Feature pubs.acs.org/est
The Growing Problem of Stranded Used Nuclear Fuel William M. Alley*,†,§ and Rosemarie Alley‡ †
National Ground Water Association, 601 Dempsey Road, Westerville, Ohio 43081, United States 3195 E. Victoria Drive, Alpine, California 91901, United States recent NRC draft generic environmental impact statement on waste confidence includes the possibility of indefinite surface storage in the event that a geologic repository never becomes available.5 While we focus on used fuel from commercial reactors, highlevel radioactive waste from the nuclear weapons program also is destined for deep geologic disposal, as is vitrified high-level waste from the former reprocessing plant at West Valley, New York.6 Finally, geologic disposal is required to address the nonproliferation risks from separated weapons plutonium, after being irradiated as mixed oxide (MOX) fuel.7 Advanced fuel cycle technologies and reprocessing potentially can reduce the volume, heat, and toxicity of these wastes, By 2050, almost all U.S. nuclear reactors will have reached their yet a geologic repository will be required for all fuel cycles. 60 year maximum expected life. Many will shut down sooner. Advanced fuel cycles also continue to be stymied by economic With no assurance that the current approach for finding a and technical challenges, and are decades away from geologic repository or interim storage sites will succeed, used commercial implementation. Given these factors, virtually nuclear fuel could be stranded indefinitely at more than 70 sites every expert panel having studied the problem has concluded in 35 states. Societal discussions about the future of nuclear that geologic disposal efforts should not be delayed by the waste should be framed in terms of the relative risks of all promise of future unproven technology.1,8 alternatives. We review and compare onsite storage, interim The current stalemate affects prospects for nuclear energy to storage, and a geologic repository, as well as how these help meet the world’s growing energy needs while combating alternatives are presented to the public. climate change. It is increasingly difficult to make the case for a INTRODUCTION new nuclear plant when the waste from the last plant has nowhere to go. There are 10 decommissioned nuclear power plants in the U.S. 1 where the used (spent) fuel remains stranded onsite. In 2013, ONSITE STORAGE operators of three additional nuclear plants announced permanent shutdowns. By 2050, virtually all U.S. commercial Two options are available for storing used fuelwet storage in nuclear reactors will have reached their 60 year maximum pools and dry storage in casks. During the first five years after expected life. discharge from a reactor, used fuel assemblies require active In 2009, after decades of work and over $10 billion spent, the cooling in pools to prevent damage to the fuel. These pools are Obama administration announced that it would terminate the increasingly packed, as a result of the nuclear waste backlog. By nation’s only proposed repository for used nuclear fuel and 2017, the used fuel pools at all but one site are expected to be at other high-level waste at Yucca Mountain, Nevada. In August capacity.9 2013, a federal court ordered the Nuclear Regulatory Gradually, used fuel is being moved to dry casks. While there Commission to complete its review of the Yucca Mountain has been considerable debate about the risks of increasingly license application,2 but the project remains mired in packed pools,10,11 less attention has been given to the risks of indefinite onsite storage in dry casks. controversy. Dry casks typically consist of a metal canister surrounded by Even if a geologic repository opened tomorrow, it would take a concrete overpack. The canisters are loaded underwater in the decades to move all of the used fuel to the repository.3 The storage pool, the water is pumped out, and the canister is filled track record for transporting radioactive wastes is good,4 yet with helium to prevent degradation by oxidation. Lids are any large-scale plan for moving used nuclear fuel will be a flash bolted or welded on. The canister is then transported to an point for opposition. Even under the best of circumstances, it outdoor concrete storage pad where it is loaded into the will take a long time to develop coordination among states of concrete overpack. Fully loaded, each cask weighs 150 tons or travel routes, security, emergency preparedness, safety more. Natural convection through vents in the concrete or via inspections, monitoring of shipments, and public information. cooling fins on bolted metal casks provides passive cooling by It is likely that within a few decades used nuclear fuel will be ambient air. stranded indefinitely at more than 70 sites in 35 states (Figure 1). The Nuclear Regulatory Commission (NRC) is evaluating the possibility of onsite storage for as long as 300 years.1 The Published: January 17, 2014 ‡
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Figure 1. Used nuclear fuel storage in metric tons of heavy metal (MTHM) in each state at the end of 2012. Three states (Illinois, Pennsylvania, and South Carolina) collectively have more than one-quarter of the used fuel. Data from Nuclear Energy Institute.
