ENS 43010
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ENS Event | |
|---|---|
01:45 Nov 25, 2006 | |
| Title | |
| Event Description | With Prairie Island Unit 2 core offloaded for the 2R24 refueling outage, it was discovered that a potential common cause failure of the 21 and 22 Residual Heat Removal (RHR) Pumps may exist. A non-safety related 120 VAC motor heater circuit from Panel 2RPA3 Circuit 28 supplies power to 21 and 22 RHR Pumps. Investigation continues. The RHR system is not required by the current operating mode.
The RHR Pumps on the operating unit (Unit 1) are supplied from separate 120 VAC panels so the concern does not exist for the 11 and 12 RHR pumps. The licensee notified the NRC Resident Inspector.
Event Number 43010 (reported 11/24/06) reported a potential single failure vulnerability of the Unit 2 residual heat removal (RHR) pumps. NMC identified that power cables for the motor heaters in each pump were powered from the same 120 Volt panel and that the heater power cables were routed for some distance in the same conduit. The concern was that an electrical fault could propagate from one RHR pump motor to the opposite train RHR pump motor. Further engineering evaluation has determined that no credible failure mechanism exists that could cause a fault in one RHR pump motor to propagate to the opposite train RHR pump motor. Since the dielectric strength of insulation on the heaters is greater than the dielectric strength of the air between the motor windings and the motor frame or the stator, any fault in the motor windings would be to ground (and, thus, interrupted by the ground fault protective relaying). Therefore, no potential single failure vulnerability existed in the as-found condition and NMC hereby retracts the event reported on 11/24/06 (Event Number 43010). The licensee notified the NRC Resident Inspector. Notified the R3DO (H. Peterson). |
| Where | |
|---|---|
Prairie Island  Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+2.48 h0.103 days <br />0.0148 weeks <br />0.0034 months <br />) | |
| Opened: | Gene Dammann 04:14 Nov 25, 2006 |
| NRC Officer: | Bill Gott |
| Last Updated: | Jan 18, 2007 |
| 43010 - NRC Website
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WEEKMONTHYEARENS 526382017-03-20T21:39:00020 March 2017 21:39:00
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