05000458/FIN-2009002-05
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Finding | |
|---|---|
| Title | Licensee-Identified Violation |
| Description | Technical Specification 3.1.7 requires, in part, that two standby liquid control subsystems shall be operable. Contrary to the technical specification requirement, from March 14, 2003, to October 28, 2008, the standby liquid control system was not capable of performing its design safety function to limit suppression pool particulate iodine to evolve into airborne iodine. In accordance with NRC Inspection Manual Chapter 0612, Appendix B, \"Issue Screening,\" the inspectors determined that the failure to drain the test tank, maintaining the seismically qualified configuration, was a licensee performance deficiency. The issue was more than minor because it was similar to Example 3.a in Manual Chapter 0612, Appendix E, and it met the not minor if requirement because changes were required in the procedure to correctly resolve the seismic concerns. The inspectors evaluated the issue using the Significance Determination Process (SDP) Phase 1 Screening Worksheet for the Initiating Events, Mitigating Systems, and Barriers Cornerstones provided in Manual Chapter 0609, Attachment 4, \"Phase 1 Initial Screening and Characterization of Findings. The inspectors determined that this finding affected the Mitigating Systems Cornerstone and that the finding screened as potentially risk significant to a seismic initiating event because assuming that the tank completely failed, affecting the nearby pumps and electrical equipment, the loss would degrade both trains of the multi-train standby liquid control system. Therefore, a Phase 3 analysis was conducted by a senior reactor analyst in accordance with Manual Chapter 0609, Appendix A, Determining the Significance of Reactor Inspection Findings for At-Power Situations. In accordance with Manual Chapter 0609, Appendix A, the analyst performed a Phase 3 assessment of the risk contributions from a seismic initiator using insights and/or values provided by the Risk Assessment of Operational Events Handbook, Volume 2, External Events. Assumptions: To evaluate the change in risk caused by this performance deficiency, the analyst made the following assumptions: a. The River Bend Station SPAR model, Revision 3.45 and a spreadsheet evaluation of the River Bend seismic hazard represented appropriate tools for evaluation of the subject finding. b. The standby liquid control system test tank had remained full of water during power operations for approximately 5 years. c. Given Assumption b. the appropriate exposure period is one year, representing the most recent assessment period was used for exposure to this failure. d. The standby liquid control system test tank would only have failed during a seismic event. Therefore only seismic initiators, seismically-induced initiators, and independent failures occurring simultaneously with seismic events were evaluated. e. The failure of the standby liquid control system would affect the core damage frequency if the seismic event occurred simultaneously with an anticipated transient without scram because the failure would impact the systems function to shut down the reactor. f. The failure of the standby liquid control system would affect the core damage frequency if the seismic event also resulted in a loss of coolant accident because the failure would impact the systems function to control suppression pool chemistry. g. The likelihood of a seismic event equal to or larger than 0.5g peak ground acceleration occurring within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of an independent plant initiator is approximately 4E-10. h. A seismic event smaller than 0.5g peak ground acceleration is not likely to affect plant operations at River Bend Station. i. Given Assumptions g and h, the probability that a seismic event large enough to affect the plant occurs at the same time as an unrelated plant initiator is inconsequential to this analysis. j. The seismic hazard vector for River Bend Station provided in Table 4A-1 of the Risk Assessment of Operation Events Handbook, Volume 2, External Events, Revision 1.01, is appropriate for evaluation of the subject finding. Analysis: In accordance with Assumptions e, f and i, the analyst determined that, for the subject performance deficiency to affect the core damage frequency, a seismic event must either occur at the same time as an anticipated transient without scram, or result in a loss of coolant accident (LOCA). As such, the analyst evaluated the subject performance deficiency by determining each of the following parameters for any seismic event producing a given range of median average spectral acceleration \"a\" [SE(a)]: • The frequency of the seismic event SE(a) (eSE(a)); • The probability that a LOCA occurs during the event (PLOCA-SE(a)); • The probability that an independent LOCA occurs (PINIT-SE(a)); and • The probability of an ATWS occurring (PATWS-SE(a)). The frequency of a seismically induced demand on the SLC system (eSLC-SE(a)) can then be quantified as follows: eSLC-SE(a) = eSE(a) * [PLOCA-SE(a) + PINIT-SE(a) + PATWS-SE(a)] Given that each range a was selected by the analyst specifically to be independent of all other ranges, the total frequency of an induced demand, eSLC, can be quantified by summing the eSLC-SE(a) for each range evaluated as follows: 1.0 ACDF = O eSLC-SE(a) a=.05 over the range of SE(a). Results: The resulting value, quantified in a spreadsheet, was 5.4 x 10-7. The analyst noted that this conditional probability is significantly higher than a best estimate because the method used was to assume that the failure of the standby liquid control system was guaranteed following a failure of the test tank and that the failure of the standby liquid control system always resulted in core damage. Both these assumptions are known to be bounding. Therefore, this finding was of very low risk significance. Entergy documented this issue in Condition Report RBS-2008-06244. This item is further discussed in Section 4OA3.3 |
| Site: | River Bend  |
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| Report | IR 05000458/2009002 Section 4OA7 |
| Date counted | Mar 31, 2009 (2009Q1) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | Licensee-identified |
| Inspection Procedure: | |
| Inspectors (proximate) | P Elkmann G Pick G Miller G Larkin C Norton |
| INPO aspect | |
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Finding - River Bend - IR 05000458/2009002 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (River Bend) @ 2009Q1
Self-Identified List (River Bend)
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