The confidence in dry casks rests on their passive and robust nature, studies of individual components, and a full-scale study that opened and examined a 15-year old dry cask containing low burn-up fuel.12 In recent years, improvements have been made in fuel technologies that have allowed plant operators to achieve higher burn-up levels, almost doubling the amount of energy captured. The Nuclear Waste Technical Review Board, a presidentially appointed oversight group, concluded that the technical basis for extended (>60 year) dry cask storage of today’s high burn-up fuel is not well established and that several degradation mechanisms require more study.13 Among these, high burn-up fuels may result in the fuel cladding becoming brittle with time.14 After the shutdown of Yucca Mountain, the Electric Power Research Institute initiated an R&D program investigating key issues with extended storage.15 Meanwhile, placement of used fuel in dry casks is well underway with more than 1700 casks in 34 states at the end of 2012.5 Dry casks can play an important role as part of a responsible nuclear waste disposal program, but open-ended onsite storage raises concerns. The limited ability to monitor conditions within the sealed canisters becomes problematic in the long term, particularly with respect to fuel retrievability. Thus, new technologies for monitoring the interior of dry casks are under development.16 Questions also remain about how the used fuel could be removed for inspection or the casks changed out, if problems develop after the pools are gone. The marginal cost of storing used fuel on a site with ongoing nuclear operations is relatively low, because most of the storage costs can be integrated with existing site operations. However, at sites with no current nuclear operations, the annual cost of used fuel storage is about $8 million per site.17
Ideally, an integrated plan for storage, transportation, and disposal would be laid out in advance. Design of the canisters would account for allowable canister size and thermal loads for disposal; however, these features cannot be determined without knowing the specific requirements of the geologic repository. Dual-purpose casks are licensed for both storage and transportation of nuclear waste, although their large size may pose problems for direct disposal with respect to factors such as criticality and thermal load. Storage-only casks, which are not suitable for transportation, will require repackaging prior to shipment or special exemptions from the NRC. Eventually, there is another crucial issue. After a century or so, the used fuel’s radioactivity will diminish to where it no longer presents a significant barrier to the plutonium.1,8 Thus, extended surface storage presents an increasing nuclear proliferation risk. A substantive analysis comparing the risks of extended onsite storage with those of a geologic repository has never been done, although a draft generic environmental impact statement recently has been completed that provides some progress in this direction.5 In 2007, the Nuclear Regulatory Commission conducted a pilot study to develop a methodology for risk assessment of dry cask storage.18 The pilot study estimated very low risk. In summary, while the current risks of dry casks appear to be low, today’s stranded waste could result in significant long-term problems for our descendants. Storing used fuel at decommissioned sites is costly. In addition, the lack of a geologic repository affects the ability to develop an integrated plan for storage, transportation, and disposal, resulting in future costs for repackaging and additional risk. 2092
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Table 1. Key Advantages and Disadvantages of Yucca Mountain and Three Alternate Rock Types for Disposal of High-Level Nuclear Waste rock type
key advantages
key disadvantages
Yucca Mountain unsaturated tuff
relative ease of retrievability, arid/semiarid climate, remote federal lands, closed basin, lack of mineral deposits, stable mining, high thermal conductivity, zeolites for sorption
tectonically active area, oxidizing environment, fractured rock difficult to characterize
crystalline rock (granite)
lack of mineral deposits, stable mining, thermally stable, widespread occurrence
difficult to characterize transmissive fractures at repository scale, weak sorption/diffusion
shale
very low permeability, high sorption capacity, self-sealing
potential gas buildup, mining challenges, potential for permeable faults, relatively poor heat transfer
salt
absence of flowing water, very low permeability, self-sealing, high thermal conductivity
effects of heat on moisture movement, difficult to retrieve wastes, potential gas buildup, risk of future drilling for resources (oil, gas, potash), low sorption capacity
