Proceedings of the Eighth International Conference on Probabilistic Safety Assessment & Management (PSAM)
269 Consequence Sensitivity Analyses for a Risk-Informed Review of a Preclosure Safety Analysis (PSAM-0440)
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The U.S. Department of Energy (DOE) is preparing a license application for a potential geologic repository for high-level waste disposal. A preclosure safety analysis would be submitted as part of a potential license application for review by the U.S. Nuclear Regulatory Commission (NRC). The preclosure period includes the geologic repository operations prior to permanent closure of the potential repository, including receipt, transfer, and emplacement of high-level waste. NRC would conduct a risk-informed performance-based review, in which in-depth technical evaluations are focused on technical areas that are significant with respect to demonstration of compliance with the performance objectives specified by the governing regulations.
The Center for Nuclear Waste Regulatory Analyses (CNWRA) developed the PCSA Tool software to aid in the regulatory review of the DOE preclosure safety analysis. One feature of the PCSA Tool is its capability for performing probabilistic assessments of radiological dose to members of the public for potential atmospheric release scenarios of spent nuclear fuel that could result from repository operations. Dose sensitivity analyses are being conducted for potential release scenarios and atmospheric conditions at the geologic repository. These analyses include probabilistic consideration of the variability and uncertainty in modeling parameters that influence calculated doses. These sensitivity analyses are intended to identify significant dose modeling parameters and associated technical areas, including uncertainties, that may be focused on in a risk-informed regulatory review of the preclosure design and operations in a potential DOE license application.
The objectives of this paper are to (i) identify individual parameters with the greatest potential to significantly influence the results and (ii) quantify the sensitivity of results to large input variations for individual parameters. Results from initial sensitivity scoping calculations for potential offsite consequences from a filtered atmospheric release of airborne radioactive material are presented in this paper. The paper identified significant radiological dose pathways, individual radionuclide contributions, and influential parameters and uncertainties. Effects on mean total dose estimates were investigated in absolute and relative senses, and results from these two approaches were found to be in general agreement. Aside from two noted exceptions resulting in large reductions in the estimated consequences, the results did not show order-of-magnitude sensitivities to individual parameter values. Sensitivity calculations were presented for a single baseline scenario. This work provides a foundation to further use sensitivity analyses to investigate other scenarios, analytical techniques, and sensitivity metrics.