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On November 23, 2017, a routine surveillance on the South Texas Unit 1 Train "C" Control Room Makeup and Cleanup Filtration System failed due to the Train "C" control room makeup filtration system heater de-energizing approximately two minutes after actuation. The makeup filtration system heater de-energized due to an improperly configured jumper on a circuit board associated with the Train "C" control room makeup filtration unit outlet low flow switch. The circuit board had been installed with the improperly configured jumper on September 27, 2017. The circuit board was properly configured and returned to service on November 24, 2017.

This resulted in the Train "C" Control Room Makeup and Cleanup Filtration System being inoperable for 58 days; the associated Technical Specification allowed outage time for this condition is 7 days. The cause of the event is the maintenance work instructions did not include steps to: (1) ensure that the circuit board jumper is in the correct position, and (2) conduct a post-maintenance test to ensure proper operation of the heaters. As a corrective action, the applicable maintenance work instructions will be revised to (1) ensure that the circuit board jumper is in the correct position, and (2) conduct a post-maintenance test to ensure proper operation of the heaters.

On 09/21/2017 at 1550, Operations started Control Room Emergency Ventilation (CREV) Air Conditioning (AC) for Tracer Gas Testing. Per Operations instructions, Mechanical Maintenance went to inspect the Control Room Emergency Ventilation system for refrigerant leaks before Tracer Gas Testing was started. Mechanical Maintenance reported a refrigerant leak on the discharge piping of the compressor, right above the inlet to the condenser. The leak was at the expansion joint of a fitting. The safety significance of this event was minimal.

The cause of the refrigerant leak on the Control Room Emergency Ventilation compressor discharge pipe fitting into the condenser was due to high cycle fatigue.

The corrective action was to replace the failed Control Room Emergency Ventilation compressor discharge pipe fitting.

The CREV AC system is a single train system. Given the impact on the CREV AC system, this report is submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

On June 5, 2017, at 0930 Eastern Daylight Time (EDT), Unit 1 was in Mode 1 at 100 percent power, and Unit 2 was in Mode 1 at 87 percent power and was increasing power after a preplanned control rod improvement evolution. Maintenance personnel were inspecting dampers in the Control Room Air Conditioning (AC) system and Control Room Emergency Ventilation (CREV) system and disconnected an air supply to a damper. This resulted in the CREV system being inoperable due to interruption of the pneumatic supply. The CREV system was restored to operable status by 1009 EDT. At 1352 EDT, a second damper was inspected, and its pneumatic supply was disconnected. During the second occurrence, the Control Room AC system also tripped and was made inoperable. Affected systems were restored by 1407 EDT.

The event is reportable as a loss of safety function per 10 CFR 50.73(a)(2)(v)(D). The event resulted from inadequate use of human performance tools and inadequate work instructions. Corrective actions for this event include restoring the affected pneumatic supply, revising work orders, and taking steps to emphasize proper use of human performance tools.

On September 19, 2016, the Control Room Ventilation exhaust fan 70FN-4A did not start when it was being placed into service. The fan outlet isolation damper actuator 70MOD-108A(OP) failed to give the fully-open permissive signal to start the fan. Gentle pressure on the actuator linkage allowed the fan to start. Prior to this, on August 16, 2016, during post-maintenance testing, 70FN-4A did not start. Troubleshooting adjusted the linkage and the fan started as appropriate. However, the intermittent fan start issue was caused by the degraded damper actuator 70MOD-108A(OP). Corrective action replaced 70MOD-108A(OP).

This event is reportable per 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

system train "B" in support of planned maintenance on the non-safety related train "A". The CREV train "B" did not start. Once the CREV train "B" system failed to start, the non-safety related train "A" was restarted. Proper operation of the CREV system and CREV air conditioning (NC) systems could not be ensured, so both CREV and CREV AC system were declared inoperable. As a result, Technical Specification (TS) 3.7.4, Condition A, and TS 3.7.5, Condition A were entered.

The cause of the CREV train "B" system failure to start was the differential pressure switch, which is installed in a vibration susceptible location on the ductwork. This differential pressure switch makes up the interlock between the CREV train "B" system and the non-safety related Control Room HVAC train "A". The differential pressure switch's normally open contacts had temporarily welded together not allowing the starting signal to be received by the CREV train "B" system.

Corrective actions included replacing the differential pressure switch. A future corrective action will relocate the differential pressure switch off of the ductwork to minimize the vibration effects.

