05000338/FIN-2010004-05
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Finding | |
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| Title | Inadequate Set Point for Balance-of-Plant Bus Undervoltage Relay |
| Description | A self-revealing finding was identified for the failure to establish an adequate set point for a balance-of-plant 4160 V bus undervoltage protection relay. The inadequate set point caused a reactor trip upon automatic start of a steam generator feedwater pump. The event was reported to the NRC in Licensee Event Report (LER) 0500339/2010-002-00. Corrective action has been taken to reduce the probability of recurrence of the problem. The licensee has placed this issue in their corrective action program as Root Cause Evaluation (RCE) 001012. The fact that the motor starting voltage dip of the twin 4500 horsepower motor feedwater pump was below the set point of the bus undervoltage protection relays was a performance deficiency. The typical industry standard practice for bus undervoltage is that the set point be below the motor starting voltage dip to preclude spurious actuation of the undervoltage relays for expected voltage transients such as motor stating. This industry standard practice is documented in Institute of Electrical and Electronics Engineers Standard 666-1991, IEEE Design Guide for Electric Power Service Systems for Generating Stations. Table 7.2, Motor Protection Devices, states that the suggested setting for undervoltage relay is that it be set to override voltage drop due to motor starting. The potential for spurious tripping of the undervoltage relays has nuclear safety ramifications, in that it can contribute to a reactor trip, as it did on May 28, 2010. The performance deficiency is more than minor because it was associated with the attribute of design control and adversely affected the objective of the initiating event cornerstone. The inappropriate undervoltage relay set point contributed to a reactor trip which is an event that upset plant stability and challenged critical safety functions. The finding was evaluated for significance using Inspection Manual Chapter 0609, Appendix E. The finding was determined to be very low safety significance, Green, because it did not contribute to both the likelihood of a reactor trip and the likelihood that mitigation functions will not be available. The cause of the finding was evaluated in the licensees corrective action program as RCE001012. According to the LER and RCE001012, the cause of the finding was determined to be lack of a design basis for the undervoltage protection relay. Since the set point was established well outside the two-year window of current performance and there was no prior event that provided an opportunity to identify this problem, this issue did not represent current licensee performance. Therefore, no associated cross-cutting aspect was identified. (Section 4OA3.3) |
| Site: | North Anna  |
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| Report | IR 05000338/2010004 Section 4OA3 |
| Date counted | Sep 30, 2010 (2010Q3) |
| Type: | Finding: Green |
| cornerstone | Initiating Events |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | J Reece P Fillion J Dodson G Mccoy R Clagg M Coursey |
| INPO aspect | |
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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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