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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.

EN Revision Text: INOPERABLE CONTROL ROOM ENVELOPE Braidwood Station was performing Control Room Envelope Testing. During testing the Station identified a failed acceptance criteria. The Control Room Envelope is a single train system and could constitute a Loss of Safety Function. If a single train system is inoperable per Technical Specifications (TS), it is Reportable as a Loss of Safety Function per 10 CFR 50.72(b)(3)(v) regardless of the system's continued ability to meet the accident analysis requirements.

Both Units remain Mode 1, 100% power. The licensee will be notifying the NRC Resident Inspector. The acceptance criteria that failed was to maintain the control room pressure above the miscellaneous electrical equipment room pressure. The station has realigned ventilation to normal, and has entered TS Limited Condition for Operation (LCO) 3.7.10 condition B, which requires the station to restore to operable the control room envelope within 90 days or shutdown the plant. The station has also initiated contingency actions to verify SCBA (self contained breathing apparatus) are available and control room personnel are qualified to use SCBA.

• * * RETRACTION ON 12/20/18 AT 1714 EST FROM ANTHONY SIEBERT TO JEFFREY WHITED * * *

On Wednesday, December 19, 2018, Braidwood Station concluded that the ENS notification 53784 could be retracted. It has been determined that the issue was not with the Control Room Envelope structure. Troubleshooting identified that the Unit 1 Upper Cable Spreading Room Area Supply Flow Control (OVC035Y) damper which supplies the Train A control room ventilation equipment room with air flow was not opening enough to supply the required flow. The subject duct work is shared by both A-train and B-train, and the flow through OVC035Y is controlled by a two-position actuator. The damper is less open when A-train is in operation (actuator energized) and more open when B-train is in operation (actuator de-energized). The only adjustments performed were to the actuator energized stroke limits which only affect the A train and thus a single train failure which could affect the safety function of both trains did not exist. Further calculations of unfiltered air inleakage into the Control Room Envelope (CRE) under a slightly negative differential pressure condition resulted in a calculated in leakage to the CRE of less than the maximum allowable unfiltered air inleakage for a radiological event of 436 scfm. The unfiltered air inleakage into the CRE assumed in the licensing basis analyses of Design Basis Accident consequences was never exceeded. Thus, TS Surveillance Requirement 3.7.10.4 continued to be met and entry into TS 3.7.10 Condition B was not required. The licensee has notified the NRC Resident Inspector. Notified the R3DO (Stone).

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 8/20/2015 at 1710 CDT, a design flaw was discovered with the pressurizer power operated relief valve (PZR PORV) block valve control circuitry. Specifically, the circuit deficiency for which a design basis fire in the Main Control Room (MCR) or cable spreading room could prevent the PZR PORV block valves from being closed from the local control switch at their associated motor control center (MCC). Engineering has reviewed this issue and determined that a potential fire induced ground in the MCR or cable spreading room could clear the associated control power fuses which would prevent the block valves from operating at the local control switch. These valves are considered to form a High/Low pressure interface which requires postulating a proper polarity DC cable to cable fault. Engineering has reviewed the circuit design and cable routing associated with PORVs 1(2)RY455A and 1(2)RY456 and determined that their associated cables are routed with other DC circuit cables in the MCR control board and cable spreading room raceways, such that this postulated fault could potentially cause spurious opening of one of the PORVs even after the control power fuses have been removed as directed by the station abnormal operating procedures for control room inaccessibility. This identified block valve circuit deficiency prevents the credited safe shutdown action of locally closing the block valves to mitigate the spurious operation of a PORV. Hourly fire watches of the affected MCR and cable spreading room fire zones have been implemented. In addition, the MCR is continuously staffed and the affected cable spreading room fire zones are equipped with detection and automatic suppression. This event is being reported under 10CFR50.72(b)(3)(ii)(B) for 'Any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety.' The licensee has notified the NRC Resident Inspector.

• * * UPDATE PROVIDED BY ROB SHERMAN TO JEFF ROTTON AT 1845 EDT ON 09/02/2015 * * *

During the extent of condition review, an additional design deficiency was identified with respect to the PZR PORV and PZR PORV Block valves. Specifically, the current mitigating strategy for removing PZR PORV control power fuses does not adequately prevent a PZR PORV from spuriously opening due to fire induced hot short. Furthermore, local actions to close the associated PZR PORV block valve at the motor control center (MCC) may not be effective because the MCC may not have electrical power during the design basis fire. Therefore, the credited safe shutdown action to remove the PZR PORV control power fuses does not prevent the PZR PORV from spuriously opening during design basis fires in some of the upper and lower cable spreading room fire zones. The affected Fire Zones are the same upper and lower spreading rooms previously identified and fire watches of the affected areas remain in place. The NRC Resident Inspector has been notified. Notified the R3DO (Skokowski)

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).

On 04/06/2015, 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 FROM GREG HARNOIS TO JOHN SHOEMAKER AT 1013 EDT ON 4/8/15 * * *

The TSC ventilation system has been restored to normal operation as of 0600 CDT on April 8, 2015. The NRC Resident Inspector has been notified. Notified R3DO (Skokowski).

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.

