At 0458
CDT on 05/30/2015, with Cooper Nuclear Station Unit 1 in Mode 4 [cold shutdown], an inadvertent trip of
Residual Heat Removal (
RHR) Pump B was experienced which resulted in a loss of
shutdown cooling. The cause of the trip is currently not known and is under investigation.
Shutdown cooling was restored with B
RHR Pump at 0520 on 05/30/2015, and there have been no other issues with the system. During the loss of
shutdown cooling, forced circulation of the core was not lost due to the Reactor Recirculation System remaining in service. Based on indication from the in-service Reactor Recirculation System A loop, reactor coolant temperature experienced a 7 (seven) degree Fahrenheit increase during the event. Reactor coolant temperature did not exceed 212 degrees Fahrenheit during the event.
This condition is reportable under 10CFR50.72(b)(3)(v) - any event or condition that, at the time of discovery, could have prevented the fulfillment of the safety function of structures or systems that are needed to: B) remove residual heat.
The NRC Senior Resident inspector has been notified of this event.
- * * UPDATE PROVIDED BY DAVID VANDERKAMP TO JEFF ROTTON AT 1646 EDT ON 06/03/2015 * * *
After further evaluation of the reported transient, it was determined that the Reactor Recirculation System A Loop increased from 186 degrees F to 204 degrees F for a heatup of 18 degrees during the loss of Shutdown Cooling. The Vessel Drain temperature increased from 190 degrees F to 210 degrees F for a heatup of 20 degrees during the same time frame.
The licensee will notify the NRC Resident Inspector.
Notified R4DO (Whitten)
