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The following is a summary of information provided by the licensee via phone: At 0819 MST on 3/19/2026, with Palo Verde Unit 2 at 95 percent power, the site declared an Unusual Event under emergency action level 'SU5.1' due to identified reactor coolant system leakage for greater than 15 minutes. The leak was isolated by securing letdown. A manual reactor trip was inserted, and Unit 2 is currently shutdown in mode 3. Palo Verde Units 1 and 3 were unaffected. State and local authorities were notified. The NRC Senior Resident Inspector has been notified. Notified DHS SWO, FEMA Ops Center, FEMA NWC, CISA Central, CWMD Watch Desk, DHS Nuclear SSA (email), and DHS NRCC THD Desk (email).

• * * UPDATE ON 03/19/2026 AT 1535 EDT FROM PEDRO REGUERA TO BETHANY CECERE * * *

The following update was provided by the licensee via phone: This update is a 10 CFR 50.72(b)(2)(iv)(B) required report of a valid RPS actuation while critical due to operators tripping Palo Verde Unit 2 at 0841 MST. Notified R4DO (Dixon), NRR EO (Feliz Adorno), IR MOC (Whited), R4RA (Monninger), NRR (Groom), R4 PAO (Smith), and NSIR (Williams).

• * * UPDATE ON 03/19/2026 AT 1717 EDT FROM COLLIN MILLER TO JOSUE RAMIREZ * * *

The following information was provided by the licensee via phone: Palo Verde Unit 2 terminated the notice of unusual event 'SU5.1' at 1410 MST. The leak was isolated, the plant is stable, and there was no release. State and local authorities were notified. The NRC Senior Resident Inspector has been notified. Internal notifications: R4DO (Dixon), NRR EO (Feliz Adorno), IR MOC (Whited), R4RA (Monninger), NRR (Groom), R4 PAO (Smith), and NSIR (Williams). External notifications: DHS SWO, FEMA Ops Center, FEMA NWC, CISA Central, CWMD Watch Desk, DHS Nuclear SSA (email), and DHS NRCC THD Desk (email).

• * * UPDATE ON 03/31/2026 AT 1920 EDT FROM SHAUN BERNAT TO IAN HOWARD * * *

This notification constitutes a retraction of the 1-hour immediate notification (EN 58211) of the unusual event made to the NRC by Palo Verde Nuclear Generating Station (PVNGS) on March 19, 2026. Palo Verde is (partially) retracting this event notification in accordance with the guidance provided in NUREG 1022, Revision 3, `Event Reporting Guidelines 10 CFR 50.72 and 50.73,' specifically Section 2.8, `Retraction and Cancellation of Event Reporting,' and Section 4.2.3, `ENS Notification Retraction.' The leakage reported on March 19, 2026, was subsequently determined to have originated from a failed O-ring on a seal injection filter housing. The leakage was isolated by closing installed isolation valves on the seal injection filter housing. Following evaluation, this condition was determined not to meet the criteria for reactor coolant system (RCS) identified leakage as defined in SU5.1 of the PVNGS emergency plan. Clarification: Leakage was not isolated by securing letdown, as originally reported in the ENS notification submitted on March 19, 2026. This update applies solely to the retraction of the unusual event declaration. The NRC Resident Inspector has been notified. Notified R4DO (Deese).

The following information was provided by the licensee via phone and email: On February 3, 2026, at 2338 CST, River Bend Station (RBS) was operating at 100 percent reactor power when the standby service water pump `C' (SWP-P2C) faulted, tripped, and locked out during the performance of a routine surveillance. The pump fault caused E22-ACB04, the normal division III 4.16 KV bus supply breaker, to trip and lock out. The division Ill emergency diesel generator (EDG) started as designed and powered the division III 4.16 KV bus. There are no signs of fire. The cause of the SWP-P2C fault is still under investigation. The trip of E22-ACB04 resulted in the inability to meet (surveillance requirement) SR 3.8.9.1 forcing entry into (limiting condition for operation) LCO 3.8.9 required action 'E.1' and declaring the (high pressure core spray) HPCS system inoperable. This event is being reported under 10 CFR 50.72(b)(3)(iv)(A) as an event or condition that results in valid actuation of emergency AC electrical power systems and 10 CFR 50.72(b)(3)(v)(D) as an event or condition that at the time of discovery could have prevented the fulfillment of a safety function. The NRC Resident Inspector has been notified.

