3
Nuclear-Explosive Materials

Chapter 2 examined the possibilities for applying monitoring and transparency measures to all categories of nuclear weapons and to their nuclear-explosive components. This chapter considers the further challenges of transparency and monitoring for military and civilian stocks of nuclear-explosive materials (NEM). These materials are readily convertible by nuclear weapon states—or other states or groups that have knowledge of nuclear weapons technology—into the nuclear-explosive components of actual weapons. And the size of the NEM stocks determines, to a reasonable approximation, how many weapons of particular types could be made. Moreover, the difficulty of producing such materials means that their acquisition is and will remain a limiting factor for states or sub-national groups aspiring to make such weapons.

Meaningful constraints on stocks of NEM require knowing how much NEM is possessed by whom and being able to monitor additions and subtractions. Achieving such constraints and the ability to monitor them is important not only for building confidence among nuclear weapon states about the current and potential future sizes of the arsenals of the other nuclear weapon states, but also for building international confidence in the durability of reductions in those arsenals and for limiting and monitoring the risks of proliferation of nuclear weapons to additional actors.

The importance of NEM stocks resides not just in their role in determining the breakout potential from agreed or unilaterally undertaken limits on the nuclear arsenals of the existing global and regional nuclear weapon states, but also in their role as a reservoir of proliferation potential to both other state and nonstate actors. Stocks of NEM held by non-nuclear weapon states confer the potential for these states to acquire nuclear weapons of the simplest types quite quickly once a decision to do so has been made. Moreover, all such NEM stocks represent nuclear weapon production potential for any state or nonstate actor that is able to steal these materials or to buy or otherwise acquire them from their legitimate or illegitimate possessors.



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Monitoring Nuclear Weapons and Nuclear-Explosive Materials 3 Nuclear-Explosive Materials Chapter 2 examined the possibilities for applying monitoring and transparency measures to all categories of nuclear weapons and to their nuclear-explosive components. This chapter considers the further challenges of transparency and monitoring for military and civilian stocks of nuclear-explosive materials (NEM). These materials are readily convertible by nuclear weapon states—or other states or groups that have knowledge of nuclear weapons technology—into the nuclear-explosive components of actual weapons. And the size of the NEM stocks determines, to a reasonable approximation, how many weapons of particular types could be made. Moreover, the difficulty of producing such materials means that their acquisition is and will remain a limiting factor for states or sub-national groups aspiring to make such weapons. Meaningful constraints on stocks of NEM require knowing how much NEM is possessed by whom and being able to monitor additions and subtractions. Achieving such constraints and the ability to monitor them is important not only for building confidence among nuclear weapon states about the current and potential future sizes of the arsenals of the other nuclear weapon states, but also for building international confidence in the durability of reductions in those arsenals and for limiting and monitoring the risks of proliferation of nuclear weapons to additional actors. The importance of NEM stocks resides not just in their role in determining the breakout potential from agreed or unilaterally undertaken limits on the nuclear arsenals of the existing global and regional nuclear weapon states, but also in their role as a reservoir of proliferation potential to both other state and nonstate actors. Stocks of NEM held by non-nuclear weapon states confer the potential for these states to acquire nuclear weapons of the simplest types quite quickly once a decision to do so has been made. Moreover, all such NEM stocks represent nuclear weapon production potential for any state or nonstate actor that is able to steal these materials or to buy or otherwise acquire them from their legitimate or illegitimate possessors.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials This chapter begins with an introduction to the characteristics of NEM, the means by which these materials are produced, and current stocks and flows of NEM in the military and civilian sectors. (This treatment is supplemented with more detail in Appendix A) The chapter then addresses the challenges of transparency and monitoring for NEM, first in conceptual terms and then in terms of the specific bilateral and multilateral measures that have been undertaken up until now in connection with cooperative efforts to account for, secure, and protect both military and civilian materials1 DEFINITION, CHARACTERISTICS, AND PRODUCTION OF NEM All nuclear weapons rely on the energy released by an explosively growing fission chain reaction—a process in which heavy nuclei split into lighter ones following absorption of free neutrons and, in splitting, release more neutrons that in turn induce more fissions, and so on. Only a few nuclides2 of the hundreds that exist are capable of sustaining the explosive nuclear chain reaction needed for a nuclear weapon. Such nuclear-explosive nuclides include U-235, U-233, and all the isotopes of plutonium, among others. A nuclear-explosive material is one in which the proportions of nuclear-explosive nuclides and nonexplosive nuclides of the same elements are such as to permit an explosive chain reaction if the material is present in suitable quantity, density, chemical form and purity, and configuration. In the simplest nuclear weapons, the fission chain reaction is the only source of the nuclear energy that is released. In more advanced nuclear weapons, such as “boosted” fission weapons and thermonuclear weapons, some of the energy is generated by fusion reactions that are ignited by energy from the fission explosion. 1   The arguments in this chapter build on those in National Academy of Sciences, Committee on International Security and Arms Control, Management and Disposition of Excess Weapon Plutonium, 2 vols. (Washington, DC: National Academy Press, 1994 and 1995); Steve Fetter, Verifying Nuclear Disarmament, Occasional Paper 29, Henry L. Stimson Center, Washington, DC, 1996; and Independent Bilateral Scientific Commission on Plutonium Disposition, Final Report, Washington, DC: President's Committee of Advisors on Science and Technology, The White House, and Russian Academy of Sciences, June 1997. 