Weapons-grade
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| Actinides | Halflife | Fission products | ||||||
|---|---|---|---|---|---|---|---|---|
| 244Cm | 241Pu f | 250Cf | 243Cmf | 10–30 y | 137Cs | 90Sr | 85Kr | |
| 232U f | 238Pu | f is for fissile |
69–90 y | 151Sm nc➔ | ||||
| 4n | 249Cf f | 242Amf | 141–351 | No fission product has halflife 102 to 2×105 years |
||||
| 241Am | 251Cf f | 431–898 | ||||||
| 240Pu | 229Th | 246Cm | 243Am | 5–7 ky | ||||
| 4n | 245Cmf | 250Cm | 239Pu f | 8–24 ky | ||||
| 233U f | 230Th | 231Pa | 32–160 | |||||
| 4n+1 | 234U | 4n+3 | 211–290 | 99Tc | 126Sn | 79Se | ||
| 248Cm | 242Pu | 340–373 | Long-lived fission products | |||||
| 237Np | 4n+2 | 1–2 my | 93Zr | 135Cs nc➔ | ||||
| 236U | 4n+1 | 247Cmf | 6–23 | 107Pd | 129I | |||
| 244Pu | 80 my | >7% | >5% | >1% | >.1% | |||
| 232Th | 238U | 235U f | 0.7–12by | fission product yield | ||||
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 isotopes of plutonium and uranium can be used in nuclear weapons. For plutonium, it is plutonium-239 (Pu-239), while uranium has uranium-233 (U-233) and uranium-235 (U-235).
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[edit] Countries that produce weapons-grade nuclear material
Because of the immense costs and difficulties of building a manufacturing facility sufficient to produce weapons-grade nuclear material, very few countries have the capability of building facilities capable of making weapons-grade nuclear material.
The only countries with facilities manufacturing weapons-grade nuclear material today are The United States, The United Kingdom, France, India, Germany, Russia, and China. Of these countries, only the governments of France and Russia are known to sell their manufacturing expertise to other countries.
Because each manufacturing process is unique, any weapons-grade nuclear material can be reliably traced back to its exact manufacturing origin by analyzing the composition and impurities in the material.
[edit] 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-238 (U-238). They are separated by their differing masses. 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.
[edit] Weapons-grade plutonium
Pu-239 is produced artificially in nuclear reactors when a neutron is absorbed by U-238. Plutonium-240 is also produced when Pu-239 absorbs an additional neutron and sometimes fails to fission. Pu-240 has a high rate of spontaneous fission, which can cause a nuclear weapon to predetonate, and its concentration must be less than 7% for the plutonium to be weapons-grade. To avoid this the uranium fuel in a reactor must typically be replaced four to six times per year. This is necessary because the concentration of Pu-240 rises over time and its mass and chemical properties are too similar for it to be separated from Pu-239. With any reactor, plutonium is separated from uranium chemically in a nuclear reprocessing plant.
It is difficult to produce weapons-grade plutonium with a light water reactor because the reactor must be shut down frequently to replace the nuclear fuel rods, so weapons-grade plutonium is generally produced in small, specialized military reactors. However, a test of a nuclear weapon that used reactor-grade plutonium was successfully detonated, although the yield was relatively low.
[edit] Other uses
Less frequently, weapons-grade refers to a substance used in chemical warfare 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.
Colloquially, 'weapons-grade' is used to describe something unusually potent (e.g., Habanero chilis) or offensive (e.g., shock sites such as Goatse.cx).
[edit] 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, Nature, Vol. 283, No. 5750, pp. 817-823
- Garwin, Richard L.. "The Nuclear Fuel Cycle: Does Reprocessing Make Sense?". in B. van der Zwaan. Nuclear energy. p. 144. http://books.google.com/books?id=cjhGcg_98kQC&pg=PA144. "But there is no doubt that the reactor-grade plutonium obtained from reprocessing LWR spent fuel can readily be used to make high-performance, high-reliability nuclear weaponry, as explained in the 1994 Committee on International Security and Arms Control (CISAC) publication."