• * * PARTIAL RETRACTION ON 02/12/2026 AT 1946 EST FROM TERRY BLANCHARD TO ADAM KOZIOL * * *

This event was initially reported under 10 CFR 50.72(b)(3)(iv)(A) as an event or condition that results in a valid actuation of emergency AC electrical power systems and 10 CFR 50.72(b)(3)(v) as an event or condition that at the time of discovery could have prevented the fulfillment of a safety function. During subsequent investigation, it was determined that the trip of E22-ACB04 did not result in the inability to meet SR 3.8.9.1 which forced entry into LCO 3.8.9 required action 'E.1'. As a result, it has been determined that the HPCS system remained operable. Therefore, this condition is not reportable as an event or condition that at the time of discovery could have prevented the fulfillment of a safety function. However, this event remains reportable as an event or condition that results in a valid actuation of emergency AC electrical power systems. The NRC Resident Inspector has been notified. Notified R4DO (Dodson)

The following information was provided by the licensee via phone: On January 26, 2026, at 1823 CST, a Notice of Unusual Event was declared on emergency action level HU1.1 due to a security event. The NRC Resident Inspector, the State of Texas, and local authorities have been notified. Notified DHS SWO, FEMA Operations Center, FEMA NWC, CISA Central Watch Officer, CWMD Watch Desk, DHS Nuclear SSA (email), DHS NRCC THD Desk (email).

• * * UPDATE ON 01/26/2026 AT 2058 EST FROM MATT MAGER TO KERBY SCALES * * *

The following information provided by the licensee via phone: On January 26, 2026, at 1940 CST, the Unusual Event was terminated. The NRC Resident Inspector was notified. Notified R4RA (Monninger), NRR (Groom), NSIR (Williams), R4DO (Dixon), NRR EO (Mckenna), IR MOC (Grant), R4PAO (Smith). Notified DHS SWO, FEMA Operations Center, FEMA NWC, CISA Central Watch Officer, CWMD Watch Desk, DHS Nuclear SSA (email), DHS NRCC THD Desk (email).

The following information was provided by the licensee via phone and email: At 0748 CST, on November 12, 2025, Callaway Plant experienced an automatic actuation of the auxiliary feedwater (AFW) system in response to auxiliary feedwater actuation signals (AFAS). A low suction pressure signal was also received which aligned the AFW pumps to essential service water (ESW). An unknown amount of water from the ultimate heat sink (UHS) entered the steam generators, necessitating a plant shutdown due to exceeding secondary water chemistry program action levels. During the shutdown, with the plant at approximately 28 percent power, high vibration was received on the main turbine, requiring a manual turbine trip. The cause of the AFAS is not yet known. The plant is currently stable in mode 3. This condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(iv)(A). There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: Decay heat is being removed via steam dump valves to the main condenser.

• * * RETRACTION ON NOVEMBER 20, 2025, AT 1409 EST FROM ZACH MILLIGAN TO JORDAN WINGATE * * *

The following is a summary of the retraction provided by the licensee via phone and email. Event Notification 58035, made on November 12, 2025, pursuant to 10 CFR 50.72(b)(3)(iv)(A), is being retracted following a review of the cause of the auxiliary feedwater system's automatic actuation. The AFW system actuation was traced to a power supply malfunction, which also caused the auxiliary feedwater pumps to align with essential service water. Because the actuation resulted from a spurious power supply failure, rather than signals triggered by plant conditions or parameters meeting system initiation criteria, it is considered invalid and not reportable under 10 CFR 50.72(b)(3)(iv)(A). The NRC Resident Inspector has been informed. Notified R4DO (Drake)

