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The following information was provided by the licensee via email: On January 18, 2024, at 0030 PST, diesel generator 2 (DG2) was shut down following a monthly surveillance run. Subsequently, a leak was discovered in the DG2 building. Service water pump '1B' was secured at 0117, effectively stopping the leak. The leak was determined to be service water coming from a diesel generator mixed air cooling coil. Service water system 'B' and DG2 were subsequently declared inoperable at 0135. After discussion with engineering, it was identified that the amount of service water leakage from the cooling coil was assumed to be greater than the leakage allowed by the calculation to assure adequate water in the ultimate heat sink to meet the required mission time of 30 days. At 1204, it was determined that entry into Technical Specification 3.7.1 condition D was warranted since the assumed leakage from the cooling coil could exceed the calculated allowed value. At 1238, the control power fuses for service water pump '1B' were removed. DG2 and service water system 'B' were declared unavailable, and the technical specification condition for the inoperable ultimate heat sink was exited. With the control power fuses removed, the pump is kept from auto starting, effectively preventing the leak and ensuring the safety function of the ultimate heat sink is maintained while the cooling coil is repaired or replaced. Due to the leakage assumed greater than the calculated allowable value this condition is reportable per 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition and per 10 CFR 50.72(b)(3)(v)(B) as an event or condition that could have prevented fulfillment of the safety function of structures or systems that are needed to remove residual heat. There was no impact to the health and safety of the public. The NRC Resident has been notified.

• * * RETRACTION ON 3/18/24 AT 1923 FROM VALERIE LAGEN TO KAREN COTTON * * *

The following information was provided by the licensee via email: On January 18, 2024 at 2138 EST, Columbia Generating Station notified the NRC under 10 CFR 50.72(b)(3)(ii)(B) of an unanalyzed condition on the available capacity of the ultimate heat sink (UHS) and under 10 CFR 50.72(b)(3)(v)(B) of an event or condition that could have prevented fulfillment of the safety function of structures or systems needed to remove residual heat. On January 18, 2024, following monthly surveillance of the diesel generator DG2, a DG2 room cooler flow alarm was received at 0115. A leak was discovered in the diesel mixed air (DMA) air handler unit. Service Water Pump '1B' was secured and the leakage was stopped at 0117. The service water system 'B' and diesel generator system 'B' were declared inoperable at 0135. The leak was assumed to be greater than that allowed to ensure adequate water in the UHS required to meet the 30-day mission time, and the UHS was declared inoperable at 1204. Control power fuses for the service water pump '1B' were removed to fully eliminate the leakage path from the cooler, and the UHS was declared operable at 1238. Following the event, engineering performed an analysis based on the size and location of the leak, and concluded it would have taken 1.4 days to deplete the available excess water in the UHS to below the minimum technical specification required water level of the spray pond. Operations were able to secure the service water subsystem of the UHS prior to exceeding the volumetric margins in the spray ponds to ensure the 30-day mission time was met. The condition did not represent a safety significant unanalyzed condition nor a loss of safety function. The NRC Resident Inspector has been notified. Notified R4DO (Gepford).