Trial application of PRATOOL: Performance of sensitivity studies on service water systems

PRATOOL is a computer program developed to supplement the Integrated Reliability and Risk Analysis System (IRRAS) probabilistic risk assessment (PRA) computer program. It is intended to be a tool for performing PRA sensitivity analyses. This will allow a PRA's results to be easily reevaluated to show its sensitivity to changing parameter (system, component type, basic event, etc.) values (i.e., failure rates). This report documents a trial application of PRATOOL. It evaluates the sensitivity of core damage frequency to service water system availability at several nuclear power plants. For the purpose of this trail application of PRATOOL, service water system sensitivity studies were performed using the results of several NUREG- 1150 PRAs. These plants were chosen because their PRAs were already loaded into the IRRAS data base. Therefore, they are readily available for this type of study. PRATOOL contains a small subset of the functions provided by IRRAS. The user can select sets of parameters that will act as the bases for sensitivity analyses. Depending on the PRA used, the parameters selected can include: systems, component types, trains, locations, failure modes, and basic events. It will also perform and AND-ing operation on selected parameters. This allows the user define any number of possible combinations of parameters. The results of the four sensitivity studies would tend to indicate that the SWS availability is important for BWRs but unimportant for PWRs. Both BWRs showed significant increases in CDF if their SWS failure rates are allowed to increase. From the results of the four sensitivity studies, it is interesting to note that no improvements made to any of the SWSs' failure rates would result in a significant decrease on CDF. 10 figs