05000338/FIN-2010002-05
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Finding | |
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| Title | Failure to Establish a Procedure for Undervoltage Timers Results in Main Turbine/Reactor Trip |
| Description | A Green, self-revealing finding was identified for the licensees failure to establish an adequate procedure for calibration of under voltage timers which resulted in the failure of the Unit 2 G bus to fast transfer from C reserve station service transformer (RSST) to the B RSST and consequent loss of main turbine condenser vacuum causing a main turbine/reactor trip. The licensee entered this problem into their corrective action program as condition report 361280.A self-revealing performance deficiency (PD) involving a Unit 2 turbine trip on loss of condenser vacuum was identified and resulted from the failure to establish an adequate procedure for the calibration of the time delay relays associated with the G bus cross-tie fast transfer circuit. This PD was the result of the failure to establish an adequate procedure for calibration of fast transfer relays. Specifically, licensee did not have mandated documentation in place to require technicians to use a proven method for timer calibration. The cause of PD was reasonably within the licensees ability to foresee and correct. Specifically, the NRC previously issued NCV 05000338/2008002-03, Inoperability of \'1H\' EDG Due to Failure to Adequately Establish Procedural Requirements for Protective Relay Testing, which involved a lack of procedural guidance and reliance of worker skill of the craft to successfully complete the activity. The PD adversely impacted the Initiating Events 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 and was related to the attribute of procedure quality because the correct timing relay calibration methodology was not documented in a procedure. In accordance with NRC Inspection Manual Chapter 0609, Significant Determination Process, a phase 1significance determination process (SDP) screening determined that a phase 2 evaluation was required as the finding contributed to both the likelihood of a reactor trip and the likelihood that mitigation equipment would not be available. A phase 3SDP evaluation was performed by a regional SRA since the North Anna Risk Informed Inspection Notebook did not have the level of detail to accurately assess the finding. The NRCs SPAR model was utilized to assess the risk significance of the finding modeling the impact of a loss of power to the 2G Bus without the fast transfer circuit available resulting in a reactor trip due to low condenser vacuum. The dominant sequence was a reactor trip without the condenser heat sink, caused by loss of power to the 2G bus with a failure of the cross-tie fast transfer circuit, with subsequent failures of main feedwater, auxiliary feedwater, and failure of feed and bleed cooling leading to core damage. The evaluation determined that the risk increase in core damage frequency was <1E-6 per year, a finding of very low safety significance, Green. This finding involved the cross-cutting area of human performance, the component of the resources, and the aspect of complete, accurate and up-to-date procedures, H.2(c), because the licensee failed to establish an accurate procedure to ensure correct calibration of under voltage timers. |
| Site: | North Anna  |
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| Report | IR 05000338/2010002 Section 4OA3 |
| Date counted | Mar 31, 2010 (2010Q1) |
| Type: | Finding: Green |
| cornerstone | Initiating Events |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | R Clagg M Meeks G Laska J Reece |
| CCA | H.7, Documentation |
| INPO aspect | WP.3 |
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Finding - North Anna - IR 05000338/2010002 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (North Anna) @ 2010Q1
Self-Identified List (North Anna)
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