Risk Impacts of Pressurizer Safety Valve Reseat Failure

In an effort to develop probabilistic safety assessments (PSAs) that are as realistic as possible, component failure rates are traditionally based on a combination of experience, component testing, and expert judgment. During various accident sequences modeled in the PSA, the pressurizer safety valves (PSVs) of a pressurized water reactor (PWR) may cycle numerous times. The PSVs will initially relieve steam. In some longer duration accident sequences, the steam relief will eventually become liquid relief. With each cycle of the PSV, there is a probability that the safety valve will fail to reseat. The PSV failure-to-reseat results in the need for additional mitigative systems to prevent core damage. This paper describes a quantitative assessment to identify risk impacts of the failure probability due to the repeated cycling operation of PSVs (pressurizer safety valves) under severe accidents