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| Discovered date | Reporting criterion | Title | Event description | |
|---|---|---|---|---|
| ENS 55896 | 13 May 2022 16:11:00 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | Control Room Envelope Inoperable | The following information was provided by the licensee via email: On 5/13/22 at 1111 CDT the station entered LCO 3.7.4 Condition B for Control Room Envelope being inoperable. This was due to results from an inspection in the Steam Jet Air Ejector room that identified steam leakage exceeding the leakage rate assumptions made in the Alternate Source Term (AST) dose analysis calculation. Therefore, this is being reported in accordance with 10CFR50.72(b)(3)(ii)(B) for an unanalyzed condition that significantly degrades plant safety and 10CFR50.72(b)(3)(v)(D) for any event or condition that at the time of discovery could have prevented fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. There is no impact to the health and safety of the public. NRC Resident has been notified. |
| ENS 55154 | 25 March 2021 14:18:00 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation | Manual Reactor Trip Due to Lowering Condenser Vacuum | On March 25, 2021 at 0901 CDT, River Bend Station Unit 1 (RBS) was operating at 93 (percent) reactor power (limited by 100 (percent) recirculation flow) when condenser vacuum began to lower due to ARC-AOV1A, Steam Jet Air Ejector Suction Valve, going closed. At 0918 CDT, a manual reactor SCRAM was inserted at approximately 80 (percent) reactor power due to condenser vacuum continuing to lower. After the SCRAM, all systems responded as designed and condenser vacuum was restored by starting a mechanical vacuum pump. The cause of the Steam Jet Air Ejector Suction Valve closure is unknown at this time and being investigated. Currently RBS is stable, and pressure is being maintained using Turbine Bypass Valves. The Main Steam Isolation Valves remained opened throughout the event. 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 level 3 isolations. No radiological releases have occurred due to this event from the unit. NRC Resident Inspector has been notified of this event. |
| ENS 48505 | 17 September 2012 09:12:00 | 10 CFR 50.73(a)(1), Submit an LER | 60-Day Optional Telephonic Notification of Invalid Actuation of Containment Isolation Signals | This 60-day telephone notification is being made in accordance with the reporting requirements specified by 10 CFR 50.73(a)(2)(iv)(A) and 10 CFR 50.73(a)(1) to describe an invalid actuation of a general containment isolation signal affecting more than one system. On September 13, 2012, Browns Ferry Nuclear Plant (BFN) personnel completed the installation of three metal-oxide varistors (MOVs), MOV1, MOV2, and MOV3, on the governor of the 3C Emergency Diesel Generator (EDG) as part of a design change. On September 17, 2012, at 0312 hours Central Daylight Time (CDT), during post-modification testing of the 3C EDG, the Direct Current (DC) control circuit breaker tripped, causing a loss of governor control power for the 3C EDG. This event resulted in the loss of the 3B Reactor Protection System (RPS) Bus. In addition, Primary Containment Isolation System (PCIS) groups 3, 6, and 8 successfully isolated. The Steam Vault Booster Fan tripped and the 3B Steam Jet Air Ejector isolated. Standby Gas Treatment (SGT) Trains 'A' and 'B' and Control Room Emergency Ventilation Train 'A' initiated. The SGT Train 'C' was already in service for BFN, Unit 3, Reactor Zone Ventilation. Plant Conditions which initiate PCIS Group 3 actuations are Reactor Vessel Low Water Level or Reactor Water Cleanup Area High Temperature. The PCIS Group 6 actuations are initiated by Reactor Vessel Low Water Level, High Drywell Pressure, or Reactor Building Ventilation Exhaust High Radiation (Reactor Zone or Refuel Zone). The PCIS Group 8 actuations are initiated by Low Reactor Vessel Water Level or High Drywell Pressure. At the time of the event, these conditions did not exist; therefore, the actuation of the PCIS was invalid. The affected equipment responded as designed. On September 17, 2012, at 0335 hours CDT, Operations personnel restored the 3B RPS Bus. This condition was the result of MOV1 and MOV3 operating due to induced current in their associated ground cables. This resulted in grounds which tripped the DC control power breaker. To address this condition, MOV1 and MOV3 were permanently removed. There were no safety consequences or impact to the health and safety of the public as a result of this event. This event was entered into the Corrective Action Program as Problem Evaluation Report 610091. The NRC Resident Inspector has been notified of this event. |