|Report date||Site||Event description|
|05000390/LER-2017-013||24 January 2018||Watts Bar||On September 6, 2017, Watts Bar Nuclear Plant (WBN) identified that the vacuum relief line airflows did not meet acceptance criteria for the Auxiliary Building Gas Treatment System (ABGTS) for Train A during the performance of 0- SI-30-7-A, ABGTS Pressure Test Troubleshooting of the low airflows identified an Auxiliary Building Secondary Containment Enclosure (ABSCE) Unit 2 General Ventilation intake damper 2-FC0-30-108 with approximately one inch gaps in the blade seals with the damper in the closed position Preliminary investigation found that the damper linkage appeared to not be adjusted correctly to allow full closure of the damper blades following maintenance in May of 2017 The low vacuum relief line airflows resulted in the Train A ABGTS being inoperable, based on identified open ABSCE breaches, from July 7, 2017 to September 5, 2017 This time period is longer than that allowed by Technical Specification (TS) 3 7 12 for ABGTS, and is therefore a condition prohibited by TS The cause of this event was an incorrectly adjusted damper linkage after replacement of the damper actuator A training needs analysis will be performed to evaluate training solutions for damper linkage adjustments Damper preventative maintenance activities will be revised to address smooth operation and absence of mechanical binding|
|05000390/LER-2017-015||8 January 2018||Watts Bar|
On November 9, 2017, an issue was identified where Technical Specification (TS) Limiting Conditions of Operation (LCOs) were not entered when non-TS Engineered Safety Feature (ESF) area coolers were removed from service for maintenance. The Watts Bar Nuclear Plant (WBN) had been performing maintenance on ESF coolers serving Auxiliary Building areas without entering the TS LCO Action Statements associated with equipment present in those areas. Specific areas of concern identified were the general areas of the 713 foot and 737 foot elevations of the Auxiliary Building. These coolers were taken out of service for time periods longer than allowed for ESF equipment (typically 72 hours), which would represent a condition prohibited by the TS.
At this time, WBN has not confirmed that for those cases where a cooler was taken out of service without entering a TS LCO if an actual adverse impact on safety function would have occurred if an accident with a single failure had occurred during those time periods. Those details, and the cause and corrective actions related to a 2010 guidance change, will be provided in a supplement to this report.
|05000390/LER-2017-014||20 December 2017||Watts Bar|
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.
|05000390/LER-2017-007||3 November 2017||Watts Bar|
On June 9, 2017. Watts Bar Nuclear Plant (WBN) personnel determined that the reporting requirements of 10 CFR 50.72(b)(3)(v) and 10 CFR 50.73(a)(2)(v), as clarified by guidance in NUREG-1022, Revision 3. were being incorrectly applied for certain events associated with single train safety systems. When events occurred that resulted in these systems not meeting Technical Specification (TS) Limiting Conditions for Operation (LCO). the short duration of these events relative to their required action completion time, coupled with prompt return to allowable values, were not considered a loss of safety function by Operations and Licensing personnel. As a result, multiple potential loss of safety function events were not reported as required. These events were related to Refueling Water Storage Tank (RVVST) level, Containment and Shield Building pressure, and Control Room Envelope integrity.
A review of these events indicate, when considering the actual system capability and the response of equipment and personnel. a loss of safety function capability impacting public health and safety did not occur for events associated with the RWST, Containment. Shield Building, or Control Room. Corrective actions include briefing personnel on the regulatory impact of these events, and the importance of the control room boundary.
.._ _ NRr, FORM Kri 2017:
|05000390/LER-2017-011||23 October 2017||Watts Bar|
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.
|05000390/LER-2017-010||16 October 2017||Watts Bar|
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). Power to the 1B-B Shutdown Board (SDBD) was restored at 1505 EDT on August 17, 2017.
During the loss of power to the 1B-B SDBD, a reduction in containment and control rod drive mechanism cooling occurred. At 1233 EDT, lower containment average temperature exceeded Technical Specification (TS) limits, and TS 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.
The cause of this event is mechanical vibration while closing a panel drawer resulting in actuation of protective relays that led to a loss of power.
