05000324/FIN-2012007-01
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Finding | |
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| Title | Failure to Properly Assemble Reactor Vessel Head Following Maintenance Outage |
| Description | A self-revealing (Green) non-cited violation (NCV) of 10 CFR 50, Appendix B Criterion V, Instructions, Procedures, and Drawings was identified for failure to properly implement plant procedures for reactor pressure vessel (RPV) reassembly following the Unit 2 maintenance outage in November 2011. This resulted in excessive leakage from the Unit 2 RPV during reactor startup and pressurization on November 15 and November 16, 2011, and the declaration of an Unusual Event for reactor coolant system (RCS) unidentified leakage in excess of 10 gallons per minute on November 16, 2011. The unit was shut down and depressurized on November 16, 2011, and the issue entered into the licensees CAP as NCR 500035. The licensees failure to correctly implement procedure 0SMP-RPV502, Reactor Vessel Reassembly, to ensure that the RPV head was properly reassembled following the November 2011 Unit 2 maintenance outage was a performance deficiency. The finding was more than minor because it was associated with the Initiating Events cornerstone attribute of equipment performance (the reliability of the RCS barrier integrity) and adversely affected the cornerstone objective of limiting the likelihood of events that upset plant stability and challenge critical safety functions during shutdown or power operations. Specifically, the failure to adequately implement this procedure resulted in excessive leakage from the Unit 2 RPV during reactor startup and pressurization. Inspection Manual Chapter 0609, Significance Determination Process (SDP), Attachment 0609.04, Phase 1 Screening Worksheet was used to screen the significance of the finding. The finding required a Phase 2 SDP analysis because it resulted in unidentified RCS leakage exceeding technical specification limits. Evaluation of the finding using the NRC pre-solved SDP table was not appropriate because the table does not contain a suitable target for RPV vessel integrity. Therefore, a Phase 3 SDP analysis was required. A Phase 3 analysis was performed by the regional Senior Reactor Analyst. Since the finding resulted in a shutdown, the SDP was analyzed as an additional transient that had a small potential to result in a Small Loss of Coolant Accident (SLOCA). The actual leak rate was low enough to not be considered to be a SLOCA, but there was potential for larger leakage. The Phase 2 SDP process uses an order of magnitude increase in the initiating event frequency for issues with the potential to increase the frequency of a particular event. This philosophy was used in the Phase 3 SDP process to allow a risk-informed input to the SDP for the SLOCA potential for this finding, due to the difficulty in calculating an exact percentage of time that the condition of the head closure would result in a larger leak. This resulted in an analysis that assumed a transient occurred that would result in a SLOCA about 1 percent of the time. This result represents an upper bound for the finding. The results were a risk in the low E-7 range, and the finding is GREEN. The SLOCA contribution was less than E-7. Dominant sequences involved loss of secondary side cooling and makeup, with either loss of containment heat removal, or loss of high pressure injection and failure to depressurize the reactor to allow the use of the low pressure systems. Because of Brunswicks concrete lined torus, and the low contribution of the high pressure sequences, the Large Early Release Frequency did not result in an increase in the significance. The cause of this finding was directly related to the cross-cutting aspect of supervisory and management oversight in the Work Practices component of the Human Performance area because oversight of the RPV reassembly was inadequate to insure that workers were able to accurately execute the steps of procedure 0SMP-RPV502, Reactor Vessel Reassembly. |
| Site: | Brunswick  |
|---|---|
| Report | IR 05000324/2012007 Section 4OA5 |
| Date counted | Jun 30, 2012 (2012Q2) |
| Type: | NCV: Green |
| cornerstone | Initiating Events |
| Identified by: | Self-revealing |
| Inspection Procedure: | |
| Inspectors (proximate) | R Musser |
| CCA | H.2, Field Presence |
| INPO aspect | LA.2 |
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Finding - Brunswick - IR 05000324/2012007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Brunswick) @ 2012Q2
Self-Identified List (Brunswick)
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