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 Start dateReporting criterionTitleEvent descriptionSystemLER
ENS 5627424 November 2022 21:21:0010 CFR 50.73(a)(1), Submit an LER60-DAY Optional Telephonic Notification of Invalid Actuation of Containment Ventilation Isolation ValvesThe 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 5487023 July 2020 13:56:0010 CFR 50.73(a)(1), Submit an LER60-Day Optional Telephonic Notification for Two Invalid Containment Ventilation Isolation ActuationsThis 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 two invalid Containment Ventilation Isolation (CVI) actuations at Watts Bar Nuclear Plant (WBN) Unit 1. On July 23, 2020, at 0956 Eastern Daylight Time (EDT), the Train A CVI actuated due to an invalid high radiation signal from 1-RM-90-130, 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-90-130 detector, and restoring the system to service. On August 7, 2020, at 2017 EDT, the Train A CVI actuated due to an invalid high radiation signal from 1-RM-90-130, Containment Purge Air Exhaust Monitor. Upon investigation, a small tear was identified in the foil covering the scintillation detector. This defect caused erratic indication and the system actuation. The foil was replaced and the system was restored to service. Prior to and following the invalid high radiation alarms, all radiation monitors except 1-RM-90-130 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. These events were entered into the corrective action program as CR 1625135 and CR 1628904. The NRC Resident Inspector was notified.
ENS 5422026 July 2019 14:03:0010 CFR 50.73(a)(1), Submit an LERInvalid Containment Ventilation Isolation ActuationThis 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 2. On July 26, 2019, at 1003 Eastern Daylight Time (EDT), the Train A CVI actuated due to an invalid High Radiation signal from 2-RM-90-130, Containment Purge Air Exhaust Monitor. Prior to and following the invalid High Radiation alarm, all radiation monitors except 2-RM-90-130 were stable at their normal values. All required automatic actuations occurred as designed. Upon investigation, the cause of the invalid High Radiation alarm was due to a failed ratemeter for 2-RM-90-130. Control room operators performed appropriate checks and confirmed that the subject indication was an invalid high radiation signal. The ratemeter for 2-RM-90-130 was replaced and the monitor returned to service. At the time of the event, plant conditions for a High Radiation alarm did not exist; therefore, the CVI was invalid. The NRC Resident Inspector was notified.
ENS 538402 December 2018 05:28:0010 CFR 50.73(a)(1), Submit an LERInvalid Containment Ventilation Isolation ActuationThis 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 December 2, 2018 at 0028 Eastern Standard Time (EST), the Train A CVI actuated due to an invalid High Radiation signal from 1-RM-90-130, Containment Purge Exhaust Radiation Monitor. In addition to the Train A CVI, instrument malfunction alarms were received for 1-RM-90-106, Lower Containment Radiation Monitor and 1-RM-90-112, Upper Containment Radiation Monitor as the associated valves isolated for the CVI. A common instrument malfunction alarm was also received for 1-RM-90-130 and 1-RM-90-131, Containment Purge Exhaust Radiation Monitors. Prior to and following the invalid High Radiation alarm, all radiation monitors except 1-RM-90-130 were stable at their normal values. All required automatic actuations occurred as designed. Upon investigation, the cause of the invalid High Radiation alarm was due to a failed ratemeter for 1-RM-90-130. Control room operators performed appropriate checks and confirmed that the subject indication was an invalid high radiation signal. The ratemeter for 1-RM-90-130 was replaced and the monitor returned to service. At the time of the event, plant conditions for a High Radiation alarm did not exist; therefore, the CVI was invalid. The NRC Resident Inspector was notified.
