ENS 41406
ENS Event | |
|---|---|
04:26 Feb 12, 2005 | |
| Title | Postulated Loss of Afw Pumps Following Tornado Damage to Condenstate Storage Tank |
| Event Description | Plant engineering staff discovered that the auxiliary feedwater (AFW) system discharge pressure trip protective equipment may not operate to protect the AFW pumps from condensate storage tanks (CST) failing from a tornado event. The AFW system protection design uses discharge pressure switches to protect the AFW pumps from a loss of suction pressure. The AFW system is required equipment to support a plant shutdown which is also assumed to occur as a result of a tornado.
Current analysis predicts substantial damage to the CSTs caused by a tornado. The CSTs are aligned as the AFW pumps' initial/preferred water source. The tank damage is predicted to result in a rapid, near complete, loss of water inventory due to a tornado. The CST volume loss quickly causes air to enter the pump suction piping to all three AFW pumps. Under the postulated conditions, the current discharge pressure switch design does not act fast enough to trip the pumps before significant pump damage can occur, it appears that the original design analyses failed to consider the consequences of a loss of suction source causing air to enter the pump suction. The design basis for AFW pump discharge pressure switches, in part, is assumed to protect the AFW pumps from damage due to a tornado. Given the event postulated as described, the pressure switches may not meet this design basis assumption. Therefore, all three AFW pump discharge pressure switches were declared inoperable at 2226 on 2/11/2005. To ensure the AFW Pumps are protected in the event of a tornado, compensatory actions were incorporated in Operating Procedure E-0-05 Response to Natural Events. At the earliest indication of a tornado threat (i.e. Tornado Watch, Warning or Strike) operators are directed to align Service Water to the AFW Pump Suction to ensure adequate NPSH In the event of a loss of the CST supply. These actions do not replace the automatic function but ensure the pumps are protected against loss of NPSH. Based on the proceduralized compensatory actions put in place, the AFW Pump Low discharge Pressure Trips were declared Operable but Non-Conforming at 0056 on 2/12/2005. The licensee has notified the NRC Resident Inspector. |
| 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:+-0.28 h-0.0117 days <br />-0.00167 weeks <br />-3.83544e-4 months <br />) | |
| Opened: | Al Prokash 04:09 Feb 12, 2005 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Feb 12, 2005 |
| 41406 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |