Analysis of core damage frequency from internal events, Grand Gulf, Unit 1: Main report

This document contains the accident sequence analyses for Grand Gulf Unit 1, one of the reference plants being examined as part of the NUREG-1150 effort by the Nuclear Regulatory Commission. NUREG-1150 will document the risk of a selected group of nuclear power plants. As part of that work, this report contains the overall core damage frequency estimate for Grand Gulf Unit 1 and the accompanying plant damage state frequencies. Sensitivity and uncertainty analyses provide additional insights regarding the dominant contributors to the Grand Gulf core damage frequency estimate. The mean core damage frequency at Grand Gulf was calculated to be 2.9E-5. Station blackout type accidents (i.e., loss of all ac power accidents) were found to dominate the overall results. Anticipated transient without scram accidents were also found to be contributors. The numerical results are largely driven by common mode failure probability estimates and, to some extent, human error. Because of significant data uncertainties in these two areas, it is recommended that the results of the uncertainty and sensitivity analyses be considered before any future actions are taken based on this analysis. In particular, the single most dominant scenario may require a more detailed data search and analysis before actions are implemented on the basis of the scenario