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| Entered date | Event description | |
|---|---|---|
| ENS 56274 | 15 December 2022 12:52:00 | The following information was provided by the licensee via email: This 60-day telephone notification is being submitted in accordance with paragraphs 10 CFR 50.73(a)(1) and 50.73(a)(2)(iv)(A) to report an invalid Containment Ventilation Isolation (CVI) actuation at Watts Bar Nuclear Plant (WBN) Unit 1. On November 24, 2022, at 1621 Eastern Standard Time (EST), the Train B CVI actuated due to an invalid high radiation signal from 1-RM-90-131, Containment Purge Air Exhaust Monitor. Upon investigation, the high radiation signal was caused by a failed power supply. Corrective action included replacing the power supply, 1-RM-90-131 ratemeter, and restoring the system to service. Prior to and following the invalid high radiation alarm, all radiation monitors except 1-RM-90-131 were stable at their normal values; therefore, the CVI was invalid. Control room operators performed appropriate checks and confirmed that all required automatic actuations occurred as designed. This event has been entered into the corrective action program as Condition Report 1819098. The NRC Resident Inspector was notified. |
| ENS 54127 | 20 June 2019 17:59:00 | At 1340 EDT on June 20, 2019, a breach in excess of allowable margin in the Unit 2 Shield Building annulus was identified. T.S. LCO 3.6.15, Condition A was entered. The breach is expected to be repaired within the 24 hours allowed LCO time. No other equipment issues were identified. The Shield Building ensures that the release of radioactive material from the containment atmosphere is restricted to those leakage paths and associated leakage rates assumed in the accident analysis during a Loss of Coolant Accident (LOCA). This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(C). NRC Resident Inspector has been notified. The breach consists of a tear in a flexible boot seal for a penetration associated with the suction path for gas treatment fans. There is no release of radioactive material associated with this event. |
| ENS 54077 | 22 May 2019 05:45:00 | On May 22, 2019, at 0233 EDT, Watts Bar Nuclear Plant (WBN) Unit 2 reactor was manually tripped due to a failure of the #2 Main Feedwater Regulating Valve during power ascension following a refueling outage. Concurrent with the reactor trip, the Auxiliary Feedwater system actuated as designed. All Control and Shutdown rods fully inserted. All safety systems responded as designed. The unit is currently stable in Mode 3, with decay heat removal via Auxiliary Feedwater and Steam Dumps. Unit 2 is in a normal shutdown electrical alignment. This reactor trip and system actuation is being reported under 10 CFR 50.72(b)(3)(iv)(A) and 10 CFR 50.72(b)(2)(iv)(B). There was no impact to WBN Unit 1. The NRC Senior Resident has been notified. |
| ENS 53196 | 4 February 2018 12:00:00 | At 0445 (EST) on February 4, 2018, Watts Bar Unit 1 entered Technical Specification 3.6.1 condition A and 3.6.3 condition A.1 and A.2 due to inoperable containment penetration thermal relief check valves 1-CKV-31-3407 and 1-CKV-31-3421 associated with one train of the Containment Incore Instrument Room Chiller system. During surveillance testing, the thermal relief check valves failed to open and pass flow as required by acceptance criteria. The two penetrations were subsequently drained and isolated in accordance with the surveillance procedure to remove any thermal expansion concerns. Technical Specification 3.6.1 was exited February 4, 2018 at 0512 once the two penetrations were drained and isolated. The purpose of the thermal relief check valves is to allow flow from an isolated penetration back into the upstream containment piping to prevent over-pressurization due to thermal expansion. Over-pressurization of an isolated containment penetration could potentially cause the penetration or both of the isolation valves to fail and provide a direct flow path to the environment from the potentially contaminated containment atmosphere under certain Design Basis Accidents. Therefore, failure of the thermal relief check valves to open could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(C). NRC Resident Inspector has been notified.