2   “Nuclide” is the general term for a species of atom as characterized by both its atomic number (equal to the number of protons in the nucleus, which determines the element to which a nuclide belongs) and its mass number (equal to the number of protons and neutrons combined, which determines which isotope of the element it is). See Appendix A.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials (Fusion reactions merge light nuclides, most notably isotopes of hydrogen, to form heavier ones, accompanied by a large release of energy.) In boosted fission weapons, the energy directly added by the fusion reactions is very modest, but the high-energy neutrons emitted by these reactions lead to a large increase in the amount of fission that takes place; in thermonuclear weapons a significant fraction of the energy released comes from fusion reactions. Countries aspiring to make boosted and thermonuclear weapons, however, cannot do so without first mastering simpler pure-fission weapons. Terrorists working without the support of a state would not be able to make the much more demanding boosted and thermonuclear weapons at all. Thus it is mastery of the explosive fission chain reaction—including possession of the quantities of NEM needed to achieve one—that governs who can make nuclear weapons. Types of NEM The most widely used definitions of the isotopic mixtures and concentrations constituting NEM are as follows: 3 Any mixture of uranium-235 (U-235) with the more abundant, non-nuclear-explosive isotope U-238 in which the U-235 concentration is 20 percent or more is considered NEM. This form of NEM is referred to as highly enriched uranium (HEU).4 Any mixture of U-233 with U-238 when the U-233 concentration is 12 percent or more is considered NEM.5 3   See IAEA, IAEA Safeguards Glossary, 2001 Edition (Vienna: International Atomic Energy Agency, 2002). Available as of January 2005, at: http://www-pub.iaea.org/MTCD/publications/PDF/nvs-3-cd/PDF/NVS3_prn.pdf and Nuclear Energy Research Advisory Committee (NERAC), Attributes of Proliferation Resistance for Civilian Nuclear Power Systems (Washington, DC: U.S. Department of Energy, October 2000). 4   Nuclear explosives can in principle be made with material containing somewhat less than 20 percent U-235, but the amount of material required at enrichments below 20 percent is very large. 5   At this percentage, the mass of material required for criticality is similar to that for a mixture of U-238 and U-235 containing 20 percent U-235. See, for example, C. W. Forsberg, C. M. Hopper, J. L. Richter and H. C. Vantine, Definition of Weapons-Usable Uranium-233, ORNL/TM-13517 (Oak Ridge, TN: Oak Ridge National Laboratory, March 1998).

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials Any mixture of plutonium isotopes in which the concentration of plutonium-238 (Pu-238) is less than 80 percent is considered NEM.6 These materials are considered NEM irrespective of whether the uranium or plutonium are present in metallic form or as oxides, or nitrates, or fluorides, or some other compound. This is because, even if a particular uranium or plutonium compound will not itself support a nuclear explosion (and some will), transforming such compounds chemically into the metal is a straightforward operation that would be within the reach of any group with a modicum of competence in chemistry. Mixtures of NEM with other elements, in compounds or otherwise, can differ greatly in the difficulty of separating out the NEM in a purity that would permit an explosion, however. In particular, the intense radiation field emitted by typical spent nuclear fuel from civil power reactors presents great technical difficulties (and hazards) in the separation of the contained NEM (a mix of plutonium isotopes amounting altogether to 1-2 percent of the mass of the spent fuel) from the accompanying fission products and low enriched uranium. Accordingly, the NEM in spent fuel is considered to be a smaller proliferation hazard than NEM in most other forms, and in international practice is subject to less stringent monitoring and security measures. Fortunately, NEM does not exist in nature in any significant quantity, and all types of NEM are quite difficult to produce, creating an important constraint on access to nuclear weapons capabilities. U-235, for example, constitutes only about 0.7 percent of naturally occurring uranium; achieving the higher U-235 concentration needed for a nuclear weapon (or for most types of nuclear reactors) requires “uranium-enrichment” technology that is difficult to master and costly, as discussed further below. The isotopes of plutonium (most importantly Pu-239, but also Pu-238, Pu-240, Pu-241, and Pu-242) are practically nonexistent in nature; they can be obtained in 6   The IAEA defines all plutonium isotopes containing less than 80 percent Pu-238 as “direct-use material,” a phrase with a meaning similar to our “nuclear-explosive material.” The IAEA’s exclusion of high-purity Pu-238 appears to have been intended to avoid complications in the use of such material for power generators on peaceful space-based and remote unmanned applications. It is also true that the higher the concentration of Pu-238 in plutonium, the greater the difficulties posed for weapon design by this isotope’s high rate of heat generation.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials quantity only by bombarding naturally occurring “fertile” materials with neutrons in an accelerator or a reactor, then separating the plutonium from accompanying elements (also discussed further below). U-233 is likewise essentially nonexistent in nature and producible in quantity only in a reactor or accelerator; relatively little U-233 appears to have been produced for weapon purposes to date, nor has this isotope been produced in significant quantities in civilian nuclear energy operations (although its use as the fissile component in a “thorium fuel cycle” has been much analyzed and discussed). More obscure nuclides that could sustain an explosive nuclear chain reaction include neptunium-237 and several isotopes of americium, curium, and californium. These have been less important than plutonium, U-235, and U-233 because they have existed until now in much smaller amounts and because producing them in quantity is even more difficult.7 The fuels that generate energy from fusion in boosted and thermonuclear weapons—notably tritium, deuterium, and lithium—might also be argued to be nuclear explosives. But no means is yet known for releasing explosive nuclear energy from these fusion fuels alone, so their possession without the material required for an explosive fission chain reaction does not enable the manufacture of nuclear weapons. It is possible that the importance of tritium in advanced weapon design might nonetheless make it a focus for limits and monitoring similar to those for NEM in a more comprehensive nuclear arms limitation and transparency regime, but we do not treat the problem of accomplishing this in this report.8 7   A case can be made, however, that attention does need to be given to monitoring and protecting the growing stocks of at least some of these nuclides, most notably Np-237 and Am-241. See David Albright and Lauren Barbour, “Troubles Tomorrow? Separated Neptunium 237 and Americium,” in David Albright and Kevin O'Neill, eds., The Challenges of Fissile Material Control (Washington, DC: Institute for Science and International Security, 1999). 