Weapons-grade nuclear material

Last updated

Actinides and fission products by half-life
Actinides [1] by decay chain Half-life
range (a)		 Fission products of 235U by yield [2]
4n 4n + 1 4n + 2 4n + 3 4.5–7%0.04–1.25%<0.001%
228 Ra№ 4–6 a 155 Euþ
248 Bk [3] > 9 a
244 Cmƒ 241 Puƒ 250 Cf 227 Ac№ 10–29 a 90 Sr 85 Kr 113m Cdþ
232 Uƒ 238 Puƒ 243 Cmƒ 29–97 a 137 Cs 151 Smþ 121m Sn
249 Cfƒ 242m Amƒ141–351 a

No fission products have a half-life
in the range of 100 a–210 ka ...

Contents

241 Amƒ 251 Cfƒ [4] 430–900 a
226 Ra№ 247 Bk1.3–1.6 ka
240 Pu 229 Th 246 Cmƒ 243 Amƒ4.7–7.4 ka
245 Cmƒ 250 Cm8.3–8.5 ka
239 Puƒ24.1 ka
230 Th№ 231 Pa№32–76 ka
236 Npƒ 233 Uƒ 234 U№ 150–250 ka 99 Tc₡ 126 Sn
248 Cm 242 Pu 327–375 ka 79 Se₡
1.33 Ma 135 Cs₡
237 Npƒ 1.61–6.5 Ma 93 Zr 107 Pd
236 U 247 Cmƒ 15–24 Ma 129 I₡
244 Pu80 Ma

... nor beyond 15.7 Ma [5]

232 Th№ 238 U№ 235 Uƒ№0.7–14.1 Ga

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 fissile isotopes of certain elements have the potential for use in nuclear weapons. For such use, the concentration of fissile isotopes uranium-235 and plutonium-239 in the element used must be sufficiently high. Uranium from natural sources is enriched by isotope separation, and plutonium is produced in a suitable nuclear reactor.

Experiments have been conducted with uranium-233 (the fissile material at the heart of the thorium fuel cycle). Neptunium-237 and some isotopes of americium might be usable, but it is not clear that this has ever been implemented. The latter substances are part of the minor actinides in spent nuclear fuel. [6]

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]

NuclideHalf-life
(y)		Critical mass
(kg)		Diameter
(cm)		Ref
uranium-233 159,2001511 [8]
uranium-235 703,800,0005217 [8]
neptunium-236 154,00078.7 [9]
neptunium-237 2,144,0006018 [10] [11]
plutonium-238 87.79.04–10.079.5–9.9 [12]
plutonium-239 24,110109.9 [8] [12]
plutonium-240 65614015 [8]
plutonium-241 14.31210.5 [13]
plutonium-242 375,00075–10019–21 [13]
americium-241 432.255–7720–23 [14]
americium-242m 1419–1411–13 [14]
americium-243 7370180–28030–35 [14]
curium-24329.17.34–1010–11 [15]
curium-24418.113.5–3012.4–16 [15]
curium-24585009.41–12.311–12 [15]
curium-246476039–70.118–21 [15]
curium-24715,600,0006.94–7.069.9 [15]
berkelium-247138075.711.8-12.2 [16]
berkelium-2490.919216.1-16.6 [16]
californium-24935169 [9]
californium-2519005.468.5 [9]
californium-2522.62.736.9 [17]
einsteinium-2540.7559.897.1 [16]

Countries that have produced weapons-grade nuclear material

At least ten countries have produced weapons-grade nuclear material: [18]

Weapons-grade uranium

Natural uranium is made weapons-grade through isotopic enrichment. Initially only about 0.7% of it is fissile U-235, 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.[ citation needed ]

U-233 is produced from thorium-232 by neutron capture. [19] 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. [20]

While U-233 would thus seem ideal for weaponization, a significant obstacle to that goal is the co-production of trace amounts of uranium-232 due to side-reactions. U-232 hazards, a result of its highly radioactive decay products such as thallium-208, are significant even at 5 parts per million. Implosion nuclear weapons require U-232 levels below 50 PPM (above which the U-233 is considered "low grade"; cf. "Standard weapon grade plutonium requires a Pu-240 content of no more than 6.5%." which is 65,000 PPM, and the analogous Pu-238 was produced in levels of 0.5% (5000 PPM) or less). Gun-type fission weapons would require low U-232 levels and low levels of light impurities on the order of 1 PPM. [21]

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. [22] It can then be separated from the uranium in a nuclear reprocessing plant. [23]

Weapons-grade plutonium is defined as being predominantly Pu-239, typically about 93% Pu-239. [24] 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 pre-detonate. This makes plutonium unsuitable for use in gun-type nuclear weapons. To reduce the concentration of Pu-240 in the plutonium produced, weapons program plutonium production reactors (e.g. B Reactor) 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 reactors 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.

