05000338/FIN-2010004-06
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Finding | |
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| Title | Failure to Follow Procedure to Trip A Reactor Coolant Pump on High Bearing Temperature |
| Description | A non-cited violation of Technical Specifications 5.4.1a was identified by the inspectors for the failure to adequately implement procedural requirements which resulted in operation of the A reactor coolant system (RCS) pump (RCP) beyond the motor high bearing temperature limit of 195 degF for approximately 10 minutes. The licensee entered this problem into their corrective action program as corrective action 170278 associated with condition report 382725. The inspectors determined that the failure to implement an alarm response procedure to trip the A RCP in a timely manner was a performance deficiency (PD). The PD was more than minor, because it could be reasonably viewed as a precursor to a significant event due to RCP motor operation in an unknown condition of bearing performance in which the melting of Babbitt material can lead to excessive shaft vibrations and consequent adverse impact on RCP seal performance leading to a seal loss of coolant accident. Significance determination process (SDP) phase 1 screening determined the finding to be a primary system loss of coolant accident initiator contributor as RCP operation without motor bearing cooling could lead to motor bearing failure, RCP vibration and potential vibration induced RCP seal damage. The finding was determined to fit under the Initiating Events cornerstone in that assuming worst case degradation the potential seal leakage could exceed the technical specification limit for RCS leakage and required phase 2 analysis. Since the North Anna SDP pre-solved worksheet did not specifically address loss of cooling to the RCP motor bearings, a phase 3 analysis was performed by a regional SRA using the NRCs North Anna SPAR model. The sequence was a reactor trip transient caused by a lightning strike in the switchyard, loss of the 1H emergency bus, RCP motor bearing damage due to loss of bearing cooling, failure to trip the RCP, RCP seal failure, failure of high pressure injection, successful depressurization and failure of low pressure injection leading to core damage. A diagnosis and action human error probability for RCP trip was developed for the event conditions. The risk of the event was mitigated by the availability of seal cooling, seal injection and the time and cues available to the operator to trip the RCP prior to vibration induced seal failure. The phase 3 risk evaluation determined that the risk increase of the finding was <1E-6 for core damage frequency and <1E-7 for Large Early Release Frequency, a finding of very low risk significance (Green). This finding involved the crosscutting area of human performance, the component of decision making and the aspect of decision communications, H.1(c), because a reactor operator failed to communicate the loss of component cooling to the RCP motors to the senior reactor operator which led to the failure to trip the A RCP on exceeding the motor bearing high temperature limit. (Section 4OA5.3) |
| Site: | North Anna  |
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| Report | IR 05000338/2010004 Section 4OA5 |
| Date counted | Sep 30, 2010 (2010Q3) |
| Type: | NCV: Green |
| cornerstone | Initiating Events |
| Identified by: | NRC identified |
| Inspection Procedure: | |
| Inspectors (proximate) | J Reece P Fillion J Dodson G Mccoy R Clagg M Coursey |
| CCA | H.10, Bases for Decisions |
| INPO aspect | CO.2 |
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Finding - North Anna - IR 05000338/2010004 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (North Anna) @ 2010Q3
Self-Identified List (North Anna)
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