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On October 30. 2017. at 0942 Eastern Daylight Time (EDT) Watts Bar Nuclear Plant (WBN) operations personnel received a Main Control Room (MCR) alarm 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 Limiting Conditions for Operation (LCO) Condition B was entered for Unit 1 (Mode 1) and Condition G was entered for Unit 2 (Mode 5). At 0945 EDT the alarm cleared, CREVS was declared operable and LCO 3.7.10, Conditions B and G were exited. The loss of the control room envelope is being reported as a loss of safety function needed to mitigate the consequences of an accident.

The cause of this issue is a human performance error in that an individual leaving the control building complex failed to confirm closure of the MCR envelope boundary door. Corrective actions have been generated to develop and install an engineering feature to inform personnel closing the door that it is fully shut and latched.

On August 23, 2017, Watts Bar Nuclear Plant (WBN) personnel identified Technical Specification (TS) 3.6.3, Containment Isolation Valves, was not entered for on-going work related to 1-FCV-31-330, Incore Instrument Room Air Handler Unit 1B Chilled Water System Isolation Valve. A clearance was placed on 1-FCV-31-330 by Operations Work Control for scheduled work on May 17, 2017 rendering the valve inoperable. Work was completed May 19, 2017, however, the clearance remained in place pending post maintenance testing after other related system work was complete. Due to a human performance error, the appropriate TS tracking program was not activated and no narrative log entry was made to signify entry into the TS as required by procedure. The in-place clearance satisfactorily met the required actions of TS 3.6.3 condition A.1. to isolate the affected containment penetration flow path by use of at least one closed and de-activated automatic valve. However, without the required TS tracking program activated, personnel failed to comply with TS 3.6.3 condition A.2. to verify the affected penetration flow path is isolated every 31 days.

Failure to enter the TS tracking program in accordance with procedure was a human performance error. Corrective actions included coaching and department operating experience communication.

On June 1, 2017, at 1550 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) Unit 1 operations personnel declared one of its two required offsite power sources to be inoperable in accordance with Technical Specification (TS) 3.8.1, Condition A. One of the poles for this power source was found cracked and not able to meet its structural load requirements for wind or icing. The pole was replaced and the line returned to service on June 2, 2017.

This crack was determined to have been caused by an earlier line failure on May 27, 2017 when adjacent poles fell during a thunder storm, which also caused the plant to enter TS 3.8.1, Condition A. Based on evidence demonstrating that the pole with the crack had not met requirements from May 27, 2017 until replaced on June 2, 2017, a condition prohibited by Technical Specification 3.8.1 occurred because the line was not functional for a period longer than the allowed outage time.

The cause for failure to repair the pole with the crack following the May 27, 2017 event was that it was covered by vegetation, and was not discovered until June 1, 2017. Corrective actions to address this issue included investigation of the offsite power source support structures and replacement of degraded offsite power line poles to maintain high reliability of offsite power

On March 23, 2017, at 0014 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant Unit 2 experienced an unplanned trip condition of both Turbine Driven Main Feed Pumps (TDMFPs) following a loss of Main Condenser Vacuum. The trip of both TDMFPs caused an automatic start of both Motor Driven Auxiliary Feed Water Pumps and the Turbine Driven Auxiliary Feed Water Pump as designed.

The plant was performing a normal startup, and had just synchronized the main generator to the grid. Subsequent to the event, the plant was transitioned to Mode 3 by inserting all control rods with a manual trip. All plant safety systems operated as expected.

The loss of condenser vacuum was the result of a significant breach of the Unit 2 main condenser - B zone. This failure is attributed to the main condenser neck support structural design being inadequate to maintain integrity within specification. Repairs to the condenser will be completed prior to Unit 2 returning to service.

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 Technical Specifications. The operator immediately identified that the pressure equalizing valve for the inner door was not fully closed when the outer door of the airlock was opened. 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 to be five minutes.

The equalizing valve did not seat properly due to a damaged part in the valve closing mechanism. The airlock remains functional, and an operations caution order was put in place related to use of this air lock. The airlock will be repaired prior to Unit 2 returning to Mode 4.

NRC I ORM 366 M6-2016; APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internal e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

On August 3, 2016, Watts Bar Nuclear Plant Unit 1 (WBN1) determined that a condition prohibited by Technical Specifications (TS) had occurred.

During maintenance of the 1B-B centrifugal charging pump (CCP) room cooler, the bearing was found in a degraded condition requiring repair. This fan is required to support Operability of the 1B-B CCP. Based on the inability of the CCP to meet its calculated mission time of 10 days, the 1B-B CCP was considered to be inoperable from July 24, 2016 until restoration of the 1B-B CCP room cooler on August 5, 2016. This represents a condition prohibited by Technical Specifications due to the 1 B-B CCP being inoperable for greater than its allowed outage time. This event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B).

