ENS 41496
ENS Event | |
|---|---|
22:30 Mar 15, 2005 | |
| Title | Kewaunee Plant Design for Flooding Events May Not Mitigate the Consequences of Piping System Failures |
| Event Description | The following was provided by the licensee:
While reviewing Nuclear Regulatory Commission's (NRC) memorandum regarding Task Interface Agreement (TIA), TIA 2001-02,'Design Basis Assumptions For Non-Seismic Piping Failures at Prairie Island Plant,' Kewaunee staff determined that the Kewaunee plant design for flooding events may not mitigate the consequences of piping system failures. As a minimum, and as a consequence of assuming failure of non-seismically qualified piping systems as prescribed in the TIA, water has been assumed to collect in the turbine building from a circulating water system piping failure that would result in substantial damage to Engineered Safeguards (ESF) and Safe Shutdown (SS) plant equipment, most notably electrical equipment. As a consequence of high water level in the turbine building, water could flow into the ESF equipment rooms that contain the Auxiliary Feedwater pumps, Emergency Diesel Generators and both the 480 volt and 4160 volt electrical switchgear. Water is assumed to flow into the equipment rooms by way of leakage past non-water-tight doors and the plant's unchecked floor-drain system. The expected water levels In the safeguards and electrical equipment rooms are assumed to increase to the point of causing multiple trains of both ESF and SS equipment to be unavailable to safely shutdown the plant. Kewaunee's primary mitigation strategy to combat flooding events is to recognize the event and initiate manual actions to open doors/ barriers. Opening the barriers to flooding directs the water out of the turbine building through the safeguards equipment rooms and returns it to the lake. Normally the manual actions would be expected to be performed before water level accumulates to a point of causing equipment damage. However, under the seismic failure assumptions, water levels are assumed to accumulate faster than the plant's ability to identify and react in order to assure protection of equipment required to initiate and complete a safe plant shutdown. Coincidental to the condition being reported, the plant had recently implemented additional precautionary measures to combat internal flooding events that lesson the significance of the condition being reported. Temporary pumping equipment, temporary sandbag barriers and additional personnel have been staged to minimize the consequences of previously questioned flooding events. Furthermore, a number of plant equipment design changes are being processed to further improve Kewaunee's defenses against internal flooding events. However, given the event being reported, the full scope of any additional actions is still to be determined. The NRC Resident Inspector was notified. |
| Where | |
|---|---|
Kewaunee  Wisconsin (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor | |
| Time - Person (Reporting Time:+0.3 h0.0125 days <br />0.00179 weeks <br />4.1094e-4 months <br />) | |
| Opened: | Harold Prokash 22:48 Mar 15, 2005 |
| NRC Officer: | Chauncey Gould |
| Last Updated: | Mar 15, 2005 |
| 41496 - NRC Website
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