ENS 5279028 April 2017 09:00:0010 CFR 50.73(a)(1), Submit an LER60-Day Optional Telephonic Notification for an Invalid Auxiliary Feedwater ActuationThis 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 Auxiliary Feedwater (AFW) actuation at Watts Bar Nuclear Plant (WBN) Unit 1. On April 28, 2017 at approximately 0500 Eastern Daylight Time (EDT), Unit 1 maintenance personnel were performing 1-IMI-3.005, '18 Month Calibration of Anticipated Transient Without Scram System Actuation Circuitry (AMSAC),' when an AMSAC actuation signal was received. Both Motor Driven Auxiliary Feedwater Pumps (MDAFWPs) were already in service when this actuation occurred. The Turbine Driven Auxiliary Feedwater Pump (TDAFWP) did not start as it had been removed from service. Additionally, steam generator blowdown isolated as required. During this event, AMSAC actuation was complete and equipment functioned as expected by its operating state. Upon identification of the AMSAC actuation, maintenance activities were halted and a prompt investigation was initiated. WBN found that the procedure in use for the 18 month calibration had been recently revised. The procedure called for maintenance to connect an analog multi-meter set on resistance to incorrect points during performance of the procedure. When the analog multi-meter was connected to the incorrect points, a relay was energized resulting in an AMSAC actuation. The procedure was revised and the test completed. The licensee notified the NRC Resident Inspector.Steam Generator
Auxiliary Feedwater
ENS 5253915 December 2016 18:32:0010 CFR 50.73(a)(1), Submit an LER60 Day Optional Telephonic Notification for an Invalid Containment Ventilation Isolation ActuationThis 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 2. On December 15, 2016 at 1332 Eastern Standard Time (EST), Unit 2 maintenance personnel were preparing to perform a breaker swap for the normal feed to the 2B1B C and A vent board. When the power was removed from Radiation Monitor 2-RM-90-131, the B Train master isolation signal status panel was unexpectedly lit for CVI. The only automatic action observed from the containment isolation status panel was that 2-FCV-30-037, Lower Compartment Purge Control valve, went closed. The loss of power to 2-RM-90-131 de-energized the relay associated with the high radiation setpoint, resulting in an invalid Train B CVI actuation. During this event, the train B CVI actuation was complete and equipment functioned as designed. Upon identification of the Train B CVI, maintenance activities were halted and a prompt investigation was initiated. WBN found that the work order to perform the breaker swap was planned to lift leads to disable actuation of CVI. The work order lifted the lead for the K622 relay, which was insufficient to prevent the actuation. Two other leads on relays should have been lifted to prevent the actuation in Mode 1. A contributor to this error was that this work had been rescheduled several times prior to actual performance. From the time it was planned to the actual performance, mode changes had been performed on the Unit and no further reviews were performed. The licensee notified the NRC Resident Inspector.
ENS 5200114 April 2016 18:06:0010 CFR 50.73(a)(1), Submit an LER60-Day Optional Telephonic Notification for an Invalid Containment Vent Isolation Actuation

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 Vent Isolation (CVI) actuation at Watts Bar Nuclear Plant (WBN) Unit 2. On April 14, 2016 at 1344 Eastern Daylight Times (EDT), Unit 2 technicians performing calibration checks on the Auxiliary Building general supply fan, connected test equipment to the wrong intake temperature switch, causing an invalid train B auxiliary building isolation (ABI) signal in both Unit 1 and Unit 2.

Because the Unit 2 containment purge system was, at that time, configured in the 'refuel' mode, the invalid train B ABI concurrently initiated a train B CVI in WBN Unit 2. Consequently, the train B CVI caused the Unit 2 containment lower compartment radiation monitor to trip and control room operators entered Technical Specification Limiting Condition for Operation (LCO) 3.4.15 RCS Leakage Detection Instrumentation at 1344 EDT. By 1422 EDT, Unit 2 control room personnel had reset the containment purge system and by 1854 EDT had completed procedural steps to restore auxiliary building ventilation to its normal alignment. By 1858 EDT, Unit 2 control room personnel had completed the procedural steps to restore the containment purge system. During this event, the train B ABI and CVI actuations were complete and equipment functioned as designed. Upon identification of the train B ABI/CVI condition, the calibration activities were halted and a prompt investigation was initiated. WBN evaluators determined the apparent cause of the event was incorrect work instructions, with a contributing cause that technicians failed to use human performance error prevention tools to ensure they were calibrating the correct equipment. Personnel responsible for performing the calibration checks have been coached and corrective actions have been taken to correct the work instructions. The licensee notified the NRC Resident Inspector.

