05000425/FIN-2013007-02
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Finding | |
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| Title | Failure to Identify and Correct Potential Emergency Diesel Generator 2B Inoperability Following Failed Surveillance Testing |
| Description | An URI was identified regarding the discovery of a condition that could have resulted in an inoperable condition on the 2B EDG due to an intermittently misaligned mechanically operated cell (MOC) switch on the 2B EDG output breaker which provided a permissive signal to the 2B EDG sequencer. The URI was opened pending receipt and NRC review of the licensees evaluation to determine the effect the misaligned switch had on past operability. The results of the licensees evaluation will allow for an appropriate characterization of the performance deficiency as minor or greater than minor. During the inspection, the team reviewed the licensees evaluations of the 2B EDG failed surveillance tests that were performed on December 13, 2011, documented in CR 383267, and June 25, 2012, documented in CR 474941. During each of the failed surveillances, the EDG experienced unexpected automatic increased electrical loading, requiring the EDG to be secured. Following the event on December 13, 2011, the licensee determined the cause of the event was due to a failed load sharing module which provided an input to the EDG governor. The licensee further determined that the condition would not have affected the EDG if it was required to operate in its emergency mode, since the module was only active while the EDG was in test mode. The EDG was retested satisfactorily following replacement of the load sharing module and was declared operable. The EDG successfully passed its monthly surveillances between December 2011 and June 2012. Following a second unexpected increased loading event on June 25, 2012, the licensee performed an apparent cause determination and concluded that the cause of the event was due to an intermittently misaligned MOC switch. The MOC switch and its associated contacts change state when the EDG output breaker is closed. One of the contacts on the MOC switch was associated with the load sharing module and the licensee determined the misaligned MOC switch was the cause of the increased loading events on December 13, 2011, and June 25, 2012. The licensee incorrectly determined that this condition could not have affected the operability of the EDG nor would it have affected its function if the EDG were to be called upon to operate in its emergency mode. The MOC switch was readjusted following the event on June 25, 2012, and the EDG was retested and declared operable. Upon review by the team, it was determined that the MOC switch controlled multiple contacts, one of which provides a permissive signal through the MOC switch to the EDG sequencer, which allows safety-related loads to be added to the EDG in a specified order for accident mitigation. Another one of the contacts on the MOC switch was associated with the load sharing module. The licensees apparent cause determination did not address how the misaligned MOC switch contacts could have affected the sequencer permissive; therefore EDG operability. It only determined that a misaligned contact associated with the load sharing module could have resulted in the unexpected increased loading events the EDG experienced on December 13, 2011, and June 25, 2012. The licensee generated CR 687752, to evaluate the effect of the condition on prior operability of the EDG. Additional inspection of the licensees evaluation is required to appropriately characterize the licensees failure to promptly identify and correct the condition following the surveillance test failure on December 13, 2011, as minor or greater than minor. This issue will be identified as URI 05000425/2013007-02, Failure to Identify and Correct Potential Emergency Diesel Generator 2B Inoperability Following Failed Surveillance Testing. |
| Site: | Vogtle  |
|---|---|
| Report | IR 05000425/2013007 Section 1R21 |
| Date counted | Sep 30, 2013 (2013Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21 |
| Inspectors (proximate) | A Alen C Baron E Stamm G Crespo G Ottenberg R Nease T Sua Alena Nielsen C Dykes F Ehrhardt G Ottenberg M Cain M Speck S Sanchez T Chandler W Loo |
| INPO aspect | |
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Finding - Vogtle - IR 05000425/2013007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Vogtle) @ 2013Q3
Self-Identified List (Vogtle)
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