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At 1106 CDT Braidwood Unit 1 experienced an automatic reactor trip due to lowering steam generator water levels following closure of the 1B steam generator feed water regulating valve.

The cause of the 1B steam generator feedwater regulating valve failing closed is unknown at this time and is under investigation.

Both trains of auxiliary feedwater started automatically following the reactor trip to maintain steam generator water levels.

All systems responded as expected with the exception of intermediate range nuclear instrument N-36 which was identified as being undercompensated following the reactor trip. Both source range nuclear instruments were manually energized in accordance with station procedures. Steam generator power operated relief valves lifted momentarily and reseated as designed in response to the secondary transient due to the reactor trip. The main steam dump valves are in service to the main condenser to provide heat sink cooling. The plant is being maintained at normal operating pressure and temperature. AC power is being provided by offsite power with the diesel generators in stand by and all safety systems available. There is no impact to Unit 2. This report is being made per 10 CFR 50.72(b)(2)(iv)(B) for a RPS actuation, 4 hour notification, and per 10 CFR 50.72(b)(3)(iv)(A) for an automatic actuation of the auxiliary feedwater system, 8 hour notification. The NRC Resident Inspector has been informed.

At 0400 (CST) on 1/23/2018 the Braidwood Technical Support Center (TSC) HVAC (Heating, Ventilation and Air Conditioning) Emergency Makeup Air Filter train was taken out of service to perform a planned Makeup Air Filter charcoal replacement. The TSC HVAC Makeup Air Filter train will be rendered nonfunctional during the charcoal replacement. Subsequent charcoal and HEPA filter testing will restore functionality of the TSC HVAC Makeup Air Filter train. The expected duration of the charcoal replacement and subsequent testing is 30 hours. If an emergency is declared requiring TSC activation during the time TSC HVAC is non-functional, the TSC will be staffed and activated using existing emergency planning procedure unless the TSC becomes uninhabitable due to ambient temperature, radiological, or other conditions. If relocation of the TSC becomes necessary, the Emergency Director will relocate the TSC staff to an alternate location in accordance with applicable site procedures. This notification is being made in accordance with 10 CFR 50.72(b)(3)(xiii) due to a major loss of emergency preparedness capability. An update will be provided once the TSC HVAC Emergency Makeup Air Filter train functionality has been restored. The licensee has notified the NRC Resident Inspector.

• * * UPDATE AT 1645 EST ON 01/26/2018 FROM PAUL ARTUSA TO JEFF HERRERA * * *

On 1/26/18 at time 1539 EST, the TSC HVAC Emergency Makeup Air Filter train was returned to service following the planned Makeup Alr Filter charcoal replacement. Functionality was verified by charcoal and HEPA filter post maintenance testing. The licensee has notified the NRC Resident Inspector. Notified the R3DO (Cameron).

On 5/27/15, planned preventive maintenance activities are being performed on the Braidwood Generating Station Technical Support Center (TSC), Ventilation System. The work will be completed within approximately 10 hours. This activity includes preventative maintenance that requires the TSC ventilation system to be out of service which will render the TSC ventilation system non-functional. If an emergency is declared requiring TSC activation during this period, the TSC will be staffed and activated using existing emergency planning procedures unless the TSC becomes uninhabitable due to ambient temperature or other conditions. If relocation of the TSC becomes necessary, the Emergency Director will relocate the TSC staff as necessary. This event is reportable per 10CFR50.72(b)(3)(xiii) for 'any event that results in a major loss of emergency assessment capability.' The planned maintenance will not be able to restore the TSC condensing unit or ventilation system to service within the facility activation time specified in the emergency plan (1 hour) in the event of an accident. The Emergency Response Organization team has been notified of the maintenance and the possible need to relocate during an emergency. The licensee informed the NRC Resident Inspector.

• * * UPDATE FROM PETER MOODIE TO VINCE KLCO ON 5/27/2015 AT 2153 EDT * * *

Planned work is complete and the Technical Support Center was restored to service on May 27, 2015 at 1808 CDT. The licensee will notify the NRC Resident Inspector. Notified the R3DO (Lipa).

