ENS 48919
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ENS Event | |
|---|---|
03:00 Apr 13, 2013 | |
| Title | Unanalyzed Condition Due to Isolated Differential Pressure Switch on Safety Relief Valve Tailpipe |
| Event Description | On April 12th, 2013 at 2200 CDT, investigation into the inability to complete a Safety/Relief Valve (S/RV) discharge line excess flow check valve test determined that a relief valve discharge monitoring instrument valve had been inappropriately closed since late June, 2011. The closed valve isolated two differential pressure switches that impact the operation of 'E' Low-Low Set (LLS) valve. The LLS logic and instrumentation were affected by the loss of two 'E' S/RV tailpipe discharge pressure switches which indicate S/RV open status and start two inhibit timers which prevent plant operators or the LLS S/RV logic from immediately re-opening the valve to allow the water leg in the S/RV discharge line to recede. The LLS logic and instrumentation is designed to mitigate the effects of postulated thrust loads on the S/RV discharge lines by preventing subsequent actuations with an elevated water leg in the S/RV discharge line. It also mitigates the effects of postulated pressure loads on the torus shell or suppression pool by preventing multiple actuations in rapid succession of the S/RVs subsequent to their initial actuation. The valve found closed has been returned to its normal open position. This condition resulted in the 'E' S/RV LLS function being aligned contrary to its design configuration and as such is being reported as an unanalyzed condition as defined by 10 CFR 50.72(b)(3)(ii)(B).
The licensee has notified the NRC Resident Inspector. |
| Where | |
|---|---|
Monticello  Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+0.3 h0.0125 days <br />0.00179 weeks <br />4.1094e-4 months <br />) | |
| Opened: | Matthew Quick 03:18 Apr 13, 2013 |
| NRC Officer: | Bill Huffman |
| Last Updated: | Apr 13, 2013 |
| 48919 - NRC Website
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