05000346/FIN-2013010-01
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Finding | |
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| Title | 10 CFR 50.59 Safety Evaluation Not Performed for Calculated Component Damping |
| Description | The inspectors reviewed the effect of the steam generator replacement on RCS 1/2-Loop Model to verify the change was consistent with the design and licensing basis reviewed by the NRC. Specifically, the inspectors reviewed Engineering Change Package () 12-0474-000, Revision 1, and the licensees associated 10 CFR 50.59 Screen 12-03404 for the RCS 1/2-Loop coupled system model. The inspectors utilized NRC endorsed NEI 96-07, Guidelines for 10 CFR 50.59 Implementation, Revision 1, for review of 10 CFR 50.59 Screen 12-03404. During review of licensee Calculation 32-9191681-001, DB-1 RCS 1/2-Loop Model and Loading Analysis, the inspectors identified that the analytical model for seismic analysis utilized a damping value higher than the value described in the USAR. Specifically, the licensee utilized friction properties associated with the steam generator slider support (Lubrite plate) to calculate an effective damping factor and modify the seismic response spectra for operating basis earthquake (OBE) and safe shutdown earthquake (SSE). The inspectors reviewed the USAR for appropriate seismic damping. Damping for the RCS 1/2-Loop Model was described in Section 3.7.2.14, Coupled System Damping, which states: Although various components within a model possess different values of critical damping (example: shield wall 2 percent, reactor, steam generators, and pressurizer - 1 percent and piping - 1/2 percent), the lowest damping value was used for all components in the model by the NSSS Supplier. Re-analysis of this model utilizes the damping factors from Subsection 3.7.1.3. As indicated in USAR Section 3.7.1.3 and Table 3.7-1, the plant was originally licensed with piping system damping of 1/2 percent of critical damping. In addition, the licensee requested and the NRC approved use of ASME Code Case N-411, Alternative Damping Values for Response Spectra Analysis of Class 1, 2, and 3 Piping, Section III, Division 1. The inspectors noted that USAR Section 3.7.1.3 had been revised to include, Higher damping values than those listed in Table 3.7-1 are allowed, provided proper justification (i.e., test results, analysis etc.) is available for specific components or equipment. The inspectors considered proper justification to include a 10 CFR 50.59 evaluation to determine whether the increase in damping change required prior NRC-approval. The inspectors further verified that 10 CFR 50.59 Screen 12-03404 did not evaluate the changes to the damping value used in the RCS 1/2-Loop Model. The inspectors further determined the licensee initially modified RCS 1/2-Loop Model damping by calculation in 1990 in Calculation 32-1177088-00 as part of the modification to remove the snubber seismic restraints at the base of the original steam generators. The inspectors verified that the supporting 10 CFR 50.50 evaluation, SE 91-0046, did not address the calculated increase in damping factors. This issue is considered a URI pending further review and evaluation by the NRC staff to establish a position on whether the licensees USAR changes and supporting 10 CFR 50.59 evaluations provided appropriate rationale to support a conclusion that prior NRC-approval is not required to increase seismic licensing basis damping by calculation. |
| Site: | Davis Besse  |
|---|---|
| Report | IR 05000346/2013010 Section 4OA5 |
| Date counted | Sep 30, 2014 (2014Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | |
| Inspectors (proximate) | D Hills J Neurautera Shaikhd Hills D Kimble J Neurauter M Mitchell N Egan T Briley V Meghani |
| INPO aspect | |
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Finding - Davis Besse - IR 05000346/2013010 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Davis Besse) @ 2014Q3
Self-Identified List (Davis Besse)
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