The cause of the bearing degradation and fan failure was over tensioning the fan belts due to a 2011 revision to a maintenance procedure which improperly removed the established method for belt tensioning. This method had been added to the procedure in 1995 as an action to prevent recurrence of a similar over tensioning event.

The 1B-B CCP room cooler had been rebuilt in December 2015 after a similar bearing failure had occurred as reported in LER 390/2016-006.

On August 30, 2016, at 2110 Eastern Daylight Time (EDT), the Watts Bar Nuclear Plant (WBN) Unit 2 reactor tripped on turbine trip as a result of an electrical fault. All control rods fully inserted and no safety or relief valves lifted. The Auxiliary Feedwater system actuated as designed.

The electrical fault was caused by an internal fault on the low voltage side of the 2B Main Bank Transformer (MBT) which resulted in a fire. The electrical fault was cleared by the 2B MBT sudden pressure and phase differential relays.

Automatic fire suppression operated as expected and a fire fighting team was established by the fire brigade with assistance from local fire departments. The fire was extinguished at 2230 EDT.

The failed 2B MBT was removed from the plant and the spare MBT was connected in its place. The unit was returned to power and replacement transformers are being procured by the Tennessee Valley Authority for long term reliability.

On August 13, 2016 Watts Bar Nuclear Plant Unit 2 (WBN2) was being stabilized following a pre-planned reactor trip.

Both motor driven auxiliary feed water pumps and the turbine driven auxiliary feed water pump (TDAFW pump) were in operation maintaining steam generator (SG) water level between 6 - 50 percent in accordance with the Reactor Trip Response Procedure.

At 0333 Eastern Daylight Time (EDT) the TDAFW pump was secured by procedure and SG water level lowered to the Lo-Lo Alarm setpoint (17 percent). With the Unit at 0 percent power, a trip time delay of 3 minutes is present for auxiliary feedwater actuation. At 0337 EDT, the TDAFW pump automatically started with SG water levels less than the Lo-Lo alarm setpoint (lowest level reached was 15 percent).

The cause of the event was a failure to brief the auto start feature of the TDAFW pump at Lo-Lo SG water level of 17 percent when briefing the control band for the SGs is between 6 to 50 percent.

The Unit 2 Turbine Driven Auxiliary Feedwater (TDAFW) pump auto-started upon a planned Reactor Trip at 0154 Eastern Daylight Time (EDT) on May 28, 2016. At 0157 EDT the Reactor Operator noted that TDAFW forward flow to Steam Generators 1 and 3 were approximately 800 gallons per minute, and placed the associated Level Control Valves in the closed position. At approximately 0203 EDT the Main Control Room received Alarm Window 60-A, TDAFW Pump Electrical Overspeed Trip. Operators walked down the TDAFW pump and determined that the turbine had tripped, by confirming that the Trip and Throttle Valve was no longer latched, and declared the TDAFWP inoperable. The equipment was repaired, the TDAFWP was re-tested successfully and returned to service. Technical Specification (TS) Limiting Condition for Operation 3.7.5 was exited on May 30, 2016.

The plant conditions at the time of the event were Unit 2 in Mode 3 at Normal Operating Temperature/Normal Operating Pressure following manual reactor trip from Mode 1. The reactor trip was unrelated to this event.

On June 29 2016, a past operability evaluation concluded that the TDAFWP had been inoperable from March 30 through May 30, 2016. This is reportable as a condition prohibited by TS.

At 1526 Eastern Daylight Time on 6/8/2016, a determination was made involving the potential impact of a tornado on the Emergency Diesel Generators (EDGs). The EDGs are required to be operable to provide power to ensure that acceptable fuel design limits, reactor coolant system pressure boundary limits, and containment integrity are not exceeded during abnormal transients. Further, the EDGs are designed with a crankcase pressure trip (setpoint of 1 inch water), which is bypassed following an emergency start. Engineering has determined that a tornado could potentially cause actuation of the crankcase pressure trip due to a low barometric condition. If an emergency start signal has NOT previously occurred, then during a tornado, actuation of the crankcase pressure trip would energize the shutdown relay causing an EDG lockout condition. The EDG lockout condition prevents subsequent EDG starts (normal or emergency) until operators manually reset the lockout condition locally at the EDG. This condition could potentially affect all four EDGs simultaneously.