At 1943 CDT on 7/23/14, Braidwood Station declared Unusual Event HU1 due to gunshots fired within the Owner Controlled area (OCA). This was a security condition without a Hostile Action. Both Units remain in Mode 1, 100% reactor power throughout the event. Local Law enforcement was contacted and investigated. Security stood down from the Security Condition at 1956 CDT. The Control Room was informed at 1930 CDT by Security of fourteen (14) gunshots heard inside the OCA. The licensee informed State and local agencies and the NRC Resident Inspector. Notified other FEDS (FEMA Ops Center, DHS NICC Watch Officer, DHS SWO) and (Nuclear SSA, FEMA NWC) via email.

• * * UPDATE AT 2311 EDT FROM JOE CONQUEST TO S. SANDIN * * *

Braidwood Station Terminated an Unusual Event, HU1 at 2134 CDT. Local Law Enforcement Agency called an 'AII Clear' and station security restored the normal security posture at 1956 CDT. The licensee informed State and local agencies and the NRC Resident Inspector. Notified R3DO (Orth), NRR (Lund) and IRD (Gott) via email. Notified other FEDS (FEMA Ops Center, DHS NICC Watch Officer, DHS SWO, Nuclear SSA, FEMA NWC) via email.

At approximately 0715 (CDT) on 7/1/2014, during the daily morning test, Braidwood Generating Station experienced Offsite Alert and Notification System (ANS) failure of sirens BD10 and BD13 due to a loss of power to the sirens. Loss of power to the sirens was due to the adverse weather conditions experienced on the evening of 6/30/2014. Siren BD10 provides coverage for 20% of Braidwood's Emergency Planning Zone (EPZ) population and siren BD13 provides coverage for 14.1% of the Braidwood EPZ population. This event is being reported in accordance with 10CFR50.72(b)(3)(viii) for 'any event that results in a major loss of emergency assessment capability, offsite response capability, or offsite communications capability (e.g., significant portion of control room indication, Emergency Notification System, or offsite notification system).' The failure of the sirens resulted in the loss of the capability to alert a large segment of the population in the EPZ (~34%) for more than 1 hour. Per NEI 13-01, Rev 0, a large segment of the population in the EPZ should be taken to mean approximately 25% of the total EPZ population. Immediate actions taken included placing a portable generator online to restore siren BD10 at 1015 CDT on 7/1/2014. ComEd is currently in the area attempting to restore normal power. Proposed long term corrective actions including an upgrade to the sirens to contain a battery backup are being evaluated. The licensee has notified the NRC Resident Inspector. The county emergency managers (for Will County - (for siren) BD10 and Grundy County - (for siren) BD13) are aware of the siren outage and the requirements to initiate mobile route alerting (FEMA approved backup) if required.

• * * UPDATE FROM MURTAZA ABBAS TO DANIEL MILLS AT 1756 EDT ON 07/02/2014 * * *

Siren BD10 was restored to functional on 7/1/2014 at 1130 CDT. Siren BD13 was restored to functional on 7/2/2014 at 1145 CDT. The NRC Resident Inspector has been notified of this ENS update. Notified R3DO (McCraw)

At 1434 (CDT) on 06/11/14, the 1A Containment Spray chemical additive flow was found out of tolerance low during surveillance testing. This resulted in an unanalyzed condition in that insufficient chemical additive flow might have resulted in lower than assumed containment spray Ph values during past periods. The impact of the unanalyzed condition has not been fully evaluated. Based on the above, this is being reported in accordance with 10CFR50.72(b)(3)(ii)(B). Engineering analyses are in progress to evaluate the past condition. Actions are in progress to restore the 1A Containment Spray chemical additive flow to within tolerance. The 1B Containment Spray system is operable per Tech Spec 3.6.6 and is capable of providing required chemical additive flow. The required flow is 30 to 63 gpm. Measured flow was 27 gpm. The last measurement was six years ago. The licensee notified the NRC Resident Inspector.

• * * RETRACTION PROVIDED BY JOHN LOGAN TO JEFF ROTTON AT 1803 EDT ON 06/13/2014 * * *

The purpose of this report is to retract EN report #50189 (June 11, 2014). This EN report was made for the 1A Containment Spray chemical additive flow which was found out of tolerance low during surveillance testing. At the time of reporting, it was concluded that this was an unanalyzed condition in that insufficient chemical additive flow may have resulted in lower than assumed containment spray pH values during past periods. This was reported in accordance with 10CFR50.72(b)(3)(ii)(B) as an unanalyzed condition that significantly degrades plant safety. At approximately 1700 CDT on Thursday, June 12, 2014, Braidwood Generating Station concluded that the prior EN notification could be retracted based on the completion of Engineering Change 398472, 'Evaluation of As-Found Results for 1A Containment Spray NaOH Additive Flow.' The Engineering Change concluded that the approval of the alternate source term (AST) license amendment resulted in the elimination of a minimum containment spray (CS) spray pH value. The current containment release analysis does not credit the addition of sodium hydroxide (NaOH) to CS spray for fission product removal from the containment atmosphere. The long-term retention of captured fission products in the sump water assumes the sump water pH is greater than 7. This is established by the transfer of the containment spray additive tank (CSAT) contents to the sump during CS system operation. To transfer the maximum CSAT inventory to the sump within 8 hours, a minimum NaOH eductor flow of approximately 10 gpm is required. The minimum NaOH injection flow for the 1A CS eductor system (27.0 ' as-found' and 27.7 'as-left' gpm) exceeded 10 gpm so the eductor injection flows meet the criteria to transfer CSAT inventory to the containment recirculation sump within the expected minimum CS system operating time. The out of tolerance flow values recorded at the time of the initial notification are acceptable. The licensee has notified the NRC Resident Inspector. Notified R3DO (Daley).