05000261/FIN-2009005-04
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Finding | |
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| Title | Emergency Diesel Generator Inoperable in Excess of Technical Specifications Allowed Completion Time |
| Description | A violation of TS 3.8.1. B was identified when the B Emergency Diesel Generator (EDG) was inoperable in excess of the TS allowed outage time. Enforcement discretion was exercised for this violation. No performance deficiency was identified. On April 20, 2009, the output breaker for the B EDG failed to close during the performance of planned surveillance testing. The licensee determined the cause of the breaker failure was due to the rotation of a cotter pin, used to retain a control relay lift linkage, during the previous breaker opening which prevented the lift linkage from returning to the normal position. The licensee entered the issue into the corrective action program as AR 331663 and initiated a root cause and extent of condition review. Based on the failure mechanism, the licensee, using engineering judgment concluded the B EDG had been inoperable for greater than the 7 days allowed by TS 3.8.1.B.4 and Condition C. The last successful breaker closure was March 28, 2009. As discussed in the licensees root cause report, the vendor had previously modified the breakers lifting link assembly. The drive screw/rolled pin that was originally used to retain the relays mechanical lift linkage was substituted with a cotter pin retaining component. This substitution created a design flaw because the cotter pin was susceptible to an unrecognized failure mechanism. The design flaw was reported by Westinghouse in accordance with 10 CFR 21 Reporting of Defects and Noncompliance, on May 28, 2009 (EN 45100). Because the cotter pin substitution was a vendor performed design change, the cause was not reasonably within the licensees ability to foresee and correct, therefore, no performance deficiency was identified. The inspector determined a violation of TS 3.8.1.B occurred since the B EDG was inoperable in excess of the TS allowed outage time (7 days). The inspectors determined that this violation was more than minor because it affected the equipment performance attribute of the Mitigating System cornerstone and because it affects the cornerstone objective of ensuring mitigating system availability. The inspectors determined that the breaker failure was not a performance deficiency because the cause of the failure was not reasonably within the licensees ability to foresee and correct to prevent the failure. Because a performance deficiency was not associated with this issue, it was not subject to evaluation under the formal Significance Determination Process (SDP) using Inspection Manual Chapter 0609. However, an assessment of the significance of the event was performed by the inspectors. This review resulted in the matter being assigned a risk assessment of low to moderate significance. In addition, the licensees risk evaluation found an increase in core damage probability of 2.72 E-6 (also low to moderate significance). The event was mitigated by the redundant A EDG and Dedicated Shutdown Diesel Generator being available to respond to an event. Additionally, the licensee concluded that several response actions to recover the B EDG, such as the discovery of the misaligned relay lift linkage or replacing the affected breaker with a spare could be accomplished in an estimated time frame which ranged from one to four hours. The inspectors reviewed the licensees assessment and corrective actions for the event, and determined they were appropriate to the circumstances. All similar breakers at the Robinson Plant which are susceptible to this failure are scheduled to be modified by May 15, 2010. Prior to implementation of this modification, satisfactory compensatory actions have been implemented which will ensure successful operation of the breaker. |
| Site: | Robinson  |
|---|---|
| Report | IR 05000261/2009005 Section 4OA3 |
| Date counted | Dec 31, 2009 (2009Q4) |
| Type: | Violation: Severity level Enforcement Discretion |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | A Nielsen J Austin R Moore G Wilson J Hickey D Mas-Penaranda D Bollock C Even R Patterson L Wert G Crespo |
| INPO aspect | |
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Finding - Robinson - IR 05000261/2009005 | |||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Robinson) @ 2009Q4
Self-Identified List (Robinson)
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