8   But see Martin B. Kalinowski and Lars C. Colschen, “International Control of Tritium to Prevent Horizontal Proliferation and to Foster Nuclear Disarmament,” Science and Global Security 5 (1995), pp. 131-230. Available as of January 2005, at: http://www.princeton.edu/%7Eglobsec/publications/pdf/5_2kalinowski.pdf, which treats the benefits, challenges, and possibilities of international controls and verification for tritium in considerable detail.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials Key Characteristics of NEM HEU can be used to make a nuclear weapon using either the relatively simple “gun type” design concept or the more complicated “implosion” design concept: plutonium isotopes, irrespective of the mixture, will work only in weapons of the implosion type.9 In either case, however, nuclear weapon design is easiest—and the mass of NEM involved is smallest—when the nuclear material is not just barely NEM but is “weapon grade.” This is generally taken to be greater than 90 percent U-235 in HEU and greater than 90 percent Pu-239 in plutonium. Because the bare critical mass of weapon-grade HEU is about 60 kilograms, a hypothetical gun-type weapon could be made with this amount of material, while an implosion weapon could be made from considerably less of the same material. The International Atomic Energy Agency (IAEA) defines a “Significant Quantity” (SQ) relevant to construction of a nuclear weapon to be 25 kilograms of U-235 in HEU; the SQ value for plutonium is set at 8 kilograms, as is the SQ for U-233 (which like U-235 will work in either gun-type or implosion designs).10 Considerably less knowledge and manufacturing skill are needed to make a gun-type weapon than to make an implosion weapon, and a gun-type design is more likely to work without nuclear testing than an implosion weapon. In addition, because of the relative ease of handling HEU compared with plutonium, HEU is even a greater threat than plutonium as the potential object of theft for use by terrorists or proliferant nations with limited access to nuclear weapon expertise. Pathways to Obtain NEM The principal pathways exploited to date for the production of NEM have been (a) mining of uranium ore, followed by enrichment of the concentration of U-235 to nuclear-explosive levels, 9   These and many other aspects of the science and technology of NEM are elaborated in Appendix A. 10   The IAEA definition of SQ reads: “the approximate amount of nuclear material for which the possibility of manufacturing a nuclear explosive device cannot be excluded. Significant quantities take into account unavoidable losses due to conversion and manufacturing processes and should not be confused with critical masses.” See International Atomic Energy Agency, IAEA Safeguards Glossary: 2001 Edition (Vienna: International Atomic Energy Agency, 2002), p. 23, as well as Appendix A.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials and (b) creation of plutonium by absorption of neutrons in U-238 in a reactor, followed by chemical separation of the plutonium from the accompanying fission products and uranium. The two approaches are described briefly here; additional detail is provided in Appendix A. Uranium-235 Natural uranium, as mined, contains 0.72 percent of the nuclear-explosive nuclide U-235 and 99.27 percent U-238, which is not a nuclear explosive. (About 0.006 percent is U-234, which is also not a nuclear explosive.) Enrichment of the U-235 concentration to nuclear-explosive levels, that is, to 20 percent U-235 or more, is a sufficient technological challenge to have constituted one of the principal technical barriers to the spread of nuclear weapons capability over the past 60 years. The currently practical processes for enriching the concentration of U-235 exploit the 1.3 percent difference in mass between U-235 and U-238 atoms. The uranium is first converted to uranium hexafluoride gas (UF6), which can then be processed to achieve a degree of separation of the slightly lighter uranium hexafluoride gas molecules containing U-235 from the slightly heavier uranium hexafluoride molecules containing U-238. The two most widely used means of doing this have been (a) gaseous diffusion plants, which exploit the difference in the diffusion rates of the lighter and heavier molecules through a “cascade” of thousands of porous barriers, and (b) centrifuge plants, which use stages of hundreds or thousands of sophisticated, ultra-high-speed, gas centrifuge machines to separate the molecules based on their differing inertial masses. The gaseous diffusion and centrifuge plants currently in use around the world in connection with civilian nuclear power generation are operated to enrich uranium only to a U-235 concentration of 3 to 5 percent, which cannot produce a nuclear explosion. In terms of the “enrichment work” needed to separate isotopes, these concentrations are more than half way toward the 90+ percent enrichment levels desirable for nuclear weapons. In principle, commercial enrichment plants could be operated in a manner to do the remaining work needed to bring this low enriched reactor fuel up to weapon-usable levels. Separated Plutonium Plutonium-239 is produced when U-238 absorbs neutrons produced in a reactor or by an accelerator. Consequently, Pu-239 is

