruction (surrounding buildings would have blocked much of the force of ground-level explosions).

-33. Destructive radius for nuclear radiation and thermal radiation increases proportional to the square root of the yield; and intensity of nuclear radiation and thermal radiation decreases proportional to the square of distance from ground zero. However nuclear radiation is strongly absorbed by the air it travels through, which causes the intensity to drop off much more rapidly. Destructive radius for blast effect increases proportional to cube root of the yield; and intensity of blast effect decreases proportional to the cube of distance from ground zero. Therefore the effects of thermal radiation grow rapidly with yield (relative to blast), while those of nuclear radiation rapidly decline due to absorption by air as higher yield leads to higher height of detonation and radiation dose is inversely proportional to the square of the distance.

When a bomb explodes it will destroy things in all directions including up and down, but for the purposes of destroying cities, the metric that matters is how much surface area on the earth is destroyed and not mere radius of destruction. Everything on the surface of the earth within that radius will be destroyed. The surface area of destruction is proportional to destructive radius square. So instead of destructive radius, if destructive area is calculated, then, destructive area for nuclear radiation and thermal radiation increases linearly to the yield; and destructive area for blast effect increases proportional to 2/3 root of the yield; however intensity and destructive area of nuclear radiation falls rapidly due to absorption by air and does not increase linearly with yield.

With yields in the range of hundreds of kilotons or greater (typical for strategic warheads) immediate nuclear radiation injury becomes insignificant. Dangerous radiation levels only exist so close to the explosion that surviving the blast is impossible. On the other hand, fatal burns can be inflicted well beyond the range of substantial blast damage. A 20 megaton bomb can cause potentially fatal third degree burns at a range of 40 km, where the blast can do little more than break windows and cause superficial cuts. For nuclear devices with a higher yield, heat damage becomes the primary initial effect of concern, eclipsing both the damage from the shockwave (blast wave) and the initial nuclear radiation.

-34. Whenever the term destructive radius and destructive area are used, it means blast destruction unless specified otherwise. The destructive radius is defined as the distance within which blast overpressure exceeds 5 pounds per square inch, and it measures 2 miles, 4.4 miles, and 9.4 miles for the weapon yields 100-kiloton, 1-megaton, and 10-megaton. The destructive radius grows approximately as the cube root of the yield while destructive area grows approximately as the 2/3 root of the yield. The destructive power of nuclear explosion in area is not in direct proportion to the yield but proportional to yield raised to the two-thirds power. The relatively slow increase in destruction with increasing yield is one reason why multiple smaller weapons are more effective than a single larger one. Thus 1 bomb with a yield of 1 megaton would destroy 80 square miles, while 8 bombs, each with a yield of 125 kilotons, would destroy 160 square miles. This relationship is one reason for the development of delivery systems that could carry multiple warheads (MIRVs). Multiple Independently-targetable Reentry Vehicle (MIRV) technology allows a single missile to carry multiple warheads that can hit different targets simultaneously. MIRVs are more difficult to defend against than traditional missiles and are considered effective countermeasures to ballistic missile defences.

-35. As a rule of thumb, approximately 35 percent of the total energy yield of an airburst is emitted as thermal radiation— light and heat capable of causing skin burns and eye injuries and starting fires of combustible material at considerable distances. Even the relatively small size nuclear weapon exploded on Hiroshima (15 kilotons TNT) released about 1000 times as much energy in the fires it ignited as in the explosion itself.

-36. The system used to deliver a nuclear weapon to its target is an important factor affecting both nuclear weapon design and nuclear strategy. The design, development, and maintenance of delivery systems are among the most expensive parts of a nuclear weapons program; they account, for example, 57% of the financial resources spent by the United States on nuclear weapons projects since 1940. Modern nuclear weapon designs are much smaller and lighter than the original US and Soviet fission bombs, ranging in size from that of a suitcase to a refrigerator and in weight from around 100 to 2000 lbs. The fact that they are small and light imply that they can be delivered in a variety of ways (e.g., ballistic missiles, aircraft, cruise missiles, artillery shells, torpedoes, etc.). Attributes affecting the suitability of a delivery system for a particular country include range, accuracy, payload weight and type, ability to penetrate enemy defences, survivability in case of a pre-emptive attack, as well as cost and the availability of assistance.