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INTERIM STORAGE In 1996, the Nuclear Waste Technical Review Board concluded there were no compelling technical reasons for moving commercial used fuel to a consolidated interim storage facility.19 The Board viewed the risks to be essentially the same for at-reactor and interim storage. With pressure continuing to build from the current impasse in licensing a geologic repository, interim storage has become more appealing.1,20 The U.S. Department of Energy proposes to have a “pilot” interim storage facility in operation by 2021 to store used fuel from decommissioned reactors. A larger interim storage facility is planned for operation beginning in 2025.21 Interim storage has several key advantages. The federal government could take charge of the waste, thereby reducing the lawsuits by utilities after the government failed to honor its commitment to begin taking charge of used fuel by 1998. The waste could be moved from populated areas. An interim site would reduce the cost and security burdens of onsite stranded waste. In addition, proponents of nuclear energy could claim progress with at least some aspect of nuclear waste disposal. Yet is interim surface storage any more possible, or palatable, than geologic disposal? Would it undermine the search for a geologic repository? What are the risks of moving the waste twice? And how interim is interim? Interim storage is not a new idea.22 In the early 1970s, the Atomic Energy Commission (AEC) proposed constructing a surface storage facility at one or more existing nuclear sites to temporarily store high-level waste while other options were pursued. The AEC was forced to back down when environmental groups argued that the storage facility could easily become a de facto repository. In 1982, the Nuclear Waste Policy Act (NWPA) provided for development of a long-term “monitored retrievable storage” facility. The community of Oak Ridge, Tennessee expressed interest until statewide opposition shut it down. The 1987 Amendments to the NWPA established a Nuclear Waste Negotiator who made every effort, but failed to find a volunteer for an interim storage site. A handful of communities expressed interest, only to be blocked by their governors. In the 1990s, the Skull Valley Band of Goshute Indians volunteered to host an interim facility on its reservation in Utah. After more than 15 years of legal battle with the state and the Department of the Interior, the NRC-approved site was abandoned in 2012. Lack of progress toward a geologic repository makes finding an interim storage site even more difficult. The NWPA
amendments expressly forbid opening an interim storage site until a repository is under construction, to ensure that the interim site does not become a de facto repository far into the future.23 In summary, while the growing problem of stranded nuclear waste makes interim storage at a centralized site more appealing, there are continuing concerns that interim storage sites could remove incentives for finding a geologic repository and no assurance that such sites are any easier to find than a geologic repository.
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DISPOSAL IN A DEEP GEOLOGIC REPOSITORY The concept of a geologic repository comes to mind almost instinctivelybury the waste deep underground (300−800 m) in mined cavities or tunnels to isolate it from the biosphere and from inadvertent or malicious intrusion by humans. Deep boreholes drilled several kilometers into crystalline basement rocks also have been proposed, although less thoroughly investigated.1,24,25 Despite 435 nuclear power reactors in 31 countries26 and the worldwide scientific consensus on the need for geologic disposal, no geologic repositories for used nuclear fuel exist anywhere in the world.27 Finland and Sweden have made substantial progress toward developing geologic repositories and expect operations to begin in the 2020−2025 time frame.28 Other countries, such as the United States, Canada, Germany, Japan, and the U.K., have fallen far behind with no current sites selected for assessment (beyond Yucca Mountain in the U.S.). Meanwhile, the World Nuclear Association reports that 45 countries without nuclear power are giving it serious consideration.29 Several others, including China, South Korea, and India, are planning to massively expand their existing programs. According to the International Atomic Energy Agency, a permanent waste repository must provide sufficient isolation so “that eventual releases of radionuclides will be in such low concentrations that they do not pose a hazard to human health and the natural environment.”30 Decades of research and site investigations suggest that a variety of rock types and geologic environments, in combination with appropriate repository design, might be suitable for achieving this objective.1,30,31 Rock types currently considered for a deep geologic repository include salt, crystalline rocks (i.e., granite or gneiss), argillaceous formations (shale, mudrocks, and clays), and volcanic tuff. Each rock type has its strengths and weaknesses (Table 1), but none are perfect. 2093
