Weapons-grade nuclear material
Actinides[1] by decay chain | Half-life range (a) |
|||||||
---|---|---|---|---|---|---|---|---|
4n
|
4n + 1
|
4n + 2
|
4n + 3
|
4.5–7% | 0.04–1.25% | <0.001% | ||
228 Ra№
|
4–6 a
|
155 Euþ
|
||||||
244 Cmƒ
|
241Puƒ | 250 Cf
|
227 Ac№
|
10–29 a
|
90Sr | 85Kr | 113m Cdþ
| |
232Uƒ | 238Puƒ | 243 Cmƒ
|
29–97 a
|
137 Cs
|
151 Smþ
|
121m Sn
| ||
248Bk[3]
|
249 Cfƒ
|
242m Amƒ
|
141–351 a |
No fission products have a half-life | ||||
241Amƒ | 251Cfƒ[4]
|
430–900 a | ||||||
226Ra№ | 247 Bk
|
1.3–1.6 ka | ||||||
240Pu | 229 Th
|
246 Cmƒ
|
243 Amƒ
|
4.7–7.4 ka | ||||
245 Cmƒ
|
250 Cm
|
8.3–8.5 ka | ||||||
239Puƒ | 24.1 ka | |||||||
230 Th№
|
231 Pa№
|
32–76 ka | ||||||
236 Npƒ
|
233Uƒ | 234U№ | 150–250 ka | 99Tc₡ | 126 Sn
| |||
248 Cm
|
242Pu | 327–375 ka | 79Se₡ | |||||
1.53 Ma | 93 Zr
| |||||||
237 Npƒ
|
2.1–6.5 Ma | 135 Cs₡
|
107 Pd
| |||||
236U | 247 Cmƒ
|
15–24 Ma | 129I₡ | |||||
244Pu | 80 Ma |
... nor beyond 15.7 Ma[5] | ||||||
232Th№ | 238U№ | 235Uƒ№ | 0.7–14.1 Ga | |||||
|
Nuclear weapons |
---|
Background |
Nuclear-armed states |
|
Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon and has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nuclear weapons are the most common examples. (These nuclear materials have other categorizations based on their purity.)
Only
Experiments have been conducted with
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 accompanying table. Most information on bare sphere masses is classified, but some documents have been declassified.[7]
Nuclide | Half-life (y) |
Critical mass (kg) |
Diameter (cm) |
Ref |
---|---|---|---|---|
uranium-233 | 159,200 | 15 | 11 | [8] |
uranium-235 | 703,800,000 | 52 | 17 | [8] |
neptunium-236 |
154,000 | 7 | 8.7 | [9] |
neptunium-237 |
2,144,000 | 60 | 18 | [10][11] |
plutonium-238 | 87.7 | 9.04–10.07 | 9.5–9.9 | [12] |
plutonium-239 | 24,110 | 10 | 9.9 | [8][12] |
plutonium-240 | 6561 | 40 | 15 | [8] |
plutonium-241 | 14.3 | 12 | 10.5 | [13] |
plutonium-242 | 375,000 | 75–100 | 19–21 | [13] |
americium-241 | 432.2 | 55–77 | 20–23 | [14] |
americium-242m |
141 | 9–14 | 11–13 | [14] |
americium-243 |
7370 | 180–280 | 30–35 | [14] |
curium-243 | 29.1 | 7.34–10 | 10–11 | [15] |
curium-244 | 18.1 | 13.5–30 | 12.4–16 | [15] |
curium-245 | 8500 | 9.41–12.3 | 11–12 | [15] |
curium-246 | 4760 | 39–70.1 | 18–21 | [15] |
curium-247 | 15,600,000 | 6.94–7.06 | 9.9 | [15] |
berkelium-247 | 1380 | 75.7 | 11.8-12.2 | [16] |
berkelium-249 | 0.9 | 192 | 16.1-16.6 | [16] |
californium-249 | 351 | 6 | 9 | [9] |
californium-251 | 900 | 5.46 | 8.5 | [9] |
californium-252 | 2.6 | 2.73 | 6.9 | [17] |
einsteinium-254 | 0.755 | 9.89 | 7.1 | [16] |
Countries that have produced weapons-grade nuclear material
At least ten countries have produced weapons-grade nuclear material:[18]
- Five recognized "1964)
- Three other declared nuclear states that are not signatories of the NPT: India (not a signatory, weapon tested in 1974), Pakistan (not a signatory, weapon tested in 1998), and North Korea (withdrew from the NPT in 2003, weapon tested in 2006)
- Israel, which is widely known to have developed nuclear weapons (likely first tested in the 1960s or 1970s) but has not openly declared its capability
- South Africa, which also had enrichment capabilities and developed nuclear weapons (possibly tested in 1979), but disassembled its arsenal and joined the NPT in 1991
Weapons-grade uranium
U-233 is produced from thorium-232 by neutron capture. The U-233 produced thus does not require enrichment and can be relatively easily chemically separated from residual Th-232. It is therefore regulated as a special nuclear material only by the total amount present. U-233 may be intentionally down-blended with U-238 to remove proliferation concerns.[19]
While U-233 would thus seem ideal for weaponization, a significant obstacle to that goal is the co-production of trace amounts of
Weapons-grade plutonium
Pu-239 is produced artificially in nuclear reactors 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
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
Plutonium recovered from LWR spent fuel, while not weapons grade, can be used to produce nuclear weapons at all levels of sophistication,
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.
