ENS 47885
ENS Event | |
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18:00 May 1, 2012 | |
Title | Floor Drain Blockage Adversely Affects Asumptions of Pipe Break Analysis for Electrical Switghear Rooms |
Event Description | At 1300 on May 1, 2012, as a result of fire water flushing operations, it was observed that the floor drains in the 'A' and 'B' ESF (Engineered Safety Features) 4160 VAC switchgear rooms were draining extremely slow. Engineering was consulted and it was identified that the floor drains in these rooms are credited with preventing any water accumulation in these rooms as a result of internal flooding due to a pipe break. It is expected that the floor drains in the 'A' ESF switchgear room can drain approximately 134 gallons per minute (gpm) and the floor drains in the 'B' ESF switchgear room can drain approximately 208 gpm. With the floor drains partially blocked, a break in the 'A' Essential Service Water pipe in the 'B' ESF Switchgear Room would result in flood levels in the 'B' ESF Switchgear Room to exceed the maximum levels calculated in the current flooding analysis. The higher flood level may result in the inoperability of 'B' train Electrical Switchgear. The 'A' train Essential Service Water supplied equipment would be adversely affected due to the reduced flow. Consequently the pipe break would result in both ESF trains being adversely affected.
Compensatory measures have been taken to restore system operability. The NRC Resident Inspector has been notified.
On May 1, 2012, Callaway Plant made an ENS notification in accordance with 10 CFR 50.72(b)(3)(ii)(B) to report the discovery of partially blocked floor drains in the safety-related 4160 V switchgear rooms. At the time of the initial notification, preliminary information indicated that the partially blocked floor drains could have caused a postulated flooding event to adversely affect independent trains of safety-related equipment inside these rooms. Upon further analysis, Callaway Plant staff determined that the pipe break assumed in the flooding calculation of these rooms was overly conservative. Specifically, based on seismic qualifications, the guillotine break of Essential Service Water piping that was originally assumed is not required to be postulated. Instead, a much smaller, through-wall crack of fire protection system piping is the most severe break that must be postulated in the safety-related 4160 V switchgear rooms. An analysis of a postulated flood hazard in these rooms was performed based on the correct water source. Even if considering a complete blockage of the floor drains in these rooms, this analysis demonstrates that a postulated fire protection system piping crack would not have adversely affected safety-related equipment. Based on the results of this analysis, the partially-blocked floor drain condition described in EN 47885 did not meet the criteria for reportability as an unanalyzed condition that significantly degrades plant safety. Event Notification 47885 is hereby retracted. The licensee has notified the NRC Resident Inspector. Notified the R4DO (Greg Pick) |
Where | |
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Callaway Missouri (NRC Region 4) | |
Reporting | |
10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
Time - Person (Reporting Time:+4.02 h0.168 days <br />0.0239 weeks <br />0.00551 months <br />) | |
Opened: | Keith Duncan 22:01 May 1, 2012 |
NRC Officer: | Donald Norwood |
Last Updated: | May 31, 2012 |
47885 - NRC Website | |
Unit 1 | |
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Reactor critical | Critical |
Scram | No |
Before | Power Operation (100 %) |
After | Power Operation (100 %) |
WEEKMONTHYEARENS 548062020-07-30T13:15:00030 July 2020 13:15:00
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