The following information was provided by the licensee via phone and email: On October 12, 2025, Columbia Generating Station (CGS) was performing a reactor building emergency cooling test. At 1428 (PDT), an air damper associated with the division 1 motor control center (MCC) room cooling failed to perform its intended function to close. This MCC supports the operation of one subsystem of the standby gas treatment system (SGT). At 1440, a second air damper, associated with the division 2 MCC room cooling, also failed. This MCC supports the operation of the other SGT subsystem. Field operators were dispatched to investigate the potential cause. At 1627, the first air damper that had failed was observed to have closed on its own without further operator action. Operators subsequently determined that failure of the air damper to close rendered the associated emergency room coolers inoperable. At 1705, (the division 2 MCC) was declared inoperable and technical specification action statement 3.8.7.A was entered. From 1440 to 1627, CGS was in a condition that required both SGT subsystems to be declared inoperable due to the loss of emergency room cooling to their associated MCCs. This condition constitutes a loss of safety function of SGT and secondary containment. It could have challenged the station's ability to control a radioactive release had one occurred during that time. This notification is being made pursuant to 10 CFR 50.72(b)(3)(v)(C) and (D) due to the loss of safety function of both trains of SGT and secondary containment for approximately 2 hours. The Resident Inspector was notified. The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance: At the time of notification, the licensee had exited all technical specification action statements.

• * * RETRACTION ON 11/5/2025 AT 1925 EST FROM JERRY AINSWORTH TO ERNEST WEST * * *

On October 12, 2025, at 2152 PDT, Columbia Generating Station notified the NRC pursuant to 10 CFR 50. 72(b)(3)(v)(C) and (D) due to the loss of safety function of both trains of standby gas treatment (SGT) and secondary containment for approximately 2 hours under Event Notification 57982. The notification was made due to the failure of two dampers to close during testing of the Reactor Building Emergency Cooling System. The dampers that failed to close were cross-divisional and affected rooms with equipment necessary for both trains of the SGT system which supports the safety function of secondary containment. Following the event, engineering conducted an evaluation to determine if both air dampers remaining open during a loss of cooling accident would have put any safety-related equipment at risk due to potential changes in radiological and environmental conditions within the associated motor control center (MCC) rooms. The engineering evaluation determined temperatures and humidities would not have exceeded limits in the MCC rooms due to the dampers being left open. Additionally, any increase in radiation would be considered negligible and would not affect the ability of the equipment to perform their design functions. Therefore, the safety-related equipment within the MCC rooms would have been available and operable to perform their design function were an accident to occur. Consequently, the failure of two dampers to close during testing is not considered to be an event or condition that could have prevented fulfillment of the safety function of SGT and secondary containment and did not impact the ability to mitigate the consequences of an accident or control the release of radioactive material, therefore, event notification 57982 is retracted. The Resident Inspector has been notified. Notified R4DO (Vossmar)

The following information was provided by the licensee via phone and email: On 9/23/2025 at 2214 CDT, the South Texas Project Unit 1 (STP-1) train 'B' reactor containment fan cooler (RCFC) chilled water supply outside containment isolation valve, 1-CC-MOV-0137, was declared inoperable due to a material condition. This rendered train 'B' component cooling water inoperable which cascaded to train 'B' emergency core cooling system (ECCS) subsystem to render it inoperable. STP-1 entered technical specification (TS) 3.5.2 action 'A' for train 'B' ECCS, requiring restoration within 7 days or apply the requirements of the Configuration Risk Management Program (CRMP). On 09/25/2025 at 1229 CDT, train 'A' essential chiller 12A was declared inoperable due to inability to maintain chiller water outlet temperature less than 52 degrees Fahrenheit. This cascaded down to the train 'A' ECCS subsystem to render it inoperable. STP-1 entered TS 3.5.2 action 'B' due to less than two of the required subsystems operable, to within 1 hour restore at least two subsystems to operable status or apply the requirements of the CRMP, or be in at least hot standby within the next 6 hours and in hot shutdown within the following 6 hours. On 09/25/2025 at 1329 CDT, STP-1 entered the CRMP based on two ECCS subsystems remaining inoperable longer than 1 hour. These subsystems are used for accident mitigation. Unit 1 remains in mode 1.

• * * RETRACTION ON 10/20/2025 AT 1636 EDT FROM MARC HILL TO JOSUE RAMIREZ * * *

The following information was provided by the licensee via phone and email: The purpose of this notification is to retract EN 57952, which was made on September 25, 2025, at 1736 EDT. (The) notification was initially made due to two of three trains of emergency core cooling system (ECCS) being declared inoperable. After the notification was made, South Texas Project determined using an engineering evaluation, that one of the two inoperable ECCS trains was operable because the elevated chilled water outlet temperature of the associated essential chiller (Train A) did not impact the technical specification specified function. Therefore, this event was not a condition that could have prevented fulfillment of a safety function. The NRC Resident Inspector has been notified. Notified R4DO (Vossmar)