ASME's interest in risk-informed IST

摘要

Over five years ago the ASME identified an application for using the PRA technology to determine the risk of IST components in nuclear power plants. This PRA technology was almost ideal for the IST of pumps and valves because every nuclear powerplant had prepared a PRA in response t6 the NRC Generic Letter 88-20 and because most of the IST pumps and about half of the IST valves are modeled in the PRA. The ASME Center for Research and Technology performed a project several years ago thatdeveloped the RI-IST methodology. This methodology is a blending process by the Expert Panel of the PRA engineering results with the traditional engineering results. The ASME O&M Committee has developed the OMN-3 Code Case to categorize IST pumps andvalves into HSSC and LSSC categories. The Committee is currently in the process of developing a series of RI-IST application code cases for various types of components as an alternative to the current IST requirements in the ASME OM Code. Those code cases include:OMN-component Code Cases - series of component testing strategies for HSSCs and LSSCs (i.e., pumps, CVs, AOVs, MOVs)OMN-s Code Case - categorization process for HSSC and LSSC snubbers, as well as testing strategies for snubbers (in harsh and benign service conditions).Since IST pumps and valves are mostly modeled in the PRA, the approach for RI-IST for pumps and valves is a component level application of the PRA. Since IST snubbers are rarely modeled in the PRA, the approach for RI-IST for snubbers is a system levelapplication of the PRA. In both the pump and valve component approach and in the system snubber approach, very few of the IST components turn out to be high risk components. For these few high risk components, the testing strategy attempts to monitorcomponent degradation and predict component failure. For some high risk components the current IST program requirements already have this highly effective testing strategy, while other components need to apply better performance-based testing strategiesto achieve highly effective testing strategies. For the numerous low risk components the current IST requirements are frequently too conservative (i.e., too much testing for the few failures found with much expended resources). Thus the application of the RI-IST methodology to pumps, valves, and snubbers enhances safety for the few truly risk significant components and provides better operating economics for the numerous low risk components.