ATTACHMENT A
PROGRESS REPORT: PRINCIPLES AND OPERATING STRATEGIES FOR STAGED REPOSITORY SYSTEMS
At the request of the U.S. Department of Energy (DOE), the National Research Council appointed a committee1 to investigate principles and operational strategies for the staged development of a geologic repository. Geologic repositories are considered, in the United States, to be the preferred disposal2 system for radioactive spent nuclear fuel and high-level waste (NRC, 1957, 1990, 2001a). To the committee’s knowledge, no one has given a simple definition of “staged development” for geologic repositories.3 The words “staged,” “staging,” and other similar terms, such as “stepwise,” “modular,” and “phased,” describe different concepts to different audiences. Therefore, in this progress report, the committee describes its view of staged development and defines a new term, “adaptive staging,” to differentiate the committee’s concept from previous definitions.
The committee has yet to complete discussion of all the points listed in the statement of task (Attachment C). This progress report confines itself to developing a provisional conceptual framework and a working definition for adaptive staging. The considerations in this report are intentionally generic, that is, they apply to any waste disposal program. The committee also provides some provisional observations, still being discussed, about the U.S. repository program, referred to as the “Yucca Mountain Project.” The final report, planned to be released in the fall of 2002, will address all points of the statement of task.
The difficulty of the committee’s task has been magnified by the necessity of completing this progress report at the time of a major policy decision on the suitability of the Yucca Mountain site as a geologic repository for U.S. high-level waste.4 This impending decision has created a heightened sensitivity to the committee’s statements concerning the Yucca Mountain Project. The committee is not charged to participate in this decision and has not considered the merits of the choice at hand. However, the statement of task does require the committee to examine the concept of staging in principle and then in application to the Yucca Mountain Project. The committee has endeavored to ensure that the results of its deliberations will be valuable and applicable no matter what decision is made on the Yucca Mountain site.
1. ADAPTIVE STAGING
This section provides a provisional conceptual framework and the working definition of adaptive staging. Adaptive staging is a strategy for geologic repository development,
based on the general principles of the adaptive management approach.5 General repository development activities include, for instance: siting, licensing, constructing, operating, closing, and monitoring.6 Geologic repositories, as distinguished from many other waste disposal systems, are unique undertakings in that they are first-of-a-kind, risk-laden, complex, and long-term projects (NRC, 1990, 2001a). In the presence of such challenges, several panels on radioactive waste management, including two previous National Research Council committees, recommended adopting a staged approach for repository development, as reported below.
1.1 Provisional Conceptual Framework of Adaptive Staging
Current mainstream thinking on radioactive waste management in the international arena suggests the adoption of a staged approach for development of geologic repositories. A key precursor and foundation for adaptive staging is the “stepwise” approach proposed by a variety of international bodies.
At an international workshop organized by the National Research Council as part of this study, specific examples of stepwise approaches for repository development were given from representatives of waste management programs in Sweden, United Kingdom, Switzerland, Finland, France, Japan, and the United States (NRC, 2001b). At another recent international conference on radioactive waste management, representatives from the United States, France, and Japan reiterated the importance of adopting a stepwise approach for repository development (WM, 2002).
Moreover, since the early 1990s, international organizations, such as the International Atomic Energy Agency, the Nuclear Energy Agency, and the International Association for the Environmentally Safe Disposal of Radioactive Material,7 specifically recommended the precursor to adaptive staging, a stepwise approach.
In 1995, the Nuclear Energy Agency concluded:
“stepwise implementation of plans for geological disposal leaves open the possibility of adaptation, in the light of scientific progress and social acceptability, over several decades, and does not exclude the possibility that other options could be developed at a later stage” (NEA, 1995; page 6).
Four years later the same agency elaborated its conclusion:
“There is a general common trend towards advocacy of prudent, stepwise approaches at the implementational and regulatory level to allow smaller incremental steps in the societal decision making process. Discrete, easily overviewed steps facilitate the traceability of decisions, allow feedback from the public and/or their representatives, promote the strengthening of public and political confidence in the safety of a facility
along with trust in the competence of the regulators and implementers of disposal projects” (NEA, 1999a; page 11).
“The acceptability of a long-term management strategy, such as geologic disposal, can only be decided at a societal or government level, after consultation with a range of relevant organisations and taking account of public views. A step-wise process leading to implementation of geologic repositories will allow more time and increased opportunities for broadening the basis of support or identifying alternative options” (NEA, 1999b; page 26).
