July 12, 2005 Telephone Report in Accordance with
10 CFR 50.73(a)(2)(iv)(A) Invalid Actuation of the "B"
Residual Heat Removal (
RHR) Pump.
SPECIFIC TRAINS AND SYSTEMS THAT WERE ACTUATED
During a maintenance activity involving replacement of a safeguards relay, "B" Train RHR Pump 2P-10B was started inadvertently. The RHR pump is part of the emergency core cooling system (ECCS).
DESCRIPTION OF WHETHER EACH TRAIN ACTUATION WAS COMPLETE OR PARTIAL
On May 17, 2005, Unit 2 was in a shutdown condition (MODE 6) for routine refueling outage. At approximately 0042, Unit 2 RHR Pump 2P-10B was inadvertently started. Since RHR Pump 2P-10A had already been running for normal shutdown decay heat removal, the inadvertent start of the B RHR pump resulted in both RHR pumps running. Operations observed an increase in RHR flow but initially attributed the flow change to the RHR Heat Exchanger (HX) Bypass Flow Control Valve, which was operating in automatic.
At the time of the inadvertent pump start, technicians were landing a wire as part of performance of a procedure to replace a safeguards relay. During this activity, the technicians heard a breaker close in the 480 VAC safeguards bus. Primary Plant Computer System (PPCS) computer data indicates that this breaker closure corresponded to the 2P-10B RHR Pump start. The technicians were not aware that this breaker closure was caused by their activity. The inadvertent RHR pump start was identified at 0525.
The investigation of this event determined that a current path was created during the relay replacement, which caused starting of 2P-10B. No other ECCS components were actuated during this event. A review of the activity could not determine the specific wire that was lifted landed to cause the pump start. Rather several wire combinations were noted, each of which could have caused what is commonly referred to as a 'sneak' current path. These current paths can result in the RHR pump starting circuit being energized.
DESCRIPTION OF WHETHER OR NOT THE SYSTEM STARTED AND FUNCTIONED SUCCESSFULLY
This event was not safety significant. The RHR pump started and functioned successfully. The RHR pump was the only ECCS component in the system affected. Since the pump was aligned in the standby mode to provide normal decay heat removal cooling, its start appropriately resulted in additional cooling flow being pumped to the reactor core. The RHR pump was secured and returned to standby mode following discovery of this condition.
As corrective action, a procedure change was initiated to add a precaution statement to ensure the associated safeguards relay cabinet is deenergized to the extent possible prior to similar maintenance activities to prevent inadvertent safeguards actuations. This item is documented in the PBNP corrective action process system (CAP 064616).
The NRC Resident Inspector was notified of this event report by the licensee.
