1

Background and Study Task

1.1 MOTIVATION AND REQUEST FOR THE STUDY

In recent years, Congress, the U.S. Department of Energy (DOE), and the private sector have expressed considerable interest in developing and deploying advanced nuclear reactors to augment, and eventually replace, the operating fleet of large light water reactors (LWRs). Much of this interest stems from the potential for advanced reactors and their associated fuel cycles to better support the energy security and low-carbon electricity generation benefits of nuclear energy than existing LWRs because of their abilities, as claimed by their designers and developers, to reduce environmental impact (e.g., via better natural resource utilization, lower waste generation¹); to provide for safer and more proliferation-resistant nuclear energy systems; to increase the economic competitiveness of nuclear energy generation technologies; and, in some cases, to provide energy applications beyond electricity generation (e.g., process heat, desalination). The projected net loss of nuclear generating power in the United States by the middle of this century provides additional motivation for pursuing new and advanced reactor designs. Of the 95 licensed U.S. LWRs operational in mid-2020 (when this study began), five are planned to close by mid-2025, and all will shut down by 2055 if the current licenses are not extended to allow for 80 years of operational life per reactor (Holt, 2021b). As of the end of 2021, 93 LWRs are operational. Almost all LWRs have received license extensions to permit 60 years of operations; several have recently applied and one has been approved for a license extension to 80 years. Only two new LWRs are under construction, both at the Vogtle Electric Generating Plant in Georgia, and these have had delayed start-ups (originally planned for 2016 and 2017)—with one unit expected to be operational in the first quarter of 2023 and the other by the fourth quarter of 2023 (based on information from August 2022; NEI, 2022).

In the Further Consolidated Appropriations Act of 2020 (Public Law 116-94) and the Consolidated Appropriations Act of 2021 (Public Law 116-260), Congress directed DOE to contract with the National Academies of Sciences, Engineering, and Medicine to evaluate these claims, with particular consideration to fuel cycles, waste management, and nonproliferation. The committee’s statement of task is shown in Sidebar 1.1. In response to these congressional requests, the National Academies assembled a committee of experts (referred to as “the committee” in this report) tasked with focusing on those advanced reactors that could be commercially deployed by 2050 and

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¹Resource utilization is typically measured as the amount of natural uranium or thorium fuel used per unit of energy produced by the reactor. Common metrics for evaluating waste generation include the mass, radioactivity, and/or volume of spent nuclear fuel, high-level waste, and/or low-level waste generated per unit of energy produced by the reactor.

on the technologies being investigated by DOE’s Office of Nuclear Energy’s (DOE-NE’s) program, and other relevant programs, such as the Generation IV International Forum and the International Atomic Energy Agency. In its 2021 Strategic Vision, DOE-NE, the sponsor of this study, lists as two of its main goals “enable deployment of advanced nuclear reactors” and “develop advanced nuclear fuel cycles” (DOE-NE, 2021a).

The Nuclear Energy Innovation Capabilities Act of 2017 (NEICA) (Public Law 115-248) defines an advanced nuclear reactor as “a nuclear fission reactor with significant improvements over the most recent generation of nuclear fission reactors.” NEICA states that these improvements may include “(1) inherent safety features, (2) lower waste yields, (3) greater fuel utilization, (4) superior reliability, (5) resistance to proliferation, (6) increased thermal efficiency, and (7) the ability to integrate into electric and nonelectric applications.” This report addresses the potential merits of advanced nuclear reactors regarding waste, fuel utilization, and proliferation resistance, and focuses the safety assessment on the front and back ends of the fuel cycles, rather than on reactor operations. The other potential merits—reactor operational safety² and security, and the contribution of advanced nuclear energy to decarbonizing the U.S. energy system—will be addressed in a separate National Academies study, Laying the Foundation for New and Advanced Reactors in the United States, which is scheduled to conclude in early 2023.

In 2015, prior to the passage of NEICA, Congress directed DOE to conduct a planning study to evaluate “advanced reactor technology options, capabilities, and requirements within the context of national needs and public policy to support innovation in nuclear energy.” The resulting report, Advanced Demonstration and Test Reactor Options Study, was published in 2017 (Petti et al., 2017). It defined advanced reactors as those that use nonwater coolants, “have the potential to expand the energy applications, enhance the competitiveness, and improve the sustainability of nuclear energy,” and may include technology innovations such as

• “higher outlet temperatures than light water reactors (LWRs), which yield enhanced efficiency of electricity generation as well as for a variety of process heat applications;
• enhanced inherent safety, including passive decay heat removal systems;
• advanced fuels (liquid, particle, metallic, ceramic) and cladding enabling high burnup, extensive actinide destruction, and enhanced accident tolerance;
• advanced power conversion systems (Brayton cycle, supercritical CO₂) to improve overall energy conversion efficiency and reduce water usage;
• modular design to shorten construction times and to support phased deployment to allow flexibility in meeting demand; and
• greater degrees of autonomous control to minimize operating cost.”