In 1990 in the United States, the Board on Radioactive Waste Management of the National Research Council recommended that DOE adopt a strategy for radioactive waste disposal that is:
“more flexible and experimental—in other words, a strategy that acknowledges the following premises:
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Surprises are inevitable in the course of investigating any proposed site, and things are bound to go wrong on a minor scale in the development of a repository.
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If the repository design can be changed in response to new information, minor problems can be fixed without affecting safety, and major problems, if any appear, can be remedied before damage is done to the environment or to public health” (NRC, 1990; page 7).
A more recent (2001) National Research Council report recommended that:
“A stepwise process is appropriate for decision making under technical and social uncertainty. […] Both fundamental knowledge and ways to deal with uncertainty are advancing, and they will continue to do so during the course of a repository development program. A stepwise decision process can utilize this evolving knowledge to make sound decisions on repository siting (including the geological setting), design, and operation. (NRC, 2001a; page 3) […] For both scientific and societal reasons, national programs should proceed in a phased or stepwise manner, supported by dialogue and analysis. […] Demonstrated reversibility of actions in general, and retrievability of wastes in particular, are highly desirable because of public reluctance to accept irreversible actions” (NRC, 2001a; page 5).
In summary, it is increasingly acknowledged by most national radioactive waste management programs that some form of staged process is useful or even necessary for developing a geologic repository. The committee supports this view and has gone further towards defining the characteristics of a staged program that could have higher chances of leading to success in a complex long-term project. The committee has refined the staged development concept and termed it “adaptive staging.”
1.2 Working Definition of Adaptive Staging
Adaptive staging is defined as a process where the development of a geologic repository is divided into stages that are separated by explicit decision points. Decision points provide the opportunity to evaluate obtained results and to decide how to proceed to the next stage. In other words, subsequent stages are predicated upon the outcomes of previous ones. Decision points allow for program improvement with respect to, for instance, safety, costs, and schedule. Under adaptive staging, the repository implementer, at each decision point between stages, would:
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analyze knowledge gathered from previous stages;
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take into account all relevant options for the next stage, including explicit consideration of reversibility;8,9
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evaluate and update the safety case;10
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decide on the next stage based on the above set of actions.
All of the above actions would incorporate input from stakeholders11 who would also receive feedback on the decisions taken. The committee is still in the process of discussing the role of stakeholders at decision points.
In other words, adaptive staging is a cautious and deliberate decision and management process that involves continuous learning and is also transparent and reversible. Adaptive staging differs from linear and predetermined repository development approaches where milestones alone define stages. A linear and predetermined process is characterized by a single path to a single end point. Adaptive staging emphasizes the management of the decision process at each stage based on knowledge gained from previous stages. Another difference between adaptive staging and a linear and predetermined process is that, in the latter case, the safety case is reevaluated only if compelling new information requires it rather than at each decision point, as is the case with adaptive staging.
1.3 Essential Attributes of Adaptive Staging
The overarching attribute of adaptive staging is that it aims to increase repository safety and to reduce repository performance uncertainties through systematic incremental learning. The safety case is at the heart of adaptive staging and drives the
identification and choice of options at each stage. Commitment to systematic learning, flexibility, auditability, transparency, integrity, and responsiveness underlie the overarching safety attribute.
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Commitment to systematic learning—designing stages specifically to increase the body of available knowledge, including scientific, technical, societal, institutional, and operational knowledge. Needs and questions to be addressed are made explicit at the outset. Information gained will be accepted and incorporated into the available knowledge base. A central feature of adaptive staging is that it intentionally seeks, is open to, and learns from stakeholder input and participation in all knowledge areas.
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Flexibility—adapting in response to available technical and non-technical knowledge, conservative interpretation of current knowledge, and experience gathered in previous stages. That is, adaptive staging is an iterative process. Flexibility implies that, before moving on to the next stage, a number of options are considered, including the possibility of changing course or reversing to a previous stage.12 As reported by the Nuclear Energy Agency:
“Reversibility denotes the possibility of reversing one or a series of steps in repository planning or development at any stage of the programme. This implies the review and, if necessary, re-evaluation of earlier decisions, as well as the means (technical, financial, etc.) to reverse a step. Reversibility denotes the fact that fallback positions are incorporated in the disposal policy and in the actual technical programme. Reversibility may be facilitated, for example, by adopting small steps and frequent reviews in the programme, as well as by incorporating engineering measures” (NEA, 2001, page 11).
