The Main Transformer goes from main generator to grid
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| | Site | Start date | Title | Description |
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| ENS 58054 | South Texas | 21 November 2025 18:08:00 | Automatic Reactor Trip | 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. | | ENS 58026 | Wolf Creek | 5 November 2025 16:03:00 | Automatic Emergency Diesel Generator Actuation | The following information was provided by the licensee via phone and email:
At 1003 Central Standard Time (CST), with (Unit 1) in mode 5 at 0 percent power, an actuation of the 'A' emergency diesel generator (EDG) occurred when energizing main transformers from the switchyard for post-installation soak. The energization was coordinated with transmission system operators using approved procedures, however, grid conditions external to the substation allowed the voltage to drop below the NB01 undervoltage relay setpoint. The EDG automatically started as designed and picked up the loads on the NB01 bus. All safety systems responded as designed. Substation parameters immediately recovered to normal values, and all systems were restored to (normal) standby conditions.
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 'A' EDG. There was no impact on the health and safety of the public or plant personnel.
The NRC Resident Inspector has been notified. | | ML25267A061 | River Bend | 24 September 2025 | Response to Request for Additionl Information and Request for Confirmation of Information - LAR to Revise the Licensing Basis and Minimum Basin Water Level for the Ultimate Heat Sink | | | 05000387/LER-2025-001, Manual Reactor Scram Following Partial Loss of Cooling to Main Transformer | Susquehanna | 22 September 2025 | Manual Reactor Scram Following Partial Loss of Cooling to Main Transformer | | | IR 05000498/2025011 | South Texas | 29 August 2025 | NRC Comprehensive Engineering Team Inspection Report 050004982025011 and 050004992025011 | | | IR 05000483/2025002 | Callaway | 11 August 2025 | Integrated Inspection Report 05000483/2025002 | | | IR 05000440/2025002 | Perry | 7 August 2025 | Integrated Inspection Report 05000440/2025002 | | | IR 05000259/2025002 | Browns Ferry | 6 August 2025 | Integrated Inspection Report 05000259/2025002; 05000260/2025002, 050000296/2025002, and 07200052/2025001 | | | ENS 57822 | Susquehanna | 22 July 2025 19:10:00 | Manual Reactor Scram | The following information was provided by the licensee via phone and email:
At 1510 (EDT) with Unit 1 in mode 1 at 96 percent reactor power, the reactor was manually scrammed due to loss of main transformer cooling. The scram was not complex, all systems responded normally post-scram. Main turbine bypass valves opened automatically to maintain reactor pressure.
Operations responded to stabilize the plant. High pressure coolant injection momentarily injected into the reactor vessel and was subsequently placed in standby. Reactor water level has stabilized and is being maintained with the '1B' reactor feed pump. Decay heat is being removed by discharging steam to the main condenser using the turbine bypass valves. Unit 2 was not impacted. Due to the reactor protection system actuation while critical and the emergency core coolant system discharge to the reactor coolant system, this event is being reported as a four-hour and eight-hour non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B), 10 CFR 50.72(b)(2)(iv)(A), and 10 CFR 50.72(b)(3)(iv)(A).
The Unit 1 reactor is currently stable in mode 3. An investigation is in progress into the cause of the loss of main transformer cooling. There was no impact to the health or safety of the public or plant personnel. The NRC Resident Inspector has been informed. The state of Pennsylvania has been informed. | | IR 05000321/2025403 | Hatch | 18 June 2025 | Cyber Security Inspection Report 05000321/2025403 and 05000366/2025403 | |
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