The purpose of this notification is to retract ENS notification 53196 made on 2/4/2018 for Watts Bar Nuclear Plant. The previous notification reported a surveillance failure of two containment penetration thermal relief check valves that, at the time of discovery, could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material. After Engineering evaluation, it has been determined there is reasonable assurance the two thermal relief check valves (1-CKV-31-3407 and 1-CKV-31-3421) were capable of performing their specified safety function to isolate containment and act as a thermal relief device during a design basis accident. The basis of the evaluation included: 1. No maintenance activities or interactions with the check valves had occurred since last tested. 2. All surveillance testing for the valves was within required frequency. 3. The opening force for a new check valve of the same size and similar to 1-CKV-31-3407 and 1-CKV-31-3421 is 0.38 pounds. Engineering analysis has determined the minimum failure pressure of the piping systems associated with the containment penetration in question is 450 psig. If it is assumed the force applied on the check valve seat reaches 450 psig, the force applied on the seat would reach 111 pounds or 300 times the force required to open a new, clean check valve. Based on engineering judgement of previous operating experience where the pressure required to open the same stuck check valve was within a safety factor of 6 to potential equipment damage, the thermal relief check valves would have opened prior to equipment damage and thus the identified condition would not have resulted in adversely affecting the containment isolation boundary. Entry into Technical Specification (TS) 3.6.1 condition A on 2/4/2018 at 0445 has been retracted. Although not a loss of safety function, the containment penetrations associated with 1-CKV-31-3407 and 1-CKV-31-3421 remain inoperable and are being tracked by TS 3.6.3 condition A.1 and A.2. The NRC Resident Inspector has been notified. Notified the R2DO (Rose). |
| ENS 53112 | 11 December 2017 11:06:00 | While operating at 97% power, the Watts Bar Unit 2 reactor was manually tripped at 0857 EST on December 11, 2017 due to multiple dropped control rods. All control and shutdown bank rods inserted properly in response to the manual reactor trip. All safety systems including Auxiliary Feedwater actuated as designed. The plant is stable with decay heat removal through Auxiliary Feedwater and the Steam Dump System. The cause of the dropped rods is being investigated. The manual actuation of the Reactor Protection System (RPS) is being reported as a four hour report under 10 CFR 50.72 (b)(2)(iv)(B). The actuation of the Auxiliary Feedwater System (an engineered safety feature) is being reported as an eight hour report under 10 CFR 50.72 (b)(3)(iv)(A). The NRC Senior Resident Inspector has been notified for this event. No safety or relief valves lifted during this event. |
| ENS 53092 | 26 November 2017 16:16:00 | On November 26, 2017, at 1225 Eastern Standard Time (EST), the Watts Bar Nuclear Plant (WBN) Unit 2 experienced an unplanned ECCS discharge to the Unit 2 Reactor Coolant System (RCS) while de-pressurized, in Mode 5, with the Pressurizer vented to the Pressurizer Relief Tank. ECCS injection via the Boron Injection flow path occurred during planned Safety Injection system Engineered Safety Features Actuation System (ESFAS) testing. The Boron Injection flow path should have been isolated and should not have resulted in any injection flow to the Unit 2 RCS. Since the injection was not a part of the pre-planned test this is reportable under 10 CFR 50.72(b)(2)(iv), System Actuation. All other systems responded as expected in accordance with the ESFAS testing procedure. The unintended ECCS injection flow was isolated and flow through the Boron Injection path was verified to be stopped at 1232 EST. The Unit 2 Pressurizer level and pressure remained below any limits and no safety limits were challenged. NRC Resident Inspector has been notified. |
| ENS 53044 | 30 October 2017 15:50:00 | At 0942 Eastern Daylight Time (EDT) on October 30, 2017, a Main Control Room (MCR) alarm was received for low control room positive pressure. At 0943 EDT, a Control Room Envelope (CRE) door was found ajar and immediately closed. Technical Specification 3.7.10 Control Room Emergency Ventilation System (CREVS) was declared not met for both trains and Condition B entered. At 0945 EDT the alarm cleared, CREVS was declared operable and LCO 3.7.10, Condition B was exited. The safety function of the CRE boundary is to ensure the in-leakage of unfiltered air into the CRE will not exceed the in-leakage assumed in the licensing basis analysis of Design Basis Accident (DBA) consequences to CRE occupants. From 0942 EDT to 0943 EDT WBN (Watts Bar Nuclear) was unable to validate that CREVS could fulfill its required Safety Function. This event is being reported pursuant to 10 CFR 50.72(b)(3)(v)(D). NRC Resident Inspector has been notified. |
| ENS 52912 | 17 August 2017 17:24:00 | On August 17, 2017, at 1205 Eastern Daylight Time (EDT), the Watts Bar Nuclear Plant (WBN) lost power to the 1B-B 6.9kV Shutdown Board. The loss of power to this safety related bus resulted in an automatic start of the Unit 1 Turbine Driven Auxiliary Feedwater Pump (TDAFWP). The motor driven AFW pumps did not start and were not expected to start for this event. No other system actuations occurred as a result of loss of power to the 1B-B 6.9kV Shutdown Board. Power to the 1B-B Shutdown Board was restored at 1505 EDT on August 17, 2017. During the loss of power to the 1B-B Shutdown Board, a reduction in containment and control rod drive mechanism cooling occurred. At 1233 EDT, lower containment average temperature exceeded the procedural limitations specified, and Technical Specification 3.6.5 Condition A was entered for containment average air temperature not within limits. Lower containment average temperature was restored to within limits at 1525 EDT on August 17, 2017. This is reportable as a potential loss of safety function. Other than several common Unit Technical Specifications having not been met, Unit 2 was not operationally impacted by the loss of power to the 1B-B Shutdown Board and remains in Mode 1 at 100% power. The NRC Resident Inspector has been notified. The loss of power occurred during restoration from Emergency Diesel Generator maintenance. |
