Shutdown seismic PSA was performed for the plant cold shutdown condition. Normally, automatic ECCS signal is blocked after the Permission Signal is indicated during the plant cooldown process of PWR. In response to this, PSA model including manual actuation of ECCS signal on the postulated LOCA condition during cold shutdown state was developed based on the actual plant Emergency Operation Manual, which consists of several steps, such as, 1) LOCA event diagnosis, 2) isolating RHR system, 3) manual actuation of ECCS signal, 4) switching RHR to Low Pressure Injection mode. This PSA model with evaluated human error rates, was quantified demonstrating that risk level for the cold shutdown condition is in the acceptable range, however, suggesting some room for model improvement considering more realistic manual ECCS actuation procedure depending on the size of the LOCA.

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