In accordance with
10 CFR 50.72 (b)(3)(v)(B) 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 August 27, 2011, following refueling, the plant was shutdown in Mode 4 with reactor coolant temperature being maintained 100-120 degrees F. Reactor coolant temperature was being controlled with
RHR B operating in the
Shutdown Cooling mode. At 2021 [EDT], an equipment failure caused a loss of
Reactor Protection System (
RPS) B resulting in a closure of RHR-V-9 (
RHR Shutdown Cooling Inboard Isolation Valve), interrupting
shutdown cooling flow. Operators transferred
RPS B to the alternate power supply and restored
RHR B to
shutdown cooling.
Shutdown cooling was out of service for 34 minutes.
During the 34 minute interruption of shutdown cooling, reactor coolant temperature rose from 107 degrees F to 111 degrees F. Following restoration of shutdown cooling, reactor coolant temperature was restored. All containment isolations resulting from the loss of RPS B occurred as expected. Further investigation is ongoing to determine the cause of the equipment failure that caused the loss of RPS B.
The licensee notified the NRC Resident Inspector.
