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Two Reactor Trips - Wolf Creek and Grand Gulf

Submitted by NUCBIZ on March 9, 2010 - 12:05

GRAND GULF - Event Date: 03/08/2010 - AUTOMATIC REACTOR SCRAM ON LOW REACTOR WATER LEVEL - An 'A' reactor feed pump trip occurred and initiated a recirculation pump flow control valve runback. During the flow control valve runback, the 'A' recirculation hydraulic power unit tripped causing an incomplete runback.

"Reactor water level 3 (11.4 inches) was reached which is an RPS scram setpoint and also a setpoint for Group 2 (RHR to Radwaste) and Group 3 (Shutdown Cooling Isolation). No valves isolated in these systems due to [the valves] being in their normally closed position. The lowest reactor water level reached was -28 inches wide range.

"Appropriate off normal event procedures were entered to mitigate the transient with all systems responding as designed. No loss of offsite or ESF power occurred. No ECCS initiation signals were reached, and no ECCS or Diesel Generator initiation occurred. All safety systems performed as expected.

"MSIVs remained open and no SRVs lifted. Main condenser and pressure control systems remained in service. Currently, reactor water level is being maintained by the condensate and feedwater system in the normal level band and reactor pressure is being controlled to limit cooldown."

WOLF CREEK - Event Date: 03/08/2010 - MANUAL REACTOR TRIP DUE TO LOSS OF ALL MAIN FEEDWATER - Wolf Creek experienced an 'A' Main Feedwater Pump (MFP) trip at 0332 CST during a plant startup. Reactor power was 42% at the time of the manual reactor trip. The loss of the 'A' MFP resulted in no feedwater flow to the Steam Generators and a manual reactor trip was ordered due to the impending reactor trip on low-low Steam Generator level.

"Post-trip decay heat was being removed by the Condenser and Auxiliary Feedwater System. Reactor Coolant System (RCS) temperature dropped below 550 degrees Fahrenheit, which required emergency boration to ensure shutdown margin was maintained. Emergency boration was secured at 0404 CST when RCS temperature was raised to greater than 550 degrees Fahrenheit. The lowest RCS temperature reached following the reactor trip was 544 degrees Fahrenheit.

"The cause of the 'A' Main Feedwater Pump trip is not known at this time.

"Primary to secondary leakage is less than 0.224 gallons per day. All systems functioned as designed.