ENS 58054
ENS Event | |
|---|---|
18:08 Nov 21, 2025 | |
| Title | Automatic Reactor Trip |
| Event Description | The following information was provided by the licensee via phone and email:
At 1208 CST on 11/21/2025, with Unit 2 in Mode 1 at 100 percent power, [the] Unit 2 reactor automatically tripped due to a main transformer lockout. The trip was not complex, with all systems responding normally post-trip. One of three essential chillers (chiller 22C) was inoperable at the time of [the] trip due to planned maintenance activities. All other engineered safety feature (ESF) equipment was operable at the time of the event. Operations responded and stabilized the plant. Decay heat is being removed by steam generator pressure operated relief valves (PORV). There was no impact to Unit 1. All control rods fully inserted. Primary pressurizer PORV '655A' opened twice to relieve pressure in response to [the] pressure transient. [South Texas Project Unit 2] entered Technical Specification 3.8.1.1.e due to a loss of two off-site power sources, `A' and `C' ESF busses. Upon main turbine trip, throttle valves closed as expected. Due to the reactor protection system actuation while critical, this event is being reported as a four-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B). This event is also being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(iv)(A) due to valid actuation of two of the three emergency diesel generators. There was no impact on the health and safety of the public or plant personnel, and Unit 2 remains at normal operating temperature and normal operating pressure. The NRC Resident Inspector has been notified. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: Emergency diesel generators '21' and '23' automatically started upon loss of power as expected. Auxiliary feedwater actuated post-trip as expected. Offsite power to ESF busses has been restored. |
| Where | |
|---|---|
South Texas  Texas (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(2)(iv)(B), RPS Actuation | |
| Time - Person (Reporting Time:+-1.25 h-0.0521 days <br />-0.00744 weeks <br />-0.00171 months <br />) | |
| Opened: | Ronald Rohan 16:53 Nov 21, 2025 |
| NRC Officer: | Ernest West |
| Last Updated: | Nov 21, 2025 |
| 58054 - NRC Website
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