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OVERVIEW

The Management and Operating Contractor established a Performance Assessment Peer Review Panel (hereinafter "the Panel") at the request of the U.S. Department of Energy Yucca Mountain Site Characterization Office. The objectives of the peer review were to provide:

The Panel conducted a phased review over a two-year period to observe the development and, ultimately, to review the Total System Performance Assessment-Viability Assessment (DOE 1998a). During the development of the Total System Performance Assessment-Viability Assessment (DOE 1998a), the Panel submitted three Interim Reports (Whipple et al., 1997a, 1997b, and 1998) to the Management and Operating Contractor with recommendations and comments on the process models, model abstractions, and draft documentation for the Total System Performance Assessment-Viability Assessment (DOE 1998a).

The Panel’s Final Report Total System Performance Assessment Peer Review Panel (Whipple et al. 1999; hereinafter "Final Report") on the Total System Performance Assessment-Viability Assessment (DOE 1998a) is based primarily on the completed Total System Performance Assessment-Viability Assessment (DOE 1998a), the Total System Performance Assessment-Viability Assessment (TSPA-VA) Analyses Technical Basis Document (CRWMS M&O 1998), and the cited references. The Final Report (Whipple et al. 1999) includes the major points from the three Interim Reports (Whipple et al. 1997a, 1997b, and 1998), updated where appropriate, as well as new findings that the Panel developed during its review of the Total System Performance Assessment-Viability Assessment (DOE 1998a).

In the Final Report (Whipple et al. 1999), the Panel notes that the objective of the Total System Performance Assessment-Viability Assessment (DOE 1998a) was to describe the probable behavior of the potential repository. The Panel states that because of the mixture of analyses (some intended to be conservative and some intended to be realistic), the Total System Performance Assessment-Viability Assessment (DOE 1998a) "cannot be viewed as an accurate projection of the probable behavior of the site." The Panel also states that it is not likely that the Total System Performance Assessment-Viability Assessment (DOE 1998a) describes the probable behavior of the potential repository system. They do, however, consider the analysis to be a useful step in evolving the understanding of how a repository could be expected to perform at Yucca Mountain.

The Management and Operating Contractor does not agree with the Panel’s position that "it is unlikely that the [Total System Performance Assessment-Viability Assessment], taken as a whole, describes the long-term probable behavior of the system." The Management and Operating Contractor believes that the Total System Performance Assessment-Viability Assessment (DOE 1998a) analyzed the long-term probable behavior of the repository system and that this behavior is likely captured within the range of results presented in the Total System Performance Assessment-Viability Assessment (DOE 1998a). The Total System Performance Assessment-Viability Assessment (DOE 1998a) was not intended to provide a precise projection of the probable behavior of the potential repository system. It was intended to provide the probable behavior of the potential repository system as a snapshot in time, given the available information and analyses, and the design concepts for the Viability Assessment design (DOE 1998b).

The Panel also noted that the Total System Performance Assessment-Viability Assessment (DOE 1998a) "has been useful in identifying aspects that are comparatively unimportant to performance, for which additional data and analyses are not likely to be beneficial." The Management and Operating Contractor concurs that the Total System Performance Assessment-Viability Assessment (DOE 1998a) has helped to identify aspects of the repository system for which additional data and analyses will not be beneficial.

The Panel goes on to state that the objective of Total System Performance Assessment-License Application will be to determine if it can be shown that the repository will comply with the applicable regulatory limits with reasonable assurance rather than to describe the probable behavior of the potential repository system. The Panel considers this objective to be significantly different from the objective of the Total System Performance Assessment-Viability Assessment (DOE 1998a) and recommends approaches for achieving it.

The Panel identifies two types of processes that need to be analyzed for the potential License Application: 1) processes for which analytical models are available, and 2) processes that may be intractable, given current analytical capabilities or current time constraints.

The Panel suggests five approaches to address these processes:

On page 44 of the Final Report (Whipple et al. 1999), the Panel also states:

For cases in which it is feasible to improve either the component models or their underlying data, the Panel recommends that efforts be made to implement such improvements wherever such changes would affect the overall assessment. Where conservative bounding analyses do not result in unduly pessimistic estimates of the total system performance, the Panel recognizes that it may not be cost-effective to spend additional time and effort refining the assessments and making them more realistic. For those issues for which, by virtue of their complexity, it is not feasible to produce more realistic models supported by data, the Panel recommends that a combination of bounding analyses and design changes be applied.
The Management and Operating Contractor concurs with these approaches. They are consistent with U.S. Department of Energy’s strategy for developing a postclosure safety case for the potential Site Recommendation/License Application, with the ongoing License Application Design Selection process, and with U.S. Department of Energy’s ongoing efforts to prioritize future work for the potential Site Recommendation/License Application.

In summary, the Panel has provided a thorough and thoughtful review of the Total System Performance Assessment-Viability Assessment (DOE 1998a). The Panel’s overarching strategy for improving the Total System Performance Assessment-Viability Assessment (DOE 1998a) analysis is consistent with the U.S. Department of Energy’s approach for developing the postclosure safety case for the potential Site Recommendation/License Application. In contrast, the Panel’s specific comments on the limitations of the component models and the associated databases were provided in the context of the Total System Performance Assessment-Viability Assessment (DOE 1998a) and the Viability Assessment design (DOE 1998b). The Management and Operating Contractor has evaluated these comments in the context of the ongoing License Application Design Selection process and efforts to re-prioritize future work. The relative importance of the Panel’s specific comments will depend on the U.S. Department of Energy’s selection of a design for the potential Site Recommendation/License Application and the evolution of the U.S. Department of Energy’s postclosure safety case. The Management and Operating Contractor will consider these specific comments for the development of the Total System Performance Assessment-Site Recommendation/License Application in the context of the design that is selected for Site Recommendation/License Application and the evolving postclosure safety case.

This report documents the comments provided in the Final Report (Whipple et al. 1999) and the Management and Operating Contractor responses to these comments. The responses were based on input from a number of scientists from the Management and Operating Contractor, several national laboratories, and the U.S. Geological Survey. The comments and responses are organized to be consistent with the major headings in the Final Report (Whipple et al. 1999). Excerpts from the Final Report (Whipple et al. 1999) are in italics; the Management and Operating Contractor responses to the comments are in straight text.

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