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| Entered date | Event description | |
|---|---|---|
| ENS 42961 | 3 November 2006 12:04:00 | This event notification is being made to report an event that could have prevented the fulfillment of the safety function to remove residual heat. On November 3, 2006, the plant was shutdown in Mode 4 (Cold Shutdown) with the reactor vessel level being maintained between 60-80 'inches' and temperature was being maintained 110-120F. Operators were performing a procedure to transfer RPS B to its alternate power supply. During the procedure, RHR-V-9 (RHR shutdown cooling inboard containment isolation valve) closed and shutdown cooling was interrupted. Reactor Recirculation Pump A remained in service providing forced flow through the core. Operators reopened RHR-V-9 and restored shutdown cooling. Reactor temperature reached 148F and vessel level reached 95 'inches' (bottom of main steam lines is 116 inches) while shutdown cooling was not in service. Shutdown cooling was restored in 45 minutes (120 minutes time to boil from 120F) after RHR-V-9 went closed. Reactor temperature and level were restored to their previous operating bands by 0451 PST. Initial indications are that RHR-V-9 closed due to an error in the procedure which failed to remove control power from RHR-V-9 during the RPS transfer. Without removing control power, a motor-closed demand would have been created in the circuit during the transfer and upon restoration of power to the valve motor, the valve would motor close. Further investigation is ongoing. The NRC Resident Inspector was notified of this event by the licensee. |