Current issues in postclosure performance assessment

Performance assessment, a type of systematic safety analysis, is a method (a) to predict the potential health, safety, and environmental effects of creating and using a nuclear waste repository, (b) to characterize these effects in terms of their magnitude and likelihood, (c) to compare the characterization of these effects to standards of acceptability, and (d) to present the results of these analyses in a format useful to regulators, scientists, and the public. Postclosure performance assessment would thus be those analyses used to predict mined geologic disposal system behavior after permanent closure. The primary focus of and motivation for performance assessment is to evaluate compliance of the repository with regulatory performance standards, although performance assessments are expected to be useful in guiding and evaluating testing, design, and site characterization activities. Given that reduction of modeling uncertainty is an important aspect of obtaining a license, a survey was made of performance assessments for high-level nuclear waste, mined geologic repositories, and of the literature addressing the major issues of performance assessment to identify potentially significant, currently outstanding issues. Given the direction that DOE received from Congress late in 1987, the issues related here are those either directly applicable to or sufficiently general tomore » be potentially applicable to a performance assessment of a Yucca Mountain, Nevada, repository.« less