05000395/FIN-2013003-04
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Finding | |
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| Title | Failure to Assess and Manage the Risk Impact of Time to Core Boil With Reactor Vessel Upper Internals Installed and Cavity Level is Greater Than Reactor Vessel Flange |
| Description | The inspectors identified a non-cited violation of 10 CFR 50.65 (a)(4) which requires in part that the licensee assess and manage the increase in risk that may result from proposed maintenance activities. Specifically, the licensee failed to assess and manage the increase in risk for shutdown operations and corresponding maintenance activities during Refueling Outage 20 because the qualitative risk evaluation failed to correctly update the time to core boil (TTCB), as determined by a computer program, for a plant operating state (POS) consisting of upper reactor vessel (RV) internals installed, RV head removed, and reactor cavity level greater than RV flange. The licensee entered this problem in their corrective action program as condition report 12-04757. The inspectors determined that the failure to assess and manage the increase in risk for shutdown operations and corresponding maintenance activities because the qualitative risk evaluation failed to correctly update the TTCB, as determined by a computer program, for the above POS was a performance deficiency (PD). The inspectors reviewed inspector manual chapter (IMC) 0612, Appendix B and determined the PD is more than minor and therefore a finding because if left uncorrected it would have to the potential to lead to a more significant safety concern. Specifically, the above POS results in a TTCB measured in minutes as opposed to hours, and the failure to accurately calculate and track for increase in risk and procedure applications would impact operator response to loss of the residual heat removal system. The finding was screened using IMC 0609 Attachment 4 which routed the significance determination to IMC 0609 Appendix K. Since the licensee used a qualitative risk assessment process during shutdown conditions, a bounding risk assessment was done in accordance with IMC 0609 Appendix M requirements. A risk assessment was performed by a regional senior risk analyst using the shutdown risk methodology of IMC 0609 Appendix G. The major assumptions included: a 39 hour4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br /> exposure period within Plant Operating State 2 (POS-2 early time window), Loss of Inventory, Loss of Offsite Power and Loss of residual heat removal (RHR) initiators were evaluated, both trains of RHR and emergency core cooling system including both emergency diesel generators were available, base case results were increased by a factor of 5 to account for the procedure SSP-004 not providing guidance that TTCB should be adjusted while the upper internals were installed (this was determined using the NRC standardized plant risk analysis human (SPAR-H) error methodology for Available but poor procedure within the Diagnosis HEP performance shaping factors). The dominant sequence was Loss of RHR with failure to recover RHR and failure to initiate injection. The risk was mitigated by the short exposure period and the availability of both trains of RHR. The result of the risk evaluation was an increase in core damage frequency of <1E-6/year a GREEN finding of very low safety significance. This finding impacts the cross-cutting area of human performance, the component of work control, and the aspect of planning work activities by incorporating risk insights, H.3(a), because the licensee failed to recognize the TTCB for the identified POS caused a high risk evolution or a Yellow risk condition. |
| Site: | Summer  |
|---|---|
| Report | IR 05000395/2013003 Section 4OA5 |
| Date counted | Jun 30, 2013 (2013Q2) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | |
| Inspectors (proximate) | E Coffman G Mccoy J Reece |
| Violation of: | 10 CFR 50.65(a)(4) 10 CFR 50.65 |
| CCA | H.5, Work Management |
| INPO aspect | WP.1 |
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Finding - Summer - IR 05000395/2013003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Summer) @ 2013Q2
Self-Identified List (Summer)
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