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6 Long-Term Disposition INTRODUCTION Long-term disposition of the excess plutonium from dismantled nuclear weapons the third stage in the process beginning with dismantlement of weapons and intermediate storage of fissile materials will be a long, complex, and expensive endeavor. All of the plausible options stretch out over decades, counting both the time required to get ready to begin and the time needed to complete the disposi- tion campaign. All options are likely to involve a net economic cost, rather than providing a net profit from this material. All options involve unresolved issues and risks of uncertain magnitude. None of the options is sufficiently developed to be chosen as the preferred approach until outstanding questions are answered. This chapter offers not a final answer but a road map for arriving at one; it is intended to provide guidelines for the necessary national and international debate to come, to narrow the focus of attention to the subset of options most likely to minimize risks, and to provide plausible end points for the dismantle- ment and storage activities now under way. 141

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142 LONG-TERM DISPOSITION In considering this situation, the committee has reached the following set of recommendations: Because of the long times required for all disposition options, Missile ma- terial storage arrangements lasting well over a decade will be an essential part of any disposition policy (see Chapter 5~. These storage arrangements should be designed to meet the same stringent standards of security and accountability applied to stored weapons, and they should include international monitoring. Because of the uncertainties surrounding all disposition options, these inter- mediate storage approaches must be designed to be capable of extension for many decades if necessary. The appropriate arrangements for intermediate storage are to a large extent decoupled from long-term disposition decisions and are currently more urgent. Storage should not be extended indefinitely. Because of the liabilities of indefinite storage of excess weapons material for the nonproliferation and arms reduction regimes, the risk of breakout involved in such storage, and the risks of theft in the event of a breakdown in government authority, there are sub- stantial reasons to pursue other disposition approaches that provide additional barriers against use of this material in weapons. Indeed, one of the key criteria by which disposition options should be judged is the speed with which they can be accomplished, and thus the degree to which they curtail the risks of pro- longed storage. Disposition options other than extended storage should be pursued only if they reduce overall security risks compared to leaving the material in storage, when both the final form of the material and the risks of the various processes needed to get to that state are considered. In the current unsettled circumstances in Russia, this minimum criterion is not trivial. To the extent practicable, safeguards and security measures should main- tain the "stored weapons standard" of accounting and security throughout the disposition process. The process must take place under agreed monitoring and security that form part of the overall regime for management of fissile materials described in previous chapters. . An appropriate standard for the ilna1 product or clsposltlon options IS that they transform the weapons plutonium into a physical form that is at least as inaccessible for weapons use as the much larger and growing stock of pluto- nium that exists in spent fuel from commercial nuclear reactors. (This existing problem will itself change over time as the radioactivity decays, repositories or monitored retrievable storage sites become available, and approaches to safe- guards and security and nuclear fuel cycles evolve.) Incurring substantial addi- tional costs, complexities, risks, or delays in order to go further and eliminate the excess weapons plutonium completely or nearly so would not be justified

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LONG-TERM DISPOSITION 143 unless the same approach were to be taken with the global stock of civilian plutonium. The two most promising alternatives for the purpose of meeting the spent fuel standard are: 1. The spent fuel option, which has several variants. The principal one is to use the plutonium as once-through fuel in existing civilian nuclear power reactors or their evolutionary variants. Candidates for this role are U.S. light- water reactors (LWRs), Russian LWRs, and Canadian deuterium-uranium (CANDU) reactors. The use of European and Japanese reactors already licensed for civilian plutonium should also be considered for Russian weapons plutonium. 2. The vitrification option, which would entail combining the plutonium with radioactive high-level wastes as these are melted into large glass logs. The plutonium would then be roughly as difficult to recover for weapons use as plu- tonium in spent fuel. A third option, burial in deep boreholes, has until now been less thor- oughly studied than options 1 and 2, but could turn out to be comparably attractive. Further research is needed to answer important outstanding questions concern- ing each of these three options. For the spent fuel option, existing or partly completed reactors are pre- ferred over newly built reactors, to avoid the delay and capital cost of building entirely new facilities. If problems of licensing and public approval for existing reactors prove insurmountable, one or more new reactors might be built on a government-owned site; if so, these should be reactors of sufficiently well- proven design so as not to create additional technical and licensing uncertain- ties. Reactors of more advanced design examined by the committee do not offer sufficient advantages for this mission to offset the delays and extra costs their use would entail. Although the spent fuel standard applied to excess plutonium is an ap- propriate goal for next steps, further steps should be taken to reduce the prolif- eration risks associated with nuclear power and the global stock of plutonium, including plutonium in spent fuel. Options for near-total elimination of pluto- nium may have a role to play in the longer-term effort to reduce the risks posed by global plutonium stocks. Research on defining and exploring these options should be continued at the conceptual level. ' The spent fuel option, in which the weapons plutonium would actually be converted to spent fuel, should not be confused with the spent fuel standard: it is merely one means of meeting that standard. As discussed later, spent plutonium fuels would have some differences from ordinary spent fuels, including higher plutonium concentrations.