Clearances will require the relays involved in this event to be isolated during drawer movement to prevent a similar occurrence.
|05000390/LER-2017-006||31 July 2017||Watts Bar|
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
|05000390/LER-2017-005||10 July 2017||Watts Bar|
On May 10, 2017, at 0907 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) Unit 1 operations personnel discovered the 1B-B Safety Injection pump discharge isolation valve (1-ISV-63-527) closed. Technical Specification (TS) 3.5.2, ECCS - Operating, Condition A was immediately entered for one or more trains of the Emergency Core Cooling System (ECCS) inoperable. TS 3.5.2 Condition A was exited at 0913 EDT when 1-ISV-63-527 was opened.
Investigation determined that the 1 B-B SI pump discharge isolation valve had been closed prior to Unit 1 entering Mode 3 on April 26, 2017, representing a condition prohibited by TS. During this time period, the 1A-A SI pump was inoperable for 21 minutes, representing a condition that could have prevented fulfillment of a safety function.
The cause of the mispositioned valve was the result of an individual failing to follow procedure use and adherence requirements during the performance of Emergency Diesel Generator (EDG) Blackout testing. The safety injection pump discharge valve was closed to support the test but was not reopened following the testing. Corrective actions for this event include personal accountability actions, revision of the EDG blackout procedures to ensure the SI pump discharge valves are reopened, and additional station focus on procedure use, particularly use of Not Applicable (N/A) in performing procedures.
|05000391/LER-2017-003||22 May 2017||Watts Bar|
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.
|05000391/LER-2017-002||12 May 2017||Watts Bar|
On March 20, 2017 at 0813 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant (WBN) Unit 2 operations personnel manually tripped the plant from approximately 91 percent power based on lowering steam generator levels. Prior to the plant trip, the 2A Hotwell pump tripped at 0759 EDT and the 2C Condensate Booster Pump subsequently tripped at 0803 EDT. Operations personnel commenced to lower plant power after the 2A Hotwell pump trip in an attempt to maintain steam generator levels, but were unable to recover level and manually tripped the unit.
All control rods fully inserted and all automatically actuated safety related equipment operated as designed. At 0905 EDT, operations personnel exited the emergency operating instructions after the plant was stabilized.
This event resulted when scaffold crews inadvertently depressed the local trip button for the 2A Hotwell pump, which resulted in the secondary system transient. Bump guard covers were subsequently installed on local pushbuttons for selected pumps in the turbine building.
NRC I ORM TEE :36'01 APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/3112018 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 internet e-mail to NEOB-10202. (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.
|05000391/LER-2017-001||3 May 2017||Watts Bar|
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.
|05000390/LER-2017-003||3 March 2017||Watts Bar|
On January 4, 2017 at 1010 Eastern Standard Time (EST), Watts Bar Nuclear Plant Operations personnel declared Essential Raw Cooling Water (ERCW) strainer flush valve 2-FCV-67-9B inoperable due to having a through-wall leak.
The valve was replaced and the ERCW strainer was returned to service on January 5, 2017 at 0952 EST. This event is reportable because the valve had had a through-wall leak since January 31, 2016 and had not been declared inoperable. With a through-wall leak, a flaw evaluation is required to be performed to demonstrate the through-wall leak was stable. The failure to perform an adequate operability evaluation allowed the valve to remain in service for a period of time longer than allowed by Technical Specification (TS) 3.7.8, Essential Raw Cooling Water, Limiting Condition for Operation (LCO) Condition A. This represents a condition prohibited by the TS. Subsequent analysis of the valve demonstrated that it remained structurally sound with the leak, and would not have impacted the operability of the ERCW system.
