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Pilgrim Nuclear Power Station (PNPS) LER: Manual Scram Inserted During Reactor Shutdown

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On Sunday, April 14, 2013 at 2217 hours, with the Pilgrim Nuclear Power Station (PNPS) Reactor Mode Select Switch (RMSS) in "Startup/Hot Standby", the turbine generator previously removed from service, and the reactor subcritical on Intermediate Range Monitors Range 2 and lowering, a manual reactor scram was inserted due to reactor pressure decreasing faster than normal. At the time of the manual reactor scram PNPS was conducting a planned reactor shutdown to commence refueling outage (RFO) -19. All control rods fully inserted and Primary Containment Isolation System (PCIS) Group II (Reactor Building) and Group VI (Reactor Water Cleanup System) actuations occurred as designed due to the expected reactor water level shrink associated with the scram signal. All plant systems responded as designed. Off-site power was unaffected and was supplied by the start-up transformer (normal power supply for refuel and reactor shutdown operations).

The Main Steam Isolation Valves (MSIV) were manually closed to terminate the pressure reduction and the High Pressure Coolant Injection (HPCI) system was manually started in the pressure control mode. The plant cooldown continued with the HPCI system in pressure control and reactor water level maintained within normal bands with the condensate and feedwater system.

The Root Cause of the event was that procedure PNPS 2.1.5 did not limit operation of MO-S-2, Steam Seal Bypass Valve, to below the steam line pressure design operating limit (250 psig) of the steam seal bypass. The procedure was revised to preclude recurrence.


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