Braidwood Generating Station has completed a review of seismic monitor performance. The emergency preparedness plan requires seismic monitoring instruments to diagnose an earthquake for emergency action levels (EAL) HA4 (natural and destructive phenomena affecting vital areas) or HU4 (natural and destructive phenomena affecting the protected area). Contrary to that requirement, this review identified 5 times in the past 3 years that the seismic monitor was non-functional such that emergency classification at the ALERT or UNUSUAL EVENT level could not be obtained with site instrumentation. The seismic monitor is currently functional; however, the seismic monitor was determined to be non-functional on the following dates:

1. April 24, 2012
2. December 5, 2012
3. December 20, 2012
4. June 17, 2013
5. October 8, 2014

These non-functional conditions of the seismic monitor have been corrected and were entered into the Braidwood Corrective Action Program. While Exelon procedural direction allowed the use of offsite sources to obtain seismic data when the seismic monitor is incapable of assessing emergency plan Emergency Action Levels (EALs), this was not explicitly referenced in the Braidwood approved EALs. The loss of assessment capability is reportable to the NRC within 8 hours of discovery in accordance with 10 CFR 50.72(b)(3)(xiii). This report is required per 10 CFR 50.72(a)(1)(ii) as an event that occurred within 3 years of the date of discovery. Corrective actions are in progress. The licensee has notified the NRC Resident Inspector.

On 8/25/2014, planned preventive maintenance activities are being performed on the Braidwood Generating Station Technical Support Center (TSC) Ventilation System. The work will be completed within approximately 42 hours. This activity includes preventive maintenance on the TSC condensing unit which affects the TSC ventilation. During the planned maintenance, the TSC condensing unit will be rendered non-functional. If an emergency is declared requiring TSC activation during this period, the TSC will be staffed and activated using existing emergency planning procedures unless the TSC becomes uninhabitable due to ambient temperature or other conditions. If relocation of the TSC becomes necessary, the Emergency Director will relocate the TSC staff as necessary. This planned maintenance will not impact the emergency filtration capability of the TSC. This event is reportable per 10CFR50.72(b)(3)(xiii) for 'any event that results in a major loss of emergency assessment capability.' The planned maintenance will not be able to restore the TSC condensing unit to service within the facility activation time specified in the emergency plan (1 hour) in the event of an accident. The Emergency Response Organization team has been notified of the maintenance and the possible need to relocate during an emergency. The licensee has notified the NRC Resident Inspector.

• * * UPDATE AT 1526 EDT ON 08/29/14 FROM ANNE MATHEWS TO S. SANDIN * * *

Braidwood Generating Station TSC ventilation was restored to available status at 1200 CDT on August 29th, 2014. The previously reported system preventative maintenance has been completed. The licensee informed the NRC Resident Inspector. Notified R3DO (Stone).

Planned preventive maintenance activities are being performed on the Braidwood Nuclear Station Technical Support Center (TSC) Ventilation System. These work activities are planned to be performed and completed expeditiously within 8 hours. This maintenance activity includes the performance of preventive maintenance on the TSC outside air supply fan unit which affects the TSC emergency filter train and air handling unit. During a portion of the time these activities are being performed, this equipment will not be available for operation. As such, the TSC Ventilation will be rendered non-functional during the performance of portions of the work activity. If an emergency condition occurs that requires activation of the Technical Support Center, during the time this work activity is being performed, it will take no more than 4 hours to return the equipment back to functional status, dependent on the stage of the work activity at the time an emergency occurs. Plans are to utilize the TSC for any declared emergency during the time this work activity is being performed as long as radiological conditions allow. This event is reportable per 10CFR50.72(b)(3)(xiii) as described in NUREG-1022, Rev. 2 since this work activity affects an emergency response facility for the duration of the maintenance. The licensee notified the NRC Resident Inspector.

• * * UPDATE AT 1107 EST ON 01/26/12 FROM RICHARD ROWE TO S. SANDIN * * *

Braidwood Nuclear Station TSC ventilation was restored to available status at 0635 CST on January 26, 2012. The previously reported system preventative maintenance has been completed. The licensee notified the NRC Resident Inspector. Notified R3DO (L. Kozak).

Unit 2 automatically tripped from 100% reactor power as a result of the over-current trip of the 2C Reactor Coolant Pump. Both station auxiliary transformers on Unit 2 subsequently tripped offline. All control rods fully inserted on the trip. Auxiliary feedwater auto-started and maintained Steam Generator water level. The unit is stable in Mode 3. The Emergency Diesel Generators auto started and loaded supplying both emergency busses with power. All systems functioned as required. There was no affect on Unit 1. The licensee notified the NRC Resident Inspector.