The cause of the failure to perform an adequate operability evaluation has been determined to be human performance errors on the part of both operations and engineering personnel. Additional training of operations and engineering personnel is planned as corrective action to address the potential for recurrence of this issue.
|05000390/LER-2017-002||22 February 2017||Watts Bar||On December 24, 2016, Watts Bar Nuclear Plant (WBN) personnel identified that a clearance associated with a containment purge valve, 1-FCV-30-17, had been incorrectly hung. The clearance was intended to pull fuses to close and de-energize this valve in support of local leak rate testing. The incorrect fuses were removed, and the valve remained energized for about 24 hours while local leak rate testing was performed on the associated containment penetration. The clearance error was discovered when operations personnel attempted to replace the fuses for valve 1-FCV-30-17. The cause of the error was determined to be a human performance error. This has been determined to be a condition prohibited by Technical Specification 3.6.3, Limiting Condition for Operation, Condition A, because the penetration was inoperable for longer than the four hour required action time.|
|05000390/LER-2017-001||9 January 2017||Watts Bar|
On November 10, 2016, Watts Bar Nuclear Plant personnel identified a failure of the non-reverse clutch key on Emergency Raw Cooling Water (ERCW) motor B-A. While performing a lubrication work order, it was discovered that the clutch key was sheared. Subsequent investigation identified that other clutch key failures had occurred in the recent past. The non-reverse clutch prevents the ERCW pump from rotating in the reverse direction after pump trip, which could cause the motor to develop a higher than normal in-rush current if the motor was subsequently started, such as following an accident.
Based on the potential common mode failure of the non-reverse clutch, immediate corrective actions were put in place to ensure that the safety function of the ERCW pumps to start following an accident would not be impaired. The cause of the failure is under investigation.
|05000390/LER-2016-011||9 December 2016||Watts Bar|
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.
|05000390/LER-2016-009||30 November 2016||Watts Bar|
On November 21, 2015, Watts Bar Nuclear Unit 1 (WBN1) operations personnel did not conduct a surveillance of the Train B Essential Raw Cooling Water (ERCW) supply inboard containment isolation valve, which represented the late date for this surveillance. WBN1 personnel recognized the potential for this surveillance to go late on November 15, 2015, and therefore the provisions of Technical Specification (TS) Surveillance Requirement 3.0.3 could not be applied. Failure to complete the surveillance required entering TS Limiting Condition for Operation (LCO) 3.6.3 and completing Required Action A.1, but the required action to isolate the affected penetration flowpath was not performed until January 30, 2016. This condition was not recognized as reportable until May 18, 2016.
This supplement clarifies the reportable event and reconciles event dates.
|05000391/LER-2016-008||28 October 2016||Watts Bar|
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.
|05000391/LER-2016-007||21 October 2016||Watts Bar|
On August 23, 2016, at 1356 Eastern Daylight Time (EDT), during power ascension testing, Watts Bar Nuclear Plant (WBN) Unit 2 reactor was manually tripped due to a loss of main feedwater. 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 loss of main feedwater was due to a leak on a hydraulic fitting associated with the Main Feedwater Pump Turbine High Pressure Governor valve, resulting in the valve going partially closed with reactor power at 48 percent. With the governor valve partially closed, feedwater flow was reduced such that the unit needed to be manually tripped.
Subsequent investigation determined the leak to be caused by the installation of incompatible fittings associated with the governor valve that occurred during plant construction.
|05000391/LER-2016-006||7 October 2016||Watts Bar|
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.
|05000391/LER-2016-002||2 September 2016||Watts Bar|
On April 14, 2016, during performance of Surveillance Requirement (SR) 184.108.40.206, the Turbine Driven Auxiliary Feedwater pump (TDAFWP) failed to achieve required rated speed of 3950 rpm ± 25 rpm due to an equipment failure. The TDAFWP was declared inoperable, and Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.5, Condition B, was entered. The equipment was repaired, the TDAFWP was re-tested successfully and returned to service. TS LCO 3.7.5 was exited on May 4, 2016.
On May 11, 2016, a past operability evaluation concluded that the TDAFWP had been inoperable from March 30 through April 17, 2016, during periods of time when the TDAFWP was required for Mode 3 operations. This is reportable as a condition prohibited by TS.