The safety significance of this event was minimal. Given the impact on the CREV system, which is common to both units, this report is submitted (for Units 1 and 2) in accordance with the requirements of 10 CFR 50.73 (a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

Emergency Ventilation (CREV) System, technicians noticed that the 'B' Air Filtration Unit (AFU) Booster Fan discharge damper became stuck in a partially open position following the 'B' AFU Booster Fan trip on a high ammonia input signal. Due to the uncertainty of being able to achieve rated airflow for the CREV System caused by recirculation that would result from running the 'A' AFU Booster Fan with the 'B' Booster Fan discharge damper partially stuck open, the CREV System was declared inoperable and surveillance testing was secured. As a result, Technical Specification 3.7.4, Condition A, was entered.

The cause of the damper failure was due to inadequate clearance between the damper seat sealing area and the damper blade to shaft fasteners which resulted in misalignment which caused the damper shaft to bend and the damper to become stuck.

Corrective actions included securing the stuck damper in the closed position and evaluating all CREV System dampers. A preventative maintenance task will be developed to stroke and inspect the dampers to identify binding; modifications will be made if necessary to other CREV System dampers to prevent binding.

The safety significance of this event was minimal. Given the impact on the CREV System, which is common to both Units, this report is submitted (for Units 1 and 2) in accordance with the requirements of 10 CFR 50.73 (a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

On March 18, 2014, the Browns Ferry Nuclear Plant (BFN) Unit 3 reactor automatically scrammed due to a turbine trip from a high main turbine moisture separator level. Initial indications show the level controller for 3B2 Moisture Separator failed to maintain level in automatic. Additionally, local manual control attempts failed to restore moisture separator level. Following the turbine trip Main Steam Isolation Valves remained open with main turbine bypass valves controlling reactor pressure.

At approximately 2232, Central Daylight Time (CDT) the 3B2 Moisture Separator Level High Alarm was received and an operator was dispatched to investigate. In accordance with the alarm response procedure the 3B2 Moisture Separator Water Level Controller was placed in manual. Attempts to control the Moisture Separator Reservoir 3B2 High Level Dump Valve manually were ineffective. At approximately 2252 CDT, the Unit 3 reactor automatically scrammed due to a turbine trip from a high moisture separator level.

The root cause was a failure to prevent the introduction of foreign material during the manufacturing process of the Moisture Separator Level Controller. The manufacturing defect was a legacy issue dating back to 1971 when the controller body was originally machined. The corrective actions to prevent recurrence requires the removal, cleaning of air passages, replacement of control relays, for similar controllers and upgrading the calibration procedure to include cleaning 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 December 14, 2012, at approximately 1306 hours Eastern Standard Time (EST), inoperability of both subsystems of the Control Room Emergency Ventilation (CREV) system occurred. Because Brunswick has a shared control room, this placed Unit 1 and Unit 2 in Technical Specification (TS) 3.7.3, Required Action C.1, for two CREV subsystems inoperable (i.e., be in Mode 3 within 12 hours).

At the time of the event, a modification to upgrade the Control Building fire detection system was in progress. The 2A CREV subsystem was placed in the radiation/smoke protection mode in compliance with the Technical Requirements Manual. This action prevented an auto-start of the 2B CREV subsystem and, as such, TS 3.7.3 Condition A was entered to restore 2B CREV subsystem to operable status within 7 days.

During work to electrically isolate one of the fire detectors associated with the 2A CREV subsystem, electrical continuity was lost resulting in a charcoal fire signal being sent to the 2A CREV subsystem circuitry and shutting it down. With the 2A CREV subsystem shut down due to the signal, TS 3.7.3 Required Action C.1 applied for both CREV subsystems being inoperable. Actions were taken to re-start the 2A CREV subsystem, and TS 3.7.3 Required Action C.1 was exited within approximately two minutes.

The safety consequences of this event were minimal. The condition existed for approximately two minutes, and plant staff took immediate action to return the equipment to service. The apparent cause of the event was inadequate documentation and communication of the required system alignment to support the ongoing modification.