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials produced automatically in any nuclear reactor containing U-238 in its fuel. The Pu-239 itself then absorbs neutrons to produce higher isotopes of plutonium in quantities depending on the irradiation time. (See Table 3-1 for the isotopic composition of various grades of plutonium.) TABLE 3-1 Compositions of Various Grades of Plutonium Grade Pu-238 Pu-239 Pu-240 Pu-241 Pu-242 Super-grade --- 0.98 0.02 --- --- Weapon-grade 0.00012 0.938 0.058 0.0035 0.00022 Reactor-grade 0.013 0.603 0.243 0.091 0.050 MOX-grade 0.019 0.404 0.321 0.178 0.078 FBR blanket --- 0.96 0.04 --- --- Pu-241 includes its Am-241 daughter. Reactor grade Pu is from 33 MWd/kg HM LEU fuel stored 10 years before reprocessing. MOX grade is from 33 MWd/kg HM 3.64 percent fissile Pu MOX stored 10 years before reprocessing. Adapted from: J. Carson Mark, “Explosive Properties of Reactor Grade Plutonium,” Science and Global Security 4 (1993), pp. 111-128. See Appendix A for elaboration of the relevant definitions and parameters. The plutonium produced in this way is, by the nature of the process, intimately mixed with fission products, as well as with uranium-238 that has not absorbed neutrons. In this form the plutonium cannot be used to make a nuclear weapon but must first be separated from the fission products and the U-238. This can be accomplished by chemical means, since Pu-239 and other isotopes of plutonium form distinct chemical compounds. The term “separated plutonium,” is used when the concentrations of accompanying fission products and uranium are reduced to levels such that the material, if present in sufficient quantity, would support a nuclear explosion. Figure 3-1 shows in schematic form the production, utilization, and disposition pathways for HEU and plutonium in the nuclear weapon and nuclear energy complexes.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials FIGURE 3-1 Production, utilization, and disposition flows for HEU and plutonium. *CSAs = Canned Subassemblies.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials STOCKS AND FLOWS OF NEM IN THE MILITARY AND CIVIL SECTORS The quantity, character, and geographic distribution of stocks and flows of military and civil NEM worldwide are important dimensions of the challenge of achieving transparency and monitoring for these materials.11 More detail on these stocks and flows is provided in Appendix A. World Military and Civilian NEM Stockpiles The United States and Russia hold the largest stockpiles of NEM, but only limited information about them is available publicly. The United States keeps a computerized national plutonium and HEU inventory, including both Department of Energy (DOE) and nongovernment stockpiles, known as the Nuclear Materials Management and Safeguards System (NMMSS).12 What has been released publicly from this database up until now includes principally detailed data on U.S. warhead dismantlement rates; a detailed production history for U.S. plutonium, plus data on the stockpiles of this material; and official information on total U.S. production of HEU (but not the detailed production history or information on the current stockpile). Official information on the size, locations, and characteristics of Russia's stockpiles of warheads and NEM remains classified at this writing. Estimates of global stocks of plutonium and HEU as of the end of 2003, compiled from publicly available information by the Institute for Science and International Security, are shown in Table 3-2. The totals are approximately 1,900 metric tons each of plutonium and HEU,13 amounting to more than 200,000 SQ of the former and about 75,000 SQ of the latter. 11   The most extensive unclassified compendium of such information is David Albright, Frans Berkhout, and William Walker, Plutonium and Highly Enriched Uranium 1996: World Inventories, Capabilities, and Policies (New York: Stockholm International Peace Research Institute and Oxford University Press, 1997). Albright and colleagues periodically post updates to this work at the Web site of the Institute for Science and International Security available as of January 2005, at: http://www.isis-online.org. 12   See the NMMSS Web site, available as of January 2005, at: http://www.nmmss.com/. 13   A metric ton is 1000 kilograms or 2204.6 pounds. The HEU estimates are expressed as “weapon-grade uranium equivalent,” in which inventories at a range of enrichment values above 20 percent have been converted, based on U-235 content, to equivalent tons of uranium enriched to 93 percent U-235.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials The HEU of military origin is mainly in intact weapons; in weapon components, ingots, oxides, and scrap; in naval fuel; and in fuel for military plutonium production and tritium production reactors. In the United States, as of the end of 2003, about 125 tons of HEU of military origin that had been declared excess to military needs was under civil control, prior to being blended down to low enriched uranium (LEU) for use in power reactors. In Russia, about 300 tons of HEU of military origin that had similarly been declared excess to military needs was likely still in military custody. The few tens of tons of HEU of civil origin, which are mainly in research reactors and the fresh or spent fuel for these, are not much compared with the major power military stockpiles, but at circa 2,000 SQ they represent a serious risk in terms of possible use in weapons by proliferant states or terrorist groups. TABLE 3-2 ISIS Estimates of Global Inventories of Plutonium and HEU (Metric tons, end of 2003, rounded) Material Military Origin Civil Origin Total HEU 1840 60 1900 Pu 260 1595 1855 of which irradiated -- 1365 1365 of which unirradiated 260 230 490 As indicated in Table 3-2, about 500 tons of the world's plutonium is in unirradiated form (often referred to as “separated” form, meaning that it has been separated from the intensely radioactive fission products that accompany it in irradiated nuclear fuel). This unirradiated or separated material requires at most straightforward chemical processing (for example, to convert it from plutonium nitrate or plutonium oxide to plutonium metal) before it can be used in a weapon. The 230 tons of this material of civil origin amounts by itself to something like 80,000 Significant Quantities. The further 1,400 tons of irradiated plutonium—mostly in the cores or spent fuel from power reactors—is considered to be a smaller proliferation hazard because of the need for technically demanding reprocessing to extract the plutonium in weapon-usable form. The actual difficulty and danger of that reprocessing operation vary considerably, however, with the degree of irradiation experienced by the fuel and the time that has passed since irradiation. Adapted from: David Albright and Kimberly Kramer, “Fissile Material Stockpiles Still Growing,” Bulletin of the Atomic Scientists, (November/December 2004), pp 14-16. See also the underlying analysis on the Web Site of the Institute for Science and International Security, available as of January 2005, at: http://www.isis-online.org. Of the world's military stockpiles of HEU and plutonium, the United States and Russia possess more than 95 percent. The remainder is possessed by the United Kingdom, France, China, India, Pakistan, Israel, and North Korea. Civilian plutonium in power reactor fuel exists in all of the dozens of countries where power reactors exist. Separated civilian plutonium exists in significant

