Event Notification Report for July 28, 2025

EN Revision Imported Date: 7/31/2025

EN Revision Text: BOTH TRAINS OF CONTROL ROOM AIR CONDITIONING INOPERABLE

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

At 2324 CDT, on July 28, 2025, control room air conditioning (CRAC) 'B' tripped at Grand Gulf Nuclear Station (GGNS) approximately 5 minutes after loading the compressor by adjusting the thermostat [down] per standby service water quarterly surveillance instructions. CRAC 'A' was manually started at 2326 CDT and at 2329 CDT it subsequently tripped. After investigating the compressors and breakers per the alarm response instructions with no abnormal indications, CRAC 'B' was restarted and tripped again. Cooling water was rotated from plant service water to standby service water and CRAC 'A' was successfully restarted at 2358 CDT and remains in service.

While both control room air conditioning subsystems were inoperable GGNS entered technical specification limiting condition of operation (LCO) 3.7.4 condition 'B', actions requiring verification of control room temperatures less than 90 degrees F and restoring one subsystem to operable status in 7 days. Control room temperatures reached 79 degrees F, maximum, before CRAC 'A' was restarted. GGNS has exited condition 'B' in LCO 3.7.4 and entered condition 'A' to restore CRAC 'B' in 30 days.

This event is being reported in accordance with 10 CFR 50.72(b)(3)(v)(D) as an event or condition which could have prevented the fulfillment of a safety function.

The NRC Senior Resident Inspector has been notified.

* * * RETRACTION FROM JEFFERY HARDY TO SAMUEL COLVARD AT 1648 EDT ON 07/30/2025 * * *

"Investigation of the cause of the control room air conditioning (CRAC) `A' and `B' trips identified a plant service water / standby service water (SSW) crosstie valve which failed in its safety-related (closed) position as the cause. In an accident or transient, cooling water to CRAC `A' compressors would have been successfully provided by the safety-related SSW. As a result, CRAC `A' remained capable of fulfilling its safety function to maintain the control room environment less than 90 degrees F.

"The NRC Senior Resident Inspector has been notified of this retraction."

Notified R4DO (Drake).

MANUAL REACTOR SCRAM

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

At 2058 CDT on 7/28/2025, a spurious trip of the reactor building exhaust ventilation [system] caused a subsequent trip of the reactor building supply ventilation [system]. This ventilation system failure resulted in the degradation of reactor building differential pressure and at 2200 CDT the differential pressure exceeded the technical specification limit, resulting in the inoperability of Secondary Containment. This condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72 (b)(3)(v).

Failure of the ventilation system also resulted in elevated temperatures in the steam chase area of the plant. Operators reduced power to slow the temperature rise, however, at 2324 CDT on 7/28/2025 with Unit 1 in mode 1 at 41 percent power, the reactor was manually scrammed due to steam chase temperatures reaching the procedural limit. The scram was not complex, with all systems responding normally post-scram. Reactor water level is being maintained via the feedwater system. Decay heat is being removed by discharging steam to the main condenser using the turbine bypass valves. This condition is being reported as a four-hour, non-emergency notification per 10 CFR 50.72 (b)(2)(iv)(B). There has been no impact to the health and safety of the public or plant personnel.

The NRC Resident Inspector has been notified.

The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance:

Steam chase temperature has begun to lower, and the licensee intends to cooldown to mode 4 for maintenance.

FITNESS FOR DUTY EVENT

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

"On July 28, 2025, Watts Bar Nuclear (WBN) operations was informed that a WBN licensed reactor operator had tested positive for a controlled substance, in violation of the Tennessee Valley Authority (TVA) fitness for duty policy. A random screening was completed on July 17, 2025. The results were sent to the TVA medical review officer on July 28, 2025. The test was declared positive for a controlled substance and WBN operations was notified at 1333 EDT on July 28, 2025. The individual's unescorted access has been revoked."

The NRC Resident Inspector has been notified.

EN Revision Imported Date: 9/29/2025

EN Revision Text: AGREEMENT STATE REPORT - LOST EXIT SIGN

The following is a summary of information provided by the Colorado Department of Public Health and Environment (the Department) via email:

The Department received a notification from the licensee that one (1) exit sign containing 10 Ci of tritium was lost in Meeker, Colorado.

Manufacturer: Isolite Corporation
Model Number: SLX60
Isotope: H-3
Activity: 10 Ci

Event Report ID No.: CO250027

THIS MATERIAL EVENT CONTAINS A 'Less than Cat 3' LEVEL OF RADIOACTIVE MATERIAL

Sources that are "Less than IAEA Category 3 sources," are either sources that are very unlikely to cause permanent injury to individuals or contain a very small amount of radioactive material that would not cause any permanent injury. Some of these sources, such as moisture density gauges or thickness gauges that are Category 4, the amount of unshielded radioactive material, if not safely managed or securely protected, could possibly - although it is unlikely - temporarily injure someone who handled it or were otherwise in contact with it, or who were close to it for a period of many weeks. For additional information go to http://www-pub.iaea.org/MTCD/publications/PDF/Pub1227_web.pdf