On December 1, 2011, at 1344 hours Eastern Standard Time (EST), the Control Building (CB) instrument air dryer failed resulting in loss of control air. As a result, the three Control Room Air Conditioning subsystems required by Technical Specification (TS) 3.7.4, "Control Room Air Conditioning (AC) System," and the two Control Room Emergency Ventilation subsystems required by TS 3.7.3, "Control Room Emergency Ventilation (CREV) System," became inoperable. Because Brunswick has a shared control room, Unit 1 and Unit 2 entered TS 3.7.3 Required Action B.1, for two CREV subsystems inoperable (i.e., be in Mode 3 within 12 hours) and TS 3.7.4, Required Action E.1, for three Control Room (CR) AC subsystems inoperable (i.e., enter LCO 3.0.3 immediately). At 1410 hours, operability of two Control Room AC subsystems and one CREV subsystem was restored, and LCO 3.0.3 was exited, when the CB instrument air dryer was bypassed. No power reduction took place as a result of the LCO 3.0.3 entry.

The failure of the CB instrument air dryer was due to low refrigerant pressure leading to ice blockage of the instrument air supply line. The cause was inadequate monitoring to detect the low refrigerant pressure.

Corrective actions include replacing the instrument air dryer and a procedure revision to bypass the dryer when low refrigerant pressure conditions exist.

On July 6, 2011 at 1410 hours, the Unit 1/2 (common) "B" Control Room Emergency Ventilation (CREV) Refrigeration Condensing Unit (RCU) was declared Inoperable due to an increase in vibration amplitude caused by a broken chiller compressor connecting rod. Operators performed required actions to safely secure the CREV RCU in accordance with procedures and training, and without complications. This resulted in entering Technical Specification 3.7.5, Condition A (30 day Action). This event affected both the Unit 1 and Unit 2 Control Rooms since they share a common control room and CREV system.

The Train B CREV Air Conditioning (AC) system is a single train safety-related system that is designed to operate in a post- accident condition to maintain design temperature in the Control Room Envelope (CRE), and loss of the CREV AC could impact the plant's ability to mitigate the consequences of an accident.

The CREV RCU chiller compressor connecting rod failure was caused by flooded starts of the compressor. The root cause of the flooded start was an unanticipated failure mode for the design application of the system.

Corrective actions included replacing the failed compressor with a new compressor, and revising the frequency for vibration analysis on the B CREV RCU to monthly. Future corrective actions include installation of an automatic pump-down modification for the B CREV RCU compressor.

The safety significance of this event was minimal.

Given the impact on the CREV AC system, this report is submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

On April 7, 2011, at approximately 1740 hours Eastern Daylight Time (EDT), a loss of the Control Room Emergency Ventilation (CREV) system occurred. At the time of the event, the plant was performing OMST- DG13R, "DG-3 Loading Test." During performance of this test, the 480 VAC Emergency Bus E-7 main feeder breaker tripped unexpectedly. As a result, the CREV emergency makeup damper 2-VA-2J-D-CB closed on loss of power, resulting in two CREV subsystems required by TS 3.7.3, "CREV System," being inoperable. This condition could have prevented the fulfillment of the safety function for this system. BSEP has a shared Control Room, but only Unit 1 was required to enter TS 3.7.3, Required Action C.1, for two CREV subsystems inoperable (i.e., be in Mode 3 within 12 hours). Unit 2 was operating in Mode 4 for a scheduled refueling outage and did not meet any applicability conditions for TS 3.7.3.

This condition is being reported as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

The safety consequences of this event were minimal. The condition existed for approximately one hour and 51 minutes, and plant staff took immediate action to return the equipment to service. The direct cause of the E-7 breaker trip was a spurious actuation of the solid state trip unit (i.e., no root cause could be determined).

The corrective actions included replacement of the breaker.

On July 8, 2009, at 1013 hours Eastern Daylight Time (EDT), during planned preventive maintenance activities, electrical power was lost to the 4160V emergency bus E2. Emergency Diesel Generator 2 automatically started and re-energized the E2 bus. The loss of power to E2 resulted in Unit 1 Primary Containment Isolation System Groups 2, 3, 6, and 10 isolations. Per design, no Unit 2 safety system group isolations or actuations occurred. Other Unit 1 actuations included the Reactor Building Ventilation System isolation (i.e., Secondary Containment isolation), automatic start of both trains of the Standby Gas Treatment System and automatic start of both trains of the Control Room Emergency Ventilation System. The affected equipment responded as designed.

