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The following information was provided by the licensee via email: At 1045 EST, on 2/19/2024, during a maintenance activity, a loss of all reactor building ventilation occurred on Unit 2. With no flow past the ventilation radiation monitors, the radiation monitors were inoperable to support their ability to perform primary and secondary containment isolation functions or start the standby gas treatment system. Reactor building ventilation was restored within 15 minutes. Due to this inoperability, the radiation monitor system was in a condition that could have prevented fulfillment of a safety function; therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v). There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector will be notified.

• * * RETRACTION ON 3/15/24 AT 1315 EDT FROM BILL LINNELL TO ADAM KOZIOL * * *

Upon further investigation, it was verified that the reactor building and the refueling floor radiation monitors are not needed to control the release of radiation for events described in chapter 14 of the updated Final Safety Analysis Report. For the analyzed loss of coolant accident (LOCA), the primary and secondary signals for this purpose were available and unaffected by this event. The radiation monitors provide a tertiary redundant method that is not credited within the station analysis. For all other analyzed accidents, the signal provided by the radiation monitors is not needed, as the secondary containment isolation function and start of the standby gas treatment system are not credited. Additionally, the fuel handling accident was not credible during the time of the event because no activities were in progress on the refueling floor. Therefore, the threshold for reporting the issue as an event or condition that could have prevented the fulfillment of a safety function was not met. The NRC Resident Inspector has been notified. Notified R1DO (Jackson)

At 0905 EDT, it was discovered both trains of Auxiliary Building Gas Treatment System (ABGTS) were simultaneously INOPERABLE due to the auxiliary building secondary containment enclosure (ABSCE) being inoperable; therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v). There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. ABSCE and ABGTS were returned to operable.

• * * RETRACTION ON 10/14/2021 AT 0756 EDT FROM TRACY SUDOKO TO THOMAS HERRITY * * *

This is a retraction of the 8-hour Immediate notification (EN55421) made to the NRC by Sequoyah Nuclear Plant on August 20, 2021. Sequoyah is retracting this event notification based on the following: Regulatory Guidance in NUREG-1022, Revision 3, 'Event Reporting Guidelines 10 CFR 50.72 and 50.73', Sections 2.8 'Retraction and Cancellation of Event Reporting', and 4.2.3 'ENS Notification Retraction'. On August 20, 2021 personnel found door A-118 open. This door is part of the ABSCE. During the initial investigation, it was found that other personnel had the door open using Precaution A of 0-TI-SXX-000-016.0 which allows material access through ABSCE doors if the door is closed within three minutes. It was found that A-118 door had been open for greater than three minutes. With this door open the ABSCE was beyond its capability for ABGTS fan to maintain the required pressure during an Aux. Building Isolation. Thus, the site declared the ABSCE and both Trains of ABGTS inoperable per LCO 3.7.12 Conditions A, B and E. With the ABSCE being a single train system, this caused a condition that "could have prevented the fulfillment of the safety function" which requires an Immediate Notification to the NRC within eight hours under 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.72 (b)(3)(v)(D). This Immediate Notification was reported on August 20, 2021 at 1600 EDT. It was later determined that at 'Time of Discovery', although Door A-118 was open, it was not obstructed, the door was open by normal means, was capable of being closed and was now attended. The time requirement per 0-TI-SXX-000-016.0 for closure of an open ABSCE door is within three minutes of notification. Although the individual found holding the door was unaware of the requirement of 0-TI-SXX-000-016.0 to close the door, communications were established and the Main Control Room (MCR), upon discovery of the 'Open Door', could have directed closure starting at the Time of Discovery if required. Since the MCR was aware the door was open, had communications established with personnel at the door, the door was capable of closure and not restricted, the three minute closure requirement of 0-TI-SXX-000-016.0 was met. Subsequently, the door was closed within approximately two minutes of notification to close. The closure of the door with these procedural measures met confirmed the integrity of the ABSCE and therefore Operability of ABGTS. Based on the above critical thinking, entry into LCO 3.7.12 Condition A, B, and E was retracted on August 22, 2021 at 2044 EDT. With the LCO conditions retracted and the above determination that at the Time of Discovery safety function was maintained, the Immediate Notification per 10 CFR 50.72 (b)(3)(v)(C) and 10 CFR 50.72 (b)(3)(v)(D) was not required. The issue of Past Operability remains for instances in time that the door did not have appropriate compensatory measures in place. Any further notification required for this event will be submitted as a Licensee Event Report. Notified R2DO (Miller)

On 5/22/2019, the 'A' Control Structure Chiller (Div I) tripped due to a loss of (motor control center) MCC 0B136. The 'B' Control Structure Chiller was already inoperable due to Div II (Emergency Service Water) ESW being out of service for planned maintenance. With the loss of Control Structure HVAC System the ability to maintain temperatures in various spaces including relay rooms, Control Room Floor Cooling and Emergency Switchgear rooms was lost. The 'B' Control Structure Chiller was restarted at 0251 EDT and cooling was reestablished to the required areas, however the 'B' chiller is not considered operable at this time. Units 1 and 2 entered (Technical Specification) TS 3.0.3 at 0256 EDT and a controlled shutdown of both units commenced, Unit 2 at 0340 EDT and Unit 1 0350 EDT. This constitutes a TS required shutdown and requires a 4 hour (Emergency Notification System) ENS notification in accordance with 10 CFR 50.72(b)(2)(i). The failure also requires an 8 hour ENS notification in accordance with 10 CFR 50.72(b)(3)(v) due to the loss of a safety function. The licensee needs to restore the 'B' loop of ESW to exit the Limiting Condition of Operation (LCO). The licensee is currently performing a flow surveillance, once complete and assuming the data is acceptable, the licensee will be able to exit the LCO. The units are in a normal electrical lineup. The licensee will be notifying the state of Pennsylvania FEMA Operations Center. The licensee has notified the NRC Resident Inspector.