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials plus military NEM in considerable detail.89 The CISAC reports recommended that the United States and Russia pursue long-term disposition options that (a) minimize the time during which this material is stored in forms readily usable for nuclear weapons; (b) preserve material safeguards and security during the disposition process, seeking to maintain the same high standards of security and accounting applied to stored nuclear weapons; (c) result in a form from which the HEU would be as difficult to recover for weapons use as from commercial LEU, and the plutonium would be as difficult to recover for weapons use as the much larger and growing quantity of plutonium in commercial spent fuel (the “spent fuel standard”); and (d) meet high standards of protection for public and worker health and the environment. Disposition of HEU In the case of HEU, achieving these goals is technically straightforward. Highly enriched uranium can be blended with natural uranium—or with the depleted-in-U-235 “tails” from previous uranium enrichment or very low enriched uranium for technical reasons—to produce proliferation-resistant LEU, which is a valuable commercial fuel. This was the basis of the “HEU deal” concluded between the United States and Russia in the early 1990s, as well as the U.S. decision to undertake a similar blending process for most of its own stockpile of excess HEU. At two of the three Russian facilities where the material is blended down under the HEU Purchase Agreement, the United States conducts continuous automated monitoring of the three pipes in the Y joint where the blending occurs; one carrying 90 percent enriched uranium hexafluoride, one carrying 1.5 percent enriched uranium hexafluoride used to blend down the HEU, and the pipe carrying the merged blend, with about 4 percent enrichment. (Slightly enriched material rather than natural or depleted uranium is being used for the blending to further dilute undesirable isotopes in the HEU, such as U-234 and U-236.) Installation of monitoring at the third facility was scheduled for late 2004. 89   Committee on International Security and Arms Control, Management and Disposition of Excess Weapons Plutonium (Washington, DC: National Academy Press, 1994) and Committee on International Security and Arms Control, Panel on Reactor-Related Options, Management and Disposition of Excess Weapons Plutonium: Reactor-Related Options (Washington, DC: National Academy Press, 1995). See also the important precursor work, Frans Berkhout, Anatoli Diakov, Harold Feiveson, Helen Hunt, Edwin Lyman, Marvin Miller, and Frank von Hippel, “Disposition of Separated Plutonium,” Science and Global Security 3, 1993.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials In order to establish some level of confidence that the HEU indeed comes from dismantled weapons as required and not reserve stocks of HEU, the United States is allowed several visits each year to the facilities where HEU metal weapon components are cut into metal shavings and converted to oxide. During these visits, the United States has the opportunity to observe rough measurements of the U-235 enrichment of the weapons components in containers and of the resulting metal shavings and oxide in containers, to tag and seal containers being readied for shipment to the blending facility, and to review records of these activities that take place when U.S. inspectors are not present. Similarly, Russian inspectors have the right to conduct monitoring at the U.S. enrichment facility where the LEU is received and processed and at the U.S. fabrication facilities where the material is fabricated into reactor fuel.90 Disposition of Plutonium Disposition of plutonium poses much more difficult technical challenges. Because all isotopes of plutonium are weapons usable, plutonium cannot be blended isotopically to an adequately proliferation resistant form in the way that HEU can. Given the current worldwide supply of cheap uranium and the high cost of fabricating reactor fuel that contains plutonium, the use of even “free” plutonium as fuel in reactors is uneconomic now and likely to remain so for at least the next few decades. Thus, all of the options for disposition of surplus weapon plutonium, including those that use the plutonium as fuel in civilian reactors, will require substantial investments. There is no disposition option that will “make money.” The 1992-1995 CISAC study examined all plausible identified options for plutonium disposition, including placing the plutonium at the bottom of deep (several kilometers) boreholes in solid rock, burying it in special zones on the deep ocean floor, and launching it into the sun or out of the solar system on rockets. The study concluded that while all plutonium disposition options have draw-backs, the two least problematic options for achieving the four aims listed above for disposition of NEM are: fabrication of the plutonium into mixed oxide fuel (a mixture of plutonium dioxide and uranium dioxide, termed 90   See, for example, Matthew Bunn, “Highly Enriched Uranium Transparency,” Monitoring Stockpiles. Available as of January 2005, at: http://www.nti.org/e_research/cnwm/monitoring/uranium.asp and references cited therein. The official Web Site of the HEU Transparency Implementation program is available as of January 2005, at: http://www.nnsa.doe.gov/na-20/heu_trans.shtml.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials “MOX”) for use on a “once through” basis in a limited number of civilian power reactors of currently operating types (albeit possibly with some modifications to increase the achievable plutonium loading per reactor in order to speed up the process or reduce the number of reactors needed); or vitrification in combination with high-level radioactive waste, achieved by mixing the plutonium with fission products from previous military or civilian nuclear energy activities into molten glass to produce glass logs with mass, bulk, radioactivity, and resistance to chemical separation of the plutonium comparable with these properties for spent fuel bundles from civilian power reactors. The residual (unfissioned) plutonium in the MOX approach would be part of the radioactive wastes similar to what would have been produced in any case from energy generation in the civilian power reactors chosen for the plutonium disposition mission, and the plutonium would remain a part of these wastes through whatever intermediate and final storage steps society choose for them.91 In the vitrification approach, the plutonium-bearing logs would likewise become part of a radioactive waste management burden that would exist in any case in the form of glass logs serving to immobilize previously generated fission products. Either of these options or a combination of them would be appropriate to achieve final disposition of plutonium. The 1995 CISAC report recommended that both options be developed expeditiously in parallel. History, Status, and TransparencyIissues The implementation of the U.S.