A team of stakeholders from industry, academia, and government carried out a range of technology readiness assessments to evaluate various advanced reactor concepts on the above criteria. While evaluations of reactor design and deployment criteria fall into the purview of the parallel National Academies study, it is important for this committee to understand DOE’s thinking on promising reactor designs in order to analyze the associated fuel cycles.

In addition to the potential merits of advanced reactors defined in NEICA and Petti et al. (2017), DOE has established criteria and related objectives for its advanced fuel cycle and waste management programs, most notably in the 2014 Nuclear Fuel Cycle Evaluation and Screening—Final Report (NFCE&S) (Wigeland et al., 2014) and the Advanced Research Project Agency-Energy’s Optimizing Nuclear Waste and Advanced Reactor Disposal Systems (ONWARDS) program. With a goal of informing DOE-NE’s research and development priorities, NFCE&S evaluated fuel cycle options against the current LWR once-through cycle based on nine criteria (Wigeland et al., 2014). Six of these criteria are related to potential benefits that could be achieved in implementing an advanced fuel cycle: nuclear waste management, proliferation risk, nuclear material security risk, safety, environmental impact, and resource utilization. The other three criteria focus on challenges associated with deploying a new fuel cycle: development and deployment risk, institutional issues, and financial risk and economics.

The ONWARDS program aims to demonstrate technologies for the back end of the fuel cycle that reduce waste disposal impacts, with an ultimate goal of a 10-fold reduction in waste volume or repository footprint and disposal

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² In some respects, reactor safety considerations are linked to fuel cycle parameters (such as fuel burnup limits).

costs less than $1/MWh (megawatt hour) (Shafer, 2021). The program focuses on technology developments in fuel recycling processes, safeguards, and high-performance waste forms. In March 2022, as this report was being completed, the ONWARDS program had awarded $36 million to 11 programs for such technology development, specifically targeting waste management associated with advanced reactors and fuel cycles (DOE, 2022a).

The committee received briefings on both NFCE&S and the ONWARDS program and considered their criteria and objectives in its analysis. The remainder of this chapter describes the status of U.S. nuclear reactors and fuel cycles to serve as a baseline against which advanced reactor technologies and associated fuel cycle and waste management strategies can be compared, summarizes previous National Academies’ reports relevant for this study’s topics, and provides a roadmap for the structure of the report.

1.2 NUCLEAR FUEL CYCLE DEFINITIONS AND THE BASIS SET OF FUEL CYCLES FOR THIS REPORT

The nuclear fuel cycle involves the passage of nuclear fuel through a series of stages. The front end involves the preparation of the fuel, leading to the service period, in which the fuel is used during reactor operations. The back end involves activities necessary to safely manage, contain, and either reprocess and recycle the fissile iso-

topes remaining in the fuel or directly dispose of spent nuclear fuel. In a 2021 study, the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development (NEA-OECD) (2021) explored the “nuclear fuel cycle options—combination of nuclear fuel types, reactor types, spent nuclear fuels treatments and disposal schemes” being contemplated by countries with active nuclear power programs. The study looked at differing characteristics for both the development and implementation of a particular option, as well as the decision drivers countries face, such as the size of their nuclear program, including research and development (R&D), extended storage and disposal of waste, safety and environmental risks, needed supporting infrastructure, and cost—to name a few. Because of the vast number of options that exist, the NEA-OECD group found it convenient and easier to understand to reduce the fuel cycles to a basis set of only three:

• Open cycle systems (also known as the once-through fuel cycle) use low-enriched uranium in LWRs and dispose of the spent nuclear fuel directly in a deep geologic repository (see Figure 1.1).
• Monorecycle systems involve a single cycle of reprocessing spent nuclear fuel to (1) separate plutonium, which is combined with depleted uranium to produce mixed oxide fuel for use in LWRs; and (2) reprocess uranium, which can be reenriched and used in LWRs, although this is rarely done because a dedicated enrichment cascade is required, as two uranium isotopes are more radioactive and increase the dose rate. High-level radioactive waste from reprocessing (e.g., fission products and minor actinides) and the spent mixed oxide and reprocessed uranium fuels are disposed of in a deep geologic repository.
• Multirecycle systems involve reprocessing spent fuel repeatedly and recycling separated plutonium (and possibly minor actinides, such as neptunium) in fresh fuel. In principle, only high-level radioactive waste from reprocessing (composed of fission products, as well as actinides that are not separated for use in fuel) would need to be disposed of in a deep geologic repository as long as the fuel cycle is active (NEA-OECD, 2021).

This basis set—open cycle, monorecycle, and multirecycle systems—is used throughout the remainder of this report to simplify the discussion of fuel cycles, refined as necessary to address specific technologies. For example, many advanced reactor developers are planning initial implementation of an open fuel cycle for their designs, which use different fuel types and enrichments than the current LWR fleet. LWRs in operation today use either an open cycle or monorecycle system, as further discussed in Chapters 2 and 4. The following section of this chapter summarizes the status of the U.S. nuclear power program that relies on LWRs and the once-through fuel cycle. The multirecycle fuel cycle, which would require introducing advanced reactors into the mix of reactor technologies, is explored in Chapters 3 and 4.

