05000275/FIN-2011002-03
Finding | |
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| Title | Requirement to Perform an Operability Evaluation Following Receipt of New Seismic Information |
| Description | The inspectors identified that seismic studies completed in January 2011 revised the maximum vibratory ground motion predicted for local earthquake faults. This issue is unresolved pending NRC review of the Diablo Canyon current licensing basis requirements for the evaluation of new seismic information. On January 7, 2011, Pacific Gas and Electric transmitted to the NRC a report updating the local seismology (Report on the Analysis of the Shoreline Fault Zone, Central Coast California to the USNRC, Adams ML110140400). This report included new deterministic evaluations for the Shoreline, Los Osos, and San Luis Bay earthquake faults. The licensee concluded that each of these faults was capable of producing between 0.6 gravity (g) and 0.7g peak ground acceleration at Diablo Canyon. The inspectors identified that these new ground acceleration values were greater than described in the FSARU for the Double Design Earthquake. FSARU, Section 3.7.1.1, Design Response Spectra, describes the three design basis earthquakes used to develop the seismic qualification basis for plant structures, systems and components
Design Earthquake (0.2g) - The amount of vibratory ground motion for which those plant features necessary for continued operation remain functional without undue risk to the health and safety of the public (all structures, systems and components must remain in the elastic range) Double Design Earthquake (0.4g) - The evaluation of the maximum earthquake potential (producing the maximum vibratory ground motion) for which structures, systems and components needed to prevent or mitigate an accident will remain functional, allowing for some plastic deformation of structural material. This evaluation includes all earthquake epicenters within 200 miles and faults within 75 miles of the plant and implements the NRC regulatory requirements for the safe shutdown earthquake as described in 10 CFR Part 100, Appendix A Hosgri Event (0.75g) - A postulated 7.5 M earthquake (unique to Diablo Canyon) assumed to occur on the Hosgri Fault line. Only equipment credited in the alternate Hosgri Event shutdown path is required to remain functional following a Hosgri design basis earthquake The inspectors determined that the seismic qualification of systems, structures and components was described by all three design basis earthquakes. Seismic qualification requirements for some structures, systems and components could be more limiting for the Design and Double Design Earthquakes based on the differences in the acceptance criteria, required load combinations, and other assumptions used in the safety analyses. The inspectors requested Pacific Gas and Electric provide a copy of the operability evaluation for the seismically qualified structures, systems and components affected by the new seismic information. In response, Pacific Gas and Electric stated that the new seismic information was neither a nonconforming nor an unanalyzed condition and an operability evaluation was not required. The licensee based this conclusion on three factors documented in Notification 50086062, Task 30 1. The current licensing basis established that new information discovered during Long Term Seismic Program (LTSP) research efforts was only required to be evaluated under the LTSP deterministic margin analysis. The licensee based this conclusion on Supplemental Safety Evaluation Report (SSER) 34, Section 2.5.2.4, which referenced a commitment Pacific Gas and Electric made to the NRC to maintain a strong geosciences and engineering staff to keep abreast of new geological, seismic, and seismic engineering information and evaluate it with respect to its significance to Diablo Canyon 2. New seismic information is only required to be evaluated under the LTSP deterministic margin analysis because the Hosgri Evaluation is the bounding seismic source for the site. The licensee based this conclusion on SSER 34, Section 1.3.2, Summary of NRC Staff Review of the LTSP, which stated that the Hosgri fault is the seismic source that could cause the maximum vibratory ground motion at the Diablo Canyon site. Because the new information is bounded by the LTSP deterministic ground motion spectrum, the plant can be safely shutdown in the event of an earthquake 3. The new information is only required to be evaluated under the LTSP deterministic margin analysis because the Hosgri Event is the safe shutdown earthquake for Diablo Canyon. The licensee based this conclusion on SSER 07, Section 2.5.2, Seismology, which said that the Hosgri earthquake is considered as the safe shutdown earthquake as defined in 10 CFR Part 100, Appendix A. Since the Shoreline Fault is completely bounded by the LTSP and the LTSP is considered bound by the Hosgri, the plant can be safely shutdown in the event of an earthquake on the Shoreline Fault The inspectors were unable to confirm the licensees statements that new seismic information was only required to be evaluated under the LTSP deterministic margin analysis (which is a margin analysis to the Hosgri Event) based on a review of docketed information and the plant safety analysis. The LTSP margin analysis only demonstrated that the new seismic information was bound by the Hosgri Event design basis earthquake, not the Design or Double Design Earthquakes. FSARU, Section 3.7.1, Seismic Input, describes the LTSP as having satisfied License Condition 2.C(7) with the completion of confirmatory analyses by Pacific Gas and Electric. The FSARU further states in Section 2.5, The LTSP contains extensive databases and analyses that update the basic geologic and seismic information in this FSAR Update. However, the LTSP material does not alter the design bases for DCPP. In SSER 34, the NRC states, The Staff notes that the seismic qualification basis for Diablo Canyon will continue to be the original design basis plus the Hosgri evaluation basis, along with associated analytical methods, initial conditions, etc. Pacific Gas and Electric committed to the NRC in a letter dated July 16, 1991, that future plant additions and modifications, as identified in that letter, would be checked against the insights and knowledge gained from the LTSP to verify that the plant margins remain acceptable. This issue is unresolved pending NRC review of the Diablo Canyon current licensing bases requirements for new seismic information, including whether or not the licensee is only required to evaluate new seismic information solely using the LTSP. Unresolved Item: 05000275; 323/2011002-03, Requirement to Perform an Operability Evaluation Following Receipt of New Seismic Information. |
| Site: | Diablo Canyon  |
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| Report | IR 05000275/2011002 Section 1R15 |
| Date counted | Mar 31, 2011 (2011Q1) |
| Type: | URI: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | E Ruesch D Reinert C Alldredge L Micewski N Makris L Ricketson G Guerra M Peck N O'Keefe M Young A Fairbanksd Reinertj Braisted C Denissen P Goldberg M Peck G Miller |
| CCA | H.14, Conservative Bias |
| INPO aspect | DM.2 |
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Finding - Diablo Canyon - IR 05000275/2011002 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Diablo Canyon) @ 2011Q1
Self-Identified List (Diablo Canyon)
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