Estimation of relay screening criteria for the NPP seismic probabilistic risk assessment

A relay may be screened out in SPRA if the relay chatter capacity is shown to be sufficiently high based upon preliminary bounding calculation. For screened out relays, no further detailed fragility analysis would be performed. Seismic capacity of relay is conservatively estimated based on the dynamic qualification data, fragility data or earthquake experience data. The fragility test data is required for the ultimate seismic capacity of relay. It is very difficult to estimate the fragility level of relays, since the fragility data for relay is rare. In past SPRAs, the relay chatter screening has been performed based on the review level earthquake used in seismic margin analysis (SMA). To account for the capacity level assumed in the screening level an additional element or surrogate element must be added to the SPRA to represent the screened out component. The state-of-the-art review and estimation of relay screening criteria were performed to proposed the realistic screening criteria and the procedures for considering the screened out element