1.3 STATUS OF THE U.S. NUCLEAR POWER PROGRAM

The United States has deployed commercial nuclear power since the 1950s, and as of 2021, nuclear power accounts for approximately 20 percent of U.S. electricity generation. The current commercial nuclear fleet consists entirely of thermal LWRs operating with low-enriched uranium dioxide fuel in a once-through fuel cycle. The LWRs operate on uranium dioxide fuel enriched to 3–5 percent uranium-235 and use light water as the coolant and moderator.³ LWRs typically achieve power outputs of up to 3,800 MWth (megawatts thermal) or up to 1,250 MWe (megawatts electric),⁴ corresponding to a thermal efficiency of 33 percent (DOE, 2015a; Murray and Holbert, 2020). There are two main types of LWRs: pressurized water reactors and boiling water reactors, which differ in method and location of steam production (U.S. NRC, 2020b). In a pressurized water reactor, the heat from the primary coolant loop is transferred to a secondary loop via heat exchangers (referred to as steam generators), in

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³ The moderator is a low–atomic number material that interacts by colliding with fission neutrons to reduce their energy to more efficiently induce the fission reaction with certain fissile isotopes. For example, uranium-235 fissions more easily with thermal neutrons (neutrons with around 0.025 eV [electron volts] of energy).

⁴ Several LWRs achieve higher power outputs; for example, Grand Gulf Nuclear Station in Mississippi has a power output over 1,400 MWe; the Barakah Power Plants in the United Arab Emirates each have a power output of 1,400 MWe; and EPR, with operational plants in China and Finland and planned reactors in France and the United Kingdom, has a power output of 1,600 MWe.

which the water in the secondary loop is transformed into high-pressure steam that drives the electricity generator via a turbine. In contrast, boiling water reactors have only one coolant loop, in which the water coolant absorbs heat from the reactor core, causing it to boil and yielding a steam–water mixture. This mixture then undergoes a separation process to generate pure steam that powers the turbine/generator set to provide electricity. In the United States, about two-thirds of the operating reactors are pressurized water reactors and one-third are boiling water reactors.

All operational nuclear reactors are supported by a fuel cycle, which includes the activities required to fuel the reactor and manage its spent nuclear fuel upon discharge from the reactor. Figure 1.1 depicts the open, or once-through, fuel cycle employed in the United States, with a dashed box around the geologic repository to indicate that none yet exist for spent fuel disposal. For use in an LWR, natural uranium, which contains about 0.7 percent of the only naturally occurring fissile nuclide, uranium-235, has to be enriched to 3–5 percent uranium-235 to provide sufficient fissile material to achieve criticality.⁵ Burnup, another important concept, measures the amount of energy produced by a unit of uranium mass, typically expressed as gigawatt-days per metric ton (GWd/MT) of uranium. Greater enrichment levels can provide for greater burnups.

The first steps to making enriched uranium fuel involve conversion of mined and milled uranium ore (U₃O₈) to uranium hexafluoride (UF₆) gas, a compound suitable for the enrichment process in gas centrifuges.⁶ UF₆ can readily undergo phase changes at temperatures and pressures compatible with relevant industrial processes. It is used in gaseous form during enrichment, in liquid phase for transfer between containers and equipment, and as a solid for storage. The enriched uranium is converted back to an oxide (UO₂) and then fabricated into assemblies of fuel rods that make up the reactor core. (Because of the chemical stability of UO₂, it is desirable to eventually deconvert UF₆ back to UO₂ prior to disposal of the enrichment tails.) Irradiation of the fuel in the reactor for 4–6 years depletes the fissile uranium in the assemblies to a point at which the fuel is no longer suitable for power production; the spent fuel is transferred into a water-filled pool (i.e., the spent fuel pool), where it will be stored for several years.

The spent uranium oxide (UOX) nuclear fuel⁷ discharged from a reactor mostly contains actinides and fission products. See Sidebar 1.2 for information about some of these radionuclides and their relative masses prior to and following irradiation of 1 MT of uranium (as UOX) enriched at 3.3 percent to a burnup of 33 GWd/MT. A burnup of 33 GWd/MT is typical of much of the spent fuel in the U.S. inventory; however, more recent spent fuel has a burnup of over 45 GWd/MT because of the practice of moving toward higher burnup, as well as enrichment of up to 4.8 percent (WNA, 2021c). Higher burnup allows utilities to extract more power from the fuel before replacing it, which translates to longer operating periods between refueling and the use of fewer fuel assemblies (U.S. NRC,

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⁵ Note that some accident-tolerant fuel designs being considered for use in LWRs have uranium-235 enrichments of up to 10 percent (U.S. NRC, 2020a).

⁶ Gaseous diffusion using UF₆ was the first technology used commercially for uranium enrichment. As the more efficient gas centrifuge technology became available, it replaced gaseous diffusion.