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144 LONG-TERM DISPOSITION Institutional issues in managing plutonium disposition may be more complex and difficult to resolve than the technical ones. The process must be carefully managed to provide adequate safeguards, security, transparency, and protection for environment, safety, and health; to obtain public and institutional approval, including licenses; and to allow adequate participation in the decision making by all affected parties, including the U.S. and Russian publics and the international community. Adequate information must be made available to give substance to the public's participation. A more effective decision making proc- ess to address these issues is needed within both the U.S. and the Russian gov- ernments, as discussed in Chapter 1. It is important to begin now to build consensus on a road map for deci- sions concerning long-term disposition of excess weapons plutonium. Because disposition options will take decades to carry out, it is critical to develop op- tions that can muster a sustainable consensus. The remainder of this chapter outlines the considerations that led to these conclusions. It begins by describing the categories into which the many techni- cal options for long-ten disposition can be divided and the criteria for judging among them. It then goes on to discuss each option and how it fares under those criteria. Finally, it outlines the committee's recommendations. THE RANGE OF CHOICE The options for long-term disposition can be divided into three broad classes, as illustrated in Figure 6-1: 1. Indefinite Storage: In this approach, the plutonium would continue to be stored in directly weapons-usable form indefinitely, with no specific decision concerning whether, when, and how storage would be terminated.2 During such storage, safeguards and security would provide the primary barrier to pro- liferation. Political measures, such as a formal commitment to non-weapons use and continuing safeguards, would provide the primary barrier to reuse of the material for weapons by the state from whose weapons the material came. Al- though intermediate storage is essential to all disposition options, for reasons already mentioned the committee does not recommend that it be extended in- definitely. 2. Minimized Accessibility: In this concept, barriers would be created physical, chemical, or radiological to make the steps needed to use the pluto- nium in weapons (acquisition of the plutonium, processing, weapon manufac- ture) more difficult either for potential proliferators or for the state from whose 2In separating "indefinite" storage from "inte~ediate" storage, this report uses "indefinite" to mean approaches in which storage itself is considered the disposition option, and no end point to the storage has been defined. In this nomenclature, storage would be considered "intermediate" even if it lasted for several decades, if the material were awaiting processing in a chosen disposition option.

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LONG-TERM DISPOSITION 145 Indefinite Storage ~ Materials Remain in Weapons / Usable Form Barriers to Reuse / in Weapons Based on Politics and Secutity Measures Intermediate Storage FIGURE 6-1 Plutonium disposition Minimized Accessibility Physical, Chemical, or Radialogical, Barriers Reduce Availability for Weapons Use Elimination ~ Material Nearly \ Completely Removed from \ Human Access \ OPTIONS Use Reactors (no reprocessing JO required) / LWR, CANDU, LMR, MHTGR, etc. Disposal Vitrification Deep Borehole Underground Explosion Sub-Seabed Repository Burial Use Reactors (reprocessing required) LWR, CANDU, LMR, MHTGR, etc. An Disposal Space Launch Ocean Dilution weapons it came. The plutonium would continue to exist, and some form of safeguards would continue to be required. The spent fuel, vitrification, and deep-borehole approaches are examples. 3. Elimination: In this concept, the plutonium would be removed from hu- man access completely, or nearly so, for example, by fissioning the plutonium atoms or by launching it into deep space. The point in such a process at which the plutonium can be considered "eliminated" for example, whether burning 99 percent of the plutonium would be sufficient- is somewhat arbitrary, but any "elimination" option should ensure that retrieving enough plutonium for a nuclear explosive from whatever remains would be extremely difficult. One plausible standard is to describe any option in which only a few grams of plu- tonium would remain in a large truckload of waste as an elimination option.3 3 The International Atomic Energy Agency (IAEA), for example, considers that materials no longer require safeguards if the remaining fissile material in them has been "consumed," or so diluted as to be "practically irrecoverable" for weapons use. Quantitative measures for termination of safeguards, which might provide one standard for judging when to consider fissile material "eliminated," have not yet been finalized. Interview with Thomas Shea, IAEA Safeguards Division, August 1993. See, for example, A. Fattah and N. Khlebnikov, "A Proposal for Technical Criteria for Termination of

