05000335/FIN-2013004-02
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Finding | |
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| Title | Partial Loss of Offsite Power due to Non-segregated Bus Failure |
| Description | A self-revealing finding was identified for the licensees failure to establish adequate preventive maintenance (PM) activities for both units startup transformers (SUTs) 6.9kV non-segregated bus runs in accordance with site PM program requirements. As a result, external corrosion of the 2B SUT 6.9kV non-segregated bus run duct was allowed to degrade until a duct vent screen collapsed onto the energized bus causing a partial loss of offsite power to both units. This issue was placed in the licensees corrective action program as action request 1809273. Corrective actions included: repair of the corroded non-segregated bus duct vent associated with this event, updating the preventative maintenance program to address periodic maintenance of non-segregated bus duct vents, and completing inspections and repairs, as necessary, of both units outdoor bus duct vents for bus runs to the SUTs and auxiliary transformers. The performance deficiency was considered to be more than minor because it was associated with the equipment reliability attribute of the initiating events cornerstone and adversely 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. Specifically, since 2003 when PM activities were established for SUTs (including 4.16kV non-segregated bus runs), the licensee failed to establish those same activities for both units SUT 6.9kV non-segregated bus runs. As a result, external corrosion of the 2B SUT 6.9kV non-segregated bus duct was allowed to degrade until a duct vent screen collapsed onto the energized bus causing a partial loss of offsite power to both units. The inspectors reviewed the finding in accordance with Inspection Manual Chapter 0609, Significance Determination Process, Attachment 4, Appendix A and Appendix G. Appendix A, The Significance Determination Process (SDP) for Findings At-Power, was used for both units because Unit 1 was operating and the failure could have reasonably occurred with Unit 2 operating prior to the fall 2012 outage. Appendix G, Shutdown Operations Significance Determination Process, was used for the time Unit 2 was in the 2012 outage. Appendix G required a detailed risk evaluation because the finding increased the likelihood of a loss of offsite power. A Senior Reactor Analyst subsequently performed an analysis of the risk impacts to both units while at-power and while the unit was shut down. The analyst determined that the risk significance of the issue was very low (i.e., Green). The dominant accident sequence was a Loss of Offsite Power during a shutdown condition, specifically when the RCS is vented such that: 1) the steam generators cannot sustain core heat removal, and 2) a sufficient vent path exists for feed and bleed. The remaining mitigation of such an accident was comprised of the Unit 2 EDGs and recovery of power from the opposite unit. The inspectors concluded that this finding did not have a cross-cutting aspect as this was not representative of present licensee performance. |
| Site: | Saint Lucie  |
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| Report | IR 05000335/2013004 Section 4OA3 |
| Date counted | Sep 30, 2013 (2013Q3) |
| Type: | Finding: Green |
| cornerstone | Initiating Events |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | J Rivera-Ortiz J Hanna T Morrissey J Reyes G Kolcum A Sengupta M Riches P Carman |
| INPO aspect | |
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Finding - Saint Lucie - IR 05000335/2013004 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Saint Lucie) @ 2013Q3
Self-Identified List (Saint Lucie)
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