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The Challenges of Managing DOE’s Excess Nuclear Materials

Nuclear weapons production in the United States was a complex series of integrated activities carried out at 16 major sites and over 100 smaller ones. Production stopped abruptly in 1992 at the end of the Cold War leaving a legacy of radioactive wastes, contaminated media and buildings, and surplus nuclear materials.1 Site cleanup and closure is the mission of the Department of Energy’s (DOE’s) Office of Environmental Management (EM). Previous National Academies’ studies have assisted the EM Science Program (EMSP) in developing a research agenda for waste and site cleanup (NRC, 2000, 2001a, 2001b, 2002). A significant difference with the excess nuclear materials dealt with in this report is that most have not been declared as waste, and disposition paths have not been decided. The statement of task for this study accordingly directed the committee to identify research opportunities for storage, recycle, or reuse as well as disposal of these materials. The surplus nuclear materials dealt with in this report differ from waste and contaminated media in several important ways:

  • Most nuclear materials in the inventory are in concentrated, relatively pure forms.

  • The United States can no longer produce these materials in quantities that approach those of the inventory.

  • Some of the materials may have beneficial future uses.

  • Some materials, for example, plutonium and spent nuclear fuels, present security concerns.

DOE’s strategy for managing these materials is to collect them at a few of its larger sites (Hanford, Washington; Savannah River, South Car

1  

Civilian nuclear energy research by DOE and its predecessors created additional nuclear materials that are now in DOE’s inventory, as did naval propulsion activities.



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2 The Challenges of Managing DOE’s Excess Nuclear Materials Nuclear weapons production in the United States was a complex series of integrated activities carried out at 16 major sites and over 100 smaller ones. Production stopped abruptly in 1992 at the end of the Cold War leaving a legacy of radioactive wastes, contaminated media and buildings, and surplus nuclear materials.1 Site cleanup and closure is the mission of the Department of Energy’s (DOE’s) Office of Environmental Management (EM). Previous National Academies’ studies have assisted the EM Science Program (EMSP) in developing a research agenda for waste and site cleanup (NRC, 2000, 2001a, 2001b, 2002). A significant difference with the excess nuclear materials dealt with in this report is that most have not been declared as waste, and disposition paths have not been decided. The statement of task for this study accordingly directed the committee to identify research opportunities for storage, recycle, or reuse as well as disposal of these materials. The surplus nuclear materials dealt with in this report differ from waste and contaminated media in several important ways: Most nuclear materials in the inventory are in concentrated, relatively pure forms. The United States can no longer produce these materials in quantities that approach those of the inventory. Some of the materials may have beneficial future uses. Some materials, for example, plutonium and spent nuclear fuels, present security concerns. DOE’s strategy for managing these materials is to collect them at a few of its larger sites (Hanford, Washington; Savannah River, South Car 1   Civilian nuclear energy research by DOE and its predecessors created additional nuclear materials that are now in DOE’s inventory, as did naval propulsion activities.

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olina; Oak Ridge, Tennessee; Idaho National Engineering and Environmental Laboratory) to allow “de-inventorying” and closing other sites. Consolidating the materials onto fewer sites has practical advantages, such as security and cost effectiveness, but the long-term character of the materials management problem remains. As discussed later in this chapter, the committee concluded that the EMSP should foster research to reduce uncertainty in current plans for dispositioning its surplus nuclear materials and to improve the scientific basis for future decisions. Research emphasis should be on stabilizing the separated materials and developing beneficial uses. Because of its limited budget, the EMSP should coordinate its nuclear materials research with other programs in the Office of Science, EM, and the National Nuclear Security Administration. DOE’s Former Nuclear Materials Production DOE’s production era activities that led to its current inventory of nuclear materials can be summarized as follows:2 uranium mining, milling, refining, and isotope enrichment; nuclear reactor fuel and target fabrication; reactor operations; chemical separations; weapon component fabrication; weapon assembly, maintenance, modification, and dismantlement. The focus of DOE’s work was making plutonium and tritium for nuclear weapons (see Figure 2.1). Approximately 100 metric tons of Pu-239 were obtained from the production reactors and separations facilities at the Hanford and the Savannah River sites. About half of this inventory has been declared as surplus. The surplus includes clean metal from weapon disassembly and other sources, and impure metals, oxides, and other forms such as scraps and residues that were in process or stored when production operations ceased. The committee concluded that managing plutonium presents the greatest excess nuclear material challenge for DOE and that research should help sup- 2   See Appendix A for a more detailed description of nuclear materials production in the DOE complex.