Plutonium recovered from LWR spent fuel, while not weapons grade, can be used to produce nuclear weapons at all levels of sophistication, [25] though in simple designs it may produce only a fizzle yield. [26] Weapons made with reactor-grade plutonium would require special cooling to keep them in storage and ready for use. [27] A 1962 test at the U.S. Nevada National Security Site (then known as the Nevada Proving Grounds) used non-weapons-grade plutonium produced in a Magnox reactor in the United Kingdom. The plutonium used was provided to the United States 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 this way. [28] The plutonium was apparently sourced from the Magnox reactors at Calder Hall or Chapelcross. The content of Pu-239 in material used for the 1962 test was not disclosed, but has been inferred to have been at least 85%, much higher than typical spent fuel from currently operating reactors. [29]

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.

Related Research Articles

In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal chain reaction can only be achieved with fissile material. The predominant neutron energy in a system may be typified by either slow neutrons or fast neutrons. Fissile material can be used to fuel thermal-neutron reactors, fast-neutron reactors and nuclear explosives.

<span class="mw-page-title-main">Nuclear fuel cycle</span> Process of manufacturing and using nuclear fuel

The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in the back end, which are necessary to safely manage, contain, and either reprocess or dispose of spent nuclear fuel. If spent fuel is not reprocessed, the fuel cycle is referred to as an open fuel cycle ; if the spent fuel is reprocessed, it is referred to as a closed fuel cycle.

Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium fuel used in the light-water reactors that predominate nuclear power generation.

<span class="mw-page-title-main">Breeder reactor</span> Nuclear reactor generating more fissile material than it consumes

A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. These reactors can be fueled with more-commonly available isotopes of uranium and thorium, such as uranium-238 and thorium-232, as opposed to the rare uranium-235 which is used in conventional reactors. These materials are called fertile materials since they can be bred into fuel by these breeder reactors.

<span class="mw-page-title-main">Uranium-238</span> Isotope of uranium

Uranium-238 is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239. 238U cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. Doppler broadening of 238U's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control.

<span class="mw-page-title-main">Fast-neutron reactor</span> Nuclear reactor where fast neutrons maintain a fission chain reaction

A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons, as opposed to slow thermal neutrons used in thermal-neutron reactors. Such a fast reactor needs no neutron moderator, but requires fuel that is relatively rich in fissile material when compared to that required for a thermal-neutron reactor. Around 20 land based fast reactors have been built, accumulating over 400 reactor years of operation globally. The largest was the Superphénix sodium cooled fast reactor in France that was designed to deliver 1,242 MWe. Fast reactors have been studied since the 1950s, as they provide certain advantages over the existing fleet of water-cooled and water-moderated reactors. These are:

<span class="mw-page-title-main">Integral fast reactor</span> Nuclear reactor design

The integral fast reactor (IFR), originally the advancedliquid-metal reactor (ALMR), is a design for a nuclear reactor using fast neutrons and no neutron moderator. IFRs can breed more fuel and are distinguished by a nuclear fuel cycle that uses reprocessing via electrorefining at the reactor site.

<span class="mw-page-title-main">Fertile material</span> Substance that can be converted into material for use in nuclear fission

Fertile material is a material that, although not fissile itself, can be converted into a fissile material by neutron absorption.

<span class="mw-page-title-main">Plutonium-239</span> Isotope of plutonium

Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years.

Uranium (92U) is a naturally occurring radioactive element (radioelement) with no stable isotopes. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in Earth's crust. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors. In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from 214U to 242U. The standard atomic weight of natural uranium is 238.02891(3).

Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be synthesized and identified was 239Np in 1940, produced by bombarding 238
U
 with neutrons to produce 239
U
, which then underwent beta decay to 239
Np
.

Plutonium (94Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940. Twenty-two plutonium radioisotopes have been characterized. The most stable are 244Pu with a half-life of 80.8 million years; 242Pu with a half-life of 373,300 years; and 239Pu with a half-life of 24,110 years; and 240Pu with a half-life of 6,560 years. This element also has eight meta states; all have half-lives of less than one second.

<span class="mw-page-title-main">Thorium fuel cycle</span> Nuclear fuel cycle

The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, 232
Th
, as the fertile material. In the reactor, 232
Th
 is transmuted into the fissile artificial uranium isotope 233
U
 which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts of fissile material, which are insufficient to initiate a nuclear chain reaction. Additional fissile material or another neutron source is necessary to initiate the fuel cycle. In a thorium-fuelled reactor, 232
Th
 absorbs neutrons to produce 233
U
. This parallels the process in uranium breeder reactors whereby fertile 238
U
 absorbs neutrons to form fissile 239
Pu
. Depending on the design of the reactor and fuel cycle, the generated 233
U
 either fissions in situ or is chemically separated from the used nuclear fuel and formed into new nuclear fuel.