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146 LONG-TERM DISPOSITION Use or Disposal. A complementary categorization is whether the pluto- nium would be used or disposed of. The use options would fission some frac- tion of the plutonium in power reactors, converting its energy content into elec- tricity. The disposal options would throw away the plutonium's energy content. Since plutonium is more expensive to use as nuclear fuel than widely available low-enriched uranium, either the use or the disposal options would require a subsidy. The different signals relating to civilian nuclear power that would be sent by using excess plutonium or throwing it away are discussed in more detail below. U.S. and Russian Contexts. It is possible-even likely that the optimal approaches to long-term plutonium disposition will be different in the United States and Russia. The risks involved in storing, handling, processing, and transporting plutonium are much higher in Russia under present circumstances, and the two countries' economies and plutonium fuel policies are different. Most of the key officials responsible for these issues in the Russian government strongly prefer options that use surplus weapons plutonium to generate electric- ity in reactors; it would be difficult to convince Russia to pursue disposal op- tions in the near term (though perhaps not impossible, particularly with suf- ficient financial incentives). Although U.S. and Russian disposition approaches may differ, rough paral- lelism in the timing and scale of long-term disposition would be desirable, so that both nations' available plutonium stocks would remain comparable. After long-term disposition, neither nation's excess plutonium should be much more accessible for use in weapons than the other' s. While the United States and other industrialized countries cannot dictate particular disposition options to Russia, they will have a significant influence on Russian decisions in a variety of ways ranging from simply setting an ex- ample on the one hand, to financial assistance, negotiated agreements to pursue particular approaches, or outright purchase of former Soviet weapons pluto- nium on the other. Other Forms of Military Plutonium. The primary focus of this report is the excess weapons plutonium resulting from arms reductions, which is initially in the form of pits from dismantled nuclear weapons. Both the United States and Russia, however, also have large quantities of military plutonium in scrap and residues from past operations of their nuclear weapons complexes, most of which are also likely to be considered excess. Although the amount of pluto- nium in these forms is smaller than the amount in pits that will result from arms reductions, the volume is much greater; the variety of forms of material is wide; and the environment, safety, and health (ES&H) risks are substantial for Safeguards for Materials Characterized as Measured Discards," Journal of Nuclear Materials Management, May 1991.

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LONG-TERM DISPOSITION 147 some forms. Even characterizing the constituents of these materials accurately is difficult. Some of these materials can readily be processed to plutonium metal or oxide that could then be fed into many of the disposition options described be- low. Some reactor options (typically the more advanced ones that would take longer to bring on-line) are more capable than others of handling variations in the form of the initial fuel feed, though there are materials that none of the re- actor options could plausibly handle. Moreover, processing of some of these materials would raise difficult environmental issues of its own. The vitrification option, described below, may be a particularly promising approach for stabiliz- ing and ultimately disposing of the plutonium in these less tractable forms. CRITERIA FOR DISPOSITION OPTIONS Security issues should be the primary criteria for choice among the long-term disposition options. Each long-term disposition approach generates risks and opportunities with respect to theft, rearmament, and the arms reduc- tion and nonproliferation regimes that depend on political and technical factors that will evolve over the long time periods involved in disposition. The commit- tee judges the following security risks related to long-term disposition choices to be of greatest concern: Risks of Storage: Prolonged storage of excess weapons plutonium would mean a continuing risk of breakout, as well as of theft from the storage site. In addition, extended storage of large quantities of excess fissile materials, par- ticularly in the form of weapons components, could undermine the arms reduc- tion and nonproliferation regimes. Thus, long-term disposition options should minimize the time during which plutonium is stored in accessible forms. The timing for each long-term disposition option is dependent on three factors: its technical readiness or uncertainty, the speed with which public and institutional approval could be gained, and the time required to implement it once developed and approved. Risks of Handling: Nearly all disposition options other than indefinite stor- age require processing and usually transportation of plutonium, in ways that could increase access to the material and complicate accounting for it, thus in- creasing the potential for diversion and theft. In order to ensure that the overall process reduces net security risks, an agreed and stringent standard of security and accounting must be maintained throughout the disposition process, ap- proximating as closely as practicable the security and accounting applied to intact nuclear weapons. The committee calls this the "stored weapons stan- dard." Hence, choices among long-ten disposition options should be weighted in favor of those that minimize:

