ENS 47010
ENS Event | |
|---|---|
18:44 Jun 27, 2011 | |
| Title | Offsite Power Sources Declared Inoperable |
| Event Description | At 1344 CDT on June 27, 2011, off-site A.C. power sources to Unit 2 were declared inoperable as a result of Transformer 2RY lockout and less than the required minimum voltage on the transmission system.
At 1310 CDT on June 27, 2011, Transformer 2RY was locked out. The Transformer 2RY lockout resulted in entering Technical Specification 3.8.1, Condition A and a single path to the transmission system. At 1344 CDT, the site was notified by transmission systems operations that the 345 KV grid voltage could not be maintained at the minimum voltage required per procedure C20.3. The path to the transmission system was declared inoperable and Unit 2 entered Technical Specification 3.8.1, Condition C. Although inoperable, transmission system sources remained connected to Unit 2; emergency diesel generators were available but not required to run. By securing a cooling tower pump and fans, the required minimum transmission system voltage was met and determined to be sustainable. Technical Specification 3.8.1, Condition C, was exited on June 28, 2011 at 0038 CDT. After additional analysis, it was determined that this condition was a safety system function failure for Unit 2 and reportable under 10 CFR 50.72(b)(3(v)(D). This condition should have been reported on June 27, 2011 under the eight-hour reporting criteria. The NRC Resident Inspector has been informed. |
| Where | |
|---|---|
| Prairie Island Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+92.37 h3.849 days <br />0.55 weeks <br />0.127 months <br />) | |
| Opened: | Mark Loosbrock 15:06 Jul 1, 2011 |
| NRC Officer: | Joe O'Hara |
| Last Updated: | Jul 1, 2011 |
| 47010 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |