Event Notification Report for April 08, 2025

POSSIBLE OVEREXPOSURE DUE TO LOSS OF CONTROL OF LICENSED MATERIAL

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

"At 1518 EDT on April 8, 2025, the radiation safety officer (RSO) was informed about an incident that happened during routine Sr-82 production and waste activities. Four workers were performing waste and remediation activities for a Sr-82 production hot cell. The work was performed under a job-specific radiation work permit and direct supervision of health physics staff. Two of the workers (Worker 1 and Worker 2) entered the waste collection space (basement) located underneath the hot cell to repair a clog in the solid waste duct and replace the liquid acid waste transfer container. Worker 1 and Worker 2 were wearing positive air pressure respirators (PAPRs) which are the appropriate personal protective equipment for work being performed and electronic dosimeters. Worker 2 surveyed the working area upon entry and the shielded waste container using a RadEye [survey meter]. Worker 2 found a partially unshielded area in the waste container reading 930 mR/hr (highest reading recorded during survey).

"Worker 1 and Worker 2 proceeded to disconnect the solid waste duct to remove a potential clog and inspected the waste container. The solid waste container was empty. While inspecting the solid waste duct, a liquid acid waste line disconnected from the bottom of the hot cell. There was no liquid in the line. Worker 1 moved the solid waste cask out of the way of the work area. Worker 1 and Worker 2 then focused on the liquid acid waste container. Worker 1 and Worker 2 moved the shielded acid waste container to the entry of the waste area and removed the lid of the container. Worker 2 removed the plastic bag from the waste container and placed it away from the working area. Worker 1 then replaced the liquid acid waste bucket.

"Worker 1 and Worker 2 returned to the solid waste chute to inspect and unclog the chute. The second liquid waste line broke at this time and fell to the floor. Worker 1 and Worker 2 returned to the entry way and communicated the problem to Worker 3 and Worker 4. It was requested that Worker 3 attempt to lift the waste plate inside the hot cell to reconnect the waste lines and lower the lines back into the waste area. A survey of the hot cell was requested prior to starting this work. Worker 3 opened the hot cell and found the working area to read between 1.5 R/hr to 5 R/hr. Worker 3 unsuccessfully tried to open the connection plate between the hot cell and the solid waste duct. Worker 1 and Worker 2 positioned the shielded waste cask under the hot cell to reconnect it to the hot cell. Worker 1 and Worker 2 noted the dose alarms (100 mrem threshold) on their dosimeters at this time. When they were unsuccessful in lifting the shielded cask into position, they abandoned the work and exited the waste collection space. Upon exiting, their electronic dosimeters were alarming. Worker 1 and Worker 2 noted that their electronic dosimeters were alarming and recorded doses of 4.399 rem for Worker 1 and 2.924 rem for Worker 2.

"Worker 2 escalated the incident to the RSO immediately. The RSO secured the area and instructed Worker 4 to survey the space between the hot cell and the solid waste plate that connects the solid waste duct. Worker 4 found the exposure rates to be 75 mR/hr. As a post-incident follow-up, the RSO instructed Worker 3 to enter the waste collection space to confirm the exposure rates. Worker 3 found exposure rates of 2 R/hr at the entry point, 25 R/hr next to the working location and a waste bucket opposite to the working area that saturated the detector (>1,000 R/hr on contact). Worker 3 electronic dosimeter recorded a dose of 457 mrem. Worker 1 exhibited a maximum of 25,000 disintegrations per minute (dpm) on their left hand. Worker 4 exhibited a maximum of 1,200 counts per minute (120 dpm) on his shirt. Preliminary urinalysis results for Worker 1 did not identify count rates above background levels (no intake).

"The RSO initiated a stop work for production waste activities. As a post-incident follow-up, the director of the radiation safety office and RSO immediately reviewed the dose to date in 2025 and found that Worker 1 total dose was 5.604 rem, exceeding the dose limit set forth in 10 CFR 20.1201. The RSO and director of the radiation safety office initiated a formal investigation."

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

Discussions with the licensee revealed that the report is being submitted pursuant to 10 CFR 20.2202(b)(1)(i) for an individual potentially exceeding a total effective dose equivalent of 5 rem within 24 hours due to a loss of control of licensed material. Additionally, a 30-day report will be submitted pursuant to 10 CFR 20.2203(a)(2)(i) for an adult receiving an annual occupational total effective dose equivalent in excess of 5 rem.

MANUAL REACTOR SCRAM

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

"On April 08, 2025, at 1607 CDT, River Bend Station (RBS) was operating at 81 percent reactor power when a manual reactor protection system (RPS) actuation was inserted due to the loss of all normal service water pumps. Standby service water initiated and operated as expected. The scram was uncomplicated and all other plant systems responded as designed. Immediately after the scram, a reactor water level 3 isolation signal was received as expected.

"Reactor pressure is being maintained by the main turbine bypass valves. Reactor water level is being maintained by condensate and main feed water. RBS is currently in mode 3. No radiological releases have occurred due to this event. The loss of all normal service water is currently under investigation.

"This event is being reported under 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A), as an event or condition that results in actuation of the RPS while the reactor is critical and as a specified system actuation due to the expected reactor water level 3 isolation signal immediately following the reactor scram.

"The NRC Resident Inspector has been notified."

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

RBS intends to maintain temperature and pressure and remain in mode 3 while the event is under investigation.

VALID ACTUATION OF EMERGENCY AC ELECTRICAL POWER SYSTEMS

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

"At 1924 MST on April 8, 2025, a loss of power (LOP) occurred to 'Train-A' 4.16 kV class 1E electrical bus while re-energizing 'Train-A' balance of plant (BOP) engineered safety features actuation system (ESFAS) from pre-planned maintenance. The LOP occurred when the circuit breaker supplying off-site power to the 'Train-A' 4.16 kV class 1E bus tripped when 'Train-A' BOP ESFAS system was re-energized. Operators restored power to 'Train-A' 4.16 kV class 1E bus with 'EDG-A' [emergency diesel generator for 'Train-A'] at 1934 MST. Operators restored all necessary plant loads which had lost power. Per the Palo Verde emergency plan, no emergency classification was required.

"At the time of the LOP, the reactor was defueled with the core offloaded to the spent fuel pool.

"Unit 2 and Unit 3 are not impacted by this event and remain in mode 1, 100 percent power.

"The cause of the circuit breaker supplying off-site power to the 'Train-A' 4.16 kV class 1E bus tripping is under investigation. NRC Resident Inspector has been notified.

"This event is being reported in accordance with 10 CFR 50.72(b)(3)(iv)(A) as an event that resulted in a valid actuation of emergency AC electrical power systems."

FAILED FITNESS FOR DUTY

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

"On April 8, 2025, at 1333 CDT, it was determined that a licensed operator violated the station's fitness-for-duty program. The employee's access to the plant has been terminated.

"This event is being reported under 10 CFR 26.719(b)(2)(ii)."

"The NRC Resident has been notified."