Seismically induced relay chatter risk analysis for the Advanced Test Reactor

A seismic probabilistic risk assessment (PRA) was performed as part of the Level I PRA for the Department of Energy (DOE) Advanced Test Reactor (ATR) located at the Idaho National Engineering Laboratory (INEL). This seismic PRA included a comprehensive and efficient seismically-induced relay chatter risk analysis. The key elements to this comprehensive and efficient seismically-induced relay chatter analysis included (1) screening procedures to identify the critical relays to be evaluated, (2) streamlined seismic fragility evaluation, and (3) comprehensive seismic risk evaluation using detailed event trees and fault trees. These key elements were performed to provide a core fuel damage frequency evaluation due to seismically induced relay chatter. A sensitivity analysis was performed to evaluate the impact of including seismically-induced relay chatter events in the seismic PRA. The systems analysis was performed by EG G Idaho, Inc. and the fragilities for the relays were developed by EQE Engineering Consultants.