This event occurred during activities associated with instrument calibration of an emergency bus E2 voltage transducer. Technicians performing the activity opened the wrong test switch. As a result, arcing occurred when test equipment was connected to an energized circuit. This caused the blown fuse in the C phase of emergency bus E2, which in turn caused a loss of power to the emergency bus and the E2 master/slave breaker to trip. The root cause of this event is inadequacies associated with procedure OPIC-CNV023 and the associated work order used to perform the preventive maintenance task. Corrective actions to prevent recurrence will correct identified problems with these documents.

February 18, 2009, at 0351 hours Central Standard Time (CST), following a scheduled preventative maintenance activity, Unit 1 reactor automatically scrammed from a turbine trip due to a power load unbalance signal on the main generator. Specifically, at 0349 hours CST, Operations swapped the Unit 1 Main Generator Isophase Bus Duct System cooling fan from the running to the alternate fan. When the alternate fan started, water entrapped in the fan housing was expelled into the bus provided a path to ground inside the bus duct.

This resulted in actuation of the generator protective relays and a turbine trip and automatic reactor scram, which resulted in the automatic actuation of the reactor protection system. Water that had settled in the idle bus duct cooling fan housing was expelled into the main generator isophase bus duct upon fan startup providing a conductive path to ground. The root cause of this event was less than adequate design process guidance for consideration of seasonal variations in the operating conditions for heating ventilation and air conditioning (HVAC) system design. The design process does not consider full range of operation of HVAC systems using raw cooling water as a cooling medium during the winter months. BFN inspected the Unit 1 isophase bus for damage. No damage was identified. BFN installed a drain with a site glass on each Unit 1 bus duct cooling fan housing. General Operating Instruction, Operations Round Logs, was revised requiring verification that there is no water in the idle fan and to drain any water that may have accumulated prior to placing it into service. BFN will modify the design change technical considerations checklist to provide design process guidance for consideration of seasonal variations in operating conditions for HVAC design.

At 1313 hours EDT on June 3, 2008, two operating Control Room Air Conditioning subsystems, required by Technical.

Specification (TS) 3.7.4, "Control Room Air Conditioning (AC) System," tripped during the replacement of a solenoid valve for the Unit 1 Cable Spread Room supply/exhaust fan dampers. The trip occurred when the control air supply line was momentarily uncapped to enable the installation of the control air supply to the newly installed solenoid valve, causing the dampers on the two operating AC subsystems to close. With the third Control Room AC subsystem in standby with the damper closed, all Control Room AC subsystems were shut down. Because BSEP has a shared Control Room, both Unit 1 and Unit 2 immediately entered TS Limiting Condition of Operation (LCO) 3.0.3. At 1325 hours, following completion of the solenoid valve replacement, the Control Room AC subsystems were restored to operable status and LCO 3.0.3 was exited. No reactor power reduction took place on either unit as a result of the LCO.3.0.3 entry.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. The root cause of this event was determined to be a reliance on an Engineering Change calculation which did not adequately consider the impact of system material condition and resulted in an inadequate assessment of risk.

The corrective action to prevent recurrence is to revise the Preventive Maintenance tasks to use a Temporary Modification whenever the Control Room AC system solenoid valves are being replaced, which will allow the Control Room AC system to run on total loss of Control Room instrument air.

On April 23, 2008, at approximately 2300 hours (CDT), with both Units 2 and 3 operating at approximately 100 percent power, the Control Room Emergency Ventilation Air Conditioning System was in operation to perform a post maintenance test. During the activity, the Control Room Emergency Ventilation Air Conditioning System experienced excessive vibration. Technical Specification 3.7.5, "Control Room Emergency Ventilation Air Conditioning (AC) System," was entered. The system was restored to operable status on May 1, 2008. This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident," as the Control Room Emergency Ventilation Air Conditioning System is a single train system.

The apparent cause is attributed to the lack of lubrication due to the oil in the compressor being displaced by refrigerant. Liquid refrigerant accumulates in the compressor due to liquid floodback during operation and flooded starts. Following the completion of the actions associated with the equipment apparent cause analysis, Plant Engineering will evaluate system operation to determine the effectiveness of the actions taken. Based on this evaluation, if it is determined that system reliability has not been improved, further actions will be developed and implement, as appropriate.

