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The following information was provided by the licensee via telephone: On March 27, 2024, at 1101 EDT, a sample containing 20.3 mCi of carbon-14 (C-14) in 1,3-Dichloropropene liquid form (348 microliters) was dropped when being removed from a storage container. The authorized user immediately called for assistance and restricted access to the laboratory where the spill occurred. Decontamination efforts began immediately after the incident, and it was confirmed that the contamination was contained to the laboratory where the spill occurred. It was determined on March 28, 2024, at 1025 EDT that restrictions would remain in place greater than 24 hours, and that this incident was reportable under 10 CFR 30.50(b)(1). Following the spill, a nasal swab was taken of the worker with no detectable activity, however, a urine bioassay taken the following day indicated a potential internal dose of 213 mrem. No other staff were exposed, and there was no risk to public safety or the environment. The applicable 10 CFR 20 Appendix B annual limit for intake for C-14 is 2000 microcuries. Decontamination efforts will continue until detectable surface contamination is less than 1000 dpm/100 square centimeters.

• * * UPDATE ON 4/26/24 AT 1609 EDT FROM KELLY WEGENER-GAVE TO ADAM KOZIOL * * *

The licensee submitted a 30-day written report for this event. Notified R3DO (Betancourt-Roldan) and NMSS Events (email).

The following information was provided by the licensee via email:

• • • 8 Hour Notification was due at 1520 CST *** Follow up discussion of conditions after recovery determined that a report is required. This report restores reporting compliance.

On March 5, 2024, at 0720 CST, the X-02 118V uninterruptible power supply air conditioning (UPS A/C) unit tripped with the associated emergency fan coil units (EFCUs) shut down for planned maintenance in the area. The X-01 UPS A/C unit was declared inoperable upon discovery due to a scheduled outage of support systems (Unit 1 station service water) via the safety function determination process. This placed the site in technical specification 3.7.20 condition A, B, and C to restore the UPS A/C system within one hour. The EFCUs were restarted at 0729 which satisfied condition B and C, and X-01 UPS A/C unit was aligned to Unit 2 cooling water at 0801, exiting condition A. The condition that could have prevented the fulfillment of the safety function lasted for approximately nine minutes. Area temperatures had no notable change based on field observations during the condition. The UPS HVAC system provides temperature control for the safety related UPS and distribution rooms during all normal and accident conditions. The UPS HVAC system consists of (a) a dedicated UPS room EFCU in each safety-related UPS and distribution room, and (b) two electrically independent and redundant A/C trains either of which can support all four safety related UPS and distribution rooms; each train consists of an air conditioning unit, ductwork, dampers, and instrumentation. The NRC Resident Inspector has been notified.

The following information was provided by the licensee via email: On February 1, 2024, a contract worker was transported offsite for medical treatment due to a work-related injury that required the individual to be admitted to the hospital. The individual was free-released from the site prior to transport. The injury and hospitalization were reported by the contract worker's employer to OSHA per 29 CFR 1904.39(a)(2). Based upon that notification to another government agency, Tennessee Valley Authority is reporting this per 10 CFR 50.72(b)(2)(xi). The NRC Senior Resident Inspector has been notified of this event.

• * * RETRACTION ON 2/29/24 AT 12:29 EST FROM MATTHEW SLOUKA TO KAREN COTTON * * *

The following information was provided by the licensee via email: The purpose of this notification is to retract a previous Event Notification, EN 56941, reported on 02/01/2024. On 02/01/2024, at 15:32 EST, Browns Ferry Nuclear Plant (BFN) made an Event Notification 56941 notifying the NRC of a notification to another government agency. During further review of NRC reporting guidance, BFN has concluded that the contract worker's employer report to OSHA was below the reporting threshold outlined in NUREG 1022, Revision 3. The NRC Resident Inspector has been notified.

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).

The following information was provided by the licensee via email: At 0227 EST on 11/16/23, Calvert Cliffs Unit 2 experienced an automatic trip from the reactor protection system (RPS) based on reactor trip bus undervoltage (UV). At that time, a loss of U-4000-22 (13 kV to 4 kV transformer) caused a loss of 22, 23, and 24 4 kV busses. This resulted in a loss of both motor generator (MG) sets causing the reactor trip bus UV. The loss of 22 and 23 4 kV non-safety related busses resulted in a loss of main feedwater. Auxiliary feedwater (AFW) was manually initiated and is feeding both steam generators. The 2B diesel generator (DG) started and restored the 24 4 kV safety related bus. Heat removal is via the normal turbine bypass valves to the main condenser. RPS actuation is reportable under 10 CFR 50.72(b)(2)(iv)(B) - 4 hour report ESFAS (engineering safety features actuation system) actuation (2B DG start on UV) is reportable under 10 CFR 50.72(b)(3)(iv)(A) - 8 hour report AFW operation is reportable under 10 CFR 50.73(a)(2)(iv)(A) - 60 day report The NRC Senior Resident Inspector has been notified. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: All rods fully inserted. There was no impact on Unit 1 operations. Unit 2 is stable in mode 3.

• * * UPDATE ON AT 0940 EST FROM KERRY HUMMER TO ADAM KOZIOL * * *

ESFAS actuation (AFW manual initiation) is reportable under 10CFR50.72(b)(3)(iv)(A) - 8 hour report Notified R1DO (Defrancisco).

The following is a summary of information provided by the licensee via telephone: A patient was prescribed Y-90 microsphere implants to the liver. The procedure occurred on 4/20/23 with no abnormal outcomes reported. The patient returned to the hospital on 7/24/23 reporting stomach pain which was diagnosed as an ulcer. A biopsy of the ulcer revealed microspheres. Due to the tissue damage, it was assessed that the dose to the stomach lining exceeded 50 Rem. This event is being reported per 10 CFR 35.3045(a)(3).

• * * RETRACTION ON 8/9/23 AT 1405 EDT FROM CHRISTIANA CARE HEALTH SYSTEM TO KAREN COTTON * * *

The following information was provided by the licensee via telephone: The Radiation Safety Officer called the NRC Headquarters Center at 1405 EDT to retract Event 56638. NRC and Christiana, the licensee, assessed the event, and determined that it was due to shunting, and thus did not meet the criteria of a medical event. Notified R1DO (Dimitriadis) and NMSS Events Notification (email) A Medical Event may indicate potential problems in a medical facility's use of radioactive materials. It does not necessarily result in harm to the patient.