Weapons-grade
Encyclopedia
A weapons-grade substance is one that is pure enough to be used to make a weapon
or has properties that make it suitable for weapons use. Weapons-grade plutonium
and uranium
are the most common examples, but it may also be used to refer to chemical
and biological weapons
. Weapons-grade nuclear material causes the most concern, but plutonium and uranium have other categorizations
based on their purity.
Only certain fissile
isotope
s of plutonium and uranium can be used in nuclear weapon
s. For plutonium, it is plutonium-239
(Pu-239), while uranium has uranium-233
(U-233) and uranium-235
(U-235).
, France
, India
, Israel
, North Korea
, Pakistan
, Russia
, South Africa
, the United Kingdom
, and the United States
.
(U-238). They are separated by their differing mass
es. Highly enriched uranium is considered weapons-grade when it has been enriched to about 90% U-235.
U-233 is produced from thorium-232 by neutron capture
. It can be made highly pure because it can be chemically separated from Th-232 rather than by mass, which is far easier. Therefore, there is no weapons-grade concentration for U-233. Since it can relatively easily be made pure, it is regulated as a special nuclear material
only by the total amount present rather than by concentration or concentration combined with the amount. Uranium-232 is a contaminant that is present only in small amounts, but whose highly radioactive decay products like thallium-208 make handling more difficult.
s when a neutron is absorbed by U-238, forming U-239, which then decays
in a rapid two-step process into Pu-239. It can then be separated from the uranium in a nuclear reprocessing
plant.
Weapons-grade plutonium is defined as being predominantly Pu-239, typically about 93% Pu-239. Pu-240 is produced when Pu-239 absorbs an additional neutron and fails to fission. Pu-240 and Pu-239 are not separated by reprocessing. Pu-240 has a high rate of spontaneous fission
, which can cause a nuclear weapon to predetonate. To reduce the concentration of Pu-240 in the plutonium produced, weapons program plutonium production reactors irradiate the uranium for a far shorter time than is normal for a nuclear power reactor. More precisely, weapons-grade plutonium is obtained from uranium irradiated to a low burnup
.
This represents a fundamental difference between these two types of reactor. In a nuclear power station, high burnup is desirable. Power stations such as the obsolete British Magnox
and French UNGG reactors, which were designed to produce either electricity or weapons material, were operated at low power levels with frequent fuel changes using online refuelling
to produce weapons-grade plutonium. Such operation is not possible with the light water reactor
s most commonly used to produce electric power. In these the reactor must be shut down and the pressure vessel disassembled to gain access to the irradiated fuel.
While it has been claimed that spent LWR fuel could be reprocessed to produce plutonium that, while not weapons grade, could be used to produce a nuclear explosion (even if only one of fizzle
yield), this has never been demonstrated. In particular, a 1962 test at the US Nevada Proving Grounds using non-weapons-grade plutonium used plutonium produced in a Magnox reactor in the United Kingdom. The plutonium used was provided to the US under the 1958 US-UK Mutual Defence Agreement
. Its isotopic composition has not been disclosed, other than the description reactor grade and it has not been disclosed which definition was used in describing the material for this test as reactor grade. The plutonium was apparently sourced from the military Magnox reactors at Calder Hall or Chapelcross. The content of plutonium-239
in material used for the 1962 test is estimated to have been at least 85%, much higher than typical spent fuel from currently operating reactors. Therefore, this test does not prove that constructing a bomb from plutonium sourced from modern spent fuel, which contains no more than 70% Pu-239, is possible.
Occasionally, low-burnup spent fuel has been produced by a commercial LWR when an incident such as a fuel cladding failure has required early refuelling. If the period of irradiation has been sufficiently short, this spent fuel could be reprocessed to produce weapons grade plutonium.
or an organism
used in biological warfare
. A chemical that is weapons-grade must be of a high enough purity and be relatively free of contaminants. When an organism, such as a bacterium
or virus
, is weapons-grade, it means that it is a strain
of that species
that is suitable for weapons use. This may mean that it has been made more infectious
or deadly. It may also mean that person-to-person transmission has been made more difficult, which helps prevent a country's own troops and citizens from becoming infected.
Weapon
A weapon, arm, or armament is a tool or instrument used with the aim of causing damage or harm to living beings or artificial structures or systems...
or has properties that make it suitable for weapons use. Weapons-grade plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
are the most common examples, but it may also be used to refer to chemical
Chemical warfare
Chemical warfare involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from Nuclear warfare and Biological warfare, which together make up NBC, the military acronym for Nuclear, Biological, and Chemical...
and biological weapons
Biological warfare
Biological warfare is the use of biological toxins or infectious agents such as bacteria, viruses, and fungi with intent to kill or incapacitate humans, animals or plants as an act of war...
. Weapons-grade nuclear material causes the most concern, but plutonium and uranium have other categorizations
Special nuclear material
Special nuclear material is a term used by the Nuclear Regulatory Commission of the United States to classify fissile materials. The NRC divides special nuclear material into three main categories, according to the risk and potential for its direct use in a clandestine nuclear weapon or for its...
based on their purity.
Only certain fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...
isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s of plutonium and uranium can be used in nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s. For plutonium, it is plutonium-239
Plutonium-239
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
(Pu-239), while uranium has uranium-233
Uranium-233
Uranium-233 is a fissile isotope of uranium, bred from Thorium as part of the thorium fuel cycle. It has been used in a few nuclear reactors and has been proposed for much wider use as a nuclear fuel. It has a half-life of 160,000 years....
(U-233) and uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
(U-235).
Countries that have produced weapons-grade nuclear material
Very few countries have produced weapons-grade nuclear material. The only countries known to have done so are ChinaChina
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...
, North Korea
North Korea
The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea...
, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
Weapons-grade uranium
U-235 is made weapons-grade through isotopic enrichment. It only makes up 0.7% of natural uranium, with the rest being almost entirely uranium-238Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
(U-238). They are separated by their differing mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
es. Highly enriched uranium is considered weapons-grade when it has been enriched to about 90% U-235.
U-233 is produced from thorium-232 by neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...
. It can be made highly pure because it can be chemically separated from Th-232 rather than by mass, which is far easier. Therefore, there is no weapons-grade concentration for U-233. Since it can relatively easily be made pure, it is regulated as a special nuclear material
Special nuclear material
Special nuclear material is a term used by the Nuclear Regulatory Commission of the United States to classify fissile materials. The NRC divides special nuclear material into three main categories, according to the risk and potential for its direct use in a clandestine nuclear weapon or for its...
only by the total amount present rather than by concentration or concentration combined with the amount. Uranium-232 is a contaminant that is present only in small amounts, but whose highly radioactive decay products like thallium-208 make handling more difficult.
Weapons-grade plutonium
Pu-239 is produced artificially in nuclear reactorNuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s when a neutron is absorbed by U-238, forming U-239, which then decays
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
in a rapid two-step process into Pu-239. It can then be separated from the uranium in a nuclear reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
plant.
Weapons-grade plutonium is defined as being predominantly Pu-239, typically about 93% Pu-239. Pu-240 is produced when Pu-239 absorbs an additional neutron and fails to fission. Pu-240 and Pu-239 are not separated by reprocessing. Pu-240 has a high rate of spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
, which can cause a nuclear weapon to predetonate. To reduce the concentration of Pu-240 in the plutonium produced, weapons program plutonium production reactors irradiate the uranium for a far shorter time than is normal for a nuclear power reactor. More precisely, weapons-grade plutonium is obtained from uranium irradiated to a low burnup
Burnup
In nuclear power technology, burnup is a measure of how much energy is extracted from a primary nuclear fuel source...
.