-Russian HEU deal described in Chapter 1 was slowed and ultimately even imperiled by a number of management decisions, most importantly the decision in the mid-1990s to privatize the theretofore government-operated uranium-enrichment industry in the United States. Once the U.S. Enrichment Corporation (later renamed USEC), which had been the “executive agent” for the HEU deal on the U.S. side from the beginning, became private the resulting tension between profit mo- 91   It is worth noting that because MOX is typically only used in one third of the reactor core, with the rest being LEU, and because both the LEU and the MOX contain large quantities of U-238, nearly as much plutonium is produced when MOX is burned in such an arrangement as is consumed. But the produced plutonium is in spent fuel, not in separated forms much easier to use in weapons. And if the same reactor core had operated without MOX, with an all-LEU core, the net plutonium generation would have been even higher.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials tive and national security goals—the former favoring implementation of the deal on terms that would maximize returns to USEC’s stockholders and the latter favoring implementation on terms that would maximize the rate of down blending and transfer of Russian HEU—led to a series of delays, disagreements, and renegotiations.92 Despite these problems, by January 2005 Russia had blended down more than 230 tons of HEU to LEU under this program. The process is now proceeding at an annual rate of about 30 tons of HEU. The program is scheduled to end in 2013, when the 500 tons of HEU covered by the original deal will have all been blended down to LEU. This figure, which represents about half of the total Russian stockpile of HEU inside and outside of weapons, is equivalent to as many as 20,000 to 25,000 nuclear weapons, depending on design.93 Progress toward final disposition of excess weapons plutonium has been much slower. Following the CISAC recommendations and reviews by U.S. governmental and bilateral U.S.-Russian panels, the two options were embraced by the official U.S. announcement of the dual-track approach for plutonium disposition in December 1996. These options had been endorsed earlier at the international level at the U.S.-Russian summit in Moscow in April 1996, and at a subsequent international experts meeting in the fall of 1996. Currently, however, the immobilization option has been largely abandoned and the pursuit of the MOX option has been seriously slowed by legal and economic problems. So far, none of the weapons plutonium declared excess has been disposed of. Both the United States and Russia have some but not all of the facilities they would need to undertake plutonium disposition. For the reactor option, new plutonium fuel fabrication facilities and plants for converting plutonium pits to oxide would be needed, and this would be the limiting requirement in both time and cost for 92   See, e.g., Thomas L. Neff, “Decision Time for the HEU Deal: U.S. Security vs. Private Interests,” Arms Control Today 31 (June 2001), pp. 12-17. Available as of January 2005, at: http://www.armscontrol.org/act/2001_06/nefjun01.asp. Most recently, USEC succeeded in forcing Russia to accept a new pricing structure that reduces payments to Russia by several tens of millions of dollars a year, compared with the previous agreement. This has generated considerable resentment among some Russian nuclear officials, but for now deliveries of the blended-down material are stabilized and USEC has an economic incentive to carry out the deal as rapidly as possible because the Russian material is now USEC’s lowest-cost source of supply. 93   USEC Fact Sheet, “US-Russian Megatons to Megawatts Program: Recycling Nuclear Warheads into Electricity,” USEC Inc., December 31, 2004. Available as of January 2005, at: http://www.usec.com/v2001_02/HTML/megatons_fact.asp.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials beginning a large-scale plutonium disposition campaign in reactors. Use of existing European fuel fabrication facilities, at least for fabrication of initial fuel assemblies and perhaps the fuel for the first reactor loads, could significantly accelerate the schedule on which the reactor option could begin. In the United States, far more reactors than needed have sufficient licensed lifetimes remaining to carry out the plutonium disposition mission, although identifying reactors willing to participate (even given substantial financial incentives) has proved to be a struggle. In Russia, only the eight 950 MWe VVER-1000 light-water reactors (LWRs) and the one BN-600 fast-neutron reactor fall into this category. Depending on the final conclusion about how much plutonium can be safely loaded into these reactors, and depending also on the desired pace of disposition under the MOX option, use of the eleven VVER-1000 reactors in Ukraine (whose fuel has been provided by Russia under long-term agreements) might be considered. Another possibility, proposed by Canada, is to use both U.S. and Russian plutonium in fuel for existing Canadian deuterium-uranium (CANDU) reactors.94 Both the United States and Russia have some but not all of the facilities that would be needed to immobilize plutonium with high-level wastes. In the United States, a major effort to vitrify high-level wastes from past reprocessing is just beginning at Savannah River and is planned at Hanford. Plutonium could be added to such waste glasses, but this would require either substantial modifications of existing facilities or the construction of new ones.95 Russia is already vitrifying high-level wastes at Chelyabinsk. Under the September 2000 U.S.-Russian Plutonium Management and Disposition Agreement (PMDA),96 Russia is supposed to 94   For a summary of a range of potential approaches to accelerating the rate of plutonium disposition, see Matthew Bunn, Anthony Wier, and John P. Holdren, Controlling Nuclear Warheads and Materials: A Report Card and Action Plan (Washington, DC: Nuclear Threat Initiative and the Project on Managing the Atom, Harvard University, March 2003), pp. 156-161. 95   An alternative method developed by DOE, known as "can-in-canister," also has promise. In this approach, the plutonium would be immobilized in small cans of glass or ceramic without high-level wastes (allowing existing glove-box facilities to be used), and these small cans would be arrayed inside the large canisters into which the high-level waste glass is being poured at the existing vitrification plant. 96   Agreement Between the Government of the United States of America and the Government of the Russian Federation Concerning the Management and Disposition of Plutonium Designated as No Longer Required for Defense Purposes and Related Cooperation. Available as of January 2005, at: http://www.nti.org/db/nisprofs/russia/fulltext/plutdisp/pudispft.pdf.