Research reactors & nuclear weapons

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In addition to conversion from HEU to LEU fuels, efforts have been made to eliminate the use of HEU targets for isotope production. Here the issue of greatest concern is the use of HEU targets to produce targets to produce fission-product radioisotopes - in particular molybdenum-99, which decays to form technetium-99m, the most commonly used isotope for diagnostic nuclear medicine.
About six countries use HEU targets for isotope production, employing a total of approximately 50 kilograms of HEU targets annually, typically enriched to 93% uranium-235. Australia is alone in using LEU targets to produce molybdenum-99 (although it should be noted that significant safety and waste management problems are associated with ANSTO's molybdenum-99 production and processing operations). Several new molybdenum-99 producers may emerge in the coming years and there is some concern that the use of HEU targets could become more widespread. (Vandegrift et al., 1999.)
Whether existing and new producers will switch to LEU or non-uranium targets depends in part on progress with research into alternative targets, and on economic and political issues. When compared to HEU, LEU targets result in larger waste streams with higher concentration uranium solutions. Some producers are concerned about the cost implications of the increased waste streams. Cost implications may vary significantly between producers depending on the adjustments required.
According to Kuperman (1999), the major producers of molybdenum-99 - Institut National des Radioelements (IRE) in Belgium, MDS Nordion in Canada, and Mallinckrodt in the Netherlands - are responsible for up to 90% of HEU commerce associated with medical isotopes. These three producers have been reluctant to adopt LEU target technology, partly for fear of putting themselves at a competitive disadvantage vis-a-vis their competitors. Nevertheless, all three producers have shown some willingness to switch to LEU targets in recent years, partly because there is no certainty of ongoing availability of HEU targets from the US or other sources.
According to Kuperman (1999), Belgium's IRE agreed to irradiate and process prototype LEU targets but without making a firm commitment to convert, while Mallinckrodt also expressed an interest in cooperating with the RERTR. In June 1999, the US Nuclear Regulatory Commission approved the export of 130 kilograms of 93.3% enriched HEU to Canada over a five year period for isotope production. Supply is conditional on demonstrated efforts to develop suitable LEU targets for the Canadian reactors; whether this condition is being taken seriously is a matter of some controversy.
N. Arkhangelsky, "Twenty years of RERTR in Russia: past, present and future", Paper Presented at the 23rd International Meeting on RERTR, Las Vegas, Nevada, October 1-6, 2000, .
Matthew Bunn, 2000, "The Next Wave: Urgently Needed New Steps to Control Warheads and Fissile Material", Washington, DC and Cambridge, MA: Carnegie Endowment for International Peace, and the Managing the Atom Project, or .
Matthew Bunn, John Holdren, and Anthony Wier, 2002, "Securing Nuclear Weapons and Materials: Seven Steps for Immediate Action", .
A. J. Kuperman (Nuclear Control Institute), 1999, "A level-playing field for medical isotope production - how to phase out reliance on HEU", Paper Presented at 22nd International Meeting on Reduced Enrichment for Research and Test Reactors (RERTR), Budapest, Hungary, October 7, 1999, .
Alan J. Kuperman and Paul L. Leventhal, 1998, "HEU core conversion of Russian production reactors: a major threat to the international RERTR regime", Paper presented at the 21st Annual International Meeting on Reduced Enrichment for Research and Test Reactors (RERTR), São Paulo, Brazil, October 19, 1998, .
Nuclear Control Institute, June 27, 2001, "NCI files petition with NRC to block export of bomb-grade uranium", .
F. Takats, A. Grigoriev, and I.G. Ritchie, 1993, "Management of spent fuel from power and research reactors: International status and trends", IAEA Bulletin, No.3, pp.18-22.
Armando Travelli, 2000, "Status and progress of the RERTR program in the year 2000", Paper Presented at the 23rd International Meeting on RERTR, Las Vegas, Nevada, October 1-6, 2000, .
G.F. Vandegrift et al., 1999, "Converting targets and processes for fission-production molybdenum-99 from high- to low-enriched uranium", in International Atomic Energy Agency, Technical Document 1065, Production technologies for Molybdenum-99 and Technetium-99m, IAEA: Vienna, pp.25-74.
World Information Service on Energy, 2001, "Germany: FRM-2 reactor to be converted to 'medium' enriched uranium", WISE News Communique, #557, November 2.


