05000348/FIN-2009005-01
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Finding | |
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| Title | Failure to Identify A Credible Source of Flooding in the Internal Flooding Evaluation of Record |
| Description | A self-revealing non-cited violation (NCV) of 10 CFR 50, Appendix B, Criterion III, Design Control, was identified for the licensees failure to identify a credible source of flooding in their internal flooding evaluation of record (performed in 1999). On March 27, 2009, the licensee performed a flushing evolution of the Unit 2 main feedwater (FW) system involving draining of water into the main steam valve room (MSVR) critical pipe chase. A drain located at the bottom of the chase connects to the floor drain system of the auxiliary building lower equipment room. This evolution resulted in water entering the lower equipment room through the floor drain system. The licensee reviewed design documents and discovered the flooding evaluation failed to identify a credible source of flooding from the floor drain system. The licensee performed a root cause analysis and determined a FW line break in the MSVR concurrent with the open drain path, would result in a worst case maximum flood level in the lower equipment room of 1 foot and 10 inches above the floor. This level was determined to adversely affect the turbine driven auxiliary feedwater pump (TDAFWP) uninterrupted power supply inverter/rectifier and would render the pump inoperable. The licensees failure to identify a credible source of flooding in their internal flooding evaluation of record was a performance deficiency. This finding was more than minor because it adversely affected the equipment reliability attribute of the mitigating systems cornerstone objective to ensure the availability, reliability and capability of systems responding to initiating events to prevent undesirable consequences (i.e., core damage). Specifically, this finding resulted in conditions that could render the TDAFWP inoperable on both units. This finding was assessed using the Phase 1 screening worksheet of the SDP and it was determined a Phase 3 analysis was required. A senior reactor analyst performed a Phase 3 evaluation under the SDP and determined that the finding was of very low safety significance (Green). The analysis used a one year exposure time with the emergency air compressors and the TDAFWP failing without the possibility of recovery due to internal flooding. Two initiating events are a steam line break outside containment and a main feedwater line break. The dominant accident sequence was a steam line break with the normal air compressors failing due to common cause, followed by operators failing to terminate the safety injection. The finding was reviewed against the cross-cutting aspects listed in IMC 0305, Operating Reactor Assessment Program, and determined not to have a cross-cutting aspect reflective of current licensee performance |
| Site: | Farley  |
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| Report | IR 05000348/2009005 Section 1R06 |
| Date counted | Dec 31, 2009 (2009Q4) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71111.06 |
| Inspectors (proximate) | E Crowe S Shaeffer W Rogers G Macdonald B Caballero S Sandal |
| INPO aspect | |
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Finding - Farley - IR 05000348/2009005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Farley) @ 2009Q4
Self-Identified List (Farley)
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