Computerization of Oconee PRA results for performing sensitivity analysis

This paper describes the use of fault tree analysis codes to construct and solve a logic model representing the important coremelt accident sequences from the Oconee PRA, a Probabilistic Risk Assessment of Oconee Unit 3. This model is based on the cutsets produced by the PRA for coremelt sequences. By appropriate changes in unavailabilities for the cutset basic events and initiator frequencies, this model is useful for performing fast, accurate sensitivity analysis. It can be applied to investigate PRA frequency sensitivity, importance of specific plant features to risk, and the risk-significance of proposed plant modifications. The paper begins with a brief description of important features of the Oconee PRA, including the results of the PRA and the format in which these results are available for follow-on analysis. The EPRI WAME-02 package of fault tree codes, which are used to solve the sensitivity model, is then described. The paper proceeds to detail the steps in constructing the sensitivity model with consideration of the technical problems that were overcome. Finally, the results of applying the model are presented to demonstrate its capabilities. The application chosen for this demonstration is the effect of hypothetical variations in the Standby Shutdown Facility (SSF), a stand-alone facility at Oconee designed to provide several important safety functions for maintaining safe shutdown when normal and emergency plant systems for reactor coolant system makeup and decay heat removal are unavailable