⁷ This report uses the term spent nuclear fuel for all fuel discharged from a nuclear reactor. Some reports (e.g., NEA-OECD, 2021) differentiate between spent fuel, if the fuel will be disposed as waste, and used fuel, if the fuel will be recycled.

2018a). As a result of its radioactive decay, spent fuel releases heat and is stored in spent fuel pools after discharge from the reactor to help dissipate this heat.

Initially, cooling pools at reactors were sized with the expectation that the spent fuel would be reprocessed. Since reprocessing never became a realistic option in the United States and a repository is not yet available, reactor operators have been faced with the need for additional storage capacity for spent fuel. Initial pool capacity expansion was achieved with the use of neutron flux traps and by reracking operations, but there are limits to these approaches. Dry cask storage technology was developed in the 1980s to cope with the pool capacity limitations, allowing spent

fuel to be dried and transferred to specially designed casks after about 5 years of water cooling. Dry storage casks manage decay heat from the spent fuel through a combination of conduction, convection, and radiation to maintain the internal environment of the cask within design specifications. Dry cask storage has the further advantage of freeing up space in a cooling pool to accommodate freshly discharged spent fuel from the reactor. At present, most wet and dry cask spent fuel storage is carried out at the reactor site pending eventual long-term disposal, likely in a deep-mined geologic repository (BRC, 2012; U.S. NRC, 2017). As there is currently no long-term disposal available for spent fuel in the United States, more than 86,000 MT of spent fuel are currently in wet or dry storage at 75 operating or shut-down reactor sites in 33 states; this figure grows by 2,000 MT per year (GAO, 2021a).

1.3.1 Status of the Front End of the Fuel Cycle in the United States

The front end of the fuel cycle includes the mining or extraction of uranium ore, milling of the uranium ore to produce U₃O₈, chemical conversion to UF₆, enrichment to increase the content of uranium-235, fabrication into fuel assemblies of UO₂, and delivery of the assemblies to the reactor (U.S. NRC, 2017). A 1,000-MWe LWR operating at 100 percent capacity requires approximately 200 MT of natural uranium per year. The majority of U.S. uranium is imported to the United States from Canada and Australia (Larson, 2019; MIT, 2011). Notably, imports from Russia are limited strictly and currently represent about 16 percent of U.S. demand. In 2019, domestic production of uranium concentrate totaled 0.17 million pounds (approximately 80 MT), a nearly 90 percent decrease from the previous year (EIA, 2020). No conversion facilities are currently operating in the United States; the primary sources of UF₆ imports are Canada and the United Kingdom (Larson, 2019). However, the Honeywell conversion facility in Illinois, which halted operation in 2018, announced plans to come back online in 2023 (Patel, 2021). The sole U.S.-based enrichment facility, which is foreign owned and operated by Urenco USA, provides about one-third of the enriched UF₆ required for U.S. reactors, with the remainder being imported from the Netherlands, Germany, Russia, and the United Kingdom (Larson, 2019). A commercial LWR requires about 20 MT of fuel per year, and three facilities capable of fabricating LWR uranium oxide fuel currently operate in the United States to meet the fueling needs of commercial U.S. reactors: Global Nuclear Fuel-Americas in Wilmington, North Carolina; Westinghouse Columbia Fuel Fabrication Facility in Columbia, South Carolina; and Framatome, Inc., in Richland, Washington (MIT, 2011; U.S. NRC, 2020c).

1.3.2 Status of the Back End of the Fuel Cycle in the United States

The back end of the fuel cycle encompasses the management of spent fuel, including interim storage, waste transportation, final geologic disposal, and—in certain countries (see Chapter 2 and Appendix H for more information)—reprocessing (chemical separation techniques) to separate fissile materials from other spent fuel constituents. In the initial stages of its commercial nuclear power development, the United States intended to establish a fuel cycle based on recovering the plutonium present in the LWR spent fuel, using reprocessing, and fueling a planned fleet of fast neutron spectrum (or simply “fast”) reactors. The U.S. intent, shared by many other international programs, originated from the perception that natural uranium resources, especially the supply of uranium-235, were scarce compared with the projected large number of LWRs that would be required to meet anticipated global electricity demand. However, as will be further discussed in the next chapter, several factors—including technical challenges, nonproliferation violations, nuclear accidents, changes in electricity market conditions, unfavorable economics of reprocessing, and expanded natural uranium resources—have resulted in abandonment of the plutonium-fueled fast reactor technology option in the United States and many other countries and have limited progress in the few countries that have continued to pursue such a program. Because the United States does not currently have any centralized interim spent fuel storage facilities or reprocessing plants, nor a deep geologic repository for final disposal, spent nuclear fuel remains at nuclear power plant sites, making at-reactor long-term dry storage the de facto endpoint of the current U.S. fuel cycle.

The Nuclear Waste Policy Act (NWPA) (Public Law 97-425) set the ultimate strategy for commercial spent fuel as disposal in a deep geologic repository, and the 1987 Amendments to that act (Public Law 100-203, Part E) selected Yucca Mountain, Nevada, as the only site to be examined for disposal. The U.S. Nuclear Regulatory Commission (U.S. NRC) developed regulations for waste disposal at Yucca Mountain based on radiation dose standards set by the U.S. Environmental Protection Agency (EPA). Under the NWPA, DOE committed to starting the transport of spent fuel from storage at nuclear power plants to a geologic disposal site by 1998, but it has missed that deadline by nearly 25 years so far. In 2008, DOE submitted a license application to the U.S. NRC to construct the Yucca Mountain repository. Although DOE filed a motion in 2010 to withdraw the application, it was denied by the Licensing Board, which, supported by the District of Columbia Court of Appeals in 2013, instructed the U.S. NRC to complete the license review. In 2015, U.S. NRC staff completed the Safety Evaluation Report, which found that the license application met regulatory requirements, pending additional licensing steps. Nonetheless, DOE terminated its technical support for the statutorily required Office of Civilian Radioactive

Waste Management, which was in charge of managing spent fuel and siting a geologic repository. Congress has not appropriated any funds to move forward on licensing for Yucca Mountain since 2010.

The 2012 Blue Ribbon Commission on America’s Nuclear Future (BRC) identified several factors contributing to the delays and challenges in establishing a repository at Yucca Mountain. These included a perceived lack of technical and scientific considerations behind site selection, opposition from the state of Nevada and its citizens, unrealistic deadlines set by DOE, and inflexibility in the process and guidelines established by the NWPA Amendments (BRC, 2012). For future attempts to site a nuclear waste disposal facility, at Yucca Mountain or elsewhere, the BRC recommended a consent-based, transparent, adaptable approach involving phased decision making and establishing a safety case for the site (BRC, 2012). In 2018, the Steering Committee on the Reset of America’s Nuclear Waste Management Strategies and Policies similarly recommended a consent-based siting approach for establishing a geologic repository, emphasizing the need to collaborate with local communities and to allow for flexibility throughout the process (Reset Steering Committee, 2018). Both the BRC and Reset reports recommended the establishment of a new, sole-purpose, independent waste management and disposal organization but differed on the form of such an organization. In Chapter 5, the committee further examines this concept and develops its related findings and recommendations for nuclear waste management and disposal. As of the writing of this report, political opposition to Yucca Mountain remains, and there are no actionable plans to site a repository in the United States.

1.4 RELATED NATIONAL ACADEMIES STUDIES

The National Academies have published a number of reports on issues related to this study, including advanced nuclear energy (fission and fusion), spent fuel and high-level waste treatment, nuclear waste management, and nonproliferation. The committee considered the results of these prior reports in its analysis. Brief summaries of select reports published in the past 30 years, including major findings, recommendations, and conclusions related to this study, are presented below.⁸ The National Academies have a long history of providing advice to the federal government on nuclear waste management and disposal, dating back to the seminal 1957 report The Disposal of Radioactive Waste on Land, which identified deep geologic disposal as the most promising option for safe disposal of radioactive wastes. The collection of summaries below includes only several of the numerous National Academies studies on the topic of nuclear waste management; a more complete list can be found in Appendix F.

As mentioned above, in parallel to this study, a separate National Academies committee is evaluating “opportunities and barriers to the commercialization of new and advanced nuclear reactor technologies in the United States over the next 30 years as part of a decarbonization strategy.” That study, with an anticipated conclusion in early 2023, focuses on the technical viability of advanced reactor technologies, including their potential use for nonelectricity applications, as well as the economic, regulatory, market, and societal challenges for commercialization. The full statement of task for that study is reproduced in Appendix I.

Bringing Fusion to the U.S. Grid (2021)

This report identifies the key goals and innovations needed to develop a fusion pilot plant in the United States. Considering input from electric utilities, the committee recommended that, for fusion to play a role in the transition to a low-carbon electricity system, net electricity production from a fusion pilot plant should occur in 2035–2040. Meeting that aggressive timeline, the committee concluded, would require urgent investments by both DOE and the private sector, possibly including public–private partnerships. To that end, the committee recommended the creation of national teams with representatives from industry, academia, and national laboratories to develop conceptual pilot plant designs and technology roadmaps.

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⁸ All of these National Academies reports are available for free at https://nap.nationalacademies.org.

Improving the Assessment of the Proliferation Risk of Nuclear Fuel Cycles (2013)

This study analyzes the use of technical assessments of proliferation risk to (1) inform R&D decisions about nuclear fuel cycles and nonproliferation policy and (2) improve communication of those decisions to stakeholders and the public. Because predefined frameworks had previously been poorly implemented and do not address extrinsic factors that can change over time, the committee recommended considering a probabilistic risk assessment approach as an alternative. On proliferation considerations for future fuel cycle decisions, the committee recommended “that fuel cycle R&D decisions include proliferation resistance (rather than proliferation risk) as one factor among others (such as cost and safety) to guide those decisions” and “that DOE-NE and NNSA [National Nuclear Security Administration] jointly decide upon a set of high-level questions comparing the proliferation resistance of proposed future fuel cycles to the current once-through fuel cycles to determine as early as possible in their development whether the former have significantly different intrinsic proliferation resistance (either for the better or for the worse).”