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148 LONG-TERM DISPOSITION the number of transport steps, and the risks involved in each; the number of sites at which plutonium is handled, and the risks at each of those sites; and any processing steps with high accessibility and low accountability. Risks of Recovery: A third key security criterion for judging disposition options is the risk of recovery of the plutonium after disposition. The committee believes that options for the long-term disposition of weapons plutonium should seek to meet a "spent fuel standard" that is, to make this plutonium roughly as inaccessible for weapons use as the much larger and growing quantity of plutonium that exists in spent fuel from commercial reactors. Options that left the plutonium more accessible than this existing stock would mean that this material would continue to pose a unique safeguards problem indefinitely. Conversely, as long as civilian plutonium exists and continues to accumulate, options that went further than the spent fuel standard and sought to eliminate the excess weapons plutonium entirely would provide little additional security, unless the same were done with the much larger amount of civilian plutonium. Thus, options for the next steps in long-term disposition of weapons plutonium shouldfocus on those in the "minimized accessibility" class. Over the longer term, however, steps should be taken to go beyond the cur- rent spent fuel standard, to further reduce the accessibility for use in weapons of the entire global stock of plutonium. Elimination options are among the pos- sibilities for this purpose and could be seen as a second, long-term step for all plutonium (both military and civilian). The difficulty of using plutonium in spent fuel for nuclear explosives arises from its chemical dilution in the fuel (with plutonium typically consisting of roughly 1 percent of the spent fuel weight); the radioactivity of the fission products with which the plutonium is mixed (which, for years after the fuel leaves the reactor, would give anyone attempting to the handle the spent fuel without appropriate protection a lethal dose of radiation within minutes); and the isotopic composition of the plutonium (which includes more of the less de- sirable isotopes of plutonium than weapons-grade material does, somewhat complicating the construction of nuclear explosives). (See "How Accessible is Plutonium in Spent Fuel?" p. 150.) Eventually, physical barriers will be im- posed as well, when this material is consigned to geologic repositories; these physical barriers will have to compensate for the long-term decline of the radio- logical barrier. Chemical barriers alone, such as diluting the plutonium or combining it chemically with other elements, will not be sufficient to match this combination of chemical, radiological, and isotopic barriers, and therefore cannot meet the spent fuel standard. Thus, the leading options the committee has examined in- volve both chemical and radiological barriers (in the case of the spent fuel and vitrification options) or substantial physical barriers (in the case of the deep-borehole option).

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LONG-TERM DISPOSITION 149 The three security criteria just outlined represent a kind of coarse filter for disposition options: any option that cannot bring the weapons plutonium to the spent fuel standard within a few decades with low to moderate security risks along the way does not deserve further consideration. Signals Relating to Civilian Nuclear Fuel Cycles. The goal of long-term disposition should be not only to ensure that the plutonium from dismantled weapons is not reused in weapons, but also to reduce net security risks from all fissile materials. Thus, policymakers must be attentive to possible indirect ef- fects that the choice of disposition options might have on the proliferation risks posed by other fissile materials in the world, as well as its direct effects on the surplus weapons material. The political signals sent by the choice of particular disposition approaches might encourage the development and use of more pro- liferation-resistant nuclear fuel cycles; encourage the use of more proliferation- prone nuclear fuel cycles; or serve to set a standard for improved safeguards and security for other fissile materials. Under the Carter administration, the United States decided not to reprocess civilian plutonium or pursue plutonium fuel cycles, and launched a major in- ternational effort to convince other countries that' such separated plutonium fuel cycles were uneconomical and posed significant proliferation risks. Elements of that policy were incorporated in the Nuclear Non-Proliferation Act of 1978, which remains U.S. law. Although the Reagan and Bush administrations re- versed the Carter administration's opposition to domestic use of separated plu- tonium, for economic reasons none 'has ensued. Both of these administrations continued to strongly oppose plutonium separation in countries judged to pose proliferation risks, while raising no objections to continuing plutonium separa- tion programs in Japan and Europe. On September 27, 1993, the Clinton ad- ministration announced a nonproliferation initiative that makes clear that, while the United States will not interfere with reprocessing in Japan and Europe, "the United States does not encourage the civil use of plutonium and, accordingly, does not itself engage in plutonium reprocessing for either nuclear power or nuclear explosive purposes." The initiative called for an exploration of "means to limit the stockpiling of plutonium from civil nuclear programs."4 Given this background, policymakers will have to take into account the fact that choosing to use weapons plutonium in reactors would be perceived by some as representing generalized U.S. approval of separated plutonium fuel cycles, thereby compromising the ability of the U.S. government to oppose such fuel cycles elsewhere. Conversely, choosing to dispose of weapons plutonium with- out extracting any energy from it could be interpreted as reflecting a general- ized U.S. government opposition to plutonium recycle. Either choice could have an impact on fuel cycle debates now under way in Japan, Europe, and Russia. 4 White House Fact Sheet, "Nonproliferation and Export Control Policy," September 27, 1993.

