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Executive Summary BACKGROUND AND CHARGE TO THE PANEL The concept of the "spent-fuel standard" was introduced, in the 1994 and 1995 reports of the NAS Committee on International Security and Arms Control (CISAC) on the disposition of excess weapons plutonium, as the criterion for judging the adequacy of resistance to theft and prolif- eration conferred by the intrinsic characteristics of the final plutonium form produced by a disposition option.) That standard held that pluto- nium in its final dispositioned forms should be roughly as difficult to acquire, process, and utilize In nuclear weapons as is the plutonium in typical spent fuel from civilian power reactors. The 1994 and 1995 reports concluded Mat He two disposition methods most likely to be able to meet the spent-fuel standard In the near future are (a) embodying the plutonium in mixed-oxide (MOX) fuel and irradi- ating this once through In civilian reactors of currently operating types ("the MOX option") and 1Committee on International Security and Arms Control, National Academy of Sciences, Management and Disposition of Excess Weapons Plutonium, Washington, DC: National Acad- emy Press, 1994, 275 pp.; and Panel on Reactor-Related Options, Committee on International Security and Arms Control, National Academy of Sciences, Management and Disposition of Excess Weapons Plutonium: Reactor-Related Options, Washington, DC: National Academy Press, 1995, 408 pp.

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2 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM (b) immobilizing the plutonium together with large quantities of fission products in a glass and/or ceramic matrix encased in steel ('`the immobilization optional. The 1995 report argued further that, because both of these options face a combination of technical and institutional barriers that translate into un- certainties about the pace at which they could be implemented, the best chances for having at least one deployable option at an early date in both the United States and Russia would result from pursuing both options in parallel ("the dual-track approach") in both countries. These CISAC recommendations have proven to be somewhat contro- versial in two main respects: the "dual track" approach (with some fac- tions, in each country, favoring one or the other approach to the exclusion of the alternative, and some favoring different approaches) and the appro- priateness and interpretation of the "spent-fuel standard" (including whether particular variants of the MOX and immobilization options meet it). The first issue has been settled, at least for the time being, by the recent U.S.-Russian Bilateral Plutonium Disposition Agreement: * specifies that Russia will disposition 34 metric tons of excess military plutonium entirely by the MOX route and that the United States will disposition the same amount, 3/4 by the MOX route and 1/4 by the immobilization route. The second set of questions those connected with clarification and applica- tion of the spent-fuel standard is the focus of the current report. The charge to the Pane} from the Office of Fissile Material Disposi- tion in the U.S. Department of Energy (DOE) was, more specifically, to (1) amplify and clarify the spent-fuel standard and the considerations to be taken into account in its application; and (2) use the results of task (1) to determine whether the final pluto- nium forms produced by the two primary-candidate disposition options currently being pursued by DOE under the "dual-track" approach"can-in-canister" immobilization of the plutonium together with high level radioactive wastes and once-through irra- diation of the plutonium in mixed-o~ade (MOX) fuel in commercial light-water or Canadian deuterium-uranium (CANDU) reactors- meet this standard. The Panel was not asked to address: the proliferation and theft resistance of the steps that lead, under these disposition options, to the final pluto- nium forms; any questions related to geologic disposal or interim storage of these final forms except insofar as the properties of the final forms under such disposal or storage relate to assessing compliance with the

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EXECUTIVE SUMMARY 3 spent-fuel standard; or disposition alternatives other than the MOX and immobilization options described above. Important issues exist under all of these headings some of them treated in the 1994 and 1995 reports- but we were not charged to revisit or explore them here, and the time and resources available for this study would not have permitted our doing so. SUMMARY OF PRINCIPAL FINDINGS . As noted above, the spent-fuel standard holds that the final pluto- nium form produced by a disposition option should be approximately as resistant to acquisition, processing, and use in nuclear weapons as is the plutonium in typical spent fuel from once-through operation in a com- mercial light-water reactor (LWR). We have used, as a specific basis of comparison, 30-year-old spent LWR fuel irradiated to 33,000 megawatt- days per initial metric ton of heavy metal in fuel (MWd/MTHM). Judgments about compliance with the spent-fuel standard should depend only on the intrinsic properties of the final plutonium form, not on the extent of engineered and institutional protections. Such protec- tions are appropriate and necessary, both for ordinary spent fuel and for plutonium disposition forms meeting the spent-fuel standard, but they are not substitutes for the built-in barriers to which the spent-fuel stan- dard relates. Meeting the spent-fuel standard should be regarded as a necessary but not sufficient condition for judging a disposition method satisfactory, and satisfactory disposition should be understood to be only one element of the needed comprehensive approach to managing the hazards of excess nuclear weapons and weapons-usable materials. No mechanistically applicable formula can avoid the need for a mul- tiplicity of informed judgments in the process of determining whether a specified plutonium disposition form meets the spent-fuel standard. We have attempted to systematize the process of making these judgments in a matrix framework that combines (a) assessments of the relative importance, against a range of prolif- eration threats, of the various intrinsic barriers provided by dispositioned plutonium forms, with (b) assessments of the performance of different dispositioned pluto- nium forms with respect to these barriers, compared with the per- formance of the reference LWR spent fuel. We have applied this approach to address the spent-fuel-standard compliance of the final plutonium forms from four disposition options: spent fuel from the once-through irradiation in light-water-reactors, to

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4 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM 40,000 MWd/MTHM, of MOX fuel made with weapon plutonium (WPu- MOX); spent fuel from once-through irradiation in CANDU reactors, to 9700 MWd/MTHM, of WPu-MOX fuel; spent fuel from once-through irradiation in CANDU reactors, to 25,000 MWd/MTH, of WPu-MOX fuel in a configuration binding numerous CANDU-sized fuel bundles into a much larger agglomeration; and the current DOE can-in-canister con- figuration, in which unirradiated weapon plutonium is immobilized in ceramic pucks contained in steel cans, in a steel frame, in a steel canister filled with radioactive glass. We have concluded that the LWR-MOX option is compliant with the spent-fuel standard; that the standard CANDU-MOX option is not com- pliant; that the compliance of the CANFLEX CANDU-MOX option is marginal; and that compliance of the reference can-in-canister option with the spent-fuel standard is contingent on the outcome of efforts to clarify this option's resistance against on-site attack and to improve its signa- tures aiding detection of separation activities. We have concluded, further, that resolution of the vulnerability of the current can-in-canister configuration to on-site attack will require addi- tional investigation. Defining the full details of the required effort was beyond the scope of the current study. But we are not recommending an open-ended R&D program. Rather, we suggest that a full scale-test be carried out involving an attack judged most likely to succeed by a group of independent subject-matter experts. The outcome of such a test would provide a basis for deciding what if any additional physical tests, model- ing and simulation studies, and perhaps other analyses are required. We believe that such a testing and development program for the can-in- canister approach might well lead to identification of variants with suffi- cient resistance to attack to meet the spent-fuel standard, even if it turns out that the resistance of the current can-in-canister configuration is inadequate. .. .0