ENS 57401
ENS Event | |
|---|---|
17:23 Oct 28, 2024 | |
| Title | Loss of Both Trains of Control Room Ventilation |
| Event Description | The following information was provided by the licensee via phone or email:
On October 28, 2024, at 0533 EDT, it was discovered both trains of the unit 1 and unit 2 control room ventilation system booster fans were simultaneously inoperable due to trip of the supply breaker to the motor control center (MCC) supplying the normally closed motor operated intake dampers for both trains. Therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v)(D). At 1059 EDT, one train of the unit 1 and unit 2 control room ventilation system booster fans was restored to operable. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: Although the control room ventilation affects both units 1 and 2, unit 1 is currently defueled and outside the mode of applicability during the timeframe of this event. For clarification regarding train separation, both trains for control room ventilation have separate power supplies for their booster fans. However, power for both of their inlet dampers and one of the booster fans are all fed from the same MCC supply breaker that tripped. Therefore, both trains were simultaneously inoperable at 0533 EDT. The loss of power to the MCC is still under investigation. Procedurally, Oconee was able to restore one train to service, the train that still had power to its booster fan, at 1059 EDT, by manually opening its inlet damper in the fail-safe position. |
| Where | |
|---|---|
Oconee  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+-4 h-0.167 days <br />-0.0238 weeks <br />-0.00548 months <br />) | |
| Opened: | Sam Morton 13:23 Oct 28, 2024 |
| NRC Officer: | Brian P. Smith |
| Last Updated: | Oct 28, 2024 |
| 57401 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |