05000317/LER-2003-001, Re Failure of 4 Kv GE Breaker Due to Cracking in Auxiliary Switch Cam Follower
| ML030710262 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 03/07/2003 |
| From: | Nietmann K Constellation Energy Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 03-001-00 | |
| Download: ML030710262 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 3172003001R00 - NRC Website | |
text
Kevin J. Nietmann Plant General Manager Calvert Cliffs Nuclear Power Plant Constellation Generation Group, LLC 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 410 495-4101 410 495-4787 Fax Constellation Energy Group March 7, 2003 U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
SUBJECT:
Document Control Desk Calvert Cliffs Nuclear Power Plant Unit No. 1; Docket No. 50-317; License No. DPR 53 Licensee Event Report 2003-01 Failure of 4 kV GE Breaker Due to Cracking in Auxiliary Switch Cam Follower The attached report is being sent to you as required under 10 CFR 50.73 guidelines. Should you have questions regarding this report, we will be pleased to discuss them with you.
Very truly yours,
'7e KJN/MJY/bjd Attachment cc:
J. Petro, Esquire J. E. Silberg, Esquire Director, Project Directorate I-1, NRC G. S. Vissing, NRC H. J. Miller, NRC Resident Inspector, NRC R. I. McLean, DNR
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Abstract
On January 6, 2003, with Unit 1 and Unit 2 operating at 100 percent power, the 1 B Diesel Generator (DG) Breaker, 1BKR152-1403, Circuit Breaker Assembly 199, failed to close on demand during a required surveillance test. Breaker 1 BKR1 52-1403 is the output breaker for the 1 B -DG, which provides power to 4 kV Alternating Current Vital Bus 14. The emergency diesel generators provide a dependable onsite power source capable of starting and supplying the essential loads necessary to safely shut down the plant and maintain it in a safe shutdown condition under all conditions. Subsequent investigation revealed Breaker IBKRI52-1403 could not have been relied on to perform its safety function since the date of the last required surveillance test on December 9, 2002. The immediate physical cause for the breaker failing to close on demand was a physical failure in one of the auxiliary switch cam followers. The auxiliary switch contact provides a close signal to the associated circuit breaker. The auxiliary switch contact will not perform its intended function with a broken cam follower. The failure of Breaker 1BKR152-1403 caused the 1B DG to be unavailable to respond and meet its intended safety function during a design basis event. The emergency on-site power safety function was maintained by the 1A DG during this period.
NRC FORM 366 (7-2001)
(If more space is required, use additional copies of NRC Formn 366A)
I.
DESCRIPTION OF EVENT
On January 6, 2003, with both Unit 1 and Unit 2 operating at 100 percent power, the 1 B Diesel Generator Breaker, 1BKR152-1403, Circuit Breaker Assembly 199, failed to close onl demand during a required surveillance test. Breaker IBKR1 52-1 403, a General Electric Magne Blast Circuit Breaker, Type AMH-4.76-250-1 D, Model Number 0052, is the output breaker for the 1 B Fairbanks Morse Diesel Generator (OG). The 1 B DG provides power to 4 kV Alternating Current (AC) Vital Bus 14. The diesel generators are designed to provide a dependable onsite power source capable of starting and supplying the essential loads necessary to safely shut down the plant and maintain it in a safe shutdown condition under all conditions. Subsequent investigation revealed Breaker IBKRI52-1403, and the lB DG, could not have been relied on to perform their safety functions since the date of the last required surveillance test on December 9, 2002. The immediate physical cause for the breaker failing to close on demand was a failure of the auxiliary switch cam followers. The auxiliary switch contact will not perform its intended function with a broken cam follower. The auxiliary switch contact provides a close signal to the associated circuit breaker.
The 1 B DG is one of two onsite standby power sources for Unit 1, each of which is dedicated to a separate 4 kV Engineered Safety Features (ESF) (1 E) bus. A DG starts automatically on a safety injection actuation signal or on a 4 kV 1 E bus undervoltage signal. In the event of a loss of offsite power to a 4 kV 1 E bus, if required, the ESF electrical loads will be automatically sequenced onto the DG in sufficient time to provide for safe shutdown for an anticipated operational occurrence and to ensure that the containment integrity and other vital functions are maintained in the event of a design basis accident. The failure of Breaker IBKRI52-1403 caused the lB DG to be unavailable to respond and meet its intended safety function during a design basis event.
No additional systems, structures, or components were inoperable during this event that would have contributed to its severity or that could have been used to mitigate this event, with the exception of the 11 High Pressure Safety Injection (H PSI) pump (back-up power from 1A DG).
The 11 HPSI pump was unavailable and therefore inoperable, for a period of 61 minutes on December 12, 2002. The actual safety significance of the loss of 11 HPSI for 61 minutes was included in the overall safety assessment. No automatic or manually initiated safety system responses occurred or were necessary to place the unit in a safe and stable condition as a result of the failure of the 1 B DG Output Breaker. Unit 2 was evaluated for applicability of this condition at the time it was discovered due to the use of identical type breakers. All similar Model GE 4 kV breakers in Unit 1 and Unit 2 were evaluated for a similar condition and found operable.
The 1 B DG Output Breaker failure to close resulted from a cracked cam follower in the auxiliary switch.
Breaker IBKRI52-1403 is a General Electric (GE) Magne-Blast circuit breaker. The breaker is a Type AMH-4.76-250-I D. The function of this breaker is to provide power to downstream equipment, provide remote control and indication, undervoltage trip protection, and other protective trip features for the 1 B DG.
(If more space is required, use additional copies of (If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A)
B.
Previous Occurrences
An additional failure mode identified by the manufacturer is cracking of the clear Lexan cam followers due to exposure to hydrocarbons. A General Electric Service Information Letter was issued for this failure mode prior to April 1980.
The analysis of the subject cam follower for this event has concluded that low cycle fatigue and not exposure to hydrocarbons was the cause of the failure.
An SBM model switch failed by the same apparent failure mode in August 2002. The 22 Saltwater Pump Breaker 2BKR1 52-2405 closed on demand, but the control circuit was lost and the breaker had to be tripped manually. Corrective actions for this incident included updating maintenance inspection procedures to require inspections of SBM model switch cam followers.
The intent of this corrective action was to replace the affected SBM switches on a schedule consistent with the probability of recurrence based upon past failure history. However, the procedure changes were not completed prior to the failure of 1 BKR152-1403. An Issue Report was generated to identify and evaluate the timeliness of this schedule, which had led to the ineffectiveness of this earlier corrective action. The inspection procedure changes were incorporated by March 4, 2003.