05000373/FIN-2007009-05
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Finding | |
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| Title | Exclusion of Potential Internal Flood Sources Under 10 CFR 50.59 |
| Description | The inspectors identified an Unresolved Item (URI) concerning changes to the licensees flooding analyses. The original licensing basis assumed all gravity fed flood sources were installed within watertight barriers. In 1995, the licensee determined that several nonsafety related, non-seismically designed piping sections in the turbine building had the potential of allowing a gravity fed internal flood from the lake. This flood could potentially communicate with vital areas in the auxiliary building and reactor building, affecting multiple trains of safety related equipment required for safe shutdown. The licensee performed evaluations of these piping sections and determined that their failure was not credible. Based on these evaluations, the licensee revised the UFSAR without prior NRC approval under 10 CFR 50.59. The inspectors reviewed documentation associated with the crack exclusion of sections of moderate energy piping in the turbine building. An Operability Assessment Process Form (PIF 373-201-95-00260), dated March 21, 1995, addressed a non-conformance with UFSAR Section 3.4.1.4.a, which stated that gravity flooding due to pipe rupture in the turbine building would be confined to watertight enclosures. Walkdowns had identified several sections of non-safety related, non-seismically designed piping that were not within watertight enclosures. A gravity fed flood from the lake could potentially result in flooding of the turbine building up to the maximum lake level of 701 feet. This flood level could potentially communicate with vital areas in the auxiliary building and reactor building, affecting multiple trains of safety related equipment required for safe shutdown. The licensee performed an evaluation to justify continued operation of the units. This evaluation determined that pipe cracks need not be postulated for any piping for which the normal operating pressure is less than 10 psig, based on Appendix J of the UFSAR (Appendix J defined moderate energy piping as being greater than 10 psig). The evaluation also determined that pipe cracks need not be postulated for any moderate energy piping that meet the pipe stress criteria of Standard Review Plan (SRP) 3.6.2. An associated 10 CFR 50.59 evaluation, dated March 21, 1995, determined that no unreviewed safety question (USQ) existed. A UFSAR change request (LU1999-032), dated May 26, 1999 was issued to revise the UFSAR to include both the 10 psig and SRP 3.6.2 crack exclusion criteria. This change also included a 10 CRF 50.59 evaluation (L99-126), dated May 20, 1999, which concluded that no USQ existed. The inspectors also noted that both these 10 CFR 50.59 evaluations stated that if a pipe crack was to occur, sufficient time would be available to isolate the flood source. In response to the inspectors questions, the licensee stated that the capability to isolate these floods had not been verified. The inspectors questioned if these 10 CFR 50.59 evaluations had been adequate to make these licensing basis changes without prior NRC approval. The original license was based on a determination that potential gravity flooding due to failure of non-safety related, nonseismically designed piping in the turbine building would be confined to watertight enclosures, and that safety related equipment was located above the maximum water level. The inspectors were concerned that the identification of non-safety related, non-seismically designed piping outside of the watertight enclosures created the possibility for an accident or malfunction of a different type than any evaluated previously in the safety analysis report. Flooding from a potential rupture of this piping could affect safety-related equipment that is located below normal lake level. In response to NRC concerns, the licensee documented this issue in IR 676923, CDBI−NRC Identified Flooding Methodology as URI. The licensee maintained that piping with an internal pressure less that 10 psi did not have to be evaluated, since it was not evaluated in the initial license application. This item is considered unresolved pending further NRC evaluation of the licensees licensing basis. (URI 05000373/2007009-05; 05000374/2007009-05). |
| Site: | LaSalle  |
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| Report | IR 05000373/2007009 Section 1R12 |
| Date counted | Sep 30, 2007 (2007Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.12 |
| Inspectors (proximate) | P Lougheed N Valos G Hausman C Baron N Feliz-Adomo G Nicely A Stone C Acosta-Acevedoc Zoiar Jickling F Ramirez S Sheldon D Reeser M Bielby D Kimble J Yesinowski |
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Finding - LaSalle - IR 05000373/2007009 | |||||||||||||||||
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Finding List (LaSalle) @ 2007Q3
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