| ENS 52618 | 17 March 2017 17:08:00 | On March 9, 2017 at 0120 EST, the equalizing valve for the Watts Bar Nuclear Plant (WBN) Unit 2 upper containment airlock inboard door was found not closed while the outboard airlock door was open. This created a containment bypass with leakage potentially greater than allowed by the design. The operator immediately identified, after opening the outer door of the elevation 757 Air Lock, the pressure equalizing valve for the inner door was not fully closed. The outer door was promptly shut to isolate the airlock. The inner door was then cycled which closed the equalizing valve. The total time that a containment bypass was present is estimated at five minutes. This condition was initially recognized as being potentially reportable. However, the assessment performed at the time, based on operator control of the outer airlock door, concluded there was a reasonable assurance of meeting the safety function. A subsequent independent review of this condition identified that this should have been reported under 10 CFR 50.72(b)(3)(v)(C) within eight hours of the event. The NRC Resident Inspector has been informed of this event. The licensee is planning on replacing the equalizing valve in the near future. |
| ENS 51780 | 9 March 2016 04:01:00 | Watts Bar Unit 2 declared an Unusual Event at 0342 EST based on a fire greater than 15 minutes in the turbine building - 2B Hotwell pump motor. The fire was extinguished by 0401 EST, at the time of notification. Unit 2 is currently shutdown in Mode 5 making preparations for startup. No offsite assistance was requested. All personnel are accounted for and there are no personnel injuries reported. The licensee notified the NRC Resident Inspector. Notified DHS SWO, DOE, FEMA OPS, FEMA National Watch (email), DHS NICC, and Nuclear SSA (email).
The licensee terminated the Unusual Event at 0508 EST based on verification that the fire was out and that the fire response team had been secured. The licensee notified the State and local agencies and the NRC Resident Inspector. Notified R2DO (Suggs), NRR EO (Morris) and IRD (Grant). Notified DHS SWO, DOE, FEMA OPS, FEMA National Watch (email), DHS NICC, and Nuclear SSA (email). |
| ENS 51079 | 18 May 2015 15:45:00 | This 60-day telephone notification is being submitted in accordance with paragraphs 10 CFR 50.73(a)(1) and 50.73(a)(2)(iv)(A) to report an invalid actuation of the Auxiliary Feedwater (AFW) system at Watts Bar Nuclear Plant Unit 1. On March 17, 2015, at 1306 EDT, Watts Bar Unit 1 was in Mode 1 at 100% power, when during the performance of 6.9 Kv phase verifications for the FLEX Diesel Generator, maintenance technicians were installing a multimeter (Simpson 260 Series) which resulted in starting the Unit 1 train B: motor-driven auxiliary feedwater pump, centrifugal charging pump, component cooling pump and thermal barrier booster pump, and isolated steam generator 1 and 3 blowdown. A secondary 6 ampere fuse opened due to an overcurrent and actuated (dropped-out) the associated blackout relays which started the identified pumps. At the time of the event, the train B standby diesel generator was removed from service for maintenance. The 6.9 Kv shutdown board did not lose power during the event and safety injection system and standby diesel generator features were not actuated. The maintenance technicians performing the phase verifications immediately recognized that several supply breakers had closed after the last test lead was connected and promptly reported the event to the control room. Work was halted and TVA conducted a prompt investigation. While not conclusive, it is likely that the maintenance technicians created a shunt or ground condition while installing test equipment, causing a circuit overcurrent which opened the fuse, activating the black-out relays and actuating the identified pumps and valves. Plant operators responded appropriately to the event and the applicable Technical Specification Required Actions were exited at 1612 EDT, when equipment restoration had been completed. TVA is continuing to evaluate this event in accordance with the corrective action program (reference: PER nos.1003213 and 1027101). The NRC Resident Inspector has been notified. |
| ENS 49950 | 24 March 2014 13:45:00 | On March 24, 2014, at approximately 0200 EDT, with Watts Bar Nuclear Unit 1 at 0% power while commencing a planned refueling outage and Unit 2 under construction, a radiation protection technician was found unresponsive in the protected area. An emergency medical team responded and the individual was transported off site to a medical facility where he was pronounced dead at 0530 EDT. The individual was not contaminated and there were no radiological or industrial safety issues associated with Watts Bar Nuclear Plant. Due to notification of OSHA at 1255 EDT, this report is submitted pursuant to 10 CFR 50.72(b)(2)(xi), as a notification to a government agency. The NRC Senior Resident Inspector has been notified. |
| ENS 49389 | 27 September 2013 13:35:00 | On July 18, 2012, TVA identified that a calculation error resulted in the inability to establish Essential Raw Cooling Water (ERCW) supply to the Component Cooling System (CCS) heat exchanger within the required time to ensure cooling is available to Reactor Coolant System (RCS) seal injection water during an Appendix R event. TVA promptly established fire watches as a compensatory measure to prevent initiation of fires in the areas of concern. Subsequently, abnormal operating instructions were revised to take action to ensure that adequate time is available to establish ERCW cooling to CCS, and ensure cooling to (Reactor Coolant Pump) RCP seal injection water. The calculation error was identified on July 18, 2012, however, it was not recognized at the time that an unanalyzed condition existed that was reportable under 10 CFR 50.72(b)(3)(ii)(B). This report documents that the condition that existed until fire watches were established is reportable under 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified of this condition.
