05000315/FIN-2015003-05
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Finding | |
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| Title | PRA Model Errors |
| Description | During review of MSPI, the inspectors identified an URI associated with the adequacy of the Probable Risk Assessment (PRA) model of record used for MSPI. Specifically, an error in the PRA model resulted in extremely high hours for system unavailability. The same error impacted the PRA for NFPA805 and internal events. Description: While reviewing MSPI, the inspectors identified an URI regarding the licensees PRA model. While reviewing margin reports as part of the inspection, the inspectors noted that available margin for unavailability for all the SSCs covered by MSPIs was extremely high. The SSC with the least amount of available margin had about 250,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of unavailability before the MSPI would cross the threshold from Green to White. The inspectors discussed the issue with licensee and learned that an error in the PRA model of record caused the high numbers. AR 20143184 documents the issue. The licensee told the inspectors that during NFPA 805 reviews, the NRC had inquired about the models treatment of test and maintenance. In response, the licensee identified the error, and corrected the model for NFPA 805. The licensee has also updated the model for on line risk management. Because of additional controls on the model used for MSPI, the corrected model did not become the PRA model of record until September 2015. The inspectors inquired if the licensee had performed any evaluation to validate that information previously submitted to the NRC using the flawed model resulted in a masked greater-than-green MSPI result. The licensee stated they believed all the prior MSPI submittals would remain green; however, the licensee also stated that the NRC endorsed NEI guidance did not require licensees to resubmit MSPI data if the model changed. In particular, the licensee noted that NEI 9902 guidance regarding model revisions requires the model to be in effect for the entire quarter. A revised PRA model becomes effective on the first day of the quarter following approval of the revised model as the PRA model of record. Thus, a revised model would not impact previously submitted MSPI data. In addition, the inspectors learned that some of the licensee conditions for NFPA 805 addressed the adequacy of the PRA model and imposed requirements for conducting peer review of the PRA model. During the inspection period, the inspectors could no
determine if the licensee satisfied the associated license conditions. The inspectors noted that NEI 9902 also requires the PRA model to be technically accurate with requirements included in appendix G. In addition, NEI 9902 also requires licensees to correct data errors for previously submitted data. In this case, the inspectors, during the inspection period, could not determine: 1) If the flawed model met the Appendix G requirements for technical adequacy; 2) if the model does not meet appendix G, would the data be considered in error and in need of correction 3) impacts of the flawed PRA model on other documents submitted to the NRC; and 4) impact of the error on license condition for NFPA 805 Pending resolution of the above items, this issue is considered a URI. (URI 05000315/2015003-05; 05000316/2015003-05; PRA Model Errors) |
| Site: | Cook  |
|---|---|
| Report | IR 05000315/2015003 Section 4OA1 |
| Date counted | Sep 30, 2015 (2015Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71151 |
| Inspectors (proximate) | G Edwards J Ellegood J Mancuso K Riemer T Go T Taylorj Ellegoodj Lennartz J Mancuso K Riemer M Garza M Learn R Edwards R Elliott T Taylor |
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Finding - Cook - IR 05000315/2015003 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Cook) @ 2015Q3
Self-Identified List (Cook)
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