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials begin loading 34 tons of excess military plutonium97 in MOX fuel into civilian reactors around 2008, at an initial rate of 2 tons of Pu per year, increasing thereafter to 4 tons per year. Rosatom (formerly the Ministry of Atomic Energy) has always considered all separated plutonium to be a valuable energy resource irrespective of cost calculations showing that even using “free” military plutonium in fuel is more expensive than making fuel with the same energy value from freshly mined and enriched uranium. Consequently, the PMDA does not commit any Russian plutonium to disposition by immobilization with wastes. The transparency and monitoring provisions in the PMDA are extensive and are the most informative available “official” wording for purposes of illustrating the complexity and sensitivity of transparency and monitoring procedures for NEM as seen by the two leading nuclear weapon states. Of particular note in these passages are (a) the extensive attention given to how monitoring can be accomplished while protecting information about the composition of the plutonium from the two countries’ weapons, which remains classified to varying degrees on both sides and (b) the delicate and ambiguous interplay of bilateral versus multilateral (IAEA) responsibilities and privileges in the verification process, leaving unresolved the question of what the IAEA role actually will be. The United States agreed under the PMDA to dispose of 34 tons of excess weapon plutonium, as well, and agreed further that at least 25 tons of this would be loaded into civilian reactors in MOX fuel.98 It had been supposed by many that the United States would choose to use immobilization with wastes for disposition of the maximum amount allowed by agreement—that is, the remaining 9 tons of the declared weapon plutonium surplus, but the Department of Energy announced in February 2002 that the immobilization option in the U.S. disposition program was being set aside as an economy measure, leaving only the MOX option.99 Aside 97   The 34 tons of military plutonium will be blended with 4 tons of Russian reactor-grade plutonium in order to preserve the confidentiality of the isotopic mix in the weapon-grade material. 98   The United States has declared a larger amount of military plutonium (52.5 tons) surplus to its needs, but 18.5 tons of this total are either reactor grade or highly contaminated and were therefore not credited by the Russians as something they needed to match. 99   National Nuclear Security Administration, Office of Fissile Materials Disposition, Report to Congress: Disposition of Surplus Defense Plutonium at Savannah River Site (Washington, DC: National Nuclear Security Administration, February 15, 2002). Available as of January 2005, at: http://www.nci.org/pdf/doe-pu-2152002.pdf.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials from the liabilities of this “all eggs in one basket” approach, this decision poses the problem that 1-2 tons of the 34 consists of material too badly contaminated with other elements and compounds to be purifiable for use in MOX. Even the slow U.S. and Russian timetables specified in the PMDA are no longer achievable. Discussions of an international financing and management approach for disposition of Russian excess plutonium have dragged on far longer than anticipated in the PDMA, and despite the inclusion of plutonium disposition as a priority item in the $20 billion G8 Global Partnership Against the Spread of Weapons and Materials of Mass Destruction, which raised hopes that sufficient financing would soon be pledged, no conclusion of these talks is yet in sight. Moreover, as a result of a dispute over liability in the event of an accident, the U.S. government was unwilling to extend the agreement that had provided the legal framework for the technical cooperation on plutonium disposition now underway, and that agreement expired in mid-2003. As a result, technical cooperation in preparation for building a MOX plant in Russia has been drastically slowed, and construction of the facility has been delayed by at least a year, and possibly more. Because both the administration and the Congress have linked the start of construction of a U.S. MOX facility to the start of construction of a Russian MOX facility, the U.S. facility has also been delayed by at least a year.100 Considerations and Options Looking Ahead We judge that achieving appropriate transparency and adequate monitoring for final disposition of surplus military NEM pose entangled political and technical challenges that will require further effort to resolve. Notable among these are (a) monitoring the transformation from item-countable objects (pits) to bulk material (e.g., plutonium oxide or mixed oxide powders) in a situation where nearly all of the characteristics of the initial objects and some of the characteristics of the bulk material are classified and so cannot be revealed to the inspectors;101 (b) coping with processes in which 100   See, for example, discussion in Matthew Bunn and Anthony Wier, Securing the Bomb: An Agenda for Action (Washington, DC: Nuclear Threat Initiative and the Project on Managing the Atom, Harvard University, May 2004) and references cited therein. 101   This particular difficulty could be alleviated in the context of bilateral monitoring by the sort of legislatively sanctioned U.S.-Russian agreement on bilateral exchange of classified information that so far has proven elusive, as discussed above. Even achievement of such an agreement, however,

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials the composition of the material being monitored is continuously changing, in which radiation barriers complicate access, and in which losses to waste products in ways difficult to measure may complicate material accounting; and (c) assaying accurately the plutonium content of spent reactor fuel (in the MOX disposition option), which by the nature of reactor physics and technology will be variable across different fuel elements and even within them. The difficulty of meeting these challenges should not be under-rated, but neither should one suppose that they cannot be surmounted.102 We believe that they are fertile ground for increased U.S.