August 29, 2022 - On August 23, 2022, at approx. 2:30 p.m., a low voltage (110 Volts) electrical cable short caused a circuit breaker to trip, causing a loss of power to the Criticality Accident Alarm System (CAAS) Stations 18 & 19 at the Columbia Fuel Fabrication Facility (CFFF). Stations 18 and 19 are two of the criticality monitoring detectors that are part of the overall CFFF criticality monitoring system. This system is designed to provide an audible and visual indication of high radiation levels that could result from a criticality event. Per system design requirements, upon the loss of power to these detectors, a signal was received at the manned guard station providing both visual indication and an audible alarm that Stations 18 and 19 were disabled.
Notifications and actions were performed in accordance with internal response procedures. It was determined that as a result of the loss of the two impacted stations, the area of lost coverage was limited to part of the outdoor UF6 cylinder storage pad. No personnel were in the affected area at the time, as such there was no movement of special nuclear material in progress.
Power was restored to the circuit at approximately 3:40 p.m., and CAAS detectors 18 and 19 were placed back in operation at approximately 4:00 p.m. Operations were cleared to resume. A reportability evaluation was performed and determined redundant equipment was available and operable to perform the safety function of the out-of-service detectors; therefore, the issue was not reportable.
On August 25, 2022, at 9:19 a.m., a follow-up investigation and extent of condition review by site engineering personnel identified that the ground fault caused the loss of some audible and visual alarm equipment for the CAAS in other external areas of the plant beyond the outdoor UF6 cylinder area. Per existing procedures, upon loss of audible alarms for the CAAS without backup alarm capability, all special nuclear material movement is required to be secured within one hour. These additional horns/visual alarms were out of service for ~90 minutes. This was not recognized on August 23.
A 24-hour NRC Event Notification was made in accordance with 10 CFR 70.50 (b)(2) due to the criticality horns being inoperable for approximately 30 minutes outside the window allowed by the license without stopping special nuclear material movement and with no redundant equipment available and operable.
The NRC Region II project inspector for CFFF received a courtesy notification on the event and indicated that a follow-up on the event will occur during a future routine inspection. This week, the event report is expected to be publicly available on the NRC and CFFF web page.