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Figure 2.1. The United States nuclear weapons complex included facilities that were constructed throughout the country. This figure indicates the location of some of the major facilities and depicts the key production steps. Source:DOE, 1996a.

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port DOE’s plans for storing and beneficially reusing its Pu-239, as described in Chapter 3. Reactor operations created the plutonium and essentially all other isotopes managed throughout the DOE complex. Enriched uranium served as fuel in production reactors, and excess neutrons from the nuclear chain reaction bred Pu-239 and other isotopes in “targets” made of depleted uranium. Irradiated spent fuel and targets were routinely reprocessed to recover the plutonium, uranium, and other isotopes. However, when the United States stopped its plutonium production, some 250 fuel types amounting to about 2,500 metric tons of heavy metal3 of spent nuclear fuel and targets were left unreprocessed. Most are stored at Hanford, Idaho, Savannah River, and Oak Ridge. While DOE’s spent nuclear fuel (SNF) inventory is only about 5 percent of the inventory of spent power reactor fuels managed by the commercial sector, DOE is challenged with a wide variety of fuel types—some of which are deteriorating. As described in Chapter 4, research should focus on means to ensure that these fuels are stabilized for several decades of storage and that they will meet yet to be defined acceptance criteria for disposal in a geological repository. In addition to separating the desired products, reprocessing generated large volumes of highly radioactive waste, which were stored mainly in million gallon capacity tanks at the reprocessing sites. Most significant among the longer-lived, heat-producing fission products in the high-level waste are strontium-90 and cesium-137. In the early 1970s, Hanford removed a large fraction of these isotopes from its tank waste in order to reduce the heat produced in the tanks, and concentrated the isotopes in capsules for potential uses (thermoelectric generators, sterilizers). The almost 2,000 capsules contain about 67 million curies of radioactivity, approximately 37 percent of the total radioactivity at the Hanford Site. Their heat and intense radioactivity present challenges for their eventual disposition as well as research opportunities to support disposition plans, as described in Chapter 5. Enriched uranium, used to fabricate reactor fuels and weapon components, resulted from multistep processes that gradually concentrated the fissile isotope U-235, which comprises only about 0.7 percent of natural uranium. Enriching a portion of the uranium in U-235 created a massive legacy of about half a million tons of uranium (metal equivalent) depleted in U-235. This depleted uranium is stored as uranium hexafluoride (UF6) in large cylinders at the former enrichment sites near Paducah, Kentucky; Portsmouth, Ohio; and Oak Ridge, Tennessee. 3   “Heavy metal” refers to the mass of uranium and/or plutonium in the fuel.

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Chapter 6 describes research needs and opportunities for managing this very large amount of slightly radioactive, chemically toxic material. DOE also used its production reactors and chemical separation facilities in a number of campaigns to produce isotopes for special applications (Pu-238 for thermoelectric power in space vehicles, see cover photograph; Cf-252 for cancer treatment). Most resulted from multiple irradiation and separation steps, which eventually built up the higher actinide isotopes through successive neutron captures. The shutdown of the DOE’s production reactors and separations facilities precludes the future, large-scale manufacture of these isotopes. As DOE continues to close not only its production facilities, but also other facilities capable of handling and storing these isotopes, the potential benefits of these unique materials may be lost. Research needs and opportunities that may lead to future beneficial uses of these isotopes or aid DOE in deciding how to disposition these materials are discussed in Chapter 7. Disposition Options DOE has developed a comprehensive set of roadmaps for dispositioning essentially all of its nuclear materials (Tseng, 2001). In most instances there are multiple disposition options, but most eventually lead to disposal end points, for example, the Waste Isolation Pilot Plant (WIPP), New Mexico or DOE’s planned repository at Yucca Mountain, Nevada. In framing this study the committee also considered a more general set of factors that affect DOE’s current and future options for dispositioning its excess nuclear materials: legal or programmatic agreements, the attractiveness of the material for theft, e.g., by terrorists, and cost. These factors are summarized in Table 2.1. Except for spent nuclear fuel (Chapter 4) and a portion of the heavier actinides (Chapter 7), there are no agreements to dispose the excess inventory as waste. Security measures to prevent theft are not new to DOE, which successfully protected its materials throughout the Cold War. The committee viewed security as a subset of the overall need for developing improved matrices for immobilizing nuclear materials. Incentives for research include the large costs for managing the inventory, safety, and the materials’ scientific potential. The committee concluded that the following options encompass the end points available and provide a framework for research for managing and dispositioning DOE’s nuclear material: shorter-term storage for materials that have an identified use;

