05000529/LER-2003-002
| Palo Verde Nuclear Generating Station Unit 2 | |
| Event date: | 11-21-2003 |
|---|---|
| Report date: | 01-16-2004 |
| Initial Reporting | |
| ENS 40349 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 5292003002R00 - NRC Website | |
1. REPORTING REQUIREMENT(S):
APS is reporting this condition pursuant to 10 CFR 50.73 (a) (2) (iv) (A) due to the automatic actuation of the emergency ac electrical power systems, emergency diesel generators (EDGs) (EI1C Code: EB).
Pursuant to 10 CFR 50.72 (b) (3) (iv) (A), a notification was made to the Headquarters Operations Officer on November 22, 2003 (reference ENS # 40349).
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The diesel generator system (EEGs) (El IC Code: EB) is a class 1E standby generation system that functions as a standby source of AC power for safe plant shutdown in the event of loss of preferred power. This system includes all necessary auxiliaries to maintain the diesel engine in a readiness condition. Each diesel generator is an independent unit capable of providing power to safety equipment in the event of the loss of the preferred (off-site) power (LOP) to safely shutdown the plant or mitigate the consequences of a loss of coolant accident (LOCA).
3. INITIAL PLANT CONDITIONS:
On November 21, 2003, at approximately 22:53 Mountain Standard Time (MST), Palo Verde Unit 2 was defueled in its 11th refueling outage.
There were no major structures, systems, or components that were inoperable at the start of the event that contributed to the event.
Isochronous Test." As part of restoring train A safety related bus in Unit #2 back to offsite power, the Diesel Generator (DG) was paralleled with the GTG. The procedure then called for unloading and disconnecting from the GTG, paralleling the DG with offsite power, and then unloading and shutting down the DG. The objective of the restoration section is to maintain uninterrupted power to the A train bus. During the process of attempting to unload the GTG, by increasing load on the DG, the GTG output breaker opened unexpectedly, and the DG accepted the load. Shortly afterwards, about the time the control room operators switched the DG to the isochronous mode of operation, the DG test mode start/run relay de-energized, the DG output breaker tripped de-energizing the bus. EDG "A" shifted from the "test run" mode to the °emergency" mode (on a loss of offsite power (LOP) signal) and the output breaker re-closed, re-supplying the train "A" 4.16 KV bus. The DG then successfully ran and accepted the required loads in the emergency mode.
Offsite power was available to both safety buses throughout the event. The other (Train "B") safety bus was being supplied by offsite power and its EDG was operable. The offsite electrical grid was stable.
Palo Verde Unit 2 was defueled in its 11th refueling outage. No other ESF actuations occurred and none were required. There were no structures, systems, or components that were inoperable at the time of discovery that contributed to this condition. There were no failures that rendered a train of a safety system inoperable and no failures of components with multiple functions were involved. The event did not result in the release of radioactivity to the environment and did not adversely affect the safe operation of the plant or health and safety of the public.
On November 22, 2003, the NRC Operations Center was notified in accordance with 10CFR50.72(b)(3) of the event at approximately 02:30 MST.
This condition did not adversely affect the safe operation of the plant or health and safety of the public. Specifically, it did not result in the release of radioactivity; it did not affect or result in any other ESF actuations, and caused no failures of the other train safety systems.
Unit 2 was in an outage and de-fueled. The affected ESF train A was removed from service for testing and the B train was not affected. Two offsite power sources were available at all times during this event. The 13G operated and accepted loads in the emergency mode within its design basis requirements; therefore there was no impact to the safety analysis or consequences due to this event.
There are no actual safety consequences as a result of this event, the event would not have prevented the fulfillment of the safety function, and the condition did not result in a safety system functional failure as defined by 10 CFR50.73 (a) (2) (v).
6. CAUSE OF THE EVENT:
APS has concluded the direct cause of the LOP on the A train bus was the de-energizing of the of the DG test mode start/run relay. The cause of why the relay de-energized has not been determined and is currently being investigated under the APS corrective action program.
No unusual characteristics of the work location (e.g., noise, heat, poor lighting) directly contributed to this event.
7. CORRECTIVE ACTIONS:
Troubleshooting was performed and the test mode start/run relay was replaced.
An administrative hold had been placed on the "GTG lsochronous Test," the test procedure in use at the time of the event. Minor revisions to this procedure were made following troubleshooting. The test was re-performed without any incidents and completed satisfactorily.
roAc FORM 366A 1/.20E/1) Any additional corrective actions taken as a result of the investigation of this event will be implemented in accordance with the APS corrective action program. If information is subsequently developed that would significantly affect a reader's understanding or perception of this event, a supplement to this LER will be submitted.
8. PREVIOUS SIMILAR EVENTS:
In the past three years, Palo Verde Nuclear Generating Station has not experienced a valid EDG actuation.
9. ADDITIONAL INFORMATION:
None.
NR( FORM 368A17-2001j