A compensatory measure has been established, that upon notification of a Tornado Warning, the EDGs would be 'emergency started' and run during the time the Tornado Warning was in effect. This action bypasses the crankcase pressure trip function and allows the EDGs to perform their required safety function.

On May 17, 2016, at 1630 hours while restoring from a plant modification related to installation of new protective relays designed to detect open phase conditions on the 6.9kV shutdown boards, the feeder breakers for the 6.9kV Shutdown Board 1B-B tripped resulting in a loss of bus voltage. The feeder breakers tripped due to actuation of the loss of voltage relays in the shutdown board protective relay trip logic circuit resulting in separation of offsite power from the 6.9kV Shutdown Board 1B-B. The 1B-B emergency diesel generator did not auto start during this event because it was out of service due to planned maintenance.

In response to the loss of power on the 6.9kV Shutdown Board 1B-B, the operators immediately entered Abnormal Operating Instruction, 0-A01-43.02, Loss of Unit 1 Train B Shutdown Boards, and manually started emergency diesel generators 1A-A, 2A-A, and 2B-B. All equipment operated properly. The emergency diesel generators were not required to be paralleled to their respective boards because offsite power was available.

Offsite power was restored to the 6.9kV Shutdown Board 1B-B at 1802 hours on May 17, 2016. Event Notification 51940 was issued May 17, 2016. This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A).

On May 13, 2016, Watts Bar Nuclear Plant Unit 1 (WBN1) determined that a condition prohibited by Technical Specifications had previously occurred. During the Fall 2015 WBN1 outage, maintenance performed on the 1B-B centrifugal charging pump (CCP) room cooling fan introduced a condition that resulted in a subsequent bearing failure of the room cooling fan on December 4, 2015. This condition would have prevented the 1B-B CCP pump from performing its specified function for its designed mission time. Based on the reduced reliability of the fan, the 1B-B CCP was considered to be inoperable from October 7, 2015 until the fan was repaired and returned to service on December 6, 2015. During this time period, there were several short time periods when the 1A-A CCP was inoperable.

An investigation into the cause of the failure was completed on April 21, 2016. The cause of the fan bearing failure was an undersized fan shaft, resulting in the 1B-B CCP fan having excess shaft to bearing clearance which caused the bearing inner ring to loosen from the eccentric locking collar. These excessive clearances allowed the fan bearing inner ring to slide on the shaft. The sliding rotation of the inner ring on the shaft resulted in excessive heat being generated within the bearing leading to catastrophic failure.

This event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) and 10 CFR 50.73(a)(2)(v)(D).

From March 18, 2016, when Watts Bar Nuclear Plant Unit 2 first entered Mode 4 to April 14, 2016 with the plant in Mode 3, it was determined that a condition prohibited by Technical Specifications (TS) existed. During this time both automatic and manual closure of the containment isolation valves and the sample isolation valves for the Steam Generator Blowdown (SGBD) sampling lines were disabled due to improperly installed electrical jumpers in the valve control circuits. The misplaced jumpers bypassed the Phase A containment isolation signals, the auto/manual start signals for the Auxiliary Feedwater (AFW) pumps, and the control valve seal-in circuits. Containment isolation on a Phase A signal is used to control potential release of radioactive material to the environ in the event of a Design Bases Accident. The AFW pump auto/manual start signals are used to isolate the SGBD sampling lines to preserve steam generator inventory. The seal-in circuits are used to allow the operator to manually position the valves in either the open or closed position from the main control room. This event occurred prior to initial reactor criticality. There was no loss of safety function.

The isolation valves for the SGBD sample lines were returned to service on April 14, 2016. This event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) and 10 CFR 50.73(a)(2)(vii)(B) and (C).

On March 11, 2016, Watts Bar Nuclear Plant (WBN) Unit 1 concluded that a condition prohibited by Technical Specification (TS) Limiting Condition for Operation (LCO) 3.5.2, ECCS - Operating, had occurred during recent performances of TS Surveillance Requirement (SR) 3.5.2.3. Due to inadequacies with gas quantification methodologies for Safety Injection (SI) and Residual Heat Removal (RHR) system discharge piping, the ability to meet TS SR 3.5.2.3 could not be demonstrated, which is required in accordance with TVA's response to NRC Generic Letter 2008-01, "Managing Gas Accumulation In Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems." This condition existed from March 2012 to December 2015. In a subsequent analysis, WBN determined that the worst case gas accumulation in SI and RHR discharge piping would not have affected the ability of the SI and RHR systems from performing their safety functions. However, because the required actions of TS LCO 3.5.2 were not taken within the required times, WBN was in a condition prohibited by Technical Specifications.

TVA is reporting this issue pursuant to 10 CFR 50.73(a)(2)(i)(B).

