PROBABILISTIC ANALYSIS OF LIMITING CONDITIONS FOR OPERATION ACTION REQUIREMENTS INCLUDING RISK OF SHUTDOWN

When the systems needed to shut down a nuclear power plant are inoperable or degraded, the risk of shutting down the plant may be comparable to, or even higher than, that of continuing power operation with the equipment inoperable but giving priority to repairs. This concern arises because the plant may have insufficient capability for removing decay heat during the shutdown. However in many cases, plant technical specifications require immediate shutdown of the plant. Risk-based analyses for various alternatives of operational policy available in such situations are examined. These analyses can be used to define the risk-effective requirements for those standby safety systems.