ENS 46690
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ENS Event | |
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18:08 Mar 22, 2011 | |
Title | Potential Flooding of Raw Water Pump |
Event Description | During ongoing investigations of flood barrier penetrations at the station, a weakness in the flood protection strategy that would prevent protection of the raw water pumps for floods above 1007'-6" Mean Sea Level (MSL) was discovered. Cell in-leakage through penetrations at 997' 10" MSL would be beyond the capacity of the raw water pumps. During the preparation of a calculation to demonstrate the validity of this method it was determined that the grid backwash pipe for each grid and the surface sluice penetrate the east wall of the intake structure through an unsealed penetration (a total of 7 penetrations). The grid backwash line is an 18" pipe passing through a 24" sleeve. Flooding through the penetrations could have impacted the ability of the station's raw water pumps to perform their design accident mitigation functions.
This eight-hour notification is being made pursuant to 10 CFR 50.72 (b)(3)(v). The penetration is at an elevation of 997'10" MSL. The design flood for the station is at 1014' MSL. The raw water pumps would not be affected until a river level of 1007'6" MSL was reached. The river level is currently approximately 993.5' MSL and has been less than 995'MSL since prior to December 1, 2010. The raw water pumps are currently operable. The National Weather Service Weather Forecast Office is predicting a rise in river level of 2 feet over the next 5 days. Actions are in progress to seal the penetration. The licensee has instituted a temporary plug contingency plan dependant on river level. The licensee will notify the NRC Resident Inspector. |
Where | |
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Fort Calhoun ![]() Nebraska (NRC Region 4) | |
Reporting | |
10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
Time - Person (Reporting Time:+-0.95 h-0.0396 days <br />-0.00565 weeks <br />-0.0013 months <br />) | |
Opened: | Erick Matzke 17:11 Mar 22, 2011 |
NRC Officer: | Mark Abramovitz |
Last Updated: | Mar 22, 2011 |
46690 - NRC Website
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Unit 1 | |
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Reactor critical | Critical |
Scram | No |
Before | Power Operation (100 %) |
After | Power Operation (100 %) |
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