International Perspectives on the Reprocessing, Storage, and Disposal of Spent Nuclear Fuel

The chief obstacle to geologic disposal is the lack of public acceptance.

The technical maturity and development potential of technologies for the storage, reprocessing, and disposal of spent nuclear fuels differ greatly, as do the political and social issues they raise. The material flows and waste products are summarized in Figure 1 (see PDF version), normalized to one tonne of reactor fuel in a light-water reactor, closed-fuel cycle. All of the operations listed in Figure 1 produce radioactive wastes in solid, liquid, or gaseous forms. Although the greatest environmental challenges may be associated with wastes at the front end of this chain - namely, the millions of tonnes of mining and milling tailings that remain on or near the land surface of uranium-producing sites - most of the time, effort, resources, and public attention have been focused on the management of the low-volume, but highly hazardous wastes from the back end of the fuel cycle - spent nuclear fuel (SNF), if this is regarded as waste, or the vitrified high-level waste (HLW) and the accompanying long-lived transuranic wastes that remain after reprocessing.

The most controversial issue today is disposal of these waste streams. Deep geologic repositories are currently the only recognized feasible method of safe permanent disposal. This will be the main focus of this paper, but let us look at the three technologies in turn.

Storage
Storage of nuclear wastes, a long-established technology, is widely practiced today and will continue to be necessary for many decades to come. During storage, the key goal is to ensure the safety and security of stored HLW and SNF. Early on, SNF was stored primarily in water pools in well protected nuclear facilities (wet storage). Increasingly, however, SNF and HLW are being stored in strong, sealed, shielded containers (dry storage) or in vaults. Both wet and dry storage can provide safety and security. Dry storage is better suited for very long periods of time, although some wastes (e.g., SNF from U.K. magnox reactors [with magnesium alloy cladding]) must be kept under water for safety reasons. Although no new technical developments are necessary to ensure the safety of stored nuclear wastes, work continues on monitoring fuel creep, hydrogen migration, and so on. The recent increase in terrorist acts has also led to a reexamination of some security concerns, such as vulnerability to missile attack.

Some important policy issues must still be addressed, especially the duration of storage and the location of storage sites. When reactors or reprocessing plants were built, it was believed that the SNF or HLW would be removed (after limited storage to allow for cooling) and shipped to a disposal facility. The huge delays in implementing disposal facilities have meant that storage periods have been drastically extended. In some countries, geologic repositories are still so far off that no date can be predicted; in a few countries, not even the feasibility of geologic disposal has been accepted, thus making storage "indefinite." Additional storage can be located at reactor sites, provided that licenses can be amended, or at new centralized storage facilities, provided that these can be sited. But, communities that currently host stores of SNF or HLW, or that are being proposed as hosts, understandably do not wish to become de facto final repositories. As the delays in disposal continue and requirements for storage are increased, this controversy grows.

The situation in the United States concerning storage and disposal illustrates how policy issues can directly affect technical programs. Reactor operators who do not have sufficient on-site storage for SNF have initiated litigation against the U.S. Department of Energy (DOE), which failed to meet the 1998 target date for DOE acceptance of such fuel. This problem has also led to proposals for storage facilities run as private enterprises. To run disposal operations as efficiently as possible, it would be advantageous to have a large storage capacity close to the repository so that waste emplacement could be decoupled from DOE acceptance and could be planned to minimize thermal-loading problems. A recently published study by the National Research Council on repository staging suggests that storage facilities should be located adjacent to the Yucca Mountain repository (NRC, 2003). However, because of the political sensitivities associated with implementing a large storage area before a repository is available, this may not be a feasible policy option.

Reprocessing
Civil reprocessing technology was developed to obtain unused uranium and plutonium for use in fast reactors. The technical challenges associated with this process have been solved, and large-scale reprocessing plants are in operation in France, United Kingdom (U.K.), Russia, and the United States; in other countries (e.g., Belgium and Italy), they have been operated as research facilities. France, the U.K., and Russia offer commercial reprocessing services that are being used or have been used by a number of countries (e.g., Japan, Germany, Switzerland, Italy, Spain, and Sweden); Japan is currently building its own commercial reprocessing plant.

Technical improvements are still possible, such as increases in separation efficiencies and reductions in emissions of radioactive substances during operation. There are bigger technical challenges, however. One is to develop an advanced reprocessing and fuel fabrication cycle that avoids having segregated plutonium at any stage. This could greatly reduce the risk of proliferation associated with reprocessing. Another technical challenge might be to develop a "second-generation" waste form to succeed the borosilicate glasses in which fission products are included. A great deal of work has been done on the development of ceramics and synthetic minerals. The question is whether the improved performance with these materials is necessary to increase the already high levels of safety predicted for repositories.