On October 30, 2007, with the plant at approximately 100 percent power, it was determined that both trains of Station Vent Normal Range Radiation Monitors were inoperable for more than one hour (on two occasions) without isolating the Control Room Normal Ventilation System as required by Technical Specification (TS) 3.7.6.1. The train 2 monitor was unknowingly inoperable due to installation of a faulty optical isolation board on October 15, 2007; which caused the monitor to be in the bypass mode for approximately 13 days. This was in excess of the seven days allowed by TS 3.7.6.1 with the ventilation not isolated. The train 1 monitor was removed from service on October 16 and 22, 2007 for routine maintenance and sampling activities. On October 23, when it was determined that train 2 monitor was in bypass mode, the monitor was declared inoperable until repairs were completed on October 25.

This issue, which is due to a faulty optical isolation board and inadequate testing specified in the Post Maintenance Test Manual and Quarterly Functional Test Procedures, is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by the Technical Specifications, and 10 CFR 50.73(a)(2)(v)(D) as conditions that could have prevented fulfillment of a safety function for systems needed to mitigate the consequences of an accident.

On September 1, 2007, at approximately 1955 hours CDT, Unit 1 Operations was notified that there was a small EHC leak in the Unit 1 Moisture Separator (MS) room in the Turbine Building. Unit 1 was operating at 100 percent power. Video monitoring was established by 0657 hours CDT. Operations noted the leak rate was approximately 120 drops per minute. On September 3, 2007, at 0214 hours CDT Operations noted that the leak rate was increasing and manually scrammed the reactor from approximately 72 percent power.

This report is submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an event that resulted in a manual or automatic actuation of the systems listed in paragraph 10 CFR 50.73(a)(2)(iv)(B) (i.e., reactor protection system including reactor scram or trip, and general containment isolation signals affecting containment isolation valves in more than one system).

On June 9, 2007, at approximately 1100 hours central daylight time (CDT) Unit 1 automatically scrammed following a turbine trip from a 1A2 main steam moisture separator tank high level signal.

Prior to the scram, at 1019 hours CDT, the Moisture Separator Reservoir High Level Dump Valve was noted opening. At approximately 1040 hours CDT operations received a low level alarm for the 1A2 moisture separator. Subsequently, at approximately 1100 hours CDT a turbine trip signal was initiated from an indicated main steam moisture separator high tank level. This was followed by an automatic reactor scram. The root cause of the event is the sizing of the Moisture Separator 1A2 Level Control Dump Valve. TVA is reviewing the design for the Moisture Separator Dump Valve and controls to determine if modifications are required. If necessary will either modify or replace the Unit 1 valves and controls.

On November 8, 2006, at 2254 hours (CST), with Unit 2 at approximately 85 percent power and Unit 3 in a refuel outage, Dresden Nuclear Power Station control room personnel identified that the Control Room Emergency Ventilation Air Conditioning System failed to maintain proper control room temperature.

Technical Specification 3.7.5, "Control Room Emergency Ventilation Air Conditioning (AC) System," was entered. The system was restored to operable status on November 9, 2006 at 0555 hours (CST). This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident," as the Control Room Emergency Ventilation Air Conditioning System is a single train system.

The cause of the event was attributed to a loss of process fluid from the Control Room Emergency Ventilation Air Conditioning System's Refrigeration Condensing Unit due to loose instrument tube fittings caused by vibration. The corrective action to address this event is to enhance existing Control Room Emergency Ventilation Air Conditioning System inspections by establishing a new maintenance activity to perform a yearly walk down to monitor for refrigerant leaks on the Control Room Emergency Ventilation Air Conditioning System.

On August 19, 2006, at 1105 hours central daylight time, Unit 3 was manually scrammed following a loss of both the 3A and 3B Reactor Recirculation pumps. Just prior to the event, the Unit 3 Unit Operator (UO) received alarms indicating low reactor water level, reactor feedwater level control system failure, and failure of the input/output modules for both the 3A and 3B Reactor Recirculation pumps. The UO also reported that main generator load was approximately 730 megawatts electrical (approximately 64 percent of full power output) and lowering. Based on these indications, the UO scrammed the reactor.

The immediate cause of the manual scram was the loss of both the 3A and 3B Reactor Recirculation pumps. The manual scram was required by the conditions presented to the Unit 3 operator following the loss of recirculation flow. The initial investigation into the trip found the Variable Frequency Drive (VFD) microprocessors non-responsive. The root cause of the event was the VFD controls malfunctioned due to excessive traffic on the connected plant Integrated Control System (ICS) network. Corrective actions include developing a network firewall device that limits the connections and traffic to any potentially susceptible devices on the plant ICS network and installing a network firewall device on each Unit's VFD controller.