ENS 57952
ENS Event | |
|---|---|
17:29 Sep 25, 2025 | |
| Title | Two Trains of ECCS Inoperable |
| Event Description | The following information was provided by the licensee via phone and email:
On 9/23/2025 at 2214 CDT, the South Texas Project Unit 1 (STP-1) train 'B' reactor containment fan cooler (RCFC) chilled water supply outside containment isolation valve, 1-CC-MOV-0137, was declared inoperable due to a material condition. This rendered train 'B' component cooling water inoperable which cascaded to train 'B' emergency core cooling system (ECCS) subsystem to render it inoperable. STP-1 entered technical specification (TS) 3.5.2 action 'A' for train 'B' ECCS, requiring restoration within 7 days or apply the requirements of the Configuration Risk Management Program (CRMP). On 09/25/2025 at 1229 CDT, train 'A' essential chiller 12A was declared inoperable due to inability to maintain chiller water outlet temperature less than 52 degrees Fahrenheit. This cascaded down to the train 'A' ECCS subsystem to render it inoperable. STP-1 entered TS 3.5.2 action 'B' due to less than two of the required subsystems operable, to within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> restore at least two subsystems to operable status or apply the requirements of the CRMP, or be in at least hot standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in hot shutdown within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. On 09/25/2025 at 1329 CDT, STP-1 entered the CRMP based on two ECCS subsystems remaining inoperable longer than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. These subsystems are used for accident mitigation. Unit 1 remains in mode 1.
The following information was provided by the licensee via phone and email: The purpose of this notification is to retract EN 57952, which was made on September 25, 2025, at 1736 EDT. [The] notification was initially made due to two of three trains of emergency core cooling system (ECCS) being declared inoperable. After the notification was made, South Texas Project determined using an engineering evaluation, that one of the two inoperable ECCS trains was operable because the elevated chilled water outlet temperature of the associated essential chiller (Train A) did not impact the technical specification specified function. Therefore, this event was not a condition that could have prevented fulfillment of a safety function. The NRC Resident Inspector has been notified. Notified R4DO (Vossmar) |
| Where | |
|---|---|
South Texas  Texas (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+0.12 h0.005 days <br />7.142857e-4 weeks <br />1.64376e-4 months <br />) | |
| Opened: | Marc Hill 17:36 Sep 25, 2025 |
| NRC Officer: | Ernest West |
| Last Updated: | Oct 20, 2025 |
| 57952 - NRC Website
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