In practice, the main technical challenge associated with reprocessing may be the mundane challenge of reducing costs. The costs of reprocessing are so high today that they cannot be recouped either by the value of the recovered materials or by the savings on storage and disposal costs. Commercial repositories will break even only if the price of the uranium feed increases far beyond the current typical uranium prices of $20 to $40/kg. Subsidies for utilities willing to use mixed plutonium-uranium oxide (MOX) fuel would make MOX fuel more attractive commercially and could help reduce excess weapons-grade plutonium.

The policy decisions that led to the development of commercial reprocessing were based on conserving uranium resources by providing a supply of plutonium for fast reactors. This argument has been severely weakened over time by the slow growth of nuclear power, which has kept the price of uranium low. Moreover, because the deployment of breeder reactors has been postponed, the demand for, and therefore the value of, plutonium has been reduced. In fact, the excess plutonium already produced from reprocessing has become a liability (it is expensive to store and degrades in storage) and has created a potential risk of proliferation. The nuclear industry is using some plutonium in MOX fuels, although the costs are high and the uranium savings are only around 20 percent. Options being seriously considered include (1) reactors designed to burn excess plutonium; and (2) disposing of plutonium as a waste.

In summary, the key policy issues associated with reprocessing are the now weak resource-conservation arguments, increasing concerns about nuclear proliferation, and the economic costs associated with the low price of fresh uranium. Countries that currently follow a reprocessing strategy do so for one or more of the following reasons:

• They believe that uranium resources may yet become scarce or that access to uranium will become difficult for countries with no indigenous resources; plutonium would then become a valuable fuel.
• They wish to move spent fuel off reactor sites, but neither storage nor disposal facilities are available.
• Reprocessing reduces the volume of high-quality waste products (vitrified HLW) that can be stored and disposed of at lower cost.
• They have invested large sums in reprocessing technology; these must in any case be amortized so that only marginal costs are relevant.

Geologic Disposal
Geologic disposal is the least tested technology of the three nuclear technologies discussed in this paper. In fact, although the concept of disposal in deep geological formations was long ago recognized as the most promising form of confinement for long-lived wastes from the nuclear fuel cycle (NRC, 1957), to date, no deep geologic repository for SNF or HLW is in operation. Every waste disposal program in the world has experienced delays - often significant delays. If the Yucca Mountain project passes its current hurdles, the United States may be the lead nation, followed closely by Finland and Sweden. By around 2020, there could be three operating repositories. Other countries (such as Japan and Switzerland) will have no need to implement deep disposal of SNF/HLW until 2030, or even 2050. In some countries (e.g., U.K., Canada, Spain, Netherlands), decisions on geological disposal are still wide open, and implementation may be a hundred years off. In fact, after catastrophic failures of their repository development programs, U.K. and Canada have officially declared that geologic disposal is no longer established policy and must be considered along with other waste-management options.

Technical Challenges
Implementing a deep repository involves designing or selecting engineered and natural safety barriers, undertaking major underground construction, building and operating equipment and facilities for transporting, encapsulating, and emplacing SNF or HLW, running emplacement operations, and backfilling and sealing the facility after many decades. Most waste-management organizations agree that a staged or stepwise program is the best approach to this major long-lasting project.

Despite the scale and complexity of the engineering and science involved, however, the only really controversial technical issue is the credibility of predictions of repository system behavior for tens or hundreds of thousands of years into the future, and the debate on this issue has been intensifying. On one hand, opponents of nuclear power fear that accepting geologic disposal as a safe end-point might encourage the use of nuclear technology. On the other hand, proponents of geologic disposal often overstate the certainty of their arguments, failing to make it clear that absolute certainty and zero risk are unattainable.

In my opinion, no strictly technical issues prevent implementation of geologic repositories, although the task is by no means trivial. In fact, this opinion is held by the majority of the scientific and technical community. Even many technical experts who are still concerned about uncertainties would be prepared to initiate the disposal process, if it could be reversible for the coming decades. The common impression that a great technical controversy exists is largely attributable to the media’s tendency to give equal coverage to both sides of every argument, regardless of where the weight of opinion lies.

Most of the controversial issues associated with geologic disposal are, therefore, questions of policy rather than questions of technology. Are there credible alternatives to geologic disposal? When should disposal projects be implemented? Where, if anywhere, can repositories be equitably sited? Can they satisfy technical safety criteria and also win sufficient support from the public? Can the disposal strategy be reversed if unforeseen problems arise? These are the key questions repeatedly being posed about geologic disposal.

