Event Notification Report for June 05, 2023

PARTIAL LOSS OF CRITICALITY ACCIDENT ALARM SYSTEM

The following information was provided by the licensee via email:

"On June 1, 2023, during inclement weather, a Phase 2 CAAS [Criticality Accident Alarm System] detector fault was received. Troubleshooting efforts indicated two CAAS nodes are impacted and SBM1005 [Process Services Corridor] was evacuated. The affected detectors are located in the north end of the SBM1005 Process Services Corridor. Compensatory measures are implemented in the affected area to support maintenance troubleshooting efforts.

"UUSA is reporting this event per 10 CFR 70.50(b)(2)."

AUTOMATIC REACTOR TRIP

The following information was provided by the licensee via email:

"The following event description is based on information currently available. If through subsequent reviews of this event additional information is identified that is pertinent to this event or alters the information being provided at this time a follow-up notification will be made via the ENS [Emergency Notification System] or under the reporting requirements of 10 CFR 50.73.

"At 0405 MDT on June 2, 2023, the Unit 2 reactor automatically tripped on low steam generator water levels due to degraded flow from the A main feedwater pump. Steam generator water levels reached the automatic Auxiliary Feedwater Actuation System (AFAS) setpoint resulting in automatic AFAS-1 and AFAS-2 actuations and subsequent start of both class auxiliary feedwater pumps.

"Steam Generator water levels are being restored to normal band with the class 1E powered motor driven auxiliary feedwater pump.

"Following the reactor trip, all control element assemblies inserted fully into the core. No emergency plan classification was required per the Emergency Plan. Safety related buses remained powered from offsite power during the event and the offsite power grid is stable. Both emergency diesel generators automatically started on the AFAS-1 and AFAS-2 actuations as designed and are currently running unloaded. This event is being reported as a reactor protection system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(2)(iv)(B) and a specified system actuation in accordance with 10 CFR 50.72(b)(3)(iv)(A).

"The NRC Senior Resident Inspector has been informed. Unit 1 and 3 are in Mode 1 at 100 percent power."

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

Decay heat is being removed to main condenser via automatic steam bypass and B auxiliary feedwater pump.

UNSCHEDULED SHUTDOWN

The following information was provided by the licensee via fax or email:

"An unscheduled shutdown of the reactor occurred on 6/2/23 at 0818 EDT due to an abnormal response of the Safety Power Level channel during the approach to power of 1 MW at 150 kW. The Reactor Operator observed a discrepancy in power indications by the Linear Power Level and Safety Power Level channels and took immediate actions required by procedure NRP-OP-105, Response to SCRAMS, Alarms, and Abnormal Conditions. The reactor was shut down and secured immediately. The Designated Senior Reactor Operator was immediately notified.

"The Safety Power Level channel is required to be operable per Technical Specification 3.3.b Table 3.3-1 while the reactor is being operated. During the startup checklist, the channel performed satisfactorily. The Safety Power Level channel is part of the reactor safety system and has two automatic shutdowns (SCRAMs) associated with it. Reactor power was correctly monitored by all other operable power monitoring channels which have redundant SCRAM capabilities. No SCRAM occurred or was needed due to the power level of the reactor. Following the reactor shutdown, the reactor staff investigated and determined that the high voltage power supply in the Safety Power channel was faulty. The power supply was replaced and a channel calibration of the Safety Power channel will be performed using procedure PS 1-05-03A:S1 to verify the channel is operable. Maintenance Log #0888 has been opened. There was no safety issue with this event. Procedures were followed during reactor operation, shutdown, and the investigation.

"This unscheduled shutdown is a reportable event per TS 6.7.1 based on the circumstances and as defined in the facility Technical Specification (TS 1.2.24.d) for reportable events from operation in violation of Limiting Conditions for Operation (LCO) established in TS. TS 1.2.24.d, does not allow for an exception for taking prompt remedial action.

"A report to the NRC is required within one working day and will be made by 1700 EDT by phone on 6/2/23, as required by TS 6.7.1. Also as required by TS 6.7.1, a written report to the NRC is due in 14 days (6/16/23)."