America’s Energy Future: Technology and Transformation (2009)

This study evaluates current (2009) and projected technologies for energy supply, storage, and end use, with particular consideration of times to readiness for deployment; R&D challenges; estimated costs and performance; and impacts on environmental, economic, policy, social, and national security factors. Nuclear energy is covered in Chapter 8 of that publication. Regarding advanced fuel cycles, the report finds

Internationalization of the Nuclear Fuel Cycle: Goals, Strategies, and Challenges (2009)

Produced by a joint committee of the U.S. and Russian Academies of Sciences, this study analyzes the possible internationalization of the nuclear fuel cycle to meet nonproliferation and fuel assurance goals. Finding that uranium enrichment and spent fuel reprocessing are the primary concerns for producing direct-use materials, the report recommends that (1) countries currently providing nuclear fuel should ensure a stable supply to disincen-tivize other nations from developing enrichment capabilities and (2) the international community should provide adequate storage capacity and/or reprocessing services for spent fuel to limit the spread of reprocessing technology. Furthermore, the committee recommends that development of new reprocessing technologies should occur in parallel with assessments of the technologies’ costs and proliferation risks, that R&D should be performed on advanced safeguards and security technologies, and that “spent fuel should only be reprocessed when its constituents are needed for fuel, or when reprocessing is necessary for safety reasons.”

Review of DOE’s Nuclear Energy Research and Development Program (2008)

This study evaluates program goals and plans for DOE-NE and recommends policies and research activities to “advance NE’s mission of securing nuclear energy as a viable, long-term commercial energy option to provide diversity in energy supply.” The report focuses on six activities: Nuclear Power 2010, the Generation IV Program, the Nuclear Hydrogen Initiative (NHI), the Advanced Fuel Cycle Initiative (AFCI), the Global Nuclear Energy Partnership (GNEP) program, and DOE-NE’s collaboration with Idaho National Laboratory (INL). The committee made recommendations related to each program and prioritized the activities based on its judgment of how each supports DOE-NE’s overall mission. High priority was given to the Nuclear Power 2010 program and university infrastructure support; medium priority was given to Generation IV, NHI, AFCI, and INL programs; low priority was given to facility deployment in GNEP. The committee further recommended,

It should be noted that two committee members provided a dissenting opinion on the recommendations for pursuing a reprocessing and fast reactor R&D program under ACFI and for DOE having a role in commercializing fuel cycle technologies.

Going the Distance?: The Safe Transport of Spent Nuclear Fuel and High-Level Radioactive Waste in the United States (2006)

This study analyzes technical and societal concerns for the transportation of spent nuclear fuel and high-level radioactive waste (SNF/HLW) in the United States, in the context of federal plans to develop a permanent geologic repository at Yucca Mountain and a commercial interim storage facility in Utah. The committee found that, while there are no fundamental technical barriers to safe transport, there may be social and institutional barriers, and the social risks present a challenge to the implementation of an SNF/HLW transportation program. Transportation packages generally provide a robust barrier to radionuclide release, but extreme accidents like long-duration fires could compromise their effectiveness. Except in these rare extreme accident scenarios, the radiological health and safety risks of SNF/HLW transportation are low. Based on its findings, the committee recommended that

• U.S. NRC perform additional analysis of long-duration fire scenarios and implement controls and restrictions on shipments based on the results;
• full-scale testing of transportation packages continue;
• transportation planners (1) identify and mitigate potential hazards along transportation routes that could lead to extreme accidents and (2) establish mechanisms to gather information and advice about social risks;
• the U.S. Department of Transportation ensure that designated shipment routes comply with regulatory requirements;
• DOE fully implement its decision to ship SNF/HLW to the repository by rail on dedicated trains and identify and publicize its preferred transportation routes;
• DOE and commercial spent nuclear fuel owners negotiate to ship older fuel first to a repository or interim storage facility; and
• DOE and Congress examine organizational changes to DOE’s SNF/HLW transportation program and consider as options (1) a quasi-independent office within DOE, (2) a quasi-governmental corporation, or (3) a fully private organization.

The committee also notes that, given its lack of access to classified information, it did not examine malevolent acts against SNF/HLW shipments; however, it recommended an independent analysis of these transportation security issues.

Monitoring Nuclear Weapons and Nuclear-Explosive Materials: An Assessment of Methods and Capabilities (2005)

This report analyzes approaches in transparency and monitoring that can be used to verify nuclear weapons and nuclear-explosive materials. The report defines nuclear-explosive materials as (1) a mixture containing uranium-235 and uranium-238 with more than 20 percent uranium-235, (2) a mixture of uranium-233 and uranium-238 with more than 12 percent uranium-233, or (3) a mixture of plutonium isotopes with less than 80 percent plutonium-238; but it also notes that “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.” The study concludes that technical tools are available to improve transparency and monitoring measures throughout the nuclear weapon life cycle and for nuclear-explosive materials and that they can be implemented

under existing international agreements to decrease uncertainties in assessing foreign stockpiles of nuclear weapons and materials.