ENS 5115215 April 2015 16:07:0010 CFR 50.73(a)(1), Submit an LERInvalid Actuations of the Containment Ventilation Isolation SystemThis 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 two related invalid actuations of the Containment Vent Isolation System at Watts Bar Nuclear Plant Unit 1 (WBN-1). On April 14, 2015 at 2101 EDT, a sample pump failed on the WBN-1 Train B containment purge exhaust radiation monitor (1-RM-90-131), prompting control room operators to enter Conditions A and B of Technical Specification (TS) Limiting Condition for Operation (LCO) 3.3.6, Containment Vent Isolation Instrumentation and Condition A of LCO 3.6.3, Containment Isolation Valves. On April 15, 2015 at 1207 EDT, 1-RM-90-131 radiation readings increased sharply (spiked), initiating an invalid Containment Vent Isolation (CVI) actuation. The spike occurred following troubleshooting and repairs to 1-RM-90-131 when maintenance technicians agitated the motor starter enclosure in an attempt to free a stuck auxiliary contact that controls local indication. As a result of the CVI actuation, flow to lower containment radiation monitor (1-RM-90-106) was isolated, prompting control room operators to enter Condition B of LCO 3.4.15, RCS Leakage Detection Instrumentation. At 1634 EDT, control room operators exited the TS 3.4.15 condition when 1-RM-90-106 was returned to service. On April 17, 2015 at 1327 EDT, control room operators exited LCO 3.3.6 Conditions A and B and LCO 3.6.3 Condition A when sample pump repairs were completed on 1-RM-90-131. On April 19, 2015 at 1550 EDT, 1-RM-90-131 radiation readings spiked and initiated a CVI, prompting control room operators to enter TS LCO 3.4.15 Condition B and LCO 3.3.6 Condition A, until flow was restored to 1-RM-90-106 at 1636 EDT and 1-RM-90-131 was returned to service on April 26, 2015 at 1229 EDT. Each CVI was documented in accordance with the corrective action program, and TVA completed an equipment apparent cause evaluation (CR 1015781) that revealed the cause of the two CVI actuations was the result of a faulted Start/Stop control unit. TVA replaced the faulted control unit. In both instances, the CVI actuations resulted from invalid signals and were limited to a single piece of Train B equipment. There was no loss of safety function and there were no actual safety consequences during the events. The NRC Resident Inspector has been informed.
ENS 5107917 March 2015 17:06:0010 CFR 50.73(a)(1), Submit an LERInvalid Actuation of Auxiliary Feedwater System During Electrical TestingThis 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.Steam Generator
Auxiliary Feedwater
ENS 5013316 April 2014 05:48:0010 CFR 50.73(a)(1), Submit an LER60-Day Optional Telephonic Notification for Inadvertent Fast Start of Diesel Generator During TestingIn accordance with 10 CFR 50.73(a)(2)(iv)(A), this 60-day telephone notification addresses an unplanned, invalid actuation of the 2B-B Diesel Generator (DG). The event occurred on 04/16/2014 at approximately 0148 EDT while Watts Bar (WBN) Unit 1 was in Mode 6 for a refueling outage. At this time, an 18 month performance of 0-SI-82-6, '18 Month Loss of Offsite Power DG 2B-B,' was in process which required that 2-HS-82-113 (Maint-Auto Hand Switch Generator 2B-B) be placed in the Auto position. When this action was taken, the 2B-B DG experienced a fast start. At 0314 EDT on 04/16/2014, while in the process of stopping the DG, the DG experienced a second fast start. For both starts of the 2B-B DG, the DG successfully functioned and achieved its rated speed of 900 RPM. Following the second start of the 2B-B DG, an emergency stop was performed on the DG in accordance with SOI 82.04, 'Diesel Generator (DG) 2B-B.' The cause of the invalid starts was determined to be an intermittent open between a relay pin on the R3 relay (DG start relay) and the relay base due to oxidation. This event was documented in TVA's corrective action program as Problem Evaluation Report (PER) 872575. The NRC Resident Inspector has been informed of this notification.
