Event Notification Report for June 12, 2026

AGREEMENT STATE REPORT - STUCK OPEN GAUGE SHUTTER

The following is a summary of information provided by the Washington State Office of Radiation Protection via email:

The licensee reported that the shutter device on a Vega Ohmart model SH-F1 fixed level gauge with a 100 mCi Cs-137 source failed. The facility maintenance department was attempting to isolate the device as part of a normal procedure but was unable to close the shutter. The licensee stated that with the shutter stuck in an open position, the device is still functioning in a normal capacity. The licensee stated the gauge is installed on a digester vessel and is not currently presenting an abnormal risk of employee exposure.

The licensee has contacted the manufacturer, who is currently providing guidance for another attempt to isolate the device. The licensee expects the manufacturer will need to provide onsite support to repair or remove the device from service. The manufacturer has communicated that replacement parts for Ohmart SH-F1 model source holders are no longer supported, so the licensee anticipates replacing the gauge with a new unit.

The licensee reported that radiation levels in the area of the gauge were recorded at 0.6 mrem/hr. The work area has been cleared and yellow tape boundaries established.

Washington report number: WA-26-008

INVALID SPECIFIED SYSTEM ACTUATION

The following information was provided by the licensee via phone and email:

"This report is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A) using the telephone option in 50.73(a)(1) in lieu of a written LER [licensee event report] concerning an event in which Callaway experienced an automatic start of the turbine driven auxiliary feedwater pump (TDAFP) in response to an invalid auxiliary feedwater actuation signal. The reactor protection system was not involved.

"This TDAFP actuation was complete, and the TDAFP started and functioned successfully in accordance with the initiating actuation signal.

"This actuation occurred at 2149 CDT on May 17, 2026.

"The most probable cause of the actuation was a voltage perturbation caused by switching inverters in preparation for tagging out the in-service inverter, resulting in the TDAFP receiving a start signal. This signal did not result from plant conditions or parameters satisfying the requirements for initiation of the system. Therefore, the actuation was invalid."

The NRC Resident Inspector was notified.

PART 21 - RELAY FAILURE

The following information was provided by the licensee via phone and email:

"On June 9, 2026, STP [South Texas Project] Nuclear Operating Company (STPNOC) completed a Part 21 evaluation which identified a defect with TE Connectivity MDR styled relays (MDR 131-1 and MDR 134-1) manufactured after mid-year 2020. Since 2023, eleven (11) of these relays in both Unit 1 and Unit 2 have experienced premature failures resulting in essential chillers being inoperable and incapable of fulfilling their intended safety function. The relays were procured as commercial grade items and were dedicated by STPNOC solely for use at STP. An investigation determined that the relay failures resulted from overheating of the relay coils during operation. The vendor informed STP that a subcontractor responsible for rotor grinding produced relay rotors that were undersized and outside of specification. The reduced rotor dimensions resulted in a looser fit between the rotor and stator, reducing eddy currents and increasing coil current consumption. The increased coil wattage then generated excessive heat that caused the relay windings to short at the finish lead, resulting in relay failure. A written notification in accordance with 10 CFR 21.21 (d)(3)(ii) will be provided within 30 days.

"The NRC Resident Inspector has been notified, June 10, 2026, at 1330 CDT."

FITNESS FOR DUTY

The following information was provided by the licensee via phone and email:

"At 1226 MST on June 10, 2026, it was determined that a non-licensed contractor supervisor failed a test specified by the fitness-for-duty testing program. The individual's authorization for site access has been terminated.

"The NRC Resident Inspector has been notified."

MANUAL REACTOR TRIP

The following information was provided by the licensee via phone and fax:

"At 0339 EDT on June 11, 2026, control element assembly '14' dropped to the bottom of the core.
"To stabilize plant conditions, the reactor was manually tripped at 0341. This resulted in the actuation of the reactor protection system (RPS) when the reactor was critical and is being reported as a four-hour non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B).
"There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.
"There has been no impact to Unit 3 which remains at 100 percent power."

FITNESS FOR DUTY

The following information was provided by the licensee via phone and email:

"At 0909 EDT, on June 11, 2026, it was determined that a non-licensed contract supervisor failed a test specified by the fitness-for-duty (FFD) testing program. The individual's authorization for site access has been removed.

"The NRC Resident Inspector has been notified."

AGREEMENT STATE REPORT - STUCK OPEN GAUGE

The following information was provided by the Utah Division of Radiation Control via email:

"The Division of Waste Management and Radiation Control (DWMRC) was initially notified of a potential incident on June 11, 2026, at approximately 1530 MDT.

"On May 29, 2026, at approximately 1330 MDT, the licensee was verbally informed by a third-party service technician that two of their fixed gauges were stuck open.

"The licensee received the written report from a third-party service provider on June 11, 2026, at 1512 MDT. These gauges were in an HF [hydrofluoric] acid area.

"The gauges are an Ohmart SH-F1 Acid settler Interface 7LT502A and an Ohmart SHRM-P-84 containing 5 sources totaling 175 mCi.

"The licensee contacted the gauge manufacturer. The affected devices are scheduled to be replaced."

Utah Event Report ID No.: UT260005