-37. A nuclear triad is a three-pronged military force structure of land-based intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and strategic bombers with nuclear bombs and missiles; meaning nuclear forces operating at sea, on land, and in the air. Countries build nuclear triads to eliminate enemy’s ability to destroy a nation’s nuclear forces in a first-strike attack, which preserves their own ability to launch a second strike and therefore increases their nuclear deterrence. Only four countries are known to have the nuclear triad: the United States, Russia, India, and China. While traditional nuclear strategy holds that a nuclear triad provides the best level of deterrence from attack, most nuclear powers do not have the military budget to sustain a full triad. The only two countries that have successfully maintained a strong nuclear triad for most of the nuclear age are the United States and Russia.

-38. Few people believe that once a nuclear conflict has begun, it will be possible to contain it. There is every reason to believe that a limited nuclear war wouldn’t remain limited.

-39. Many people seem unable to comprehend or even imagine the difference between conventional and nuclear warfare, in extent or in kind. A total of approximately 140,000 in Hiroshima and 73,000 in Nagasaki died instantaneously or within five months due to the combined effects of three components of physical energy generated by nuclear fissions: blast wind (pressure), radiant heat, and ionizing radiation. For 210,000 survivors, the damage to their health has continued, consisting of three phases of late effects: the appearance of leukemia, the first malignant disease, in 1949; an intermediate phase entailing the development of many types of cancer; and a final phase of lifelong cancers for hibakusha who experienced the bombing as a child, as well as a second wave of leukemia for elderly hibakusha, and psychological damage such as depression and post-traumatic stress disorder. Studies of the Hiroshima and Nagasaki bombings showed a disproportionate propensity for children to experience leukemias and other cancers years after the bombings. There were also great increases in perinatal deaths and cases of microcephaly and retardation in children exposed in utero to the bombs. Actively dividing cells are more susceptible to ionizing radiation effects, so younger people are more sensitive.

-40. A striking similarity exists between acquired immunodeficiency syndrome (AIDS) and the anticipated immunosuppressed condition of survivors of a nuclear war: both are characterized by absolute depression of the helper T lymphocyte population, reduced helper-to-suppressor T lymphocyte ratios, reduced lymphocytic response to mitogens and antigens, and reduced to absent antibody response following immunization.

-41. Staying indoors for 48 hours after a nuclear blast is recommended. That time allows fallout levels to decay by a factor of 100.

The safest place to be during a nuclear blast is in a large, secure building. The best shelter location is in the center of a large building of heavy construction (e.g., concrete, reinforced brick, cement), away from windows and doors, or in basements and other underground areas (e.g., parking garages, subways).

-42. Regional nuclear war between India and Pakistan that involved about 100 15-kiloton nuclear weapons launched at urban areas would result in 27 million direct deaths. It would result in global ozone loss of 25% due to injections of nitrogen oxides (NOx) and smoke; and injection of 5 Tg of stratospheric soot would cause fall in temperature 1.25 C and fall in rainfall 10% for many years leading to 2 billion starvation deaths.

A global all-out nuclear war between the United States and Russia with over four thousand 100-kiloton nuclear warheads would lead, at minimum, to 360 million quick deaths. It would result in global ozone loss of 75% due to injections of nitrogen oxides (NOx) and smoke; and injection of 150 Tg of stratospheric soot would cause fall in temperature 8 C and fall in rainfall 45% for many years leading to 5 billion starvation deaths.

It doesn’t matter who is bombing whom. It can be India and Pakistan or NATO and Russia. Once the smoke is released into the upper atmosphere, it spreads globally and affects everyone. As millions of tons of soot aerosols are released into the atmosphere, it reduces the amount of sunlight reaching the Earth’s surface. This would lead to global surface cooling, a phenomenon called “nuclear winter.” In the case of such a catastrophic event, vast crop failure could follow, leading to widespread food scarcity. A war that detonated less than 1/20th of the world’s nuclear weapons would still crash the climate, the global food supply chains, and likely public order. Famines and unrest would kill hundreds of millions, perhaps even billions.

As horrific as these statistics are, the tens to hundreds of millions of people dead and injured within the first few days of a nuclear conflict would only be the beginnings of a catastrophe that eventually will encompass the whole world. Global climatic changes, widespread radioactive contamination, and societal collapse virtually everywhere could be the reality that survivors of a nuclear war would contend with for many decades. The destruction of civilization that would follow a nuclear war would render any disaster ever recorded insignificant. Survival would exist only in the strictest sense of the word, since societal disorganization, famine, drought, darkness, and nuclear winter would envelope the earth.