This represents a fundamental difference between these two types of reactor. In a nuclear power station, high burnup is desirable. Power stations such as the obsolete British Magnox
Magnox
Magnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...
and French UNGG reactors, which were designed to produce either electricity or weapons material, were operated at low power levels with frequent fuel changes using online refuelling
Online refuelling
In nuclear power technology, online refuelling is a technique for changing the fuel of a nuclear reactor while the pile is critical.Online refuelling has been provided for three main reasons:...
to produce weapons-grade plutonium. Such operation is not possible with the light water reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...
s most commonly used to produce electric power. In these the reactor must be shut down and the pressure vessel disassembled to gain access to the irradiated fuel.
While it has been claimed that spent LWR fuel could be reprocessed to produce plutonium that, while not weapons grade, could be used to produce a nuclear explosion (even if only one of fizzle
Fizzle (nuclear test)
In nuclear weapons, a fizzle occurs when the testing of a nuclear bomb fails to meet its expected yield. The reason for the failure can be linked to improper bomb design, poor construction, or lack of expertise. All countries that have had a nuclear weapons testing program have experienced fizzles...
yield), this has never been demonstrated. In particular, a 1962 test at the US Nevada Proving Grounds using non-weapons-grade plutonium used plutonium produced in a Magnox reactor in the United Kingdom. The plutonium used was provided to the US under the 1958 US-UK Mutual Defence Agreement
1958 US-UK Mutual Defence Agreement
The 1958 US–UK Mutual Defence Agreement is a bilateral treaty between the United States and the United Kingdom on nuclear weapons cooperation.It was signed after the UK successfully tested its first hydrogen bomb during Operation Grapple. While the U.S...
. Its isotopic composition has not been disclosed, other than the description reactor grade and it has not been disclosed which definition was used in describing the material for this test as reactor grade. The plutonium was apparently sourced from the military Magnox reactors at Calder Hall or Chapelcross. The content of plutonium-239
Plutonium-239
Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 has also been used and is currently the secondary isotope. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in...
in material used for the 1962 test is estimated to have been at least 85%, much higher than typical spent fuel from currently operating reactors. Therefore, this test does not prove that constructing a bomb from plutonium sourced from modern spent fuel, which contains no more than 70% Pu-239, is possible.
Occasionally, low-burnup spent fuel has been produced by a commercial LWR when an incident such as a fuel cladding failure has required early refuelling. If the period of irradiation has been sufficiently short, this spent fuel could be reprocessed to produce weapons grade plutonium.
Other uses
Less frequently, weapons-grade refers to a substance used in chemical warfareChemical warfare
Chemical warfare involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from Nuclear warfare and Biological warfare, which together make up NBC, the military acronym for Nuclear, Biological, and Chemical...
or an organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
used in biological warfare
Biological warfare
Biological warfare is the use of biological toxins or infectious agents such as bacteria, viruses, and fungi with intent to kill or incapacitate humans, animals or plants as an act of war...
. A chemical that is weapons-grade must be of a high enough purity and be relatively free of contaminants. When an organism, such as a bacterium
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
or virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
, is weapons-grade, it means that it is a strain
Strain (biology)
In biology, a strain is a low-level taxonomic rank used in three related ways.-Microbiology and virology:A strain is a genetic variant or subtype of a micro-organism . For example, a "flu strain" is a certain biological form of the influenza or "flu" virus...
of that species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
that is suitable for weapons use. This may mean that it has been made more infectious
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
or deadly. It may also mean that person-to-person transmission has been made more difficult, which helps prevent a country's own troops and citizens from becoming infected.
External links
- Reactor-Grade and Weapons-Grade Plutonium in Nuclear Explosives, Canadian Coalition for Nuclear Responsibility
- Nuclear weapons and power-reactor plutonium, Amory B. Lovins, February 28, 1980, NatureNature (journal)Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
, Vol. 283, No. 5750, pp. 817–823