05000423/FIN-2014005-02
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Finding | |
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| Title | Failure to Manage Risk of RSST Testing |
| Description | The inspectors identified a Green NCV of Title 10 of the Code of Federal Regulations (10 CFR) 50.65 (a)(4) for the failure to properly assess and manage the risk of work in the switchyard during the Unit 3 refueling outage. On October 19, the 345 kilovolt (kV) south bus tripped during U3 reserve station service transformer (RSST) leakage reactance testing. Dominion determined the direct cause for the loss of the 345 kV south bus was an incorrectly wired B RSST Y winding ground differential current transformer, which caused the RSST 6.9 kV side ground differential protective relay to actuate and the south bus to trip. This testing was performed in response to updated industry guidance on transformer maintenance and uncovered the latent error in the windings which has existed since initial installation of the current transformer. Dominion performed an extent of condition review and verified correct windings in the B RSST X winding circuit and A RSST X and Y winding circuits to ensure the proper protection schemes still existed for the transformer. In response to the unplanned loss of the south bus, Dominion stopped all work in the switchyard, took other compensatory actions to protect the remaining offsite power to the station, and entered the issue into the corrective action program (CAP) as condition report (CR)562570 and CR562580. The inspectors determined that Dominion risk mitigation plans inadequately assessed the possible consequences of the maintenance activity. Because Dominion neither considered the potential for the 15T breaker to open during the RSST leakage reactance testing nor established any mitigating actions in the case of this event, they incorrectly classified the evolution as Yellow risk instead of Orange. The inspectors determined that the failure to properly assess and manage risk is a performance deficiency which is more than minor because it would affect the protection against external factors attribute of the Initiating Events cornerstone. The underlying issue is that Dominion did not take adequate mitigating actions to reduce risk associated with the reliability of offsite power to the station. In addition, it is similar to Example 7.e from IMC 0612, Appendix E, Examples of Minor Issues, which states that the failure to perform an adequate risk assessment when required to do so is more than minor if the overall elevated plant risk would put the plant into a higher licensee-established risk category. An adequate risk assessment would have assessed the plant risk as Orange, not Yellow. The inspectors evaluated the significance of the finding using IMC 0609, Appendix K, Maintenance Risk Assessment and Risk Management Significance Determination Process. There is a note in this appendix which directs review of the issue if the licensee only uses qualitative analyses of plant configuration risk due to maintenance activities. The inspectors followed the guidance of this note and determined the issue was of very low safety significance (Green) in consultation with NRC management. The duration of the unplanned south bus outage was short (13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />), and the station took additional risk mitigation actions after the event, including suspending all work in the switchyard and transformers and the control room briefed emergency operating procedure (EOP) 3501, Loss of All AC Power. The inspectors determined this issue had a cross-cutting aspect in the area of Human Performance, Change Management, where managers maintain a clear focus on nuclear safety when implementing the change management process to ensure that significant unintended consequences are avoided. Specifically, the RSST testing performed during the outage was the initial performance of this specific test and all failure modes were not fully assessed prior to the test date. |
| Site: | Millstone  |
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| Report | IR 05000423/2014005 Section 1R13 |
| Date counted | Dec 31, 2014 (2014Q4) |
| Type: | NCV: Green |
| cornerstone | Initiating Events |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.13 |
| Inspectors (proximate) | B Fuller B Haagensen E Burket H Gray H. Anagnostopoulus J Ambrosini J D'Antonio L Mckown N Floyd R Mckinley |
| Violation of: | 10 CFR 50.65(a)(4) 10 CFR 50.65 |
| CCA | H.3, Change Management |
| INPO aspect | LA.5 |
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Finding - Millstone - IR 05000423/2014005 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Millstone) @ 2014Q4
Self-Identified List (Millstone)
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