05000333/FIN-2011003-03
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Finding | |
|---|---|
| Title | Main Steam Isolation Valve Leak Rate Exceeds Authorized Limit |
| Description | This issue was considered within the traditional enforcement process because there was no performance deficiency identified, and NRC lnspection Manual Chapter (lMC) 0612, Appendix B, lssue Screening directs disposition of such issues in accordance with the NRC Enforcement Policy. The inspectors used the Enforcement Policy, Section 6'1, Reactor Operations, to evaluate the significance of this violation. The inspectors concluded that the violation was more than minor and best characterized as Severity Level lV (very low safety significance) because it is similar to Enforcement Policy Section 6.1, Lxample 0.1. Additionally, the inspectors assessed the risk associated with the issue by using IMC 0609, Appendix A, Determining the Significance of Reactor Inspection Findings for AlPower Situations. The inspectors screened the issue in accordance with Attachment 0609.04, Phase 1 - lnitial Screening and Characterization of Findings, and determined that a Phase 2 evaluation was required, because the issue constituted an actual open pathway in the physical integrity of the reactor containment, that being the 'C' main steam line with leakage past both MSIVs in excess of the TS limit. The Phase 2 SDP process for containment barrier issues is conducted in accordance with the guidance provided in IMC 0609, Appendix H. IMC 0609, Appendix H, does not provide specific guidance on establishing the risk associated with penetration leakage for Mark I containments. Therefore, a Region I Senior Reactor Analysis (SRA) conducted a Phase 3 risk evaluation to evaluate the potential increase in the large early release frequency (LERF). The Phase 3 risk assessment uses the best available risk information to make a risk informed decision on the significance of inspection findings. The Phase 3 risk evaluation determined that the increase in LERF was likely less than the 1E-7 per year threshold and that the finding was, therefore, of very low safety significance. The SRA determined the top fifteen dominant core damage sequences from the NRC's FitzPatrick Standardized Plant Analysis Risk (SPAR) model version 8.16. The SRA used the method as outlined in Section 3.2.8, Main Steam lsolation Valve Leakage, of NUREG 1785, Basis Document for Large Early Release Frequency (LERF) Significance Determination Process (SDP). The result indicated that there was essentially no increase in LERF because the SDP already assumed that all high pressure core damage sequences would cause a large early release, so having a pair of MSIVs leaking would be no worse. ln their LER, the FitzPatrick staff documented an increase in LERF in the low E-8 per year range using their current level 2 PRA modelwhich includes MSIV leakage as a contributor to containment failure. This model goes beyond the SDP assumption that all high pressure core damage sequences result in a large early release, allowing for operator actions to reduce RPV pressure and improving the possibility of getting water to the reactor vessel or the drywell floor before reactor vessel breach. The SRA considered several qualitative factors in reaching a final risk determination for this issue. Considerations which tended to decrease the risk associated with this finding were that: 1) the leak testing methodology (low rate of pressurization) may not seat an MSIV in the same manner that would occur under actual operating conditions, given the reactor steam pressure tending to close the valves; 2) given the actual mechanisms which allowed the leakage (as described in the LER), it is likely that the two leaking MSIVs with reactor presiure tending to close the valves would have offered considerably more resistance to steam flow than if they were fully open; 3) the downstream turbine bypass and stop/throttle valves would be closed if the condenser was not available, and as such, these valves would also provide some additional (though not specifically quantifiable) isolation function; and 4) there would be significant deposition of radioactive nuclides in the main steam lines and condenser, thus limiting the radiological inventory transported to the site boundary and limiting the potentialfor a large early release. The SF{A also determined that external initiating events such as a seismic event or a fire would not significantly affect these quantitative factors, given the robustness of the main steam piping downstream of the MSIVs and the very low chance that a fire would damage this piping. Therefore, the SRA determined that both the quantitative LERF calculation and qualitative factors supported the conclusion that this finding was of very low risk significance (Green). Because this issue was of very low safety significance (Green) and it has been determined that the issue was not within Entergy personnel's ability to foresee and correct, that Entergy staff actions did not contribute to the degraded condition, and that actions taken were reasonable to identify and address this matter, and as such no performance deficiency existed, the NRC has decided to exercise enforcement discretion in accordance with Section 3.5 of the NRC Enforcement Policy and refrain from issuing enforcement action for the violation of TSs (EA-1 1-170). Further, because licensee actions did not contribute to this violation, it will not be considered in the assessment process or the NRC's Action Matrix, |
| Site: | FitzPatrick  |
|---|---|
| Report | IR 05000333/2011003 Section 4OA3 |
| Date counted | Jun 30, 2011 (2011Q2) |
| Type: | Violation: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | G Meyer S Rutenkroger J Noggle T Fish E Knutson D Roberts |
| INPO aspect | |
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Finding - FitzPatrick - IR 05000333/2011003 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (FitzPatrick) @ 2011Q2
Self-Identified List (FitzPatrick)
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