Accident characterization methodology

The Nuclear Regulatory Commission (NRC) is preparing NUREG-1150 to examine the risk from a selected group of nuclear power plants. NUREG-1150 will provide technical bases for comparison of NRC research to industry results and resolution of numerous severe accident issues. In support of NUREG-1150, Sandia National Laboratories has directed the production of Level 3 Probabilistic Risk Assessments (PRAs) for the Surry, Sequoyah, Peach Bottom, and Grand Gulf nuclear power plants. The Accident Sequence Evaluation Program (ASEP) at Sandia has been responsible for the Level 1 portion of the analyses, which includes estimation of core damage frequency and characterization of the dominant sequences. The ASEP analyses are being documented in NUREG/CR-4550. The purpose of this paper is to briefly describe and evaluate the methodology utilized in these analyses. The four Level 1 PRAs have several objectives. They provide estimates of the internal event core-damage frequencies for the four plants along with identification of the dominant accident sequences and the events that drive those sequences. Uncertainty and sensitivity analyses are presented for each plant