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that a prescriptive regulatory regime, based on direct comparison of performance assessment results with regulatory standards for the first few thousand years, is a necessary part of the safety case.37 It is beyond this period where opinions diverge.38 Field-based studies and underground research laboratories play a critical role in demonstrating fundamental understanding of the natural system.27,39,40 Particularly compelling evidence comes from natural analogues of repository behavior over geologic timeframes. These analyses also may be more easily understood by the public. For example, uranium deposits at Peña Blanca in Chihuahua, Mexico, provided a natural analogue for the long-term behavior of uranium in used fuel in the unsaturated volcanic tuff at Yucca Mountain.41 Very low permeability in clay and shale can be demonstrated by anomalous pressures that are still responding to forcing by geologic processes, such as glacial ice load changes.42 In addition, natural tracers such as chloride ions and stable isotopes measured in pore waters of shale and clay have been shown to attain their present distributions by diffusion over millions of years.42,43 Studies of naturally occurring radon, radium, and helium have been used to study molecular diffusion in matrix pore water and connectivity to water in fractures at scales up to millions of years in the deep granitic rocks of Sweden and Finland.44 Following recommendations of the Blue Ribbon Commission on America’s Nuclear Future, the U.S. is in the beginning stages of a consent-based approach to find a community willing to host an interim storage site or geologic repository.1,21 As demonstrated by the history of interim storage, finding a volunteer community is the relatively easy part. States, which share fewer benefits than local communities, are much more difficult to convince. Officials of Nye County, Nevada, which encompasses Yucca Mountain, have consented to host the proposed repository, while the state of Nevada remains vehemently opposed. Similarly, in the U.K., two local communities near the Sellafield nuclear complex are in favor of taking the next steps toward siting a repository, yet were recently overruled by their County Council.45 Given that public acceptance is the Achilles’ heel of nuclear waste disposal, the manner in which the safety case is presented to the public is of primary importance. Developing the technical basis for a repository is a decades-long process that should be undertaken with no predetermined outcome.46 From the outset, humility is needed about the uncertainties involved. Unanticipated findings, such as the chlorine-36 findings at Yucca Mountain, may require major adjustments. The Board on Radioactive Waste Management of the National Research Council forewarned decades ago that surprises inevitably occur and setting unrealistic expectations for prior knowledge of a geologic repository risks undermining public trust.47 For more than 25 years, Yucca Mountain has been the sole candidate for a geologic repository, resulting in no plan B and no other geologic settings for comparison within the U.S. The United States is also the only country in the world to have set a deadline (January 31, 1998) for opening a high-level waste repository, contributing to a perception that meeting deadlines was more important than thoughtful deliberation.35 Lessons can be learned from the Waste Isolation Pilot Plant (WIPP) in New Mexicothe world’s only operational geologic repository for long-lived (but not high-level) radioactive wastes. The success of WIPP is in part attributed to an independent, technical group who advised the state on possible health and
The uncertainty in long-term repository performance is offset, in part, by adopting a defense-in-depth philosophy, whereby the repository safety does not depend on the performance of any single barrier. Multiple barriers comprise both natural and engineered barriers. Natural barriers comprise the geologic system’s capability to dilute, retard, and even retain radionuclides during transport. The engineered barrier system includes the waste form, the canister or waste package, and any backfill. While the principal challenge with natural barriers is in characterizing the local geology, the principal difficulty with engineered barriers is the lack of data on their long-term performance. Engineered barriers are designed to contain the waste during the initial period of highest radiological toxicity. However, no matter how robust the engineered barrier system might be, it is virtually guaranteed to eventually fail. At this juncture, waste containment relies solely on the natural system. The relative roles of the barriers may vary. For example, the natural system is considered the major barrier in shale and clay, while the main role of the natural system in the granitic rocks of Sweden and Finland is to provide a chemically and mechanically stable environment for the engineered barriers.32 In the early years of the Yucca Mountain studies, it was believed that the regulatory standards could be achieved without additional engineered barriers.33 By the late 1990s, the engineered barrier system dominated the waste isolation safety case after bomb-pulse levels of chlorine-36 were found in the exploratory tunnels.34 The chlorine-36 results were never confirmed,22 yet the abrupt about-face from the dependence on the natural to the engineered barriers dealt a substantial blow to the project’s credibility.35 The most fundamental challenge in making the safety case is that nuclear waste remains dangerous over timeframes beyond human experience and even our comprehension. The principal means of addressing this problem has been through mathematical modeling to simulate the long-term behavior of the geologic repository to features, events, and processes that could conceivably contribute to its eventual failure.36 Known as performance assessment, the approach requires hundreds of component models with thousands of input parameters. Each model (climate change, groundwater flow, used fuel corrosion, etc.) presents a major challenge to represent processes