Event Notification Report for December 14, 2023

AGREEMENT STATE - SOURCE STUCK IN UNSHIELDED POSITION

The following information was provided by the Texas Department of State Health Services (the Department) via email:

"On December 7, 2023, the Department was notified by a Texas licensee's radiation safety officer (RSO) that while testing an MDS Nordion, Model Eldorado 8, teletherapy unit, the 1,817 curie cobalt-60 source became stuck in the unshielded position. The RSO stated that the room was isolated and dose rates taken outside the room did not create an exposure risk to any individual. The RSO stated that a service contractor would likely repair the unit on December 9, 2023. Access to the room was posted to prevent inadvertent entry into the room. An update will be provided when the source is returned to the shielded position and then further information will be provided per SA-300."

Texas Incident Number: I-10070

NMED Number: TX230056

* * * UPDATE ON 12/9/23 AT 1137 EST FROM RANDELL REDD TO KAREN COTTON * * *

"On December 9, 2023, the Department was notified that the cobalt-60 source had been returned to the shielded position by the licensed servicing company. The technician who returned the source received around 0.3 millirem. The source activity is likely around 1,000 curies and not 1,817 curies, as originally reported. The Department will wait for the licensee and service company reports for information regarding the cause of the incident and report this to NMED per SA-300."

Notified R4DO (Dixon) and NMSS Events Notification via email.

AUTOMATIC REACTOR SCRAM

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

"At 0102 CST, while operating at 100 percent [reactor] power, River Bend Station experienced an automatic reactor scram caused by a turbine trip signal. The cause of the turbine trip signal is not known at this time and is being investigated. At 0108, reactor core isolation cooling (RCIC) was initiated due to a loss of reactor feed pumps following feedwater heater string isolation. At 0114, reactor water level control was transferred back to feedwater and RCIC was secured. Reactor water level is being maintained by feedwater pumps and reactor pressure is being maintained by turbine bypass valves. The scram was uncomplicated and all other plant systems responded as designed.

"This event is being reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical and 10 CFR 50.72(b)(3)(iv)(A) specified system actuation as result of expected post scram [reactor water] level 3 isolations and manual initiation of RCIC.

"No radiological releases have occurred due to this event from the unit.

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

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

The cause of the turbine trip, while still under investigation, was likely due to an electrical transient involving the main generator. Walkdowns in the switchyard post-scram identified damage to one of the output breaker disconnects.

PART 21 - CIRCUIT BREAKER DEFECTS

The following information is a synopsis of information provided by the licensee via phone and email:

On December 11, 2023, Tennessee Valley Authority Sequoyah Nuclear Plant completed an internal 10 CFR Part 21 evaluation concerning Siemens 6.9kV, 1200A vacuum circuit breakers, Model No. 7-HKR-50-1200-130. Three separate breakers were found with issues including loose wires terminated incorrectly and the mechanism-operated control switch clevis pin missing a cotter key. Additionally, the mastic insulating pads were found defective on all three lower primaries by way of separation. The affected breakers were never installed in a safety related application.

The NRC Resident Inspector will be notified.

A written notification will be provided within 30 days.

The manufacturer, Siemens, was notified of the defects.

The only plant known to be affected at the time of the report is the Sequoyah Nuclear Plant.