Although recent documentation by various organizations has confirmed the confidence of the scientific community in geological disposal, a significant fraction of the public does not share this confidence. The lack of public support is often related directly to the controversial issue of siting nuclear facilities, which has a troubled history that has led to continual changes in the selection processes. Early on, some sites were chosen purely by experts and officials behind closed doors. The selection of the Gorleben site in Germany in the 1970s is a prime example. In the 1980s, international bodies, primarily the International Atomic Energy Association (IAEA), mapped out a top-down, technical procedure intended to narrow a range of choices through objective criteria to a single site that would be recognized by all stakeholders as the most appropriate. However, experience in various countries (e.g., France, U.K., and Switzerland) showed that this "decide, announce, and defend" (DAD) strategy could lead to controversy, delays, or failures.

Since then, more importance has been put on societal criteria, particularly the degree of acceptance in potential host communities, although the capability of a site to provide long-term isolation remains a condition sine qua non. This approach has been successful, particularly in the Scandinavian countries. In Finland, the implementer, the local community, the parliament, and the government have agreed on a geological repository site. In Sweden, local communities at two potential sites have agreed to investigations that could lead to implementation. Japan has requested that interested municipalities volunteer (more than 3,000 have been contacted).

Must every country have its own geological repository? In fact, the nuclear fuel cycle is already international, and there are no ethical, technical, or other reasons to compel countries to implement national solutions. Mining, enrichment, fuel fabrication, and reactor construction are all carried out by relatively few nations for the dozens of countries that use nuclear power. In a similar way, other toxic wastes are imported and exported when better environmental results can be achieved. International agreements (e.g., the IAEA Radioactive Waste and Spent Nuclear Fuel Convention) recognize the legitimacy of these transfers, as long as the waste-producing country is responsible for the safe and secure management of the waste. Nevertheless, some individual countries have legislated against importing waste. This is a national prerogative that must be respected, even though it is based more on considerations of public opinion and political feasibility than on ethical considerations.

A final policy-related issue in waste disposal concerns the security implications of moving wastes and spent fuel from distributed surface-storage facilities to centralized underground repositories. It seems clear that more safeguards against misuse and better physical protection against terrorists can be offered at repositories. Counterarguments are the risks involved in transporting wastes to repositories and the potential attraction of centralized sites for terrorist groups. This debate is, however, of little immediate relevance because there is no way of accelerating repository programs enough to have a major impact on security in the next 10 years or more.

Conclusions
The technologies for storing, reprocessing, and disposing of HLW and SNF have all been developed to the implementation stage. The challenges are in all cases more societal than technical.

Storage technologies are well tried and present no technical problems. As reactor storage facilities fill up, the siting of centralized storage facilities presents a serious societal challenge.

Reprocessing technology has been developed and implemented in various countries; improvements could be made, but there is little incentive to pursue them, primarily for economic reasons. The recurring debate about the hazards of proliferation associated with reprocessing may result in the development of new technologies that avoid segregating plutonium.

The technology for geologic disposal is developed and could be implemented today, although significant optimization of designs is possible. The chief obstacle has been the lack of public acceptance. Some countries, however, are moving ahead in a way that promises the operation of repositories in the next 10 to 20 years; these facilities could then act as reference facilities.

With the implementation of the project at Yucca Mountain, the United States could become the first country to implement deep geologic disposal of spent fuel, thus following upon the long-delayed success of the Waste Isolation Pilot Plant (WIPP) Project in New Mexico. But not all of the lessons that can be drawn from the U.S. programs are positive. First, the enormous costs involved are horrific examples for smaller nations. Second, the laudable transparency of progress has been somewhat tarnished by political bargaining and legal wrangling.

The National Academies have had a long-lasting, important influence on waste-management strategies. This is illustrated by reports produced at regular intervals, from the landmark report of 1957 (NRC, 1957) through various other strategic reports (e.g., NRC, 1990, 1995, 1996, 2001) to the staging report released on the day of this symposium (NRC, 2003). In addition, numerous technical reports have been produced by scientists and technologists working within the framework of the extensive committee system of the National Research Council. These reports continue to provide unbiased input on issues vital to the safe management of all radioactive wastes.

References
NRC (National Research Council). 1957. The Disposal of Radioactive Waste on Land. Washington, D.C.: National Academy Press.
NRC. 1990. Rethinking High-Level Radioactive Waste Disposal: A Position Statement of the Board on Radioactive Waste Management. Washington, D.C.: National Academy Press.
NRC. 1995. Technical Bases for Yucca Mountain Standards. Washington, D.C.: National Academy Press.
NRC. 1996. Nuclear Wastes: Technologies for Separations and Transmutation. Washington, D.C.: National Academy Press.
NRC. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, D.C.: National Academies Press.
NRC. 2003. One Step at a Time: The Staged Development of Geologic Repositories for High-Level Radioactive Waste. Washington, D.C.: National Academies Press.