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Table 2.1 Factors Affecting DOE’s Options for Disposing of Excess Nuclear Materials Material Agreements Security Issues Cost Perspective Plutonium-239 In June 2000, the United States and Russia agreed that each country will reduce its inventory of excess weapons grade plutonium by about 34 metric tons (DOE, 2000c; NAS, 2000). Pu-239 is a principal component in nuclear weapons. DOE’s efforts to enhance security of its surplus Pu-239 have been guided by recommendations in a series of NAS reports (See Chapter 3).1 DOE estimated that the cost of managing its excess plutonium amounted to about 30 percent of its overall budget for managing excess nuclear materials in FY 2001.2 Cost of converting excess plutonium into mixed oxide fuel is estimated to be about $3.8 billion over 20 years (Siskin, 2002). Spent DOE nuclear fuel The Nuclear Waste Policy Act of 1982 (and its amendments) require DOE’s Office of Civilian Radioactive Waste Management to develop a geological repository for high-level radioactive waste and spent nuclear fuel. Some spent DOE nuclear fuels contain quantities of Pu-239, U-235, or fission products that could make them attractive for theft. Applying the NAS spent fuel standard would require that DOE SNF be no more attractive for theft than commercial SNF. DOE estimated that the cost of managing its excess SNF amounted to about 50 percent of its overall budget for managing excess nuclear materials in FY 2001. DOE projected a life cycle cost for managing and disposing of DOE SNF of about $5 billion (DOE, 1998a). Cesium-137 and strontium-90 capsules Plans to accelerate the Hanford site cleanup call for transferring the capsules to an on-site dry storage facility by 2007. Final disposition has not been determined. Acts to disperse radioactive fission products might be contemplated by terrorists. The radiation from the Hanford capsules is so intense that theft is unlikely; dispersal from the storage facility itself is a concern. DOE estimated that the cost of managing its “other” materials, including the capsules, amounted to under 5 percent of its overall budget for managing excess nuclear materials in FY 2001. Depleted uranium The McConnell Act (Public Law 105-204) required DOE to submit a plan for treating and recycling its DUF6 (completed July 1999) and constructing conversion facilities. In 2002 DOE signed an 8-year contract for constructing and operating the facilities. Final disposition has not been determined Depleted uranium is not a security concern. For FY 2001 DOE estimated that the cost of managing all its excess uranium amounted to about 15 percent of its overall budget for managing excess nuclear materials (DOE, 2000c). Cost of the DUF6 would be less than 15 percent. The recently awarded contract for converting the DUF6 has an estimated value of $558 million (DOE 20002e.) Higher actinides Facility closures require moving or disposing the stored materials. For example, closing the Savannah River Site F-canyon may require disposing stored Am-243 and Cm-244 as high-level waste. Given their relatively small quantities these materials are not attractive for theft. DOE estimated that the cost of managing its “other” materials, including the higher actinides, amounted to under 5 percent of its overall budget for managing excess nuclear materials in fiscal year 2000. 1The Committee on International Security and Arms Control (CISAC) of the National Academy of Sciences (NAS) found that dispositioned DOE plutonium would continue to pose a unique safeguards challenge unless it were rendered approximately as inaccessible for weapons use as the much larger and growing quantity of plutonium in spent fuel from commercial reactors. A series of three reports (NAS, 1994, 1995, 2000) proposed and developed a “spent fuel standard” for comparing the accessibility of dispositioned DOE plutonium with the accessibility of plutonium in spent fuel from commercial nuclear power reactors. 2DOE provided cost estimates for managing excess nuclear materials in its Strategic Approach to Integrating the Long- Term Management of Nuclear Materials (DOE, 2000c) only on a “percent of total” basis. Because excess nuclear materials are managed by several DOE offices, which budget this activity differently, more detailed cost data are not available