One Step at a Time: The Staged Development of Geologic Repositories for High-Level Radioactive Waste (2003)

This report advises DOE on staged implementation of repository development throughout the construction, operation, closure, and postclosure phases and examines the associated programmatic, safety, security, institutional, regulatory, and societal issues. The study analyzes two approaches to staging: linear staging, in which there is “a single, predetermined path to a selected, well-defined endpoint, where stages are defined principally as milestones at which costs and schedules are reviewed and modified as necessary,” and adaptive staging, which provides a reference framework for the project but maintains flexibility using a deliberate decision-making process between stages “to guide the implementer in identifying program improvements with respect to, for instance, safety, environmental impacts, costs, and schedules.” The committee recommended that the adaptive staging approach be used, both for a generic repository program and specifically for the Yucca Mountain case, believing it to be more effective and less error-prone than linear staging. The committee further recommended that any repository program should (1) reevaluate safety at each decision point in a structured decision-making process; (2) use learning opportunities from in situ testing (e.g., in pilot, test, or demonstration facilities); (3) continually and actively incorporate learning during the repository operation period; and (4) incorporate independent technical advice and stakeholder input via a technical oversight group and stakeholder advisory board, respectively.

Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges (2001)

This report addresses the questions of whether and when to implement geologic disposal of high-level waste, aiming to help policy makers with decision making and inform the interested public. The committee found that monitored surface storage and geologic disposition are feasible options to handle the inventory of high-level waste, with the latter being the only long-term solution. Furthermore, the greatest barrier to waste disposition is lack of public support; individual countries have to decide whether, when, and how to move forward with a repository; and successful approaches involve stepwise processes, transparent and participatory decision making, and international cooperation. The committee recommended the formation of national organizations responsible for management of high-level waste that address technical and safety issues with project development; involve the public in decision making; develop stepwise programs with realistic alternative options; engage in international cooperation on standards and strategies; and perform integrated, comprehensive, and risk-based analyses to ensure the safety and security of waste management facilities.

Electrometallurgical Techniques for DOE Spent Fuel Treatment: Final Report (2000)

This study evaluates the technical viability of electrometallurgical processing of spent nuclear fuel, focusing on the treatment of sodium-bonded spent fuel from the Experimental Breeder Reactor-II (EBR-II). This 10th and final report in a series of studies on the topic analyzes waste streams and waste form options for electrometallurgically treated EBR-II fuel; evaluates the EBR-II Spent Nuclear Fuel Treatment Demonstration Project on criteria related to process, waste streams, and safety; and recommends postdemonstration activities if the same treatment is used for the remaining spent fuel. The committee noted no technical barriers to electrometallurgical treatment of EBR-II spent fuel, but emphasized that waste form qualification would be required before applying the process to other spent fuel inventories. The committee recommended, “If the DOE decides to treat the remaining sodium-bonded spent fuel inventory and the waste form qualification efforts are successful, the required equipment upgrades and facility modifications should be adequately funded to ensure that treatment can be completed in a reasonable time and at a reasonable cost.”

Nuclear Wastes: Technologies for Separations and Transmutation (1996)

This report evaluates separation and transmutation systems as alternatives to the once-through fuel cycle and reviews options for processing high-level waste from defense programs. It considers the technical feasibility, ability for system integration, economics and financing methods, effect on repository capacity, proliferation risk, public acceptance, health impacts, and R&D needs of three transmutation concepts: (1) an LWR with a thermal neutron spectrum to transmute transuranic elements and some fission products; (2) an advanced liquid metal reactor with a fast neutron spectrum as a transuranic burner; and (3) an accelerator-driver subcritical nuclear reactor to reduce transuranic waste to Class C or lower levels. The committee reached four primary conclusions:

• Implementing any of these advanced separation and transmutation systems would not eliminate the need for a geologic repository for spent LWR fuel.
• The once-through LWR fuel cycle for commercial reactors should be continued.
• The time period for fuel retrievability should be extended to facilitate future implementation of alternative fuel cycle strategies.
• The United States should perform “a sustained but modest research and development program” on separation and transmutation technologies for spent fuel and defense waste to improve their cost effectiveness for potential future deployment.

Technical Bases for Yucca Mountain Standards (1995)

Mandated in Section 801(a)(2) of the Energy Policy Act of 1992, this study provides advice to EPA on the scientific basis for standards for deep geologic disposal of high-level radioactive waste at Yucca Mountain. The committee recommended the following:

• EPA should use an individual risk-based standard, rather than a dose-based standard, to limit negative health impacts from radiation release.
• A critical-group approach should be used to set the Yucca Mountain standards, where the group represents a relatively homogeneous set of individuals who would face the highest risk upon radiation release.
• The compliance assessment should be performed for the time of peak risk within the timeline of geologic stability of the repository, or around 1,000,000 years.
• EPA should require the estimated risk for a future intrusion scenario be no greater than the risk limit used for an undisturbed repository.

The committee also notes that the study only addressed the scientific basis for a repository standard and not the social, economic, and political aspects that must also be considered.