ranging from molecular to regional scales. The output of one model serves as input to others, often involving coupled processes. Methods of uncertainty analysis are used to assess effects of parameter and conceptual uncertainties on the uncertainty in simulated outcomes. There is general agreement that performance assessment is useful to evaluate the relative risk of different repository designs, identify data needs, and provide insights on long-term behavior as qualitative information. Controversy arises when performance assessment is used to compare model predictions with regulatory standards up to one million years in the futurea time frame that is at odds with what most geoscientists believe that science can provide.22,36 Aside from the technical challenges, many highly subjective aspects place constraints on analyzing a problem with this time frame. Where do people live? What do they eat and drink? How might contaminated and uncontaminated groundwater mix in their well? What is their use of the water? Given that it is not good enough to simply say that a site “looks safe,” some sort of model analysis and comparison to standards is required. There appears to be general consensus 2094
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Present Address
safety impacts of the proposed repository and ensured that important technical issues would be addressed in a rigorous fashion.48 There is no comparable group for Yucca Mountain. The Nuclear Waste Technical Review Board has proved advantageous in raising key technical areas, yet its purpose is to advise the President and Congress, not to represent concerns of the affected communities, tribes, and states. There never will be complete agreement among scientists about future repository performance, nor will all questions be answered. However, some degree of consensus within the scientific community is necessary to build credibility with the public. Such a consensus was not fully achieved at Yucca Mountain. In future studies, greater emphasis should be given to the refereed scientific literature and to fostering more open debate among scientists both within and outside the project.
§
(W.M.A.) 3195 E. Victoria Drive, Alpine, California 91901, United States. Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes
The authors declare no competing financial interest. Biographies William Alley is Director of Science and Technology for the National Ground Water Association. He previously served as Chief of the Office of Groundwater for the U.S. Geological Survey (USGS) where he oversaw the USGS studies of Yucca Mountain from 2002 to 2010.
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Rosemarie Alley is a freelance writer and co-author with William Alley of “Too Hot to Touch: The Problem of High-Level Nuclear Waste,” about the science, history, and politics of nuclear waste.
CONCLUDING REMARKS Solving the nuclear waste dilemma requires staying the course over decades with a technically complex and politically sensitive program. It also requires decisiveness in the face of unprecedented long-term uncertainty. While it is widely accepted among experts in nuclear waste management that the waste problem is solvable, this view is not shared by the public at large.8 When viewed in isolation, almost any approach for dealing with used nuclear fuel will be viewed as unacceptable by a large segment of society.49 Thus all options, including the status quo, should be publically addressed and the risks of each option openly acknowledged. Transfer of used nuclear fuel to a geological repository is, at best, decades away with indefinite onsite storage a growing possibility. While the risks of dry casks appear to be low for the short-term, today’s stranded waste could pose significant problems for our descendants. Open recognition of the risks of indefinite onsite storage could lead to greater societal awareness of the need for a repository. Given the length of time required to study a potential repository, coupled with an uncertain outcome, the United States should pursue interim storage and investigate multiple sites for a repository, as advocated by the Blue Ribbon Commission.1 With so much invested, Yucca Mountain should remain an option, as others are sought. The tactics must change; however, with an open-ended dialogue addressing Nevadan’s concerns. In the meantime, any community volunteering for an interim storage site should be aware of the open-ended time frame of such a facility. In this respect, consolidated surface storage may be a less misleading term. Replacing the top-down approach with a consent-based policy could help break the current deadlock, yet a policy change is only a first step. Several decades ago, science writer Luther Carter argued that, “trust will be gained by building a record of sure, competent, open performance that gets good marks from independent technical peer reviewers and that shows decent respect for the public’s sensibilities and common sense.”50 These ingredients do not ensure success, but in their absence, failure is guaranteed.
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ACKNOWLEDGMENTS The views expressed in this article do not represent the official policy or position of the National Ground Water Association. REFERENCES
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. 2095
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