05000261/FIN-2010009-09
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Finding | |
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| Title | Failure to Repair Circuit Breaker 52/24 Resulting in Breaker Being Unable to Operate |
| Description | Circuit breaker 52/24 is the non safety-related tie circuit breaker between 4 kV Bus 4 and Bus 5. Following an electrical fault on cabling between this breaker and Bus 5 as described in Section 4.1, the breaker failed to open to clear the fault due to a lack of control power. The team reviewed equipment records related to circuit breaker 52/24 and determined that Work Request 357740 was written in November 2008 to repair the closed position indicating light located on the front of the circuit breaker. Because the closed position light would not illuminate after the light bulb was replaced, licensee personnel assumed the problem involved the socket for the bulb. Although the licensee had subsequently developed a work order to repair the socket, the licensee had not performed any additional repairs up to the time of the event. A number of opportunities existed to identify the source of the problem, including additional work requests and walkdowns by the system engineer. The additional work requests were canceled to the work order and the system engineer failed to recognize the potential impact of the failed indicating light regarding breaker operation. Following the event, the licensee determined that one of the control power fuses in the breaker trip circuit was failed. Laboratory examination by the licensee revealed that the fuse had a cracked internal element. The licensees ERT found that the overcurrent relays and the circuit breaker were fully functional. The failed fuse caused the breaker trip circuit to be deenergized, resulting in the indicating lamp being off and preventing the circuit breaker from tripping. Operations, Maintenance, and Engineering personnel did not fully understand the significance of the deenergized breaker indicating light. Operations personnel did not request an engineering assessment when they reviewed the work order. However, because station engineering was independently aware of the condition, it is not evident that a request for an engineering assessment would have resulted in a different outcome. The broken fuse, style LPN-RK-30SP, was manufactured by Bussman Division of Cooper Industries. As part of their corrective actions for this problem, the licensee checked the resistance of 16 fuses of the same style to determine whether any incipient degradation was taking place. The tested group included in-service fuses of various sizes as well as three new fuses. The licensee determined all the fuses had acceptable resistance readings. The licensee stated they would also provide training to appropriate plant personnel regarding this event and expectations for response to circuit breaker indicating lamps being off when they should be on. (Note: On April 14, 2010, the NRC issued Information Notice 2010-09, Importance of Understanding Circuit Breaker Control Power Indications, which described the problem with circuit breaker 52/24 control power). Section 4.1 states that, because of the high magnitude of the fault current, a reactor trip would have occurred as a result of the March 28 event, regardless of whether circuit breaker 52/24 was fully functional. However, for potential faults resulting in smaller currents, proper operation of circuit breaker 52/24 would prevent a reactor trip. The team concluded the licensee failed to understand the possible implications of circuit breaker 52/24 indicating light being off and should have pursued the issue in a timely manner. The problem existed for approximately 17 months until this event revealed the circuit breaker was unable to isolate a fault condition. Additional review by the NRC will be needed to determine whether the failure to correct, in a timely manner, a problem with the indicating light for circuit breaker 52/24 and the underlying problem with the control power fuse represents a performance deficiency. An Unresolved Item will be opened pending completion of this review. The issue will be identified as URI 05000261/2010009-09, Failure to Repair Circuit Breaker 52/24 Resulting in Breaker Being Unable to Operate. |
| Site: | Robinson  |
|---|---|
| Report | IR 05000261/2010009 Section 4OA5 |
| Date counted | Jun 30, 2010 (2010Q2) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 93800 |
| Inspectors (proximate) | J Hanna J Hickey L Miller L Wert P Fillion P Pieringer R Monk S Currie F Ehrhardta Nielsenc Kontz D Bollock D Mills G Laska G Skinner J Beavers J Brady J Hickey J Worosilo M Bates P Braxton R Musserc Rappd Bollock G Hopper J Polickoski J Rivera Ortiz R Curetonr Monkf Ehrhardt J Hanna L Miller J Hickey P Fillion L Wert P Pieringer S Currie |
| INPO aspect | |
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Finding - Robinson - IR 05000261/2010009 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Robinson) @ 2010Q2
Self-Identified List (Robinson)
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