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150 LONG-TERM DISPOSITION

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LONG-TEAM DISPOSITION 151

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212 LONG-TERM DISPOSITION Accelerator-based Conversion (ABC). Accelerator-based conversion (ABC) systems have been under study as a means of eliminating plutonium, and of fissioning actinides and transmuting fission products in order to reduce the longevity of radioactive wastes. In this concept, a reactor that was subcriti- cal meaning that the neutrons within it could not sustain a chain reaction without outside input is driven by neutrons produced by a beam of particles from an accelerator hitting a target. In the concepts that have received most examination, the subcritical reactor would have a fluid fuel (either an aqueous slurry or a molten salt) that would be fed continuously out of the reactor, re- processed to remove fission products, and fed back into the reactor.47 This option is only at the early paper-study stage and cannot be available on a large scale for decades. Both the proposed subcritical fluid fuel reactor technology and its fuel cycle technology are extremely challenging and un- proven. The reactor, for example, would have a radiation flux of order 10 times that in current LWRs, raising serious engineering issues concerning the sur- vival of the reactor materials. Reprocessing would take place within days or weeks after the fuel left the reactor, forcing the approach to deal with unprece- dented levels of radioactivity; at the same time, proponents claim that reproc- essing losses would be unprecedentedly low. If the estimated performance could be attained, however, such systems could destroy plutonium at a rate (per unit of thermal energy) comparable to those of the other destruction-oriented options and could reach high reduction factors for plutonium inventory more rapidly than many of the other options. The continuous on-line reprocessing proposed for ABC would offer some advantages in waste reduction and in safeguards against plutonium theft or covert diversion (but again, probably not against open diversion by the system's operators) shared in varying degrees by other advanced systems that use such reprocessing. Molten-Salt Reactors. Molten-salt reactors, based on the system explored in the 1950s-era Molten Salt Reactor (MSR) Experiment have also been pro posed as destroyers of plutonium. This concept is similar in many respects to the molten-salt ABC, except that the reactor is fully critical and therefore no accelerator is required. Proponents claim that MSRs offer major safety advan tages over existing light-water reactor technology. However, like ABC, MSRs would take decades to develop, license, and deploy. Pebble-Bed Reactors. Pebble-bed reactors (PBRs), originally developed for nuclear rocket applications, have also been proposed for use as plutonium destroyers. Like ABC and molten-salt systems, they are in the early stages of development. 47Solid-fue} concepts have also been examined but are perceived as not having some of the advantages of the fluid fuel approach.

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LONG-TERM DISPOSITION 213 Modular High-Temperature Gas-Cooled Reactors (MHTGRs). In principle, the MHTGR could also be used in an elimination mode, by reprocess- ing and recycling its spent fuel. Reprocessing this fuel would be complex, how- ever, and MHTGR advocates have not pursued this approach in recent years. As indicated above, it is too soon to choose among these options. Addi- tional research is desirable to clarify the issues involved in elimination options in general and to identify the most promising options for that purpose. CONCLUSIONS Figure 6-5 summarizes the committee's judgments concerning the long- term disposition options described in this chapter. Any figure of this kind can only be an illustrative overview of the options and issues; by their nature, such figures are oversimplifications. Moreover, these ratings are inevitably judg- mental. The committee chose to use only three ratings high, moderate, and low" because the information available cannot confidently support more de- tailed assessments. This inevitably means that there may be wide variations among options that receive the same rating; two options might each be expen- sive enough to be rated as having "high" cost, for example, but one might be several times as expensive as the other. The committee has not attempted to reach an "overall" rating for each op- tion, since readers may rank the criteria differently. Such an overall rating can- not be reached simply by averaging highs and lows across columns. For exam- ple, as described earlier, the committee does not consider indefinite storage an acceptable option, because the black mark under "risks of recovery" with all it implies for the risks of theft, breakout, and the arms control and nonprolifera- tion regimes more than outweighs the low risks and costs of this option. Criteria. All the criteria are described in the negative, so that "high" cor- responds to high risks or costs, whereas "low" is a more favorable rating. The first three columns of the chart are all related to the speed with which an option could be accomplished, which the committee considers to be one of the principal criteria for choice (discussed under "Risks of Storage" in the text). "Technical Uncertainty" affects both timing and the degree of assurance of suc- cess, as does the following column, "Difficulty of Public/Institutional Accep- tance." The latter category includes licensing and public approval issues, and, where necessary, issues related to the approval of international parties. The third column, "Time to Execute," refers to the time required for implementa- tion once the obstacles represented by the first two columns have been over- come that is, once development is complete and the requisite licenses and approvals have been obtained. This includes the time required for any necessary facility construction or modification, and the time during which the option would be processing the excess plutonium stock.