Nuclear Power: Technical and Institutional Options for the Future (1992)

Under the premise that nuclear power should continue to contribute to U.S. electricity supply, this report examines institutional and technological options for achieving that goal. The committee attributed the slowed growth of nuclear generation in the United States to reduced electricity demand; high cost; regulatory uncertainty; and public concerns around safety, economics, and waste disposal. It presented the following summary:

The report also analyzes several advanced reactor technologies on criteria related to “safety in operation, economy of construction and operation, suitability for future markets, fuel cycle and environmental considerations, resistance to diversion and sabotage, technology risk and development schedule, and amenability to efficient and predictable licensing.” The committee concluded that LWRs (both large evolutionary and midsized advanced designs) have the greatest potential to be cost effective. It recommended that Canadian Deuterium Uranium reactors, safe integral reactors, process inherent ultimate safety reactors, and modular high-temperature gas reactors should be low priorities for federal funding and that liquid metal reactors should receive high priority for long-term development despite their limited near-term market potential.

1.5 REPORT ROADMAP

To guide its response to the statement of task (see Sidebar 1.1), the committee developed several framing questions (see also Table 1.1 for a roadmap for the key topical areas covered in each chapter):

• What are the merits and viability of fuel cycle options for existing commercial light water reactors?
• What are the proposed merits of advanced reactors and fuel cycles? What are the relevant metrics to use in assessing those proposed merits to determine viability?
• What factors have the greatest impact on the viability of advanced reactors and fuel cycles?
• What factors affect having the requisite infrastructure for supplying the various advanced fuel types and for producing high-assay low-enriched uranium (HALEU), which almost all advanced reactor designs are projected to require?
• Do advanced reactors require reprocessing to achieve the proposed benefits related to waste reduction?
• Do advanced fuel cycles reduce the waste management problem, and if so, how?
• What will be the constituents of waste streams (including high- and low-level wastes, including Greater than Class C wastes) from advanced reactors, and how will these wastes impact storage, transportation, and disposal?
• What would be the costs of developing the required front- and back-end processes to support advanced reactors and fuel cycles?
• What are the safety considerations and risks for the front- and back-end processes required to support the development of advanced reactors and fuel cycles?
• What are the proliferation risks and security risks of advanced reactors and fuel cycles compared with the baseline once-through fuel cycle with LWRs?

These questions are addressed in Chapters 2–6 of the report, which is organized as follows:

Chapter 1 (this chapter) provides the background on the study request, sets the baseline for the current and projected status of the commercial U.S. nuclear power program, summarizes prior related work from the National Academies, and provides a roadmap for the report.

Chapter 2 considers the merits and viability of fuel cycle options for existing commercial reactor technologies. Beginning with an overview of the global development of nuclear power, including the initial rationale for development of fast breeder reactors, the chapter describes types of nuclear fuel cycles and examines various front- and back-end processes applicable to LWRs, with particular focus on the once-through and monorecycling fuel cycles.⁹ The chapter also compares national policies related to nuclear fuel cycles, focusing on the experiences and lessons learned of France and the United States, the world’s two leading nuclear power producers.

Chapter 3 describes the status and outlook for the advanced reactors under development. It provides background on the Generation IV International Forum’s multinational work on six advanced reactor designs and details

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⁹ The committee highlights that the U.S. House of Representatives’ Appropriations Committee initially requested a separate report on this topic but agreed at the first information-gathering meeting that the committee could include this task within this integrated report on advanced reactors and fuel cycle options.

U.S. efforts, focusing on DOE-NE’s programs, to support the development of advanced reactors and associated fuel cycles, including the policy, economic, and regulatory factors for this development.

Chapter 4 examines the developments needed in the front and back ends of the fuel cycle to support potential deployment of advanced reactors and production of their associated fuel cycles and discusses safety and cost aspects of advanced fuel cycles.

Chapter 5 addresses the waste management and disposal options for three representative classes of advanced reactors: high-temperature gas-cooled reactors, sodium-cooled fast reactors, and molten salt reactors. In particular, it examines unique waste streams that would arise from these advanced reactors and their impact on storage, transportation, and geologic disposal.

Chapter 6 assesses the nonproliferation and security risks of fuel cycles associated with advanced nuclear reactors compared with the once-through cycle with LWRs.

Several key topical areas appear in multiple chapters of the report, as outlined in Table 1.1.

The appendixes provide brief biographies of the committee and staff (Appendix A), descriptions of the information-gathering meetings (Appendix B), a list of the acronyms and abbreviations (Appendix C), information on waste classifications (Appendix D), technical information on the flow sheets of representative advanced reactors and selected nuclear fuel cycle options (Appendix E), a list of National Academies reports on waste management (Appendix F), information on reprocessing and geologic disposal of TRistructural ISOtropic (TRISO) fuel (Appendix G), information on reprocessing and recycling practices in other countries (Appendix H), and the statement of task for parallel National Academies’ study Laying the Foundation for New and Advanced Nuclear Reactors in the United States (Appendix I).