On January 12, 2016, at 1645 Eastern Standard Time (EST), Watts Bar Nuclear Plant (WBN) Maintenance personnel were performing a 92 day Channel Operational Test for radiation monitor 1-RM-90-106A, Lower Containment Atmosphere Particulate Radiation Monitor, and found the mode switch in the "DIFF" position, which was not expected.

The surveillance was stopped and an investigation was conducted. It was determined that the design requires the mode switch to be in the "INT" position to be operable. The mode selector switch was placed in the "INT" position and the surveillance was completed. The radiation monitor was restored to OPERABLE status at 1743 EST on January 12, 2016.

Placing the mode selector switch in the "DIFF" position resulted in 1-RM-90-106A being INOPERABLE due to the loss of alarm function of the monitor. Investigation determined that the switch had been repositioned on December 8, 2015.

Because the containment particulate radiation monitor was inoperable for a period of time greater than permitted by Technical Specification 3.4.15, this condition is reportable as an operation or condition prohibited by Technical Specifications per 10 CFR 50.73(a)(2)(i)(B). During the time the monitor was inoperable, other means of leak detection (e.g., containment pocket sump level indication, reactor coolant system inventory balance) remained available.

On July 13, 2014 at 1937 (EDT), Watts Bar Nuclear Plant operators manually tripped the Unit 1 reactor due to automatic isolation of all low pressure feedwater heaters. 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 and the unit was stabilized in Mode 3, with decay heat removal via Auxiliary Feedwater, steam dumps and the main condenser, with the station in a normal shutdown electrical alignment.

The need to manually trip the reactor was determined to be the result of two separate age related failures associated with the control scheme of the #7 Heater Drain Tank (HDT). The root cause of these failures was that replacement preventative maintenance (PM) tasks did not exist for these components. The components in question were replaced and corrective actions have been developed to generate replacement PMs for both components. In addition, replacement PMs will be developed for similar critical components of the Secondary Systems based on EPRI Guidance.

On May 2, 2013 at 0845, B-train Emergency Gas Treatment System (EGTS) was removed from service for planned maintenance and Operations declared Technical Specification (TS) Limiting Condition for Operation (LCO) 3.6.9 not met and entered Condition A for one EGTS train inoperable. On May 3, 2013 at 0111, the Main Control Room was notified that the A-A Auxiliary Air Compressor Air Dryer was not purging due to failure of the Auxiliary Control Air System (ACAS) A-A dryer central timing unit. Operations declared A-train ACAS and supported Technical Specification systems inoperable, including A-train EGTS.

WBN operations entered LCO 3.0.3 due to the inoperability of two trains of EGTS and began preparations to initiate an orderly shutdown within one hour. Operations initiated actions to restore B-train EGTS to standby in accordance with System Operating Instruction (S01)-65.02, Emergency Gas Treatment System. At 0155, B-train EGTS was declared operable and the actions of LCO 3.0.3 exited. No action was taken to reduce reactor power while in LCO 3.0.3.

The A-A Auxiliary Air Compressor Air Dryer central timing unit motor was replaced. The apparent cause of this event was that there were missed opportunities to identify the need for replacement preventive maintenance (PM) for the central timing unit. Change requests have been initiated for periodic replacement of the ACAS dryer central timing unit. Components in other systems which could be subject to the same failure mechanism will be reviewed and PM activities initiated as necessary.

On October 16, 2012, at 2330 EDT, Watts Bar Nuclear Plant (WBN-1) licensed operators attempted a manual fast transfer of the 1B-B 6.9kV Shutdown Board (SDBD) from the normal feeder breaker to the alternate feeder breaker. The transfer was not successful, resulting in the automatic start of the four Emergency Diesel Generators (EDGs). After the 1B-B 6.9kV SDBD de-energized and the loads were shed, the alternate feeder breaker closed and re-energized the 1B-B 6.9kV SDBD. The loads supplied by the 1B-B 6.9kV SDBD were subsequently reconnected, and required tests were successfully completed to ensure operability of the 1B-B 6.9kV SDBD.

At the time of the event, WBN-1 was in MODE 5 following a refueling outage. Operations personnel promptly entered the appropriate response procedure and re-established power to required loads. Required safety systems functioned as designed. This condition did not adversely affect the safe operation of the plant or the health and safety of the public.

The cause of this event was that plant operators did not ensure the alternate feeder breaker hand-switch was held firmly in the "closed" position while initiating the fast board transfer.

This report is being submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A), a condition that resulted in automatic actuation of the EDGs.

