Model validation from a regulatory perspective: a summary

Building confidence in the mathematical models used in safety assessments of HLW repositories is necessary if such models are to be applied successfully to the support of regulatory decisions. Conventional comparisons of model predictions to actual performance are not possible for such models over the temporal and spatial scales of interest. Uncertainties inherent in describing and modeling complex natural and engineering systems, as well as their interactions, make it difficult to discriminate between inadequacies in the mathematical models and the inadequacies of input data. This document summarizes an approach jointly developed by members of the staff of the U.S. Nuclear Regulatory Commission and of the Swedish Nuclear Power Inspectorate for the validation of models used to assess the performance of geologic repositories for high-level waste disposal. Confidence building reflects a recognition that full scientific validation of models for performance assessment of the repository system may be impossible and that the acceptance of mathematical models for regulatory purposes should be based on appropriate testing which will lead to a reasonable assurance that their results are acceptable. (authors). 8 refs., 2 figs