• * * UPDATE ON 05/22/2019 AT 1302 FROM SCOTT MYRTHEL TO THOMAS KENDZIA * * *

On 5/22/2019 at 0601 EDT Susquehanna Steam Electric Station reported a shutdown had been commenced at 0340 EDT for Unit 2 and 0350 EDT for Unit 1 due to inoperability of both control structure chillers. Power has been restored to MCC 0B136, and at 0901 EDT the 'A' control structure chiller was declared operable and LCO 3.0.3 was exited. Power reduction for both units was halted at 0901 EDT and preparations for power restoration initiated. As of 1255 EDT on 5/22/2019, Unit 1 power is 94% and Unit 2 power is 92%. Notified the R1DO (Arner).

At 2006 (MST), on 3/31/2019, the Palo Verde Nuclear Generating Station Unit 1 Shift Manager was informed that leakage was measured from the Train A Emergency Core Cooling System (ECCS) piping at approximately 100 ml/minute through a High Pressure Safety Injection (HPSI) A drain valve. This value exceeds the assumed 3000 ml/hour ECCS leakage for a large break loss of coolant accident analysis. At 0230 (MST) on April 1, 2019, the valve was flushed and the leakage reduced to 10 ml/minute (600 ml/hour) and was no longer above the limit of the safety analysis. This condition is being reported as an unanalyzed condition per 10 CFR 50.72(b)3)(ii)(B) and a condition that could have prevented the fulfillment of a safety function to the control the release of radioactive material per 10 CFR 50.72(b)(3)(v)(C). This event did not result in an abnormal release of radioactive material. Notification received by Caty Nolan and emailed to HOO.HOC@NRC.GOV The NRC asked a followup question: Why was the criterion for Control of Radioactive Material selected? per the PVNGS Unit 1 Shift Manager, this criterion was selected due to the potential of exceeding offsite dose projections, post recirculation, following a Design Basis Accident. The resident inspector has been notified.

• * * UPDATE ON 05/15/19 AT 1417 EDT FROM SEAN DORNSEIF TO BETHANY CECERE * * *

An engineering evaluation concluded that the as-found ECCS leakage would not have degraded the performance of the Pump Room Exhaust Air Cleanup system; therefore, it remained operable. The evaluation also concluded that the as-found leakage was within the analysis margins for HPSI pump hydraulic performance and containment flood level following a Large Break Loss of Coolant Accident; therefore, the ECCS also remained operable. Based on the above information, the condition identified on March 31, 2019, was an unanalyzed condition per 10 CFR 50.72(b)(3)(ii)(B), but did not prevent the fulfillment of the safety function of the structures or systems that are needed to control the release of radioactive material per 10 CFR 50.72(b)(3)(v)(C). The NRC resident inspectors have been informed. Notified R4DO (Proulx).

EN Revision Text: INOPERABILITY OF EQUIPMENT FOR CONTROL OF RADIOLOGICAL RELEASE At 2130 CST on 11/27/2018, Division 1 Main Steam Positive Leakage Control System (MS-PLCS) was declared inoperable because of a leaking check valve that caused excessive cycling of the associated air compressor. Division 2 MS-PLCS had been declared inoperable on 11/27/2018 at 1400 CST when a pressure control valve in the system exceeded the maximum allowable stroke time. Because MS-PLCS supplements the isolation function of the main steam isolation valves (MSIVs) by processing fission products that could leak through the closed MSIVs, both divisions of MS-PLCS inoperable at the same time represents a condition that could prevent the fulfillment of a safety function of an SSC (Structures, Systems and Components) that is needed to control the release of radioactive material. The station diesel air compressor is available to supply backup air to the safety relief valves as required by the Technical Requirements Manual." (This is associated with operability of the safety relief valves, due to the inoperable MS-PLCS air compressor.) The unit is in a 7 day shutdown Limiting Condition for Operation (LCO), 1-TS1-18-Div 1 & 2 MSPLCS-685, for the two divisions of MS-PLCS being inoperable. The licensee notified the NRC Resident Inspector.

• * * RETRACTION ON 12/03/18 AT 1551 EST FROM TIM GATES TO BETHANY CECERE * * *

This event was initially reported under 10 CFR 50.72(b)(3)(v)(C) as a condition that could have prevented the Main Steam Positive Leakage Control System (MS-PLCS) from fulfilling its safety function to control the release of radioactive material. Division I was declared inoperable due to a failed component. Division II was declared inoperable due to a pressure control valve in the system exceeding the maximum allowable time to close by 0.50 seconds. An engineering evaluation has since been performed and concluded that the 2 second maximum allowable time to close was based on the pressure control valve being classified as a rapid closure valve and was established from the original baseline data of 0.50 seconds. This baseline data is an administrative target value per the In-Service Testing Program. There are no technical specification requirements associated with the 2 second closure time. The engineering evaluation also determined that the volume of air supplied through the pressure control valve during the extra 0.50 seconds of valve closure would have an inconsequential effect on the pressure within the volume of leakage barrier between the Main Steam Isolation Valves associated with the MS-PLCS pressure control valve or have any effect on containment over-pressurization. Based on the information provided by the engineering evaluation, the Division II MS-PLCS has been declared operable-degraded non-conforming since time of initial discovery. Consequently, this event is not reportable as a condition that could have prevented the Main Steam Positive Leakage Control System (MS-PLCS) from fulfilling its safety function. The (NRC) Resident Inspector has been notified via e-mail. Notified the R4DO (Gaddy).