05000298/FIN-2017011-01
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Finding | |
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| Title | Emergency Transformer Bus Failure due to Inadequate Inspection and Testing Activities |
| Description | AV. The inspectors identified a preliminary low -to-moderate safety significance (White) finding with two NRC- identified apparent violations of Technical Specification 5.4.1.a, for the licensees failure to implement and maintain Maintenance Procedure 7.3.41, Examination and High Pot Testing of Non- Segregated Buses and Associated Equipment, Revision 10, during testing and inspection of the emergency station service transformer 4160 V bus bars. Specifically, the inspectors identified: 1. A violation of Technical Specification 5.4.1.a, for the failure to implement inspection instructions to examine the emergency transformer bus insulation for discoloration and repair the associated components on March 23, 2015; and 2. A violation of Technical Specification 5.4.1.a, for the failure to maintain adequate instructions for performing high potential testing of the emergency transformer bus bars between March 23, 2015 , and April 18, 2017. As a result, the licensee did not properly assess corona- related degradation on the emergency transformer bus, which resulted in a n emergency transformer bus fault and a loss of the emergency transformer and the supplemental diesel generator on January 17, 2017. Corrective actions to restore compliance included replacement of the faulted portions of the emergency transformer bus, extent of condition inspection and cleaning of the remainder of the emergency transformer bus bars, long term corrective actions to replace the emergency transformer bus insulation, and revision of high potential testing procedure instructions. The licensee entered these issues into the corrective action program as Condition Reports CR- CNS -2017- 00223 and CR -CNS -2017 -02164. The licensees failure to implement and maintain Maintenance Procedure 7.3.41 to properly assess degradation of the emergency station service transformer bus, in violation of Technical Specification 5.4.1.a, was a performance deficiency. The performance deficiency was determined to be more than minor, and therefore a finding, because it was associated with the equipment performance attribute of the Initiating Events Cornerstone and affected the cornerstone objective to limit the likelihood of events that upset plant stability and 3 challenge critical safety functions during shutdown, as well as power operations. Specifically, the finding resulted in an emergency transformer bus fault and a loss of the emergency transformer and the supplemental diesel generator. Using NRC Inspection Manual Chapter 0609, Appendix A, The Significance Determination Process (SDP) for Findings At -Power, dated June 19, 2012, the inspectors determined that the finding required a detailed risk evaluation because it involve d the partial loss of a support system that contributes to the likelihood of, or causes, an initiating event (loss -of-offsite power), and the finding affected mitigation equipment (supplemental diesel generator). A senior reactor analyst performed a detailed risk evaluation in accordance with Inspection Manual Chapter 0609, Appendix A, Section 6.0, Detailed Risk Evaluation. The calculated increase in core damage frequency was dominated by station blackout initiators. The NRC preliminarily determined that the increase in core damage frequency for internal and external initiators was 6.3E -6/year, a finding of low -to-moderate risk significance (White). The performance deficiency had a cross -cutting aspect in the area of problem identification and resolution associated with evaluation, because the licensee failed to thoroughly evaluate emergency transformer electrical bus discoloration and high potential test failures to ensure that resolutions addressed the causes and extent of conditions commensurate with their safety significance [P.2 ]. |
| Site: | Cooper  |
|---|---|
| Report | IR 05000298/2017011 Section 4OA2 |
| Date counted | Sep 30, 2017 (2017Q3) |
| Type: | AV: White |
| cornerstone | Initiating Events |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71152 |
| Inspectors (proximate) | P Voss C Henderson J Watkins R Deese T Pruett |
| Violation of: | Technical Specification - Procedures |
| CCA | P.2, Evaluation |
| INPO aspect | PI.2 |
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Finding - Cooper - IR 05000298/2017011 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Cooper) @ 2017Q3
Self-Identified List (Cooper)
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