A decision to retreat to a previous stage should be evaluated with the same rigor as a decision to move ahead to a subsequent stage. Because evidence and logic will accumulate as the project moves through stages and makes choices, the likelihood of reversal will probably decrease as the project develops. Similarly, choices among alternatives will likely reduce the number of future choices and the scope of flexibility. Flexibility and reversibility are intrinsic attributes of adaptive staging and are therefore available to the decision process at each stage.
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Auditability—adequately documenting decision records to allow examination and verification by external credible bodies. At the end of each stage, an evaluation and decision process takes place to support the transition to a next stage. This process involves the implementer, the regulator, external review bodies, and other stakeholders, all of whom maintain a dialogue throughout the entire process. The role of these parties in the process will be defined in the final report.
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Transparency—making the decision path available and clearly explained to all stakeholders throughout the process. For instance, a statement of intent and rationale behind each stage and decision point is developed and tested for understandability and then broadly publicized to stakeholders. Uncertainties or indeterminacies are identified and labeled as such. Policy and technical decisions are clearly differentiated. The implementer justifies technical decisions with scientific or engineering data. Because repository programs span several generations, special efforts are needed to ensure that
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transparency is maintained over time. The variety of roles and means for stakeholder involvement in the process will be discussed in the final report.
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Integrity—incorporating in the decision-making process all relevant evidence, including that offered by parties external to the repository program. Adaptive staging objectively, accurately, and understandably reports results of technical work at each stage, whether positive or negative, giving also their context and limitations. Adaptive staging makes clear to all stakeholders what is intended at each stage and why. The possibility that the site may not ultimately be suitable for repository development remains openly acknowledged throughout all stages, and particularly up to the licensing stage.
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Responsiveness—ensuring timely feedback for new information to enter in the decision process. Adaptive staging allows schedule planning and deliberate evaluation periods to integrate lessons learned from prior stages. Stages are sufficiently separated in time to allow compilation of relevant data to guide the next stage.
The sidebar below explains how introducing a pilot stage into a waste management program is consistent with adaptive staging.
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SIDEBAR ILLUSTRATIVE EXAMPLE OF ADAPTIVE STAGING Below is a generic scenario for a pilot disposal stage. A pilot stage is often introduced in first-of-a-kind, risk-laden, and complex engineering projects. Pilot scale facilities are less expensive and faster to build than full-scale facilities. The goal of a pilot stage is to test as far as possible the entire waste management system—including the larger social and institutional contexts—to gain more understanding and to discover specific problems that had not been visible earlier. These problems can then be addressed with lower risks and consequences. In the radioactive waste repository context, the scope of the pilot stage is to test conceptual models and the implementer’s capability to safely manage waste and conduct repository operations, including waste retrievability. While direct evidence of long-term performance will not be achieved by a short-term pilot stage, a well-formulated monitoring and research and development program can provide data that will enhance (or diminish) confidence in the many assumptions inherent to the total system performance assessment. This scenario posits that the implementer obtains a conditional, or staged, license or permit based on the fullscale repository design. The staged license is for building a surface and a subsurface module of the full-scale repository for waste acceptance, process, storage, and pilot disposal. The implementer obtains a second staged license to receive a small fraction of the total amount of waste allowed. The implementer takes title to this waste; removes it from the storage site(s); transports it to the repository; unloads it; stores it; packages it for disposal; emplaces it in the pilot modules; monitors the near-field repository environment; and tests waste retrievability options. During this pilot stage, the implementer also continues to incorporate stakeholder input to help evaluate non-technical issues, such as institutional and social aspects of the program. The implementer conducts research and development in parallel with monitoring activities. Data from monitoring are used to evaluate assumptions (e.g., thermal and mechanical effects from waste emplacement) while research and development activities stress the conditions in the repository (e.g., corrosion effects on waste package or thermal effects on the surrounding rock) to gain understanding of repository behavior. |