While performing Surveillance Instruction 1-SI-67-1 on June 22, 2009, TVA discovered that both Primary Essential Raw Cooling Water (ERCW) Supply Valve (2-FCV-67-66) and Backup ERCW Supply Valve (2-FCV-67-68) to the 2A-A Emergency Diesel Generator heat exchangers were open. Under normal operating conditions, 2-FCV-67-66 is open and 2-FCV-67-68 is closed. With both supply valves open, the system was not properly aligned, and ERCW supply headers 1A and 2B were cross-connected. This misalignment caused the ERCW system to be inoperable in accordance with Technical Specifications (TS) Limiting Condition for Operation (LCO) 3.7.8 and the system could not meet surveillance requirement (SR) 3.7.8.1, to verify valves are in the correct position. With both ERCW trains inoperable, the plant entered LCO 3.0.3. Valve 2-FCV-67-68 was closed immediately upon discovery, and the plant exited LCO 3.0.3. Evaluation of the system alignment indicates that there was no loss of safety function, but because of the incorrect alignment, the ERCW system was inoperable for over nine hours, and Watts Bar failed to be in mode 3 within seven hours as required by LCO 3.0.3.

This event is reported as a condition prohibited by TS under 10 CFR 50.73(a)(2)(i)(B) because the plant was in LCO 3.0.3 for a period longer than allowed by TS.

On October 29, 2008, a discrepancy in the setpoint of the particulate channel of the radiation monitor being credited for meeting Technical Specification (TS) 3.4.15 was identified and the appropriate Limiting Condition for Operation (LCO) was entered. On October 14, the radiation monitor had been calibrated to a setpoint that was no longer within the specified tolerance as a result of a design change. From October 14 to October 29, the Reactor Coolant System Leakage Detection System had been inoperable due to this incorrect setpoint. Consequently, WBN had been operating in a condition prohibited by Technical Specifications.

The cause of this event was determined to be a human performance error during the preparation of design change impact forms. An insufficient level of Question, Validate, and Verify (QV&V) was used, and self-checking was flawed by a wrong assumption regarding design change scope. The setpoint was corrected October 30.

NRC Inspection Report 05000390 identified in a noncited violation (NCV) that WA started Watts Bar Nuclear Plant (WBN) Unit 1 since initial plant startup without an operable channel of auxiliary feedwater (AFW) automatic start on a trip of all main feedwater pumps as required by Technical Specification (TS) 3.3.2 Function 6.e. The NCV finding was determined to be of very low safety significance because the finding did not represent an actual loss of safety function of a single train for greater than its TS allowed outage time since other initiation signals were available to automatically start the auxiliary feedwater pumps if needed.

With this inspection report, NRC clarified that the instrumentation channels must not only be capable of transmitting a trip signal, but must also reflect the actual operating condition of the main feedwater pump.

WA has submitted a TS change to permit operation without the AFW autostart on trip of all main feedwater pumps until a main feedwater pump is actually providing feedwater flow to the steam generators. Until operation in accordance with the revised TS is approved, WA will startup using all three AFW pumps, which will eliminate the need for the autostart, since the signal would be to start the pumps that are already running.

At 0824 EDT on September 27, 2002, Watts Bar Nuclear Plant (WBN) Unit 1 was operating at 100% power when 6.9 kV shutdown logic board panel 1A-A load stripping relay actuated. At 0842 EDT, the 6.9 kV shutdown logic board panel 1B-B load stripping relay actuated. These actuations occurred due to a loss of both offsite power lines which resulted in an automatic start and loading of both trains of Emergency Diesel Generators. At 0852 EDT, WBN declared a notification of unusual event (NOUE) due to the loss of both offsite power sources which resulted from a fire at the Watts Bar Hydroelectric Generating Plant (WBH). The WBN fire brigade was dispatched to fight the fire and remained there until the fire was extinguished. Since the brigade remained at the fire location and callout of additional brigade staffing took greater than two hours, 10 CFR 50.54(x) was invoked to address this departure from the minimum fire brigade staffing requirement of the WBN Fire Protection Report. WBN remained at 100% power with all four emergency diesel generators operating throughout the event. Offsite power was restored using an interim offsite configuration from Sequoyah and Rockwood lines. TVA evaluated and determined this configuration to be a Generic Letter (GL) 91-18 non-conforming condition that supports functionality and operability of both 161 kV preferred power sources per GDC 17. Condition D of LCO 3.8.1 was exited at 0125 EDT on September 28, 2002, when the first qualified offsite source was returned to service. WBN remained in Condition A of LCO 3.8.1 until the second qualified offsite source was returned to service at 0300 EDT. The NOUE was exited at 0308 EDT on September 28, 2002.

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