05000259/FIN-2011004-03
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Finding | |
|---|---|
| Title | Unit 1 Loss of Shutdown Cooling Caused by Emergency Diesel Generator Output Breaker Trip |
| Description | A self-revealing non-cited violation of Technical Specifications 5.4.1.a was identified for the licensees failure to establish an adequate maintenance procedure to ensure appropriate calibration and alignment of the Emergency Diesel Generator (EDG) overspeed trip limit switch (OTLS) arm. The lack of procedure guidance resulted in an improperly adjusted OTLS that caused a premature trip of the A EDG output breaker and loss of Unit 1 shutdown cooling (SDC) on May 2, 2011. The licensee replaced and properly set the OTLS on the A EDG, verified the OTLS setpoint on all other seven EDGs, and initiated revisions to applicable maintenance procedures. This issue was entered into the licensees corrective action program as problem evaluation report (PER) 362340. The finding was determined to be greater than minor because it was associated with the Initiating Events Cornerstone attribute of Equipment Performance, and adversely affected the cornerstone objective to limit the likelihood of those events that upset plant stability and challenge critical safety functions during shutdown. Specifically, the misadjusted A EDG OTLS resulted in a premature trip of the A EDG output breaker and a loss of Unit 1 SDC. According to Inspection Manual Chapter (IMC) 0609, Significance Determination Process (SDP), Appendix G, Shutdown Operations, Table 1, Losses of Control, the safety significance of the finding was initially characterized to be potentially greater than very low safety significance because the inadvertent loss of SDC represented a loss of control due to a loss of thermal margin to boiling greater than 20 percent. However, a Phase 3 analysis was performed by a Senior Reactor Analyst, it was determined the loss of SDC event was of very low risk significance (i.e., Green), due in part to a low change in risk because of a high chance of recovery of offsite power before the duration of time required to cause the EDG to trip, and the likelihood of recovery of the tripped EDG. The cause of this finding was directly related to the cross-cutting aspect of appropriate self assessments in the Self and Independent Assessments component of the Problem Identification and Resolution area, because inadequate technical rigor applied by the licensee to recognize single point system vulnerabilities resulted in inadequate procedural guidance for maintenance personnel to appropriately calibrate and align the OTLS switch arm and overspeed trip lever |
| Site: | Browns Ferry  |
|---|---|
| Report | IR 05000259/2011004 Section 4OA3 |
| Date counted | Sep 30, 2011 (2011Q3) |
| Type: | NCV: Green |
| cornerstone | Initiating Events |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | C Stancil E Guthrie L Pressley P Niebaum T Ross |
| CCA | P.6, Self-Assessment |
| INPO aspect | CL.2 |
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Finding - Browns Ferry - IR 05000259/2011004 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Browns Ferry) @ 2011Q3
Self-Identified List (Browns Ferry)
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