Current Event Notification Report for June 25, 2025

AGREEMENT STATE REPORT - LOST SEED

The following is a summary of information provided by the New York City Department of Health via email:

The licensee reported a loss of licensed material in quantity more than 10 times the value in 10 CFR Part 20 Appendix C. Memorial Sloan-Kettering reported via email on 5/22/2025 that a I-125 localization seed was discovered to be lost by the licensee on 3/25/2025 during a routine reconciliation. The seed had been implanted in a patient on 3/20/2025 and explanted on 3/21/2025. The activity was estimated as 115 microcuries on the date of clinical use.

New York Identification Number: NY250004

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

AGREEMENT STATE REPORT - LOST SEED

The following is a summary of information provided by the New York City (NYC) Department of Health via email:

The licensee reported a loss of licensed material in quantity more than 10 times the value in 10 CFR Part 20 Appendix C. Memorial Sloan-Kettering reported via email on 5/22/2025 that a I-125 localization seed was discovered to be lost by the licensee on 3/26/2025 during an inventory. A discarded seed from a procedure done on 1/23/2025 was not able to be located. The activity was estimated as 98 microcuries on the date of use.

New York Identification Number: NY250005

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

VALID EMERGENCY DIESEL GENERATOR START

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

"At 2204 EDT on 6/22/2025, with unit 1 and unit 2 operating at 100 percent power, the 'A' reserve station service transformer (RSST) was lost which resulted in the loss of power to the '1J' emergency bus. As a result of the power loss, the '1J' emergency diesel generator (EDG) automatically started as designed and restored power to the '1J' emergency bus. During the event, the unit 1 'A' charging pump (1-CH-P-1A) automatically started as designed due to the loss of power event. Security footage reported a bright white flash associated with the 'A' RSST at the time of the event.

"The valid actuation of these ESF components due to loss of electrical power is reportable per 10 CFR 50.72(b)(3)(iv)(A).

"The '1J' emergency bus off-site power source was restored to service via an alternate source and the '1J' EDG was secured and returned to automatic. Restoration of offsite power to operable is complete. 1-CH-P-1A was secured and returned to automatic. Both units are currently stable, and an investigation is underway to determine the cause of the loss of the 'A' RSST."

Unit 2 was unaffected. The NRC resident inspector was notified.

UNIT 1 MANUAL REACTOR TRIP

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

"At 0014 EDT on 6/24/2025, Sequoyah Unit 1 operators performed a manual reactor trip. All safety systems responded normally, and the plant is currently stable in mode 3 (hot standby) at normal operating temperature and pressure. Unit 1 was manually tripped due to lowering steam generator water levels caused by a secondary control system malfunction.

"Unit 2 is not impacted and remains at 100 percent power in mode 1.

"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) and in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the auxiliary feedwater system.

"There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified."

UNIT 2 MANUAL REACTOR TRIP

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

"At 0351 EDT on 6/24/25, Sequoyah Unit 2 operators performed a manual reactor trip. All safety systems responded normally, and the plant is currently stable in mode 3 (hot standby) at normal operating temperature and pressure. Unit 2 was manually tripped due to lowering level in the loop 1 steam generator caused by main feedwater regulating valve malfunction.

"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) and in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that results in a valid actuation of the auxiliary feedwater system.

"There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified."