05000269/FIN-2012002-01
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Finding | |
|---|---|
| Title | Evaluation of Probable Maximum Flood Event |
| Description | During a walkdown of Manhole 7 on February 1, 2012, inspectors noted that two conduit penetrations used to route PSW cabling into the AB were not sealed and provided a direct flooding pathway into the AB. These penetrations were identified as requiring seals whenever not being used for cable pulls or sealed immediately following cable pulling activities. Flooding from these penetrations would exceed the capacity of the AB sump pumps and fill the high pressure injection (HPI), low pressure injection (LPI) and reactor building spray (RBS) pump rooms rendering the pumps inoperable. The inspectors also identified that a field change rerouted the internal drainage system from the yard drain system to the adjacent radwaste trench. Rainwater accumulating in Manhole 7 would flow through the internal drains to the radwaste trench and into the AB through a non-isolable line which drained into the low activity waste tanks. These tanks would eventually overflow flooding the HPI, LPI and RBS pump rooms rendering the pumps inoperable. The design change in the original design package for Manhole 7 and the field change for rerouting the drain did not evaluate the impact they would have on the AB features to mitigate external floods. Consequently, the currently described Updated Final Safety Analysis Report (UFSAR) described PMF event would result in rendering safety-related/risk significant equipment inoperable. Additionally, the licensee recently completed a site inundation study which projected site water levels to be greater than the maximum flood protection measures for a PMF event as described in UFSAR Section 3.4.1.1 even with a fully functional yard drain system. Changes in site topography and construction of new buildings since initial construction appear to be contributing to the increased water levels. The licensee is currently evaluating the impact of the new site inundation level and has implemented interim actions to provide protection from increased water levels on-site. The NRC will perform additional inspection to ensure the impact to the AB from a PMF event is understood, an accurate timeline on Manhole 7 construction activities is developed, and that the extent of condition is fully defined. This issue is identified as URI 05000269, 270, 287/2012002-01, Evaluation of Probable Maximum Flood Event. |
| Site: | Oconee  |
|---|---|
| Report | IR 05000269/2012002 Section 1R01 |
| Date counted | Mar 31, 2012 (2012Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.01 |
| Inspectors (proximate) | J Bartley A Sabisch S Walker A Vargas-Mendez G Ottenberg J Hamman K Ellis G Crespo M Rileya Sabischg Ottenberg B Collins K Ellis E Stamm A Sengupta S Darbali J Bartley W Loo |
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Finding - Oconee - IR 05000269/2012002 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Oconee) @ 2012Q1
Self-Identified List (Oconee)
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