-43. Nuclear holocaust became an anti-nuclear issue with the start of nuclear weapons testing. Over 2,000 nuclear tests have been conducted in over a dozen different sites around the world. Over 500 atmospheric nuclear weapons tests were conducted at various sites around the world from 1945 to 1980. Radioactive fallout from nuclear weapons testing can cause long-term harm to human health including cancers. International Physicians for the Prevention of Nuclear War (IPPNW) estimates that roughly 2.4 million people will eventually die as a result of the atmospheric nuclear tests conducted between 1945 and 1980, which were equal in force to 29,000 Hiroshima bombs. The continued existence of around 12,100 nuclear weapons poses ongoing risks of intentional, accidental or unauthorized nuclear weapons use.

-44. Nuclear weapons are still the greatest long-term existential threat to the world. Nuclear war could dwarf a pandemic in terms of health impacts, pressure on health services, difficulties in protecting essential workers, societal effects, and overwhelming global ramifications No health service in any area of the world would be capable of dealing adequately with the hundreds of thousands of people seriously injured by blast, heat or radiation from even a single 1-megaton bomb. Medical rescue teams perished and hospitals were all destroyed on the first day of the bombing in Hiroshima and Nagasaki. It’s important to acknowledge that there is no effective medical response to the use of a strategic nuclear weapon on a civilian population.

-45. While a nuclear war would cause immense damage and suffering, it would not necessarily result in the extinction of humanity. This depends on several factors, such as the number, type, size, and target of the nuclear weapons used, the weather conditions, the population density, the level of preparedness and response, and the resilience and adaptation of human societies. The idea that global nuclear war could kill most or all of the world’s population is critically examined and found to have little or no scientific basis.

-46. AI applications in nuclear war included the ability to track and target adversary launchers for counterforce targeting and the incorporation of AI into decision support systems informing choices about the use of nuclear weapons. The dangers of the use of AI to take military decisions is more likely than the threat of autonomous drones and other so-called killer robots. Some experts fear that an increased reliance on AI could lead to new types of catastrophic mistakes.

-47. Nine countries are known or believed to possess nuclear weapons. None of the nine nuclear-armed states is disarming; instead, all invest enormously in new and more hazardous nuclear weapons. Nor has any of the 32 states claiming reliance on another state’s nuclear weapons yet ended such reliance. Risks of a nuclear war are growing. These factors: abrogation of existing nuclear arms control agreements, policies of first nuclear use and war fighting, growing armed conflicts worldwide, and increasing use of information and cyberwarfare, exacerbate dangers of nuclear war. In today’s fragmented and polarized world, there is a significant probability that, either by accident or by deliberate act, these horrible weapons may be used.

The risks of a nuclear weapon detonation, whether by accident, miscalculation or design, stem notably from:

the vulnerability of nuclear weapon command-and-control networks to human error and cyberattacks
the maintaining of nuclear arsenals on high levels of alert, with thousands of weapons ready to be launched within minutes
the dangers of access to nuclear weapons and related materials by non-state actors.

On October 27, 1962, a nuclear war was averted not because President Kennedy and Premier Khrushchev were doing their best to avoid war (they were), but because Capt. Vasily Arkhipov had been randomly assigned to submarine B-59. He refused to give his assent and convinced the sub’s top officers that launching the nuclear torpedo would be a fatal mistake. This is but one of countless examples where global and military history has been dramatically altered by chance and luck. It would be foolish to depend on luck all the time to prevent nuclear war. We have to formulate policies and actions, both technical and political, which would reduce the chance of accidental or inadvertent nuclear war. The decision of whether or not to launch a nuclear weapon should not be confined to mere minutes and mere one individual.

In my view, accidental launch, electronic or human error, false alarm, misinformation, cyberattack, irrational leaders and nuclear materials falling in hands of wrong guys; are strong points for nuclear non-proliferation and disarmament. We ought to eliminate nuclear weapons.

-48. Misuse of public funds.

Spending on nuclear weapons detracts limited resources away from vital social services. Currently states that are armed with nuclear weapons spend close to US $225 million a day on nuclear forces. Current estimates of global spending on development and production of nuclear weapons reached US $72.6 billion in 2020. The total cost of nuclear weapons programs, including environmental clean-up and legacy costs, is far greater. A cumulative $387 billion has been spent by nine countries to build and maintain their nuclear arsenals over the past five years diverting public funds from poverty alleviation, health care, education, renewable technologies, disaster relief and other vital services.

-49. Nuclear weapons are complex and expensive enough to build that non-state actors seem unlikely to get access to nuclear weapons unless they’re intentionally supplied by a state actor. Despite thefts and trafficking of small amounts of fissile material, there is no credible evidence that any terrorist group has ever obtained or produced nuclear materials of sufficient quantity or purity to produce a viable nuclear weapon. The most important single step to prevent nuclear terrorism is to secure all nuclear weapons and fissile material, so they can’t be stolen and fall into terrorist hands. Pakistan’s nuclear stockpile faces a greater threat from Islamic extremists seeking nuclear weapons than any other nuclear stockpile on earth.