ENS 4820419 June 2012 03:49:0010 CFR 50.73(a)(1), Submit an LERInvalid Actuation of Containment Ventilation IsolationWatts Bar Nuclear Plant's (WBN's) containment ventilation isolation systems provide the means of isolating ventilation systems that pass through containment penetrations to confine to the containment any radioactivity that may be released following a design basis event. The containment ventilation system isolates following a manual or automatic safety injection signal, high containment purge exhaust radiation levels, or manual actuation. On 6/18/12 at 2349 EDT, a B train containment ventilation isolation signal was received in the Main Control Room due to an invalid high radiation signal from a containment purge exhaust radiation monitor (1-RM-131). Corrective action replaced the 1-RM-131 ratemeter following the 6/18/12 B train containment ventilation isolation. However, on 7/2/12 at 1252 EDT, a second B train containment ventilation isolation signal was received in the Main Control Room due to another invalid high radiation signal from 1-RM-131. An investigation found that 1-RM-131 was spiking repeatedly due to a defective Power On indicating light socket which affected the 120 VAC power circuit that is common with the 24 volt power supply. 120 VAC signal fluctuations could affect the 24 volt power supply signal to the rate meter causing output spikes. Corrective action replaced the defective Power On indicating light socket on 7/3/12. This event notification is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A) as a 60 day telephone notification of the invalid initiation of a containment isolation signal. The specific system and train that was actuated was B train containment ventilation isolation. The system functioned as designed and the complete train operated. WBN's NRC Resident Inspector has been notified.
ENS 4416023 February 2008 04:00:0010 CFR 50.73(a)(1), Submit an LER60-Day Verbal Notification of Invalid Specified System ActuationOn February 23, 2008, a control room operator was aligning the Containment Purge system for Train B operation and triggered an invalid Containment Vent Isolation (CVI) and Auxiliary Building Isolation (ABI). The operator was removing Train A of the system from operation in accordance with system Operating Instruction (SOI) 30.02, 'Containment Purge System'. The operator made an incorrect assumption that a portion of SOI 90.02, 'Gaseous Process Radiation Monitors', that would have properly blocked and aligned power to the Purge Radiation Monitors had been performed. Therefore, when the operator proceeded with the next step in realigning the radiation monitors, a spike occurred on Radiation Monitor 1-RM-90-131. This caused an invalid actuation of Train B of the CVI and ABI systems. Operators verified the isolation and its cause, and suspended movement of irradiated fuel within the Spent Fuel Pool in response to the Train B CVI/ABI signal. The ABI/CVI signal was reset and Auxiliary Building ventilation was restored in accordance with SOI 30.05, 'Auxiliary Bldg HVAC Systems'. The following information addresses the criteria for a 60 day verbal report defined in Section 3.2.6, 'System Actuation' of NUREG 1022, 'Event Reporting Guidelines 10 CFR 50.72 and 50.73'. This telephone notification is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A). (a) The specific train(s) and system(s) that were actuated: The spike on the Radiation Monitor initiated an invalid actuation of Train B of the CVI system and ABI system. (b) Whether each train actuation was complete or partial: The Train B CVI and ABI actuation was complete. (c) Whether or not the system started and functioned successfully: The system started and functioned successfully, and all components operated as expected. The licensee has notified the NRC Resident Inspector.HVAC
ENS 4118315 September 2004 14:14:0010 CFR 50.73(a)(1), Submit an LERInvalid Actuation of Containment Vent Isolation ValveThe following information is provided as a 60 day telephone notification to NRC under 10 CFR 50.73(a)(1) in lieu of submitting a written LER to report a condition that resulted in an invalid actuation of the WBN (Watts Bar Nuclear) Train A Containment Vent Isolation signal. NUREG1022 Revision 2 identifies the Information that needs to be reported as discussed below. (a) The specific train(s) and system(s) that were actuated. On September 15, 2004, at 0914 EDT, a Train A Containment Vent Isolation (CVI) signal was received when the A Train Containment Purge Radiation Monitor momentarily spiked above the High Radiation Trip set-point. The B Train Containment Purge system was in operation at the time of the CVI signal and automatically shutdown as designed. (b) Whether each train actuation was complete or partial. The actuation was considered complete. The CVI signal for Train A automatically isolated the containment ventilation system as designed. The A Train Containment Purge Radiation Monitor was removed from service and considered inoperable due to no supporting indication of actual radiation by redundant radiation monitors or recorded trend data. (c) Whether or not the system started and functioned successfully. Train A Containment Vent Isolation signal automatically actuated and functioned successfully. The CVI signal was not in response to an actual plant condition. Maintenance on the Train A Containment Purge Radiation Monitor, revealed a loose connection in the detector cable. The radiation monitor was repaired and returned to service and the containment ventilation air cleanup unit was also returned to service." The NRC Resident Inspector was notified of this by the licensee.
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