Watts Bar Nuclear Plant Unit 1 is retracting this 8 hour non-emergency notification made on September 27, 2013, at 1335 EDT (EN #49389). The notification on September 27, 2013, reported a calculation error which resulted in the inability to establish Essential Raw Cooling Water (ERCW) to supply the Component Cooing System (CCS) heat exchanger within the required time to ensure cooling is available to Reactor Coolant System (RCS) seal injection water during an Appendix R event. Subsequent analysis of actual plant data concluded that TVA could have established cooling to RCS seal injection during the subject Appendix R event, and achieved and maintained fire safe shutdown. Therefore, this event was not reportable under 10 CFR 50.72(b)(3)(ii)(B). The NRC Resident Inspector has been notified. R2DO (Bartley) notified. |
| ENS 48995 | 3 May 2013 07:54:00 | On May 3, 2013, at 0111 (EDT), Technical Specification Limiting Condition of Operation (TS LCO) 3.0.3 was entered due to the loss of both trains of Emergency Gas Treatment System (EGTS). The Train B EGTS had been removed from service for scheduled maintenance and at 0111 the Train A auxiliary air dryer stopped functioning. On May 3, 2013, at 0155, Train B EGTS was restored to service and declared Operable, and TS LCO 3.0.3 was exited. The auxiliary air system is required to support multiple safety related systems. The auxiliary air system is the safety grade air supply for EGTS. As Train A auxiliary air was no longer Operable, and the B train EGTS system was inoperable, the safety function supported by EGTS was not available. The EGTS establishes a negative pressure in the annulus between the shield building and the steel containment vessel. Filters in the system then control the release of radioactive contaminants to the environment. Watts Bar Unit 1 remained in Mode 1 at 100% power. No reactivity was added to the plant. This event is reportable under 10 CFR 50.72(b)(3)(v)(C) and (D) as a condition that could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified. |
| ENS 46448 | 2 December 2010 18:32:00 | TVA notified TN Dept of Environment and Conservation (TDEC) of an incident at Watts Bar as follows: On December 2, 2010, a contractor employee of PAR-Westinghouse was processing in through Watts Bar Nuclear Plant Radiological Protection Program for his first day of work. He was discovered to have been previously contaminated with radioactive material from another worksite. It is clear that the radioactive contamination did not come from any TVA source and was found before he entered the rad control area. The contamination was discovered during required in-processing activities for workers by TVA's radiation monitoring and detection equipment. The contamination was found to be a particle on the individual's shoe. The individual's clothing was also found to contain measurable contamination and was confiscated. The radioactive contamination found on the individual has been safely contained. TDEC Division of Radiological Health was notified of this event as of 1610 Eastern Time and this notification under 10 CFR 50.72(b)(2)(xi) is for that Government Agency notification. TVA has notified the NRC Resident Inspector and Regional Administrator of this incident. |
| ENS 46177 | 15 August 2010 22:25:00 | At 1524 EDT, on 8/15/2010, Watts Bar Nuclear Plant Unit 1 had a valid actuation of the Auxiliary Feedwater System in response to a trip of all Main Feedwater Pumps. The Auxiliary Feedwater Pumps were started manually in anticipation of the trip of all Main Feedwater Pumps. Main Feedwater Pump B had been tripped manually as part of the power reduction in preparation for taking the Main Turbine offline to perform repairs on the Electrohydraulic Control System. Main Feedwater Pump A was tripped manually before it experienced a loss of suction in response to an unplanned isolation of the Intermediate Pressure Heater string. Following manual actuation of the Auxiliary Feedwater Pumps, reactor power was further reduced, and at 1526 (EDT), Watts Bar Unit 1entered MODE 2. No plant safety systems beyond Auxiliary Feedwater were required or actuated in response to this event. The plant was stabilized using Auxiliary Feedwater and the Main Steam dump valves. Operators followed their Abnormal Operating Instruction, and reactor trip was not required. This event is being reported as a valid actuation of the auxiliary feedwater system in accordance with 10 CFR 50.72(b)(3)(iv). Offsite power is normal and EDG's are operable. The licensee notified the NRC Resident Inspector. |