Risk-based in-service testing pilot project. Final report

At nuclear power plants, all safety-related pumps and valves are tested regularly pursuant to requirements of USNRC in 10 CFR 50.55 as implemented by ASME Code Section 11. However, many Probabilistic Safety Analyses have shown that only a small fraction of these components are truly risk significant. By using a blend of deterministic and risk information, a procedure has been developed to delineate between safety significant components and others. By focusing resources on safety significant components and reducing the frequency of testing for others, utilities can reduce costs while maintaining safety. Ten pilot plant utilities performed a series of risk ranking studies that applied PSA methods in conjunction with deterministic analysis to establish the safety significance of IST components. In each instance expert panels finalized the placement of components into more safety significant and less safety significant groupings. The pilot projects found that the Fussell-Vesely risk indicator was useful when assessing operational readiness and Risk Achievement Worth when considering out-of-service conditions. Using an expert panel provided considerable flexibility and allowed qualitative information to be incorporated in the rankings. The pilot plants demonstrated that the IST risk-ranking methodology developed in the project gave consistent results