05000482/FIN-2014005-02
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Finding | |
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| Title | |
| Description | An unresolved item (URI) is being opened to assess whether the cause for the request for enforcement discretion associated with the fire in the exciter circuit of emergency diesel generator B on October 6, 2014, involved a violation of NRC requirements. On October 6, 2014, at 1:26 p.m., emergency diesel generator B was declared inoperable when it tripped during a 24-hour surveillance test and operators identified a fire in an associated exciter cabinet. An Alert was declared and operators entered Technical Specification 3.8.1, AC Sources Operating, Required Action B.4.1, which required emergency diesel generator B be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Actions in response to the fire were completed, the fire was quickly suppressed, and WCNOC exited the Alert. Following the completion of repairs, WCNOC identified that postmaintenance testing required to demonstrate system operability included completing a 24-hour run. Since the postmaintenance testing and subsequent system restoration was expected to exceed the time remaining in the 72-hour action statement, WCNOC requested that the NRC exercise discretion to not enforce compliance with the actions required in Wolf Creek Generating Station Technical Specification 3.8.1, Required Action B.4.1, and approve an additional 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> to restore the system. NOED NO. 14-4-02, documents this request and the NRCs approval. Following postmaintenance testing, emergency diesel generator B was restored to operable status at 5:17 p.m. on October 9, 2014. WCNOC concluded that the most likely cause of the event was the failure of the power current transformers power rectifier bridge. WCNOC postulated that when the bridge failed, power from the power current transformers to the generator field was lost. As a result, the voltage regulator attempted to maintain the field current using only the power potential transformer. Since the power potential transformer is not rated to sustain full field current, the transformer was overloaded, which caused it to overheat and catch fire. Troubleshooting also indicated that the emergency diesel generator B tripped on phase differential current for the same reasons. WCNOC removed the failed rectifier bridge for further analysis in December 2014; at the end of the inspection period, WCNOC personnel were awaiting additional failure analyses of the failed rectified bridge to determine the specific direct causes of the fire and unplanned emergency diesel generator B inoperability. The root cause is being evaluated by Condition Report 88665. When an NOED is issued, Inspection Manual Chapter 0410, Notice of Enforcement Discretion, requires that a URI will be opened to assess whether the cause(s) of the events leading up to the request for the Notice of Enforcement Discretion involved violations of NRC requirements. This issue will be tracked as a URI in order to review and evaluate WCNOCs additional rectifier bridge failure analyses, root cause analysis, and other supporting documentation to determine if a violation exists: URI 05000482/2014005-02, Notice of Enforcement Discretion 14-4-02 for Emergency Diesel Generator B Exciter Cabinet Fire. These activities constitute completion of two event follow-up samples, as defined in Inspection Procedure 71153. |
| Site: | Wolf Creek  |
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| Report | IR 05000482/2014005 Section 4OA3 |
| Date counted | Dec 31, 2014 (2014Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | D Dodson D Loveless F Thomas G Pick T Pruettb Correllc Peabody D Dodson D Proulx G Apger M Kennard N O'Keefe R Stroble S Hedger T Hartman |
| Violation of: | Pending |
| INPO aspect | |
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Finding - Wolf Creek - IR 05000482/2014005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Wolf Creek) @ 2014Q4
Self-Identified List (Wolf Creek)
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