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longer- or indefinite-term storage for materials that do not have an identified use but cannot or should not be disposed; disposal in WIPP as transuranic waste; dispersion into high-level waste (HLW) tanks for processing and disposal along with the tank waste; disposal in a geological repository designed for SNF and HLW; and disposal as low-level waste. Uncertainties in waste acceptance criteria to be developed at the disposal sites make many of the planned end points for nuclear materials appear to be outside of DOE’s control. Therefore, there is need and opportunity for research to support both the primary disposition options and the development of alternatives. Setting Priorities in EMSP Nuclear Materials Research A salient characteristic of nuclear materials is their potential for unforeseen, beneficial future uses. There is a tension between the needs of today’s milestone-driven decisions and the planning of a longer-term research program. Currently, for example, meeting programmatic milestones is being treated as a fundamental objective. It appears to the committee that research opportunities are being foreclosed by a perceived need to adhere to programmatic milestones when the programs themselves are changing (DOE, 2002a). Several themes emerged in the course of committee discussions of information gathered during the site visits: Plans and priorities for dispositioning nuclear materials are being set based on a fairly narrow focus, predicated on program schedules for meeting short-term objectives, for example, facility closure and process selection. The significance of the program schedules or even the continuity of these programs is not necessarily commensurate with the consequences of the decisions being made, for example, loss of unique materials. Nuclear materials pose special problems and unique opportunities. For example, handling radioactive materials requires expensive facilities and trained personnel. Some materials present security risks, and all present potential toxicological and radiological risks. On the other hand, some irreplaceable materials may have unforeseen beneficial applications, including basic scientific research.

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It is not easy for any DOE office to formulate clear objectives when multiple stakeholders’ and technical experts’ points of view must be addressed within a realistic schedule and budget. DOE has recognized this challenge and developed a standard for risk-based prioritization, which includes the following high-level objectives (DOE, 1998b): maximize accomplishment of mission, minimize adverse effects upon public health and worker safety, minimize adverse effects upon the environment, maximize compliance with regulations, minimize adverse/maximize desirable socioeconomic impacts, maximize safeguards and security integrity, maximize cost effectiveness, and maximize public trust and confidence. Each of these objectives addresses a particular type of risk, for example, health, safety, environmental, economic. To help accelerate site cleanup, EM has announced that it will prioritize its work to reduce risks (DOE, 2002a). Research to Reduce Uncertainty: The Value of Information In instances where a program objective has been established, uncertainty in how well an alternative approach might meet the objective may diminish the apparent advantages of that alternative. The value of research for reducing the uncertainty associated with the alternative can be quantified by using the tools of decision analysis. Given a carefully developed set of objectives and associated performance measures, a widely accepted way to decide among alternatives is to evaluate their performance with respect to a utility function that maps each alternative’s performance into a number that can be used to rank the alternatives with respect to the decision maker’s objectives and preferences. Once the expected utility of each possible alternative is determined, the alternative with the best utility is chosen for implementation. One purpose of research is to reduce uncertainties in such decision models. Uncertainty can reduce the expected utility of the decision alternatives; therefore, research can, in principle, add value by reducing uncertainty. For example, uncertainty with respect to a safety issue could drive selection of a costly alternative in order to assure mitigation of a hazard that may not be real. Examples include selecting treatments for impure plutonium to preclude pressurization of storage containers (Chapter 3) and conditioning spent fuel to meet yet-to-be-developed repository acceptance criteria (Chapter 4). Elimination of this uncer

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tainty would allow selection of an alternative with a better resource allocation. In general, each key technical uncertainty in a decision analysis represents one or more candidate research projects, perhaps an entire subfield of research. An upper bound on the value of a given research project is quantified as the difference in the expected utility of the preferred alternative, with and without the uncertainty in the corresponding element of the decision analysis. This is called the “value of information” (see, for example, Clemen, 1996). Research to Inform Future Decisions The DOE Office of Science’s mission includes both research and construction and operation of facilities as top-level fundamentals. The four goals are to (1) maintain world leadership in scientific research relevant to energy (including environmental impact); (2) foster the dissemination of results; (3) provide world-class scientific user facilities; and (4) serve as a steward of human resources, essential scientific disciplines, institutions, and premier scientific facilities (Dehmer, 1998). However, even such broad objectives are not sufficient for establishing a research agenda. Any selection process based on these objectives still tends to value a given research project only in the context of individual focused decisions. A more global view is needed to properly value research aimed at generating new knowledge. Moreover, a decision process using only these objectives tacitly assumes the permanence of technical and programmatic decisions made today, without making allowances for new information or changing circumstances. Such an approach devalues longer-term research. However, the committee found that most of EM’s science needs are derived from current program plans and milestones. The EMSP has traditionally accorded high priority to research directed to focused, mission-oriented “gaps” identified by technology coordinating groups at the DOE sites. The committee was guided in its deliberations by considering a different sort of objective, namely the objective of preparing to make more informed decisions in the future. This approach has been formalized in recent papers on risk assessment and decision making, especially in the context of climate change research. There are important analogies between climate change policy and DOE’s management of nuclear materials. Both areas affect future generations as well as the present generation, and neither can be addressed optimally by a static decision model aimed at resolving all issues now, in the face of all of today’s uncertainties. The main point is that there is a better approach than trying to settle policy now, for all time, in light of substantial uncertainties.

