05000458/FIN-2014007-06
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Finding | |
|---|---|
| Title | Licensee-Identified Violation |
| Description | The inspectors reviewed a licensee identified violation for 10 CFR 50 Appendix B, Criterion III, Design Control, which states, Measures shall be established for the selection and review for suitability of application of materials, parts, equipment, and processes that are essential to the safety-related functions of the structures, systems, and components. Contrary to the above, since November 20, 1985, the licensee failed to review the suitability of relays in the main steam isolation valve closure reactor trip loop of the reactor protection system to prevent the selection of relays that could drift to challenge the response time test acceptance criteria. The licensee entered this issue into the corrective action program as Condition Report CR-RBS-2014-02833. The performance deficiency was more than minor, and therefore a finding, because if left uncorrected, the finding would have the potential to lead to a more significant safety concern. In accordance with NRC Inspection Manual Chapter 0609, Attachment 4, Initial Screening and Characterization of Findings, the finding represented a potential loss of system safety function; therefore a detailed risk evaluation was necessary. The finding required a detailed risk evaluation because it involved the potential loss of a safety function. A senior reactor analyst performed the detailed risk evaluation. When main steam isolation valves, turbine trip valves, and control valve fast closure events occur, the reactor core experiences a pressure transient. The pressure transient causes voids in the core to collapse, which constitutes a significant reactivity addition. To prevent exceeding reactor core thermal limits, the reactor is designed to trip early in the valve closure stroke. The two affected thermal limits included the Critical Power Ratio and the Linear Heat Generation Rate. The analyst noted that the worst case consequence, if these trips did not function at all, would involve exceeding these thermal limits and possibly causing limited fuel cladding damage. Even if these trips did not function, backup trips, such as high pressure trips, were functional and would have shut down the reactor. If the thermal limits were exceeded fuel leaks could occur, but significant core damage would not occur. The purpose of the significance determination process is to assess the potential for significant core damage. Therefore, there was no quantifiable increase in the core damage frequency from this finding. The core damage frequency was much less than 1E-6 and the finding was of very low safety significance (Green). The diverse reactor protection system helped to minimize the significance of this finding. |
| Site: | River Bend  |
|---|---|
| Report | IR 05000458/2014007 Section 4OA7 |
| Date counted | Sep 30, 2014 (2014Q3) |
| Type: | NCV: Green |
| cornerstone | Initiating Events |
| Identified by: | Licensee-identified |
| Inspection Procedure: | |
| Inspectors (proximate) | G Gardner G George J Zudans M Kennard N Okonkwo T Farnholtz T Skaggs Ryan A Dunlop |
| Violation of: | 10 CFR 50 Appendix B Criterion III, Design Control |
| INPO aspect | |
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Finding - River Bend - IR 05000458/2014007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (River Bend) @ 2014Q3
Self-Identified List (River Bend)
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