ENS Event | |
|---|---|
08:49 Jul 12, 2023 | |
| Title | ECCS Potentially Inoperable |
| Event Description | The following information was provided by the licensee via email:
At 0449 [EDT] on 7/12/2023, Millstone Unit 3 declared the 'B' train of the emergency core cooling system (ECCS) inoperable due to a degraded damper associated with the ventilation support system for the 'B' charging pump. At the time of this event, the 'A' train of service water was already inoperable due to planned maintenance on a breaker that would have prevented an 'A' service water valve powered from this breaker from closing on a safety signal. This configuration resulted in the possibility that the 'A' train of ECCS would not have been available to fulfill its design function under all postulated accident conditions. This event is being reported under 10 CFR 50.72(b)(3)(v)(B), '[any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to: (B) remove residual heat].' Subsequently, the 'A' train of service water was restored to operable at 0548 on 7/12/2023. Repairs and investigation continue on the 'B' train ECCS damper. The NRC resident has been notified. This event did not impact Millstone Unit 2. There was no impact to the public. |
| Where | |
|---|---|
Millstone  Connecticut (NRC Region 1) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat | |
| Time - Person (Reporting Time:+4 h0.167 days <br />0.0238 weeks <br />0.00548 months <br />) | |
| Opened: | Todd Stringfellow 12:49 Jul 12, 2023 |
| NRC Officer: | Kerby Scales |
| Last Updated: | Jul 12, 2023 |
| 56620 - NRC Website
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Unit 3 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 566202023-07-12T08:49:00012 July 2023 08:49:00
[Table view]10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat ECCS Potentially Inoperable ENS 518892016-04-28T00:07:00028 April 2016 00:07:00 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident High Energy Line Break Door Discovered Open ENS 402452003-10-14T08:04:00014 October 2003 08:04:00 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration Unusual Event Declared - Loss of Shutdown Cooling 2023-07-12T08:49:00 | |