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Rather than attempt to model the long-term consequences of current decisions, analysts should use near-term proxy measures to describe the government’s ability to deal effectively with future decisions when they are made. . . . [T]he framework outlined here . . . argues for an adaptive approach that focuses on selecting policies based on near-term consequences, and the learning they will provide to place governments in better positions to address climate change decisions in the future [emphasis added] (Keeney and McDaniels, 2001, p. 992). In other words, for purposes of the near term, one supplements a preliminary set of fundamental objectives with the proxy objective “to position ourselves better to address these same fundamental objectives later on.” This includes fostering intellectual capital, fostering institutional capital, and developing an improved basis for evaluating alternatives or for formulating better ones in the first place. This implies a program of research to position ourselves better in the future, and it declines to presume that current programmatic assumptions should foreclose certain kinds of research (see also NRC, 2003). Framework for the Committee’s Recommendations In the spirit of the aforementioned considerations, the committee has identified the following proxy objectives that, together with the specific DOE programmatic objectives, drive the research recommendations. Develop and maintain intellectual capital. As in any field of science, research on nuclear materials requires special expertise. It is well known that expertise in many relevant subfields is being lost, for example, actinide chemistry. One important dimension of a research program is maintaining (even recovering) expertise in these subfields. Maintain critical facilities. Research with nuclear materials requires special facilities, e.g., for containment and often for remote operations. A substantial investment exists in certain kinds of facilities. This investment will be lost if these facilities are decommissioned. A snapshot of strictly near-term fundamental objectives might not provide a basis for maintaining critical facilities, but a longer-term view might lead to a different conclusion. Keep options open. Preserve unique materials. Certain materials were produced by repeated cycles of high-flux neutron irradiation followed by purification. Lacking an immediate use for these materials, they may simply be designated as waste. It is easy enough to see how irretrievable disposal of these materials rates favor-

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ably in light of a set of objectives that prioritizes minimizing current hazard and “mortgage” costs; but once lost, these materials would be extremely difficult to re-create. Metaphorically speaking, these materials transmute from “waste problem” to “opportunity” depending on the set of objectives being considered. Do not foreclose fundamental research programs just because a current program plan seems to moot the expected results. At some sites, current milestones for disposition of certain materials seem to preclude research into the phenomenology of those materials. This approach seems to base research decisions having long-term consequences on programmatic conditions that are subject to change. Improve the knowledge base. More knowledge supports better evaluation of alternatives. Better alternatives might be forthcoming from an improved knowledge base. EM, charged with cleaning up and closing sites across the complex, for very good reasons is focused on going out of business as soon as possible. Disposing of surplus nuclear materials as waste is the simplest expedient. However, DOE will continue to use and supply nuclear materials. Furthermore, given the fundamental constraints on energy production, there is a real potential for new developments in nuclear power. Maintaining the nuclear material resources in DOE’s current inventory, as well as research investments to expand the knowledge base for their future beneficial application, were overarching considerations for the committee as it developed its research recommendations. Improvements in the knowledge base have downstream potential value that goes well beyond the current EM mission. Conclusions Research activities serve two fundamentally different kinds of objectives. EM’s cleanup objectives require near-term solutions to specific current problems. A second kind of objective is to be better able to address future problems: to be able to formulate, analyze, and implement new alternatives that may be needed to address changing needs or make better use of new information. By more explicitly recognizing this latter objective, which is a proxy for today’s unidentified longer-term needs, the EMSP can strengthen its research planning.