Event Notification Report for March 20, 2011
U.S. Nuclear Regulatory Commission
Operations Center
EVENT REPORTS FOR
03/19/2011 - 03/20/2011
EVENT NUMBERS
46844
Power Reactor
Event Number: 46844
Facility: RIVER BEND
Region: 4 State: LA
Unit: [1] [] []
RX Type: [1] GE-6
NRC Notified By: DANNY WILLIAMSON
HQ OPS Officer: JOHN SHOEMAKER
Region: 4 State: LA
Unit: [1] [] []
RX Type: [1] GE-6
NRC Notified By: DANNY WILLIAMSON
HQ OPS Officer: JOHN SHOEMAKER
Notification Date: 05/12/2011
Notification Time: 11:29 [ET]
Event Date: 03/20/2011
Event Time: 07:24 [CDT]
Last Update Date: 05/12/2011
Notification Time: 11:29 [ET]
Event Date: 03/20/2011
Event Time: 07:24 [CDT]
Last Update Date: 05/12/2011
Emergency Class: NON EMERGENCY
10 CFR Section:
50.73(a)(1) - INVALID SPECIF SYSTEM ACTUATION
10 CFR Section:
50.73(a)(1) - INVALID SPECIF SYSTEM ACTUATION
Person (Organization):
DAVID PROULX (R4DO)
DAVID PROULX (R4DO)
| Unit | SCRAM Code | RX Crit | Initial PWR | Initial RX Mode | Current PWR | Current RX Mode |
|---|---|---|---|---|---|---|
| 1 | N | Y | 100 | Power Operation | 100 | Power Operation |
"A" TRAIN REACTOR PROTECTION SYSTEM UNEXPECTEDLY DE-ENERGIZED RESULTING IN A HALF SCRAM SIGNAL
"On March 20, 2011, at approximately 7:24 a.m. CDT, the 'A' reactor protection system (RPS) bus was unexpectedly de-energized. Plant systems responded as designed, resulting in a half-scram signal and the actuation of the Division 1 primary containment isolation sub-system. The Division 1 primary containment isolation valves closed in several balance-of-plant systems. After confirming that no valid RPS trip signal had occurred, operators executed the appropriate procedures to return the affected systems to the proper configuration, and to reset the half-scram signal. Plant capacity was not affected by this event.
"This event is being reported in accordance with 10CFR50.73(a)(1) as an automatic actuation of the Division 1 primary containment isolation valves in multiple systems resulting from an invalid signal.
"Each of the two redundant distribution buses in the RPS system is normally powered by its own motor-generator (MG) set. The investigation of this event determined that the output breaker of the 'A' MG set had tripped open. The most likely cause for this trip was a malfunction of the over-voltage relay circuit card in the MG set. Although the troubleshooting was inconclusive, there apparently was a momentary transient in the output of the trip setpoint adjustment potentiometer on the card, likely caused by oxidation on the contacting surface between the wiper arm and the windings.
"The over-voltage relay card on the 'A' MG set was replaced, and the unit was restored to service. Preventative maintenance tasks are being revised to periodically cycle all potentiometers in the MG set control circuits to wipe oxidation from the windings."
The Licensee has notified the NRC Resident Inspector.
"On March 20, 2011, at approximately 7:24 a.m. CDT, the 'A' reactor protection system (RPS) bus was unexpectedly de-energized. Plant systems responded as designed, resulting in a half-scram signal and the actuation of the Division 1 primary containment isolation sub-system. The Division 1 primary containment isolation valves closed in several balance-of-plant systems. After confirming that no valid RPS trip signal had occurred, operators executed the appropriate procedures to return the affected systems to the proper configuration, and to reset the half-scram signal. Plant capacity was not affected by this event.
"This event is being reported in accordance with 10CFR50.73(a)(1) as an automatic actuation of the Division 1 primary containment isolation valves in multiple systems resulting from an invalid signal.
"Each of the two redundant distribution buses in the RPS system is normally powered by its own motor-generator (MG) set. The investigation of this event determined that the output breaker of the 'A' MG set had tripped open. The most likely cause for this trip was a malfunction of the over-voltage relay circuit card in the MG set. Although the troubleshooting was inconclusive, there apparently was a momentary transient in the output of the trip setpoint adjustment potentiometer on the card, likely caused by oxidation on the contacting surface between the wiper arm and the windings.
"The over-voltage relay card on the 'A' MG set was replaced, and the unit was restored to service. Preventative maintenance tasks are being revised to periodically cycle all potentiometers in the MG set control circuits to wipe oxidation from the windings."
The Licensee has notified the NRC Resident Inspector.