During the same time period, the 2A-A Motor Driven Auxiliary Feedwater Pump (MDAFWP) experienced an oil leak through the inboard bearing housing vent cap that resulted in the need to add approximately 4 ounces of oil on a daily basis. The MDAFWP was determined to be operable.
|05000391/LER-2016-003||2 September 2016||Watts Bar|
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.
|05000391/LER-2016-005||19 August 2016||Watts Bar|
On June 20, 2016, the 2B Main Feedwater Pump (MFP) tripped on a loss of vacuum in the 2B MFP turbine condenser, resulting in a loss of normal feed, and the subsequent trip of the main turbine. While operators were reducing power to within the capacity of Auxiliary Feedwater (AFW), the reactor tripped at 1540 Eastern Daylight Time (EDT) on Steam Generator Water Level (SGWL) Lo Lo in Steam Generator No.4. SG water level lowered rapidly due to shrink from the relatively cold AFW following the trip.
All control and shutdown rods fully inserted. All safety systems responded as designed. The trip response was uncomplicated.
The trip was caused by a human performance error during the drain down of the 2A MFP turbine condenser which resulted in a loss of vacuum on the 2B MFP turbine.
|05000390/LER-2016-010||8 August 2016||Watts Bar|
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.
|05000391/LER-2016-004||4 August 2016||Watts Bar|
On June 5, 2016 at 1227 Eastern Daylight Time (EDT), Watts Bar Nuclear Plant Unit 2 was in MODE 1 at approximately 12.5 percent power when a safety injection (SI) actuation occurred, followed by an automatic reactor protection system (RPS) trip. No primary safety barriers (Reactor Coolant System, containment and fuel clad) were challenged and no primary or secondary safety or relief valves actuated during the event. The Unit 2 plant trip was considered a complicated trip due to SI actuation. Safety equipment operated as expected and SI was promptly terminated.
The reactor trip and SI were caused by a turbine governor valve failing open, causing a steam header pressure rate of decrease SI actuation signal.
|05000390/LER-2016-008||15 July 2016||Watts Bar|
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).
|05000390/LER-2016-005||13 July 2016||Watts Bar|
On March 14, 2016, Watts Bar Nuclear Plant (WBN) Unit 1 determined through engineering analysis that both trains of emergency gas treatment system (EGTS) were inoperable for 8 minutes, 10 seconds during preoperational testing of Unit 2 EGTS. The inoperability of A and B trains of Unit 1 EGTS took place on October 22, 2015, while Unit 1 was in Mode 1 and two trains of EGTS were required to be operable in accordance with technical specification (TS) limiting condition for operation (LCO) 3.6.9, "Emergency Gas Treatment System (EGTS)." At the time of the event, Unit 2 was in "no Mode," prior to initial fuel loading.
This condition is being reported pursuant to 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D), "Event or Condition That Could Have Prevented Fulfilment of a Safety Function.
|05000390/LER-2016-006||30 June 2016||Watts Bar|
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).
|05000390/LER-2016-007||20 June 2016||Watts Bar|
On April 21, 2016, Watts Bar Nuclear Plant (WBN) Unit 1 concluded that a condition prohibited by Technical Specification (TS) Limiting Condition for Operation (LCO) 3.1.8, Rod Position Indication, had occurred during the dropped rod event on November 05, 2015. The Surveillance Requirement for TS 3.1.8 states that each Analog Rod Position Indication, (ARPI), agrees within 12 steps of the group demand position for the full indicated range of rod travel.
Since the ARPI was indicating correctly for the dropped rod and was verified by diverse indications, it was considered operable. However, the Bases for TS 3.1.8 states that for the position indication to be operable, the Rod Position Indication System indicates within 12 steps of the step counter demand position as required by TS 3.1.5, Rod Group Alignment Limits. In the case of a dropped control rod, the Rod Position for the affected rod would not be within 12 steps of the demand counter. Since WBN Unit 1 at the time of the dropped rod was in a mode of applicability, the above conditions would have been met warranting entry into TS 3.1.8 Condition A. Because the actions of TS 3.1.8 were not taken within the required times, WBN Unit 1 was in a condition prohibited by TS.
TVA is reporting this issue pursuant to 10 CFR 50.73(a)(2)(i)(B).
|05000391/LER-2016-001||13 June 2016||Watts Bar|
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).
|05000390/LER-2016-004||23 May 2016||Watts Bar|
On March 22, 2016, at 1131 Eastern Daylight Time, the Watts Bar Nuclear Plant Unit 1 (WBN1) reactor tripped due to the actuation of the Over Temperature Delta Temperature bistables. Concurrent with the reactor trip, the Auxiliary Feedwater system actuated. All control rods inserted upon the reactor trip and safety systems functioned as expected.
