05000321/FIN-2014004-06
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Finding | |
|---|---|
| Title | Licensee-Identified Violation |
| Description | 10 CFR Part 50 Appendix B, Criterion III, Design Control, requires in part that design changes shall be subject to design control measures commensurate with those applied to the original design. Contrary to the above, during design activities to replace safety related low voltage breaker pan assemblies, the licensee incorrectly classified Cutler Hammer thermal overload blocks as like-for-like replacements of the previous Westinghouse design. The new Cutler Hammer thermal overload blocks had different operating characteristics which resulted in newly installed pan assemblies having incorrectly sized thermal overload heaters. The nonconforming thermal overload heaters tripped the fan motors under normal operating conditions which resulted in the 2A emergency diesel generator being declared inoperable. The inspectors determined that the violation required a detailed risk (Phase 3) assessment because there was an actual loss of function for greater than the TS AOT. A Senior Reactor Analyst performed a Phase 3 analysis for the finding using 20 the NRCs Hatch PRA model modified to include the EDG room ventilation fan breakers including common cause failure terms. Since the EDG 1B fan breakers were not included in the licensee breaker upgrade program, they were not included in the breaker common cause assumptions. The screening analysis assumed an increase in failure rate of the fan breakers based on actual run data that was applied to the 6 breakers that control the EDG 2A and EDG 2C fans, and also conservatively assumed no recovery of the tripped breakers. The exposure time was assumed to be one year for SDP purposes, in accordance with the program assumptions, since the exposure time exceeded one year. The dominant sequences involved a Loss of Offsite Power initiator, independent failure of the EDG 1B fans, common cause failure of the EDG 2A and 2C fans, and no recovery of the EDGs or offsite power for 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />. Because of the multiple successful operations of the EDG fans prior to failure, and the lack of a common cause failure tie for the fan breakers for the 1B swing EDG, the finding screened well below the 1E-6 threshold. Therefore, this finding was determined to be of very low safety significance (Green). This condition was documented in the licensees corrective action program as CR 822819. |
| Site: | Hatch  |
|---|---|
| Report | IR 05000321/2014004 Section 4OA7 |
| Date counted | Sep 30, 2014 (2014Q3) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | Licensee-identified |
| Inspection Procedure: | |
| Inspectors (proximate) | D Hardage D Retterer M Franke T Su |
| Violation of: | 10 CFR 50 Appendix B Criterion III, Design Control Technical Specification |
| INPO aspect | |
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Finding - Hatch - IR 05000321/2014004 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Hatch) @ 2014Q3
Self-Identified List (Hatch)
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