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216 LONG-TERM DISPOSITION As in the text, "Risks of Handling" refers to the risks of theft or diversion of materials during the various processes involved before the material reaches its final state, while "Risks of Recovery" refers to the risks that the material might be recovered for weapons use (by the state from whose weapons it came or by others) after disposition was complete. Hence, the latter, combined with the several timing criteria, effectively portrays the committee's judgment of the option's political impact on arms reduction and nonproliferation (assuming that equivalent levels of transparency would be applied to all options); this impact does not receive a separate column in the chart. The "ES&M Risk" and "Cost" categories are self-explanatory. The final column, "Fuel Cycle Policy Signal," refers to the issue relating to more general U.S. fuel cycle and nonproliferation policies described in the text: those options involving the use of weapons plutonium in reactors would send the signal that the United States approved of such use, at least for this limited purpose, whereas the disposal options would send the signal that even for the pressing problem of plutonium disposition, the United States did not approve of the use of plutonium fuels. In this column, therefore, the committee simply indicates whether the option would or would not use plutonium in reactor fuel, rather than attempting a high, moderate, and low categorization. Ratings. For all the criteria other than "Technical Uncertainty," the option of using 100 percent MOX fuel in U.S. LWRs is used as the standard for a moderate rating. (Technical uncertainty for the LWR MOX option is rated low.) Options that involve greater risks or costs than MOX in LWRs are rated high, while those that involve significantly lower risks or costs are rated low. Options Indefinite Storage Indefinite storage is among the more complex options to rate, because for the next several decades storage would be relatively simple, safe, and low cost (at least in the United States), but these judgments would change if it were truly extended indefinitely. Indefinite storage is rated as having low technical uncertainty and time to execute because storage can be (and is being) implemented immediately. Stor- age is rated as low in risks of handling and ES&H risks (because no processing is involved), and low in cost (by assuming costs comparable to those at Pantex, rather than commercial charges for plutonium storage). The difficulty of ob- taining public and institutional acceptance is rated moderate, although it would probably be quite difficult to gain public approval for storage that was explicitly presented as lasting indefinitely, at least in the United States. Indefinite storage is the only option on the chart rated as having high risks of recovery, since the

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LONG-TERM DISPOSITION 217 material could be removed from the storage site and used for weapons at any time. Minimized Accessibility LWRs with 113 MOX refers to the use of existing or modified LWRs, either U.S. LWRs using U.S. plutonium or Russian VVER-1000s using Russian plu- tonium. These are rated as having low technical uncertainty. They are rated moderate in most other categories, but high under risks of handling, because the material would have to be transported to three times as many sites as in the case of LWRs with 100 percent MOX cores. As described in the text, there are likely to be higher risks of handling in the former Soviet Union under present circumstances than in the United States. LWRs with 100 percent MOX (which, like the previous entry, refers to the use of existing or partly completed LVVRs, in this case with modifications as necessary for use of full-MOX cores) are rated moderate in all categories except technical uncertainty, which remains low, as in the case of LWRs with one- third MOX, because the modifications needed to accommodate full-MOX cores are not sufficient to create substantial uncertainties or require major development. CAND Us, like full-MOX LWRs, are rated moderate under all criteria ex- cept technical uncertainty, which is rated low, because this option would not require a major development program. The moderate rating for difficulty of acceptance is more doubtful than in the case of LWRLs, since Canadian accep- tance of plutonium fuel use remains uncertain. Similarly, the cost rating for CANDU reactors is more uncertain. Substitution for civil plutonium is rated high for difficulty of acceptance, because of the complex web of arrangements that would have to be changed to implement this option, but low for time to execute, because the scale of MOX use already planned is large enough to consume 50 or 100 tons of weapons plu- tonium quite rapidly if this option were agreed to. ES&H risks are rated low because there would be virtually no net additional risks compared to the pluto- nium use already planned; risks of handling would be rated low for the same reason, except that there is some significant difference in theft and diversion risk in the shift from reactor-grade to weapons-grade plutonium, and there are the risks of transport of the plutonium from its current location. Hence the risks of handling are rated moderate. Vitrification with high-level waste is rated moderate on all criteria except risks of handling, where it is rated low, because of the somewhat greater ease of safeguarding described in the text. The technical uncertainty, which is moder- ate, is greater than in the case of the reactor options just described. Although time to execute is also rated as moderate, vitrification might be accomplished somewhat more rapidly than the LWR and CANDU options if technical uncer- tainties are resolved.