-50. Ionizing radiation from meltdown of nuclear power reactor is far greater than nuclear bomb explosion.

(1. The amount of radioactive material loaded onto the bombs is relatively small – seventy kilograms of uranium on the “Little Boy” and seven kilograms of plutonium on the “Fat Man”. By comparison, nuclear reactors contain several tons of radioactive material.

(2. Nuclear bombs are a one-time source of radiation, while the melting reactors continue to release large amounts of radiation even today, years after the disaster. The bomb sites are intensely radioactive for the first few hours after the explosions, but thereafter the danger diminished rapidly. The decay of radioactivity of a nuclear reactor is much slower than that following a nuclear explosion, because of a greater inventory of long-lived isotopes.

(3. Using some worst-case assumptions for a speculative nuclear war scenario wherein 100 GW(e) of the nuclear power industry is included in the target list, the 50-year global fallout dose is estimated to increase by a factor of 3 over similar estimates wherein nuclear power facilities are not attacked. Radiation dose will be much greater and spread to greater area when nuclear weapon is detonated over nuclear reactor or spent fuel storage tank than alone.

-51. The only way to completely eliminate nuclear risks is to eliminate nuclear weapons from the planet. Till total global disarmament is achieved; no first use policy, removing hair-trigger alert, international treaties and agreements, securing nuclear weapons & fissile materials, export controls, nuclear test-bans and fissile material production cut-offs are helpful.

-52. There are nine nuclear weapon states. Only the presidents/prime ministers can take the decision to launch nuclear weapon, and once it is taken, no one has the authority to block it. It means a handful of men have the power to end the world in few minutes, without having to consult anyone. This is the fallacy of human intelligence. You would want to have a commander-in-chief who is of sound mind, who is fully in control of his mental capacity, who is not volatile, who is not subject to anger. No one person can be so wise that he/she alone can take decision to launch nuclear weapon. We need checks and balances as basic defense against mistakes, accidents, miscalculations, and recklessness. I propose that unanimous decision of three people; president (or prime minister), leader of opposition (or speaker of parliament) and chief justice of supreme court is required to launch nuclear weapon.

-53. I condemn assassination of nuclear scientists to retard nuclear weapon program. Nuclear scientists are different from terrorists. They are working under instructions of their political and military leadership. If America and Japan were not at war, even if Oppenheimer designed a fission bomb, it would not be used. Don’t blame scientist for faulty leadership. The same fission reaction is generating electricity thanks to scientists. It is the political and military leaders of the world that are pursuing nuclear weapon program and they ought to be held accountable for the mess we are in.

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Dr. Rajiv Desai. MD.

December 3, 2024

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Postscript:

If Ukraine hadn’t given up its nukes after the collapse of the Soviet Union, would Vladimir Putin have dared invade? If you give up your nukes, you give up your national security. This line of thinking is unwise. South Africa dismantled its nuclear weapons program in the 1990s without compromising national security. Since 1945 the eight countries possessing nuclear weapons have been involved in over eight times as many wars, on average, as all the non-nuclear countries. Possession of nuclear weapons does not prevent war. History shows that the existence of nuclear weapons has done nothing to prevent the many terrible conflicts since 1945, including acts of aggression against countries with nuclear weapons. The money spent on nuclear weapons can be used for poverty alleviation, health care, education, environmental conservation, infrastructure, renewable technologies, disaster relief and other vital services. It’s time for the world to disarm and prosper.

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Footnote:

President Vladimir Putin said that Russia would use all weapons at its disposal against Ukraine if Kyiv were to acquire nuclear arms. The research conducted by Turco et al. (1983), Sagan (1984), Pittock et al. (1986), Robock, Oman, and Stenchikov (2007), Mills et al. (2008), Robock and Toon (2012), Mills et al. (2014) and Joshua Coupe, Charles G. Bardeen, Alan Robock, Owen B. Toon (2019) confirms that a full-scale nuclear attack would be suicidal for the country that decides to carry out such an attack.

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One comment on “Nuclear Holocaust”

Cabozantinib (S-malate) says:

December 4, 2024 at 7:39 am

Hi! This is kind of off topic but I need some help from an established blog.
Is it very difficult to set up your own blog?
I’m not very techincal but I can figure things out pretty quick.
I’m thinking about setting up my own but I’m not sure where to begin. Do you have any ideas or suggestions?

Thank you

Dr Rajiv Desai

Nuclear Holocaust

One comment on “Nuclear Holocaust”

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