05000352/FIN-2010004-02
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Finding | |
|---|---|
| Title | Failure to Identify Incorrectly Adjusted Control Power Relay Resulting in Unit 1 Manual Scram |
| Description | A self-revealing Green finding was identified for the failure to identify that the latching mechanism on a bus 114A1124A control power auxiliary relay (27X) was incorrectly adjusted during prior post-maintenance testing activities. Specifically, proper post-maintenance testing activities in 1992 and 2004 should have identified that the latching mechanism was incorrectly adjusted. The incorrectly adjusted latching mechanism prevented the automatic swap of control power to the alternate source (bus 124A) when preferred power (bus 114A) was lost due to an electrical fault. This resulted in a loss of stator water cooling run back signal that would have caused the trip of both recirculation motor-generator sets and resulted in operators having to manually initiate a reactor scram. Exelon\'s corrective actions taken or planned included verifying the latching mechanism adjustment on the site\'s other Similarly designed control power auxiliary relays, testing the automatic undervoltage transfer circuit on a periodic basis, and performing a failure analysis on the faulted underground supply cable which initiated the event. The finding was more than minor because it was associated with the Equipment Performance attribute of the Initiating Events cornerstone and affected the cornerstone objective to limit the likelihood of those events that upset plant stability and challenge critical safety functions during shutdown as well as power operations. The finding was determined to have very low safety significance (Green) in accordance with NRC IMC 0609, Attachment 4, Phase 1- Initial Screening and Characterization of Findings, because it did not contribute to both the likelihood of a reactor trip and the likelihood that mitigating equipment or function would not be available. Because the opportunities to identify the incorrectly adjusted latching relay occurred in 1992 and 2004, the inspectors determined that this finding was not reflective of current licensee performance, and, therefore, did not have a crosscutting aspect. Enforcement action does not apply because the performance deficiency did not involve a violation of regulatory requirements. |
| Site: | Limerick  |
|---|---|
| Report | IR 05000352/2010004 Section 1R12 |
| Date counted | Sep 30, 2010 (2010Q3) |
| Type: | Finding: Green |
| cornerstone | Initiating Events |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71111.12 |
| Inspectors (proximate) | E Dipaolo J Lilliendahl N Sieller J Bream P Krohn |
| INPO aspect | |
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Finding - Limerick - IR 05000352/2010004 | ||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Limerick) @ 2010Q3
Self-Identified List (Limerick)
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