An investigation into the cause of the trip determined that a failure of a Valve Position Limit up/down counter circuit card in the Analog Electro-Hydraulic Turbine Control System resulted in the closure of the turbine high pressure governor valves, resulting in an automatic reactor trip and turbine trip on WBN1. The failed card was replaced and WBN Unit 1 was returned to service.
This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A).
|05000390/LER-2016-003||10 May 2016||Watts Bar|
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) 220.127.116.11. 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 18.104.22.168 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).
|05000390/LER-2016-002||4 May 2016||Watts Bar|
On March 5, 2016, at 1512 Eastern Standard Time (EST), Watts Bar Nuclear Plant (WBN) Unit 1 entered Technical Specification (TS) 3.6.3, Containment Isolation Valves, Condition A for a containment isolation valve being inoperable.
During a containment walkdown, leakage was found on valve 1-FCV-61-122, Glycol Cooled Floor Return Header Isolation and the valve was declared inoperable. TS 3.6.3 Condition A requires that a penetration flow path with one containment isolation valve inoperable to be isolated by use of at least one closed and de-activated automatic valve, closed manual valve, blind flange, or check valve with flow through the valve within 4 hours. The penetration associated with this containment isolation valve was not isolated until 2113 EST on March 5, 2016. The cause of this event was operations staff misunderstanding the applicability of the Note associated with TS 3.6.3, which allows administrative controls under certain conditions.
Because the action specified by TS 3.6.3 was not completed within four hours, this condition is reportable as an operation or condition prohibited by TS per 10 CFR 50.73(a)(2)(i)(B).
|05000390/LER-2016-001||9 March 2016||Watts Bar|
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.
|05000390/LER-2015-001||22 April 2015||Watts Bar|
reactor was manually tripped by control room operators due to a decreasing main condenser vacuum. Subsequent to the reactor trip, the Auxiliary Feedwater system actuated. Control and Shutdown rods fully inserted into the reactor core, and safety systems responded as designed. The unit was stabilized in Mode 3, with decay heat removal via Auxiliary Feedwater and the Steam Generator Atmospheric Dump Valves. The Main Steam Isolation Valves were closed and remained closed during the event.
Tennessee Valley Authority (TVA) has determined that the decreasing condenser vacuum was due to a failure of an expansion joint boot seal in the "C" zone of the main condenser. This seal functions as the expansion joint between the condenser and low pressure turbines. The failure of the seal was due to a non-optimal vulcanization process and inadequate overlap in a joint splice, which significantly weakened the seal and allowed seal water to permeate the seal, further weakening the joint. The failed main condenser boot seal was replaced with a new boot seal on the "C" zone of the condenser. As a preventative measure, the boot seals on the "A" and "B" zones were also replaced.
|05000390/LER-2014-003||11 September 2014||Watts Bar|
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.
|05000390/LER-2014-002||11 April 2014||Watts Bar|
On February 11, 2014, Watts Bar Nuclear Plant (WBN) engineering and operations personnel discovered that non- conservative operator manual action times were credited in Appendix R analyses. Preliminary Westinghouse transient analysis calculations of WBN Unit 1 fire protection features revealed that there was less time than previously credited to perform certain operator manual actions to prevent pressurizer overfill during certain Appendix R fire scenarios. The Westinghouse analysis assumes the time required to isolate the normal charging path, secure the second charging pump and isolate the emergency charging path is approximately 12.5 minutes. Watts Bar Unit 1 procedures are non- conservative in that they allow these actions to be completed in 18 minutes.
The Tennessee Valley Authority (TVA) has verified that potentially impacted Appendix R equipment remains functional; however, a compensatory fire watch has been established for the affected areas until plant modifications are completed.
This event was caused by an error in a fire protection program design calculation prior to commercial operation of Unit 1.