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A technical board oversees the repository program. The role and composition of this technical oversight board will be addressed in the final report. The implementer, together with this technical oversight board, compare assumptions with the information collected, identify significant divergences, propose remedies, and obtain data to improve repository design or operations. At the end of the pilot stage, the implementer conducts an analysis updating the repository safety concept for the full safety case. The implementer, the regulator, and the oversight board evaluate the information gathered and decide among different options, which might include: 1) apply for a further staged license and proceed to emplace more waste under the current repository design, 2) obtain additional information, 3) improve the repository design, or 4) consider returning to a previous step or a complete reversal of the process. If design changes are necessary, the implementer requests the appropriate license amendments before proceeding with the subsequent stages. A pilot phase implemented as explained above would have the following attributes: Commitment to systematic learning: A pilot stage is a typical example of systematic learning because it is done on purpose, it is a trial, and its objective is to gather as much information as possible. The information gathered during this pilot stage is fed back into the decision-making process to decide what the next stage will be. A new stage may become evident only after this pilot stage. For instance, new tests with a different backfill or longer cooling time before waste emplacement may be necessary. Research and development and monitoring activities in this pilot stage are structured to obtain maximum benefit from learning. For instance, different backfill materials or emplacement options can be tested in parallel to anticipate future changes in the characteristics of waste. Flexibility: From a technical, institutional, and societal point of view, this pilot stage offers opportunities to apply the lessons learned when a next stage is undertaken. Based on the information gathered, the implementer may introduce significant changes in the program; a new scope for the next step may become evident only after this pilot stage is completed. Multiple options are considered in determining the following step, including reversal to previous stages. Auditability, transparency, and integrity: The purpose of the pilot stage (in particular if there are tests involving radioactive waste) is explained clearly to stakeholders to avoid assertions that the pilot stage is a mere tactic to begin site work or waste emplacement. The oversight board promotes the auditability, transparency, and integrity of the decision-making process. This communication promotion could lead to an increase of public confidence in the program: the pilot stage demonstrates that the implementer (along with other involved actors) is acutely aware of safety issues, knows how to identify flaws in the system, and is ready to modify or even halt the project, if necessary. Responsiveness: A pilot-scale facility is faster to build compared to a full-scale repository. Therefore, information about the performance of the pilot stage can be fed back into the decision-making process earlier. For instance, information about parameters relevant to the performance of the repository, potential technical and non-technical difficulties, as well as options to address these difficulties can be gathered in this early pilot stage. |
2. POTENTIAL BENEFITS AND DRAWBACKS OF ADAPTIVE STAGING
As shown in section 1.1, staged development is increasingly recognized in the radioactive waste management arena as beneficial in the implementation of long-term waste disposition strategies. However, adaptive staging, a refined interpretation of staged development, is a new concept that also presents some potential drawbacks. These benefits and drawbacks are described briefly below and will be further elaborated in the final report.
2.1 Potential Benefits of Adaptive Staging
In section 1.1, expert panels in radioactive waste management describe some of the benefits of adopting staged strategies for the development of geologic repositories. As mentioned previously, geologic repositories are unique projects in that they are first-of-a-kind, complex, and long-term undertakings having strongly interacting technical, institutional, and societal characteristics. The committee’s initial arguments in favor of adaptive staging are the following:
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Programmatic: Adaptive staging is a logical approach to manage complicated projects, such as geologic repositories. When the project is divided into smaller stages with the possibility of reversal, the decision-making process can become more manageable. Adaptive staging allows decision-making only on those stages of repository development where knowledge is available (near-term stages), thus keeping options open for the future. Adaptive staging’s flexibility could help the implementer in reacting to unavoidable “technical surprises” and unavoidable political, economic, or societal surprises. Adaptive staging’s incremental aspect could also help the implementer identify problems early, problems that may become too complicated to rectify at later stages. These interventions could avoid program flaws that may slow down or halt the entire program, or produce irreversible harm to humans and the environment. Adaptive staging also allocates sufficient effort and time for quantification and analysis of the relative risks of different options. Such assessment is based on experience, available technical knowledge, or on conservative interpretations of current knowledge.
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Technical: Adaptive staging not only allows for learning and incorporating new technical data throughout repository development, but also after the waste is in place. For instance, adaptive staging encourages the implementer to develop a long-term monitoring plan, beginning early on and evolving through post-closure activities as more is learned. Data from this monitoring plan could improve scientific and engineering understanding of the behavior of the repository system. The attribute of commitment to systematic learning and the staged approach to repository development not only facilitate the analysis of potential risks and uncertainties, but also provide opportunities for their remediation. Uncovering potential problems can only enhance the safety case and reduce uncertainties.
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Regulatory: Regulators have the advantage of evaluating the program more often because of adaptive staging’s increased number of transparent, auditable decision points. Adaptive staging provides the regulator with better oversight of the repository design, operations, and safety case.
