ENS 55612

v t e ENS Event
10:19 Nov 27, 2021
Title	Automatic Actuation of the Emergency AC Electrical Power System
Event Description	At 0519 EST on November 27, 2021, with Unit 2 in Mode 5 at zero percent power, an actuation of the Emergency AC Electrical Power System occurred. The reason for the Emergency AC Electrical Power System auto-start was a lockout of the CT-2 transformer; causing a temporary loss of AC power to the main feeder bus. The Keowee Hydroelectric Units 1 and 2 automatically started as designed when a main feeder bus undervoltage signal was received. This event is being reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the Emergency AC Electrical Power System. Additionally, the temporary loss of AC power resulted in a loss of Decay Heat Removal (DHR) that was restored upon power restoration to the main feeder bus. Therefore, this condition is also being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v) for an event or condition that could have prevented fulfillment of a safety function. There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. The loss of the CT-2 transformer is under investigation. Main feeder bus power was restored within a minute so no plant heat up occurred as a result of the loss of the decay heat removal system.

ENS 55612 +/-
Where
Oconee South Carolina (NRC Region 2)
Reporting

10 CFR 50.72(b)(3)(iv)(A), System Actuation 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat
Time - Person (Reporting Time:+2.95 h0.123 days <br />0.0176 weeks <br />0.00404 months <br />)
Opened:	Will Beekman 13:16 Nov 27, 2021
NRC Officer:	Howie Crouch
Last Updated:	Nov 27, 2021
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v • d • e

v t e Emergency Notification System
Oconee with 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(iv)(A), System Actuation
WEEKMONTHYEAR2025-11-15T03:54:00 [Table view]
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