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218 LONG-TERM DISPOSITION Deep boreholes are rated high on technical uncertainty because they would require more development than either the existing reactor options or the vitrifi- cation option. They are rated high for difficulty of public and institutional ac- ceptance because of the likely difficulties of obtaining the necessary licenses. Boreholes are rated as having moderate risks of recovery, with the caveat that recovery would be less difficult for the state in control of the borehole site than would recovery of plutonium in spent fuel. Although the cost of implementation itself would probably rate as low, boreholes are rated moderate on cost because of the development and licensing programs required. These costs could in fact ultimately be in the high category (as is also the case with other nonrepository disposal options). Boreholes are judged moderate on ES&H risks, but if techni- cal uncertainties are resolved favorably, these risks could turn out to be low. Sub-seabed disposal is rated high in technical uncertainty because consid- erable development would still be required before this option could be imple- mented-but it is the most fully developed of the options receiving this rating. This approach is rated as having high difficulty of public and institutional ac- ceptance, because of the legal barriers and likely intense international oppo- sition to such disposal. As with deep-borehole disposal, however, time to exe- cute and risks of handling are rated low, and cost is rated moderate because even though implementation costs could be low, the costs of development and licensing would be substantial. Detonation with underground nuclear explosions is rated high for technical uncertainty, even though it is clear it could be done, because of the many unre- solved safety and environmental issues. Similarly, it is rated as having high ES&H risks and acceptance difficulties. Existing LMRs without reprocessing are less susceptible to across-the- board ratings than some of the other options because there are wide variations in the design and characteristics of these facilities; moreover, some are in coun- tries where the excess weapons plutonium is located, whereas for others, the plutonium would have to be shipped and agreements negotiated. Existing LMRs are rated as low in technical uncertainty because the use of plutonium in these reactors is amply demonstrated; however, there are outstanding technical issues regarding the safety of some of these facilities. The time necessary to execute is rated high, because of the relatively small capacity, advanced age, or poor availability records of the existing LMRs. ALWRs refers to LWRs built for this mission, whether existing or follow- on designs. Technical uncertainty is rated low (though this judgment applies primarily to existing and evolutionary designs). Time to execute is rated high because licensing and building new reactors would take substantially longer than using existing facilities. New LMRs (without reprocessing, and MHTGRs are rated high on time to execute and cost, because of the delays and costs of development, licensing, and construction for these advanced reactors, both of which are estimated to involve higher life cycle costs in the current market than evolutionary LWRs.

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LONG-TERM DISPOSITION 219 Elimination Ocean dilution is rated as having high technical uncertainty, because al- though it is clear it could be done, there are large uncertainties concerning the ultimate ecological impact. It is rated moderate for cost, although the cost of implementation would be low, because of the likely costs of developing the op- tion and attempting to gain approval for it. Space launch is rated high for ES&H risks, because of the risks involved in possible launch accidents, but this rating could be reduced with a payload de- sign that provided high-confidence plutonium containment for all plausible accidents. LWRs or CANDUs with reprocessing are rated as having high time-to- execute and costs (as are all of the other reactor reprocessing options) because of the very long time required to eliminate nearly all of the plutonium by this means, and the high costs of reprocessing and recycle. Technical uncertainty is rated as moderate because the plutonium use demonstrated to date has not in- volved multiple-recycle fuel with its different mix of isotopes. Risks of handling are rated as high, because these options would involve repeated separation, transport, and use of separated plutonium, while several of the other reprocess- ing options are or can be designed to maintain the plutonium in a more theft- resistant form. ES&H risks are rated as high because of the record of ES&H impacts of reprocessing in some countries, but the committee notes that appro- priate application of resources would greatly reduce these risks. LMRs with reprocessing are also rated as having moderate technical uncer- tainty, because while some of these systems are being designed for a similar actinide-burning mission, considerable development is still required. Their handling and ES&H risks are rated as only moderate, rather than high, on the assumption that new reprocessing techniques that reduce wastes and safeguards risks would be employed. MHTGRs with reprocessing are rated as having high technical uncertainty, since a reprocessing approach has not been pursued for HTGRs in recent years, and such a plutonium elimination objective has not been examined in detail. Like LWRs and CANDUs with reprocessing, they are rated as having high risks of handling, because of the repeated reprocessing and use of fully sepa- rated plutonium that would be required. ES&H risks are rated as high, on the analogy to LWRs and CANDUs with reprocessing, but the same caveat applies. ABC is rated as having high technical uncertainty, because of the large amount of technical development still required. It is rated moderate for ES&H risk, but that judgment is quite uncertain: if ABC fulfills its proponents' expec- tations, ES&H risk could be quite low, but it is also possible that unexpected ES&H risks could arise. MSR and PBR receive the same ratings across the board as ABC, for much the same reasons. It is too soon to tell which of these technologies would be

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220 LONG-TERM DISPOSITION preferable for the missions their advocates propose, if these missions are pursued. RECOMMENDATIONS It is important to begin now to build consensus on a road map for deci- sions concerning long-term disposition of excess weapons plutonium. Because disposition options will take decades to carry out, it is critical to develop op- tions that can muster a sustainable consensus. Storage should not be extended indefinitely, because of (1) the negative impact that maintaining this material in forms readily accessible for weapons use would have on nonproliferation and arms reduction, (2) the risk of breakout and (3) the risks of theft from the storage site. One of the key criteria by which disposition options should be judged is the speed with which they can be ac- complished, and thus the degree to which they curtail the risks of prolonged storage. Disposition options beyond storage should be pursued only if they reduce overall security risks compared to leaving the material in storage, considering both the final form of the material and the risks of the various processes re- quired to get to that state. In the current unsettled circumstances in Russia, this . . . . . . ., - . minimum cnter~on IS a slgnlilcant one. The United States and Russia should begin discussions with the aim of agreeing that whatever disposition options are chosen, an agreed, stringent standard of accounting, monitoring, and security will be maintained throughout the process-coming as close as practicable to meeting the standard of security and accounting applied to intact nuclear weapons. Disposition options should be designed to transform the weapons pluto- nium into a physical form that is at least as inaccessible for weapons use as the much larger and growing stock of plutonium that exists in spent fuel from commercial nuclear reactors. The costs, complexities, risks, and delays of going further than this "spent fuel standard" to eliminate the excess weapons plutonium completely or nearly so would not be justified unless the same ap- proach were to be taken with the global stock of civilian plutonium. The two most promising alternatives for the purpose of meeting the spent fuel standard are: 1. The spent fuel option, which has several variants. The principal one is to use the plutonium as once-through fuel in existing commercial nuclear power reactors or their evolutionary variants. Candidates for this role are U.S. light- water reactors (LWRs), Russian LWRs, and Canadian deuterium-uranium (CANDU) reactors. The use of European and Japanese reactors already licensed

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LONG-TERM DISPOSITION 221 for civilian plutonium should also be considered for Russian weapons plutonium. 2. The vitrification option, which would entail combining the plutonium with radioactive high-level wastes (HLW) as these are melted into large glass logs. The plutonium would then be roughly as difficult to recover for weapons use as plutonium in spent fuel. A third option, burial in deep boreholes, has until now been less thor- oughly studied than alternative 1 and 2, but could turn out to be comparably attractive. A coordinated program of research and development should be under- taken immediately to clarify and resolve the uncertainties the committee has identified regarding each of these three options. The aim should be to pave the way for a national discussion, with full public participation, in order to make a choice within a very few years. Applying the spent fuel standard narrows the options considerably: 1. Options that irradiate the weapons plutonium in reactors only briefly ("spiking"), leaving it far less radioactive than typical spent fuel, and with little change in its isotopic composition, should not be pursued except possibly as a preliminary step on the road toward the spent fuel option. (Even for that pur- pose, in those cases the committee has examined, the possible advantages of the spiking option over continued storage do not appear to be worth the substantial cost of such spiking approaches.) 2. Options that involve only a chemical barrier to reuse such as vitrifica- tion of plutonium without HEW or other fission products should not be pur- sued, except possibly as a first step toward adding radiological or physical bar- riers as well. 3. Advanced reactors should not be specifically developed or built for transforming weapons plutonium into spent fuel, because that aim can be achieved more rapidly, less expensively, and more surely using existing or evolutionary reactor types. 4. Options that strive to destroy a large fraction of the plutonium without reprocessing and recycle, using existing or advanced reactors with nonfertile fuels, should not be pursued because such approaches cannot destroy enough of the plutonium to obviate the need for continuing safeguards, and the modest reduction in security risk that could be achieved is not worth the extra delay, cost, and uncertainty that development of such approaches would entail. Production of tritium should not be a major criterion for choosing among disposition options. Institutional issues in managing plutonium disposition are complex and the process to resolve them must be carefully managed. The process must pro- vide adequate safeguards, security, and transparency, as well as protection for

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222 LONG-TERM DISPOSITION the environment, safety, and health; obtain public and institutional approval, including licenses; and allow adequate participation in the decision making by all affected parties, including the U.S. and Russian publics and the interna- tional community. Adequate information must be made available to give sub- stance to the public's participation. Although the committee did not conduct a comprehensive examination of the proliferation risks of civilian nuclear fuel cycles, which would have gone beyond its charge, the risks posed by all forms of plutonium must be addressed. While the spent fuel standard is an appropriate goal for next steps, fur- ther steps should be taken to reduce the proliferation risks posed by all of the world's plutonium stocks, military and civilian, separated and unseparated; the need for such steps exists already, and will increase with time. Options for near-total elimination of plutonium may have a role to play in this effort, and research on defining and exploring these options should be continued at a con- ceptual level. These options, however, can only realistically be considered in the broader context of the future of nuclear electricity generation, including the minimization of security and safety risks-the assessment of which is beyond the scope of this report. Studies of that broader context should have as one im- portant focus minimizing the risk of nuclear proliferation, and should consider nuclear systems as a whole, from the mining of uranium through to the disposal of waste; should consider feasible safeguarding methods as elements of devel- opment and design; and should take an international approach, realizing that other nations' approaches reflect their differing economic, political, technical, security, and geographic situations and perceptions.