Plutonium-239 is the desired isotope for plutonium weapons. As neutron irradiation of uranium-238 proceeds, the greater the quantity of isotopes such as plutonium-240, plutonium-242 and americium-241, and the greater the quantity of plutonium-238 formed from uranium-235. These isotopes have unwanted effects such as decreasing the potential yield of the weapon or increasing the radioactivity of the material thus making it more difficult and dangerous to manufacture and transport weapons.
Definitions of plutonium usually refer to the level of plutonium-240, which is highly toxic and close in atomic weight to plutonium-239 (and thus difficult to separate). "Super grade" plutonium contains 2-3% plutonium-240, "weapon grade" plutonium contains less than 7% plutonium-240, "fuel grade" plutonium contains 7-18% plutonium-240 and "reactor grade" plutonium contains over 18% plutonium-240.
With the exception of plutonium comprising 80% or more of the isotope plutonium-238, all plutonium 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", and is subject to equal levels of safeguards. (Australian Safeguards and Non-Proliferation Office, 1998-99, pp.55-59.)
Although plutonium grades with lower percentages of plutonium-240 (and other unwanted isotopes) are more suitable for weapons manufacture, reactor grade plutonium can still be used for weapons manufacture. (Makhijani and Saleska, 1995, p.48.)
The ease or difficulty of producing a nuclear weapon using reactor grade plutonium is debated. According to the Australian Safeguards and Non-Proliferation Office, theoretical studies show that reactor grade plutonium could be made to explode under certain conditions, but characteristics required for a practical nuclear weapon, including reliability, useful yield, a deliverable size and storage life would be adversely affected by the difficulties associated with reactor grade plutonium. (Australian Safeguards and Non-Proliferation Office, 1998-99, pp.55-59.)
A report from the US Department of Energy (1997) puts a different view:
"Virtually any combination of plutonium isotopes - the different forms of an element having different numbers of neutrons in their nuclei - can be used to make a nuclear weapon. ... The only isotopic mix of plutonium which cannot realistically be used for nuclear weapons is nearly pure plutonium-238, which generates so much heat that the weapon would not be stable. ... At the lowest level of sophistication, a potential proliferating state or subnational group using designs and technologies no more sophisticated than those used in first-generation nuclear weapons could build a nuclear weapon from reactor-grade plutonium that would have an assured, reliable yield of one or a few kilotons (and a probable yield significantly higher than that). At the other end of the spectrum, advanced nuclear weapon states such as the United States and Russia, using modern designs, could produce weapons from reactor-grade plutonium having reliable explosive yields, weight, and other characteristics generally comparable to those of weapons made from weapons-grade plutonium."
"The disadvantage of reactor-grade plutonium is not so much in the effectiveness of the nuclear weapons that can be made from it as in the increased complexity in designing, fabricating, and handling them. The possibility that either a state or a sub-national group would choose to use reactor-grade plutonium, should sufficient stocks of weapon-grade plutonium not be readily available, cannot be discounted. In short, reactor-grade plutonium is weapons-usable, whether by unsophisticated proliferators or by advanced nuclear weapon states."
The US government has acknowledged that a successful test using reactor grade plutonium was carried out at the Nevada Test Site in 1962. The exact isotopic composition of the plutonium remains classified information. It has been suggested (e.g. by Carlson et al., 1997) that because of changing classification systems, the plutonium used in the 1962 test may have been weapon grade plutonium using current classifications, not reactor grade plutonium.
The main technical barrier to using plutonium contained in spent fuel for weapons comes not from the plutonium's different isotopic composition compared to weapon grade plutonium, but from the bulk and the intense radioactivity of the spent fuel. The bulk and radioactivity make it difficult and dangerous to steal, and a considerable degree of chemical and engineering sophistication is required to separate the plutonium from the fission products and the uranium while avoiding lethal radiation doses to workers.
Australian Safeguards and Non-Proliferation Office, 1998-99, Annual Report.
J. Carlson, J. Bardsley, V. Bragin and J. Hill (Australian Safeguards and Non-Proliferation Office), "Plutonium isotopics - non-proliferation and safeguards issues", Paper presented to the IAEA Symposium on International Safeguards, Vienna, Austria, 13-17 October, 1997,
Arjun Makhijani and Scott Saleska, "The Production of Nuclear Weapons and Environmental Hazards", in Arjun Makhijani, Howard Hu and Katherine Yih, 1995, Nuclear Wastelands, Cambridge, Mass.: MIT Press, p.48.
US Department of Energy, Office of Arms Control and Nonproliferation, 1997, "Final Nonproliferation and Arms Control Assessment of Weapons-Usable Fissile Material Storage and Excess Plutonium Disposition Alternatives", Washington, DC: DOE, DOE/NN-0007, January, pp.37-39.

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