Modifications to address this issue will be completed during the Fall 2015 refueling outage.
|05000390/LER-2013-002||27 June 2013||Watts Bar|
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.
|05000390/LER-2013-001||8 April 2013||Watts Bar|
The root causes of the condition were an organizational behavior which allowed the latent input inconsistencies to go undetected and management failure to provide oversight of the impact of river system changes on the calculated value of the PMF. The corrective actions to prevent recurrence are to procedurally require a Flood Protection Program, develop formal Flood Protection Program Management Implementing Procedure(s) and Design Standards/Guides, create a formal documented risk management process for all engineering products, formalize the elements of engineering technical rigor, and implement an upper tier integrated risk management process.
Upon discovery, TVA implemented both immediate and interim corrective actions to ensure the Fort Loudoun, Cherokee, Tellico and Watts Bar dams would not overtop during an assumed PMF event.
|05000390/LER-2012-005||15 December 2012||Watts Bar|
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.
|05000390/LER-2011-001||8 July 2011||Watts Bar|
On May 9, 2011 at 15:17 Eastern Standard Time (EST) with Watts Bar Nuclear Plant, Unit 1 in Mode 5, and the Reactor Coolant System (RCS) in a near water solid condition, the licensed operator started Safety Injection Pump 1A-A (SIP 1A-A) to fill and vent the Cold Leg Accumulators (CLAs) in accordance with System Operating Instruction SOI- 63.01. Following startup of SIP 1A-A, RCS pressure immediately began to rise and reached a maximum pressure of 328 psig before the operators secured the pump. The RCS pressure transient during this event did not exceed the Cold Overpressure Mitigation System (COMS) setpoint. The unexpected pressure transient was due to improper alignment of the Safety Injection System (SIS) when used to fill and vent the CLAs. Specifically, SIP 1A-A Crosstie Valve (1-FCV-63-152) was opened when it should have been closed. Misalignment of the SIS was due to a failure to follow procedures for a temporary clearance lift.
LCO 3.4.12 was not met because a SIP was capable of injecting into the RCS in Mode 5, which is reportable as a condition prohibited by Technical Specifications in accordance with 10 CFR 50.73(a)(2)(i)(B).
|05000390/LER-2011-002||10 June 2011||Watts Bar|
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) 22.214.171.124, 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.
|05000390/LER-2009-001||27 July 2009||Watts Bar|
On 5/27/09, TVA identified that the Watts Bar Nuclear Plant (WBN) Unit 1 Auxiliary Building (AB) Gas Treatment System (ABGTS) pressure test surveillance instruction was inadequate, as closed nonsafety related dampers could mask leakage through credited safety related dampers in the AB Secondary Containment Enclosure (ABSCE).
AB General Ventilation manipulation to place WBN in a known tested condition created a pressure differential that caused failure of temporary ABSCE boundary doors installed to facilitate Unit 2 construction. WBN entered LCO 3.7.12 Condition B for 2 trains of ABGTS inoperable. WA repaired the boundary, and the LCO Condition was exited in approximately 3.5 hours.
Subsequently, WA retested ABGTS, and both trains were verified as operable. From initial licensing until 5/27/09, WBN operated in noncompliance with TS because of the inadequate surveillance instruction.
On 6/27/09, another AB General Ventilation manipulation created a pressure differential that caused the temporary doors to fail once again. One temporary door and a permanent steel door are now closed to ensure boundary operability.
Failures of the temporary doors were due to an inadequate design and insufficient interim actions after the first event to prevent another failure. This event is reported in accordance with 10 CFR 50.73 (a)(2)(i)(B) and (a)(2)(v)(C) and (D).
|05000390/LER-2008-005||29 December 2008||Watts Bar|
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.
|05000390/LER-2008-004||19 November 2008||Watts Bar|
During normal plant operation on September 20, 2008, unexpected annunciator alarms were received in the control room indicating an automatic reactor trip based on a loss of electrical load. Subsequently, the control room was informed by a Nuclear Assistant Unit Operator that he had tripped open the Exciter Field Breaker, leading to the turbine trip and successive reactor trip.
The cause of this event has been determined to be human performance error in that the NAUO failed to recognize the need to utilize error reduction techniques when opening the exciter field breaker cabinet door. Corrective action has been taken to add the applicable information to operator requalification programs.