• * * UPDATE AT 0218 ON 8/2/2009 FROM DEAN YARBROUGH TO MARK ABRAMOVITZ * * *

At 2059 on July 30, 2009, a reactor trip of Unit 2 at Braidwood occurred. A loss of offsite power occurred and an Unusual Event was declared at 2108. NRC Headquarter Operations was notified at 2155 (ENS call # 45238). Power from System Auxiliary Transformer (SAT) (credited offsite power supply) 242-2 was restored to buses 241 and 242 (safety related buses) at 0036 on August 2, 2009. The Unusual Event was terminated at 0036 on August 2, 2009. This call is being made due to the termination of the Unusual Event declared on July 30, 2009. An Event Summary Report is required by Exelon procedures within 24 hours of termination of the Unusual Event and will be communicated to the Headquarter Operations later today. The initial event was the result of the actuation of the SAT sudden pressure relay. When the transformer tripped, a slow automatic bus transfer resulted. When the RCPs (Reactor Coolant Pump) and condensate pumps were reenergized, they tripped on overcurrent causing the reactor trip. The sudden pressure relay has subsequently tripped during testing and may have caused the initial event. The licensee reported no damage to the plant. The licensee notified the NRC Resident Inspector. Notified the R3DO (Daley), IRD (McDermott), NRR (Howe), DHS (An), and FEMA (Biscoe).

• * * UPDATE AT 1617 ON 8/2/2009 FROM SCOTT BUTLER TO VINCE KLCO * * *

The Event Summary Report was received and documented the following technical conclusions: The Unusual Event declaration was caused by a sudden pressure relay on SAT 242-1 causing a lockout of both SATs followed by a trip of Unit 2 due to the 2C RCP tripping during the automatic bus transfer for bus 258. This led to a loss of offsite power to Unit 2. It is currently unknown why the sudden pressure relay on SAT 242-1 actuated. Troubleshooting on the sudden pressure relay is in progress. The licensee will notify the NRC Resident Inspector. Notified the R3DO (Daley). Notified the IRD (McDermott) and NRR (Howe) via e-mail.

Switchyard line 2001 tripped and re-energized during a thunderstorm. This caused main generator output breaker, ACB 3-4, to trip open. At this time '1D' reactor coolant pump (RCP) tripped and caused a reactor trip. Cause for the '1D' RCP trip is under investigation. The heat sink is being provided by Aux Feedwater and the use of Steam Dumps. Electrical power is being provided by offsite power. All rods inserted. There were no complications during the trip and all systems functioned as required. Offsite power remained available throughout the transient. The electrical transient had no impact on Unit 2. The licensee notified the NRC Resident Inspector.

• * * UPDATE AT 2217 EDT ON 6/28/07 FROM B. SHEAR TO W. HUFFMAN * * *

This is a revision to a previously transmitted ENS call on 6/27/07 EN# 43449. Braidwood Unit 1 Reactor automatically tripped on a loss of '1D' RCP greater than P-8 setpoint. The cause of the RCP trip was an electrical disturbance during a thunderstorm. The reactor trip automatically caused a main turbine and generator trip. Auxiliary feedwater system automatically started on the low-2 S/G water level that is expected from a full power reactor trip. Auxiliary feedwater and main steam dumps are providing a heat sink. A switchyard line also tripped during this electrical transient causing multiple switchyard breakers to open. Electrical power is being provided by offsite power. All control rods fully inserted. There were no complications during the trip and all systems functioned as required. Offsite power remained available throughout the transient. The electrical disturbance had no impact on Unit 2. The licensee notified the NRC resident inspector." R3DO (Louden) notified.

Unit 2 reactor trip due to 2C steam generator LO-2 reactor protection signal. Auxiliary Feed Water actuated as expected. No additional malfunctions or unexpected plant response. Cause of LO-2 steam generator reactor protection signal under investigation. This is a 4 hour notification of an RPS actuation per 10 CFR 50.72(b)(2)(iv)(B). The 8 hour notification of Auxiliary Feed Water system actuation per 10 CFR 50.72 (b)(3)(iv)(B) is being made under this same telephone call. The licensee notified the NRC Resident Inspector. All control rods fully inserted. Decay heat is being removed to the main condenser via the turbine by-pass valves. The electrical grid is stable.

• * * UPDATE FROM F. EHRHARDT TO M. RIPLEY 15:55 ET 12/22/04 * * *

The licensee has determined that the RPS and Auxiliary Feed Water actuations were the result of an actual low level in the 2C steam generator. The cause of the low level is under investigation. The NRC Resident Inspector was informed. Notified R3 DO (L. Kozak).