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Institutional: Adaptive staging could help build public trust in the capabilities of the implementing institution to fulfill very long-term responsibilities because it allows many opportunities for the implementer to demonstrate competence and integrity. For instance, adaptive staging ensures that a decision to proceed from a siting to a licensing
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stage is not automatic. Nor does licensing automatically imply building and operating a full-scale repository without further input from regulators and stakeholders. Institutional benefits of staged approaches similar to adaptive staging have also been discussed by the Nuclear Energy Agency (1999a).
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Societal: Allowing stakeholder participation in the decision-making process can make the repository program more credible and trustworthy. Previous National Research Council committees have discussed the benefits of broad public participation in governmental agencies’ decision-making processes (NRC, 1994, 1996, 2001a). The committee’s discussion on mechanisms for stakeholder participation is in progress. The Nuclear Energy Agency (NEA, 1999a) and other National Research Council committees (NRC, 1990, 2001a) have also commented on the societal benefits of implementation approaches similar to adaptive staging. Public involvement in siting geologic repositories has been effective in Finland and Sweden, as briefly illustrated in Attachment B.13
2.2 Potential Drawbacks of Adaptive Staging
The committee also has identified potential programmatic, technical, regulatory, institutional, and societal drawbacks of adaptive staging:
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Programmatic: Adaptive staging calls for financial investments without a “guarantee” that any of the potential future stages in the process will be reached. Adaptive staging may also extend the time scale needed for full-scale operation of the repository, thereby changing interim storage requirements and other factors, such as costs and security issues.
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Technical: Adaptive staging may lead to longer periods in which the waste is more accessible to humans. In this case, operational exposures could be higher and security risks could be increased.
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Regulatory: More intensive regulatory oversight may delay the repository program. A drawback for the regulator is that adaptive staging requires flexibility and acceptance of the risk involved in permitting or licensing individual stages in an openended program.
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Institutional: Stakeholders may perceive adaptive staging as a stratagem to develop a specific site or to begin waste emplacement prematurely, thus decreasing trust. Public trust in the institution may never be achieved, even if adaptive staging is implemented, especially if there already exists a climate of institutional distrust.
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Societal: Stakeholders opposed to the repository project may have additional opportunities to deliberately delay the program.
2.3 Identifying Benchmarks for Adaptive Staging Approaches
The committee is currently trying to identify benchmarks of success for an adaptive staging strategy.14 Staging approaches have not yet been developed throughout the entire repository development process either in the United States or internationally.
Sweden, Switzerland, and Finland have implemented staging approaches through the siting phase only. France is implementing staging in the research and development phase of its repository program. In many of the radioactive waste management programs that have adopted a linear, prescribed, multi-step approach to develop geologic repositories for high-level waste there have been delays or failures, as described in a previous National Research Council report (NRC, 2001a; page 10). The committee is still weighing applicability to the U.S. repository program of these staged development attempts.
3. WORK IN PROGRESS ON THE RELATIONSHIP BETWEEN ADAPTIVE STAGING AND THE U.S. REPOSITORY PROGRAM
To date, the committee has not completed its analysis of the relationship between adaptive staging and the U.S. approach to repository development. Below are some of the provisional observations the committee is currently considering.
Not all of the attributes of adaptive staging are currently included in the U.S. repository program. This is in part due to the historical legacy of the U.S. radioactive waste management program, which, for instance, narrowed down the site selection process in a policy decision taken by Congress (NWPAA, 1987). DOE appears to be incorporating a few selected elements of adaptive staging into its program by considering a “modular repository design.” This “modular repository design” consists of building the repository and infrastructures, as well as carrying on operations in a modular fashion:
“Construction of the emplacement drifts and subsurface facilities would be accomplished in phases. In the current plan, about 10 percent of the emplacement drifts would be completed during the initial construction phase (prior to initiation of waste emplacement), with the remainder of the emplacement drifts being completed during the operation phases. This phased construction would allow the DOE flexibility to develop the repository based on future deliveries of spent nuclear fuel” (DOE, 2002a, pages 2–1 and 2–2).
Although this is a staged development approach, this “modular repository design” is proposed to overcome annual budget restrictions, schedule, and regulatory uncertainties rather than to increase opportunities for learning, which would be the prime justification for implementing adaptive staging. The following is quoted from a letter that DOE wrote to a contractor providing the rationale for conducting a study on the modular repository design:
“It has become apparent that a staged repository development approach that includes modular repository design and construction…may provide significant advantages in meeting [Yucca Mountain] Program schedules and provide flexibility to address Program technical and regulatory issues. In addition, a modular repository design may reduce the near-term annual costs for repository design and construction. It is possible that annual funding for the Program will be constrained until a repository is constructed and begins operation, thus putting a priority on repository
designs that can be constructed under reduced funding levels” (DOE, 2001a).