As a result of the plant trip, the actuation of the Reactor Protection and the Auxiliary Feedwater Systems were reported in accordance with 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A), respectively, as ENS notification 44506. This event is also being reported as this Licensee Event Report in accordance with 10 CFR 50.73(a)(2)(iv)(A).
|05000390/LER-2008-003||6 October 2008||Watts Bar|
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.
|05000390/LER-2008-001||19 May 2008||Watts Bar||Jumpers installed near the beginning of the Cycle 8 refueling outage to block automatic actuation of Safety Injection (Auto SI) had not been removed when Mode 4 was achieved at 0020 EDT on March 20, 2008, or when Mode 3 was entered at 0100 EDT on March 21, 2008. At 0913 EDT on March 21, 2008, plant personnel identified that the jumpers installed during the outage had not been removed. The Auto SI function is required in Modes 1, 2, 3, and 4 per Function 1.b of Table 3.3.2-1 of LCO 3.3.2. Since both trains of Auto SI actuation instrumentation were inoperable, LCO 3.0.3 was entered until jumpers were removed at 0958 EDT. At 2133 EDT on March 21, 2008, it was identified that the Auto SI function was still inoperable because the Auto SI function had not been reset. The reactor trip breakers were cycled to reset Auto SI and LCO 3.0.3 exited at 2206 EDT. Safety consequences of this event were not significant for the existing plant conditions. The cause assessment for the event identified an inadequate General Operating (GO) Instruction and an inadequate Instrument Maintenance Instruction (IMI). The corrective actions include revisions to selected GOs, the IMI, and establishment of a jumper tracking program.|
|05000390/LER-2002-005||26 November 2002||Watts Bar|
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.
F RN1 "-2001
|05000390/LER-2002-003||11 September 2002||Watts Bar|
On July 13, 2002, at approximately 1622 EDT, while the plant was in Mode 1, at 100% power, Watts Bar Unit 1 experienced an automatic turbine/reactor trip when a C-Phase Main Transformer differential relay actuated This occurred because a bolted cable splice associated with a C-phase current transformer (CT) came into contact with the CT junction box; thereby shorting the differential relay protection circuit to ground.
The apparent factors contributing to this short circuit condition include temperature, cable splice material, vibration, and configuration of the splice inside the junction box.
All control rods inserted properly in response to the reactor trip. The Auxiliary Feedwater (AFW) System actuated in response to the trip, as designed. Plant response was in accordance with design with no complications. Operations shift personnel performance was in accordance with applicable procedures.
Subject to confirmatory laboratory testing, the root cause of this event was determined to be inadequate work instructions that allowed lower temperature rated tape to be used on a cable replacement and/or inadequate application of splice material. Corrective actions include revision and training on TVA's engineering and maintenance procedures for high temperature jacketing material, laboratory analysis of damaged splices, and reinspection and taping of similar vulnerable cable splices.
|05000390/LER-2001-004||19 February 2002||Watts Bar||On December 19, 2001, an invalid AMSAC signal was initiated that resulted in a turbine/reactor trip. The unit was operating at 100% power at the time of the event and work was in process for the placement of a clearance (tagout) to support the implementation of a design change to the control instrumentation for the Turbine Driven Auxiliary Feedwater (TDAFW) pump. The clearance activities opened the breakers which supply power to the instrumentation. The loss of power to the instruments resulted in an invalid steam generator (SG) lo lo level (12%) signal and satisfied the logic (3 out of 4 SGs less than 12% level) for the initiation of an AMSAC signal. All control rods inserted properly and the Auxiliary Feedwater (AFW) system started, as required, in response to the AMSAC signal and the reactor trip. The cause of the event was inadequate interface requirements in the planning and scheduling of trip sensitive activities along with inadequate implementation of the clearance preparation process. The corrective actions included the review of open on-line clearances, development of a standard for the tagging of low voltage equipment, establishment of a formal process which reviews plant work activities for trip sensitive actions, counseling of involved personnel, training on the lessons learned from the event, identification and labeling of trip sensitive breakers, development of an instruction to define the expectations for independent review and to provide controls for the operation and tagging of low voltage breakers.|