-Russian technical cooperation and joint demonstrations, as well as for trilateral (US-Russia-IAEA) efforts. Final disposition is a long-term project no matter what its priority and no matter what its pace; it cannot alleviate the need for rapid improvements in MPC&A. As with most long-term projects that are badly needed, however, the difficulty and duration of the disposition project make it all the more important to start early and come up to speed quickly. Large stocks of HEU and separated plutonium, no matter how well accounted for and protected against theft, represent a risk of breakout from nuclear arms limitation agreements by the states that own the material and control the territory on where it is stored, as well as a risk of the material falling into other hands as a result of a major societal disruption. The longer the wait before the NEM is finally disposed of in ways that make its use in nuclear explosives very unlikely, the greater the chance that currently unforeseen developments could turn it into a major menace. Certainly there are significant transparency and monitoring challenges associated with the processes of final disposition that exceed the challenges of simple guarded storage on a continuing basis. Like the other challenges of disposition, however, we believe that those of transparency and monitoring will likely yield to concerted and cooperative effort if the political will exists to get it done.     would not permit multilateral involvement in monitoring except through the use of innovative approaches to protect the classified information. 102   A more extended treatment of the challenges in transparency and monitoring of final disposition, which also summarizes the approaches that have been envisioned for dealing with them, is provided by Annette Schaper, “Monitoring and Verifying the Storage and Disposition of Fissile Materials and the Closure of Nuclear Facilities,” in Nicholas Zarimpas, ed., Transparency in Nuclear Warheads and Materials (New York: Oxford University Press and Stockholm International Peace Research Institute, 2003), pp. 206-228.

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials CONCLUSIONS This chapter has examined the record of and potential for applying monitoring and transparency measures to military and civilian stocks of NEM. In doing so it has addressed, among other issues, the benefits of transparency and monitoring that would be associated with reductions in NEM stocks and flows and in the number of sites where NEM are stored—steps of obvious value in reducing opportunities for NEM theft and diversion—as well as the challenges that transparency and monitoring for the reductions processes themselves would pose. The United States and Russia have acquired substantial experience through their cooperation to improve the security of Russian stocks of NEM, including joint work on technologies and methods for enhanced transparency and monitoring. The work of the IAEA has provided extensive multilateral experience with monitoring and transparency for civilian NEM and some limited experience with military NEM as well. Accounting, management control, and protection for NEM—the measures collectively referred to as MPC&A, which are pursued by nations for both economic and security reasons and by the international community as part of the nuclear nonproliferation regime—interact with transparency and monitoring in important and multifaceted ways. Transparency and monitoring are of limited value without competent MPC&A. Thus implementing and strengthening MPC&A, in addition to its direct benefits for security, is therefore sometimes the most important step that can be taken toward improved transparency and monitoring. At the same time, improved transparency and monitoring conversely can lead to identification and thus remedy weaknesses in MPC&A. Increases in transparency and monitoring of NEM, if accepted, could also accelerate efforts to strengthen MPC&A through cooperative measures. On the other hand, increased transparency can also complicate the task of MPC&A by providing information useful to those who would steal NEM. We conclude that: Transparency and monitoring measures for declared stocks of NEM at declared sites, comparable to those for nuclear weapons, could include: comprehensive declarations describing the quantities and locations of all existing inventories of NEM, to-

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials gether with information on chemical forms and isotopic composition on the material; declarations of inventories of NEM surplus to military and civilian needs; and provisions for inspections of all declared facilities as well as of any undeclared suspicious activities. A number of additional measures could help to reduce the stocks and flows of NEM, as well as to reduce the number of sites at which NEM are stored. Immediate efforts related to HEU are especially important given its greater utility for terrorists or states seeking simple nuclear weapons. These measures include: accelerated disposition of excess HEU inventories through down blending and eventual use in reactor fuel; replacement of HEU fuels in research reactors with high-density LEU fuels, where feasible, and decommissioning of nuclear reactors using HEU fuels when replacement is not possible; disposition of excess separated plutonium either by conversion to MOX fuel for use in civil reactors or by mixing with fission products and immobilization; a comprehensive cutoff of production of NEM for weapons; a serious international effort to develop nuclear fuel cycles for civil reactors that minimize or eliminate the exposure of NEM; and possible centralization under multinational control of all facilities capable of enriching uranium or reprocessing plutonium. Two efforts that would provide great benefits for international efforts to increase transparency and monitoring for NEM are: continued substantial improvements in national management, protection, control and accounting of all national holdings of NEM so that individual countries, in particular Russia and the United States, are fully aware of the quantity and status of all of their holdings of NEM and have provided effective protection against theft or diversion for all stocks of NEM; and continued strengthening of the safeguards regime administered both bilaterally and by the IAEA, including universal applicability of the Additional Protocol, with

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Monitoring Nuclear Weapons and Nuclear-Explosive Materials increased manpower and funding to carry out the expanded mandate. Important efforts to support both these goals are underway, but they should be enhanced and accelerated. Greatly improved management and decreased inventories of NEM, which are priorities on their own account, would be critical if limits on total numbers of warheads were contemplated. The lower such limits became, moreover, the greater would be the need for reduction of NEM stockpiles and high confidence in monitoring the stocks that remained. While the technologies exist to achieve monitoring of NEM quantities with considerable accuracy and confidence under a cooperative framework, a new strengthened international consensus on the value of doing this would be necessary to solve cooperatively the many difficult problems involved.