05000364/LER-2007-001
| Joseph M. Farley Nuclear Plant - | |
| Event date: | 10-03-2007 |
|---|---|
| Report date: | 11-19-2007 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3642007001R00 - NRC Website | |
Plant and System Identification Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
On October 3, 2007 at 1410, with the reactor at 100% power, Unit 2 automatically tripped due to a loss of power to the Unit 2 8-train electrical distribution system [EA]. This occurred during a Unit 1 refueling outage while performing testing on Unit 1 Main Generator Differential Lockout relay. Upon manual actuation of an HEA relay for testing of the Unit 1 Main Generator Differential Lockout Relay, all breakers to the #1 - 230 KV bus and the Webb offsite power line unexpectedly tripped, including breaker 944, which was supplying the 2B Startup Transformer. As a result, the supply breaker to 2B Startup Transformer was inadvertently tripped.
Loss of power from the 28 Startup Transformer ultimately de-energized the Reactor Coolant Pump (RCP) breaker position indication relay.
Cause of Event
This event was caused by a testing procedure that lacked a step to block the High Voltage Switchyard (HVSY) breaker failure sequence relays. The failure to block resulted in the breaker failure sequence relays actuating.
The breaker failure sequence relays tripped the associated HVSY breakers, which then de-energized the 2B Startup Transformer. Loss of the 28 Startup Transformer ultimately led to loss of RCP Breaker Indication relay (1 out of 3 coincidence), resulting in Unit 2 reactor trip. The de-energization of the 2B Startup Transformer was caused by a loss of feed associated from the HVSY breaker failure sequence relay actuation and an Auto Bank transformer being removed from service for maintenance.
Safety Assessment All safety systems functioned as designed after the trip. Loss of power to Emergency Safeguards Features (ESF) busses was restored automatically by the Emergency Alternating Current (EAC) power system Diesel Generator set. Both main feedwater pumps tripped following the reactor trip. In each case, the trip was attributed to a slow automatic startup of a redundant support pump following loss of electrical power. The main feedwater pumps remained recoverable from the control room using established procedures, if they had been needed. Therefore, the health and safety of the public were unaffected by this event.
This event does not represent a Safety System Functional Failure.
This event represents an Unplanned Scram. According to data reporting guidelines, this event did not represent an Unplanned Scram with Complications since power to ESF busses was restored automatically and main feedwater pumps were recoverable.
Corrective Action The subject testing procedure has been revised. In addition, similar procedures were reviewed and revised during U1RF21.
The Maintenance procedure writer's guide has been revised to include requirements to obtain utility transmission personnel's concurrence with technical content for procedures that include circuits that interface with the HVSY.
Prior to use, remaining relay test procedures will be revised in accordance with Maintenance procedure writer's guidance.
Additional Information
Other systems affected: No systems other than those already mentioned in this report were affected by this event.
Commitment information: This report does not create any permanent licensing commitments.
Previous similar events: There have been no similar LER's in the past two years.
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