<span class="mw-page-title-main">Plutonium-238</span> Isotope of plutonium

Plutonium-238 is a radioactive isotope of plutonium that has a half-life of 87.7 years.

<span class="mw-page-title-main">Spent nuclear fuel</span> Nuclear fuel thats been irradiated in a nuclear reactor

Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor. It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and, depending on its point along the nuclear fuel cycle, it will have different isotopic constituents than when it started.

<span class="mw-page-title-main">Plutonium</span> Chemical element with atomic number 94 (Pu)

Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric. It is radioactive and can accumulate in bones, which makes the handling of plutonium dangerous.

Uranium-236 is an isotope of uranium that is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in the reprocessed uranium made from spent nuclear fuel.

Reactor-grade plutonium (RGPu) is the isotopic grade of plutonium that is found in spent nuclear fuel after the uranium-235 primary fuel that a nuclear power reactor uses has burnt up. The uranium-238 from which most of the plutonium isotopes derive by neutron capture is found along with the U-235 in the low enriched uranium fuel of civilian reactors.

<span class="mw-page-title-main">Nuclear transmutation</span> Conversion of an atom from one element to another

Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.

REMIX-Fuel (REgenerated MIXture of U, Pu oxides) was developed in Russia to simplify the reprocessing process, reuse spent fuel, reduce the consumption of natural uranium and to enable multi-recycling.

References

  1. ↑ 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.
  2. ↑ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
  3. ↑ Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
    "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]."
  4. ↑ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ Reevaluated Critical Specifications of Some Los Alamos Fast-Neutron Systems
  8. 1 2 3 4 Nuclear Weapons Design & Materials, The Nuclear Threat Initiative website.[ dead link ][ unreliable source? ]
  9. 1 2 3 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.
  10. ↑ Chapter 5, Troubles tomorrow? Separated Neptunium 237 and Americium, Challenges of Fissile Material Control (1999), isis-online.org
  11. ↑ P. Weiss (October 26, 2002). "Neptunium Nukes? Little-studied metal goes critical". Science News . 162 (17): 259. doi:10.2307/4014034. Archived from the original on December 15, 2012. Retrieved November 7, 2013.
  12. 1 2 Updated Critical Mass Estimates for Plutonium-238, U.S. Department of Energy: Office of Scientific & Technical Information
  13. 1 2 Amory B. Lovins, Nuclear weapons and power-reactor plutonium, Nature, Vol. 283, No. 5750, pp. 817–823, February 28, 1980
  14. 1 2 3 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.
  15. 1 2 3 4 5 Okuno, Hiroshi; Kawasaki, Hiromitsu (2002). "Critical and Subcritical Mass Calculations of Curium-243 to -247 Based on JENDL-3.2 for Revision of ANSI/ANS-8.15". Journal of Nuclear Science and Technology. 39 (10): 1072–1085. doi: 10.1080/18811248.2002.9715296 .
  16. 1 2 3 Institut de Radioprotection et de Sûreté Nucléaire: "Evaluation of nuclear criticality safety. data and limits for actinides in transport", p. 16
  17. ↑ Carey Sublette, Nuclear Weapons Frequently Asked Questions: Section 6.0 Nuclear Materials February 20, 1999
  18. ↑ [ dubious – discuss ]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.
  19. ↑ "Thorium - World Nuclear Association". world-nuclear.org. Archived from the original on October 18, 2024. Retrieved October 18, 2024.
  20. ↑ Definition of Weapons-Usable Uranium-233 ORNL/TM-13517
  21. ↑ Nuclear Materials FAQ
  22. ↑ "All about plutonium | Orano". orano.group. Archived from the original on October 18, 2024. Retrieved October 18, 2024.
  23. ↑ "Development of Advanced Reprocessing Technologies" (PDF). International Atomic Energy Agency . October 24, 2024.
  24. ↑ "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.
  25. ↑ Matthew Bunn and; John P. Holdren (November 1997). "MANAGING MILITARY URANIUM AND PLUTONIUM IN THE UNITED STATES AND THE FORMER SOVIET UNION". Annual Review of Energy and the Environment. 22 (1): 403–486. doi:10.1146/ANNUREV.ENERGY.22.1.403. ISSN   1056-3466. Wikidata   Q56853752..
  26. ↑ 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.
  27. ↑ Rossin, David. "U.S. Policy on Spent Fuel Reprocessing: The Issues". PBS. Retrieved March 29, 2014.
  28. ↑ "Additional Information Concerning Underground Nuclear Weapon Test of Reactor-Grade Plutonium". US Department of Energy. June 1994. Retrieved March 15, 2007.
  29. ↑ "Plutonium". World Nuclear Association. March 2009. Archived from the original on March 30, 2010. Retrieved February 28, 2010.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.