05000325/LER-2007-002
| Brunswick Steam Electric Plant (Bsep) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 3252007002R00 - NRC Website | |
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Introduction On April 1, 2007, at approximately 1528 Eastern Daylight Time (EDT), Unit 1 entered Mode 3 in accordance with Required Action 11.1 of Technical Specification (TS) 3.8.1, "AC Sources - Operating;" Mode 4 was entered at approximately 1215 EDT on April 2, 2007. The TS required shutdown was due to inoperability of emergency diesel generator (EDG) [EK] 4, which was removed from service on March 25, 2007, for planned maintenance. This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(A), due to the completion of a plant shutdown required by the plant's TSs. The NRC was notifed of the initiation of a plant shutdown required by TSs at 1255 EDT on April 1, 2007 (i.e., Event Number 43269).
Event Description
Initial Conditions At the time of the event, Unit 1 was in Mode 1, operating at approximately 100 percent of rated thermal power. Unit 1 systems necessary to support plant shutdown were operable. Unit 2 was in Mode 4, having been previously shutdown on March 3, 2007, for refueling.
Discussion At 0415 EDT on March 25, 2007, EDG 4 was removed from service for scheduled maintenance. The scope of the maintenance activities included: (1) preventive maintenance replacement of the electrical and mechanical governors with refurbished governors, (2) replacement of certain Allen-Bradley relays due to a failure experienced on EDG 2 on February 19, 2007, (3) modification of the 27PK under voltage relay, and (4) other minor maintenance activities.
On March 28, 2007, at approximately 1427 EDT, EDG 4 was started for post-maintenance testing. During this run, the mechanical governor (EGB) that had been installed (i.e., refurbished and bench tested by Engine Systems, Inc. (ESI) and supplied to BSEP in March 2007) was discovered to be failed, requiring replacement. Additionally, a "Fail to Start" annunciator was received when EDG 4 was shutdown. As a result, the decision was made to replace the EGB governor with another, in-stock, refurbished and bench tested EGB governor supplied to BSEP in 2004. The EGB governor was replaced and relays which could potentially have caused the "Fail to Start" annunciator were checked. On March 29, 2007, at 1300 EDT, EDG 4 was again started for post-maintenance testing. During this run, the EGB governor functioned properly; however, the "Fail to Start" annunciator was received when EDG 4 was shutdown.
Troubleshooting efforts, including several EDG 4 starts, were performed on March 30, 2007, and it was determined that the likely cause of the "Fail to Start" annunciator was a relay race and that this condition did not affect operability of EDG 4. This condition was introduced as a result of the Allen-Bradley relay replacement. The new style relays had differences from the old style, including a longer response time.
Event Description (continued) Additionally, the relays introduced electromagnetic interference as a result of a more precipitous voltage change when the relay changed state. The EGB governor functioned properly during these starts.
After resolving the relay issues, on March 31, 2007, at approximately 0436 EDT, EDG 4 was again started for post-maintenance testing. During this run, the EGB governor operated somewhat erratically and a vendor representative recommended that the governor be adjusted while in the loaded condition. The run was secured to make necessary procedure changes to support the recommended adjustments. Three additional EDG 4 runs were conducted to perform EGB governor adjustments and the EGB appeared to be successfully adjusted upon completion of the third run at 1723 EDT on March 31, 2007. At approximately 2016 EDT on March 31, 2007, EDG 4 was again started for post-maintenance testing. Once again, the EGB governor did not function properly.
was placed in Mode 3 at approximately 1528 EDG on April 1, 2007, and entered Mode 4 at approximately 1215 EDT on April 2, 2007.
The original EGB governor was being replaced as a result of planned preventive maintenance activities.
Engineering personnel, in conjunction with Engine Systems, Inc. (ESI) (i.e., the supplier of the governor) representatives inspected the original EGB governor and determined that it would operate acceptably for at least one more operating cycle. As such, the original governor was reinstalled and EDG was successfully returned to operable status at 0100 EDT on April 4, 2007.
Event Cause The direct cause of the TS required shutdown of Unit 1 was the inability to return EDG 4 to operable status within the seven day completion time of Required Action D.4 of TS 3.8.1. The extended out-of-service time was due to multiple equipment issues; including two failed refurbished governors and latent design problems discovered during the Allen-Bradley relay replacements only after extensive post-maintenance testing. Each individual equipment issue was manageable within the allowed outage time, but the number and sequence of discovery was such that the cumulative effect of these issues precluded EDG 4 recovery.
The mechanical governor for the emergency diesel generators is a Woodward EGB device. Woodward has identified ESI as the preferred supplier for Woodward EGB to the nuclear industry. ESI has been refurbishing Woodward governors for Carolina Power & Light Company (CP&L), now doing business as Progress Energy Carolina, Inc., for several years. The testing plan used by ESI to certify refurbished EGB governors failed to identify that the governor supplied to BSEP in March 2007 was failed or that the governor supplied in 2004 would fail early in service. ESI is performing a failure analysis of the failed EGBs and will use the results to determine changes to their refurbishment and testing practices.
Safety Assessment The safety significance of this condition is considered minimal.
The remaining three EDGs as well as offsite power were available during the inoperability of EDG 4.
Unit 1 completed a controlled shutdown in accordance with the plant's TSs. Unit 1 systems necessary to support plant shutdown were operable. Unit 2 was in Mode 4, having been previously shutdown on March 3, 2007, for refueling.
Corrective Actions
The following corrective actions to prevent recurrence have been identified as a result of this event.
- CP&L will monitor ESI's performance of the failure analysis of the failed EGBs and will use the results to determine if additional actions are warranted. This determination is currently scheduled to be made by June 15, 2007.
- Appropriate engineering changes are in progress to address the relay race and electromagnetic interference issues introduced by the replacement of Allen-Bradley relays. These changes include use of surge protection on relays of the same type to prevent the electromagnetic interference concern. These changes are currently scheduled to be completed by July 15, 2007.
Previous Similar Events
Voluntary LER 1-2005-006, submitted on September 30, 2005, reported the shutdown of Units 1 and 2 due to EDG operability concerns. Additionally, LERs 1-2004-001, dated March 4, 2004, 1-2004-003, dated October 13, 2004, and 1-2006-007, Supplement 1, dated January 26, 2007, dealt with operation prohibited by TSs due to EDG inoperability. The root causes and corrective actions associated with these events could not have been expected to prevent the event reported in this LER (i.e., LER 1-2007-002).
Commitments No regulatory commitments are contained in this report.