References
- ^ Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
- thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
- .
"The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk248 with a half-life greater than 9 [years]. No growth of Cf248 was detected, and a lower limit for the β− half-life can be set at about 104 [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]." - sea of instability".
- ^ Excluding those "classically stable" nuclides with half-lives significantly in excess of 232Th; e.g., while 113mCd has a half-life of only fourteen years, that of 113Cd is eight quadrillion years.
- ^ David Albright and Kimberly Kramer (August 22, 2005). "Neptunium 237 and Americium: World Inventories and Proliferation Concerns" (PDF). Institute for Science and International Security. Retrieved October 13, 2011.
- ^ Reevaluated Critical Specifications of Some Los Alamos Fast-Neutron Systems
- ^ a b c d Nuclear Weapons Design & Materials, The Nuclear Threat Initiative website.[dead link][unreliable source?]
- ^ a b c Final Report, Evaluation of nuclear criticality safety data and limits for actinides in transport, Republic of France, Institut de Radioprotection et de Sûreté Nucléaire, Département de Prévention et d'étude des Accidents.
- ^ Chapter 5, Troubles tomorrow? Separated Neptunium 237 and Americium, Challenges of Fissile Material Control (1999), isis-online.org
- ^
P. Weiss (October 26, 2002). "Neptunium Nukes? Little-studied metal goes critical". doi:10.2307/4014034. Archived from the originalon December 15, 2012. Retrieved November 7, 2013.
- ^ a b Updated Critical Mass Estimates for Plutonium-238, U.S. Department of Energy: Office of Scientific & Technical Information
- ^ a b Amory B. Lovins, Nuclear weapons and power-reactor plutonium, Nature, Vol. 283, No. 5750, pp. 817–823, February 28, 1980
- ^ a b c Dias, Hemanth; Tancock, Nigel; Clayton, Angela (2003). "Critical Mass Calculations for 241Am, 242mAm and 243Am" (PDF). Challenges in the Pursuit of Global Nuclear Criticality Safety. Proceedings of the Seventh International Conference on Nuclear Criticality Safety. Vol. II. Tokai, Ibaraki, Japan: Japan Atomic Energy Research Institute. pp. 618–623.
- ^ .
- ^ a b c Institut de Radioprotection et de Sûreté Nucléaire: "Evaluation of nuclear criticality safety. data and limits for actinides in transport", p. 16
- ^ Carey Sublette, Nuclear Weapons Frequently Asked Questions: Section 6.0 Nuclear Materials February 20, 1999
- ^ [dubious ]Makhijani, Arjun; Chalmers, Lois; Smith, Brice (October 15, 2004). "Uranium Enrichment: Just Plain Facts to Fuel an Informed Debate on Nuclear Proliferation and Nuclear Power" (PDF). Institute for Energy and Environmental Research. Retrieved May 17, 2017.
- ORNL/TM-13517
- ^ Nuclear Materials FAQ
- ^ "Reactor-Grade and Weapons-Grade Plutonium in Nuclear Explosives". Nonproliferation and Arms Control Assessment of Weapons-Usable Fissile Material Storage and Excess Plutonium Disposition Alternatives (excerpted). U.S. Department of Energy. January 1997. Retrieved September 5, 2011.
- Wikidata Q56853752..
- ^ J. Carson Mark (August 1990). "Reactor Grade Plutonium's Explosive Properties" (PDF). Nuclear Control Institute. Archived from the original (PDF) on May 8, 2010. Retrieved May 10, 2010.
- ^ Rossin, David. "U.S. Policy on Spent Fuel Reprocessing: The Issues". PBS. Retrieved March 29, 2014.
- US Department of Energy. June 1994. Retrieved March 15, 2007.
- ^ "Plutonium". World Nuclear Association. March 2009. Archived from the original on March 30, 2010. Retrieved February 28, 2010.
External links
- Reactor-Grade and Weapons-Grade Plutonium in Nuclear Explosives, Canadian Coalition for Nuclear Responsibility
- Nuclear weapons and power-reactor plutonium Archived March 16, 2007, at the Amory B. Lovins, February 28, 1980, Nature, Vol. 283, No. 5750, pp. 817–823
- Garwin, Richard L. (1999). "The Nuclear Fuel Cycle: Does Reprocessing Make Sense?". In B. van der Zwaan (ed.). Nuclear energy. World Scientific. p. 144. 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.