According to the information gathered, DOE is currently weighing the benefits of flexibility and greater program manageability in the near term against the higher estimated life-cycle costs of this “modular repository design.” DOE is also recognizing that flexibility will provide opportunities for changes in the repository program if there are significant problems discovered in the early repository modules (DOE, 2001b). Based on this work in progress, the committee believes that emphasizing further the fundamental attributes of adaptive staging could increase program flexibility and responsiveness to new information obtained during successive stages. In its final report, the committee will provide specific suggestions for incorporating additional elements of adaptive staging into the U.S. repository program.
If the license application for the Yucca Mountain site is filed, a multi-year period of interaction between DOE and the U.S. Nuclear Regulatory Commission will take place. This appears to allow time for DOE to develop adaptive staging, to reflect on completed stages, and to outline the nature of future stages and decision points. Based upon discussions of the information gathered to date, the committee believes that adaptive staging is compatible with the existing U.S. regulatory framework. The rationale will follow in the final report.
4. CONCLUDING REMARKS OF THIS PROGRESS REPORT
There are various ways to implement a staged development for a geologic repository, including adaptive staging. Adaptive staging is not achieved by simply defining milestones for repository development. Equally important is the management of the decision processes at each stage based on knowledge gained from previous stages.
The committee is currently investigating the benefits and drawbacks of adaptive staging as they impact the programmatic, technical, institutional, regulatory, and societal objectives of a geologic repository. In many of the radioactive waste management programs that have adopted a linear, prescribed, multi-step approach to develop geologic repositories for high-level waste there have been delays or failures, as described in a previous National Research Council report (NRC, 2001a; page 10).
Based upon its own judgment and recommendations from previous panels on waste disposal programs, the committee believes that adaptive staging may address challenges and uncertainties associated with geologic repository development programs more effectively than a linear approach. Adaptive staging brings together technical and social knowledge gained from implementation of one stage to provide an integrated judgment of the safety case for proceeding to a following stage. The presence of several decision points in the overall repository development plan may improve the likelihood of incorporating knowledge and understanding gained from experience, and opens up the possibility for more effective stakeholder involvement.
Although the committee believes that adaptive staging is a promising approach, it also recognizes that adaptive staging is an unproven concept. However, the adaptive staging strategy is consistent with any project management approach that requires simultaneous attention to societal, institutional, and technical concerns.
REFERENCES
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DOE. 2001a. Office of Civilian Radioactive Waste Management. Letter from Sandra Waisley, DOE’s Contracting Officers Representative to Ken G.Hess, President and General Manager of Bechtel SAIC Company, LLC. November 2, 2001.
DOE. 2001b. Office of Civilian Radioactive Waste Management. Presentation before the committee during public meeting on September 7, 2001. Washington, District of Columbia .
DOE. 2002a. Final Environmental Impact Statement for a Geologic Repository for the Disposal of Spent Nuclear Fuel and High-level Radioactive Waste at Yucca Mountain, Nye County, Nevada. Available at: <http://www.ymp.gov/documents/feis_a/index.htm>.
DOE. 2002b. Yucca Mountain Science and Engineering Report. Technical Information Supporting Site Recommendation Consideration. Revision 1. February 2002. DOE/RW-0539–1. Available at: <http://www.ymp.gov/documents/ser_b/front.pdf>.
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NEA. 1999b. Progress Towards Geologic Disposal of Radioactive Waste: Where Do We Stand? An International Assessment. Organization for Economic Cooperation and Development. Paris, France.
NEA. 1999c. Confidence in the Long-Term Safety of Deep Geological Repositories: Its Development and Communication. Organization for Economic Cooperation and Development. Paris, France.
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NRC. 1990. Rethinking High-Level Radioactive Waste Disposal. National Academy Press. Washington, District of Columbia.
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NRC. 2001a. Disposition of High-Level Waste and Spent Nuclear Fuel. The Continuing Societal and Technical Challenges. National Academy Press. Washington, District of Columbia.
NRC. 2001b. International workshop organized within the study Principles and Operational Strategies for Staged Repository Systems. There are no proceedings from this workshop. September 5–6, 2001. Washington, District of Columbia.
NWPAA (Nuclear Waste Policy Act as amended), 1987. Nuclear Waste Policy Act as amended by P.L. 100–203.
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