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The following information was provided by the licensee via email: On 10/19/2023, at approximately 1110 (CST), with Unit 1 in mode 1 at 100 percent power, the reactor automatically tripped. All control rods fully inserted into the core following the trip. All safety functions operated as designed. The cause of the trip is being investigated. Operations responded and stabilized the plant. Auxiliary feedwater actuated as expected. Decay heat is being removed by the steam generator through the steam generator power operated relief valve. The trip was complex as non-safety related power was lost to both Unit 1 and Unit 2. Unit 1 is currently in mode 3 and on natural recirculation as both reactor coolant pumps are without power. Unit 2 is currently in a refueling outage with all fuel in the spent fuel pool (SFP). SFP cooling was lost for approximately 70 minutes. No impacts to the SFP temperature were observed. Due to the reactor protection system actuation while critical, this event is being reported as a four-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B). Due to the actuation of the auxiliary feedwater system following the reactor trip, this event is being reported as a specified system actuation in accordance with the reporting criteria of 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.

• * * UPDATE ON 10/19/2023 AT 1646 EDT FROM MARTIN CABIRO TO ERNEST WEST * * *

The second paragraph of the original report is amended as follows to correct information regarding the spent fuel pool for Unit 2: Unit 2 is currently in a refueling outage with all fuel in the spent fuel pool (SFP). SFP cooling was maintained at all times with one train of SFP cooling. The second train lost power and was restarted approximately 70 minutes (after power was lost). No impacts to the SFP temperature were observed. Notified R3DO (Orth) and IR MOC (Crouch) and NRR EO (Felts) via email

The following information was provided by the licensee via email: Notification of Unusual Event, HU4.1 declared based on multiple fire alarms in the containment building not verified within 15 minutes. Turbine trip causing reactor trip due to fault on 2GT transformer. At 1845 CDT, verification of no fire in the containment building. Notified DHS Senior Watch Officer, FEMA Operations Center, CISA Central watch officer, DOE Operations Center (email), HHS Operations Center (email), EPA Emergency Operations Center (email), USDA Operations Center (email), FDA EOC (email), FEMA NWC (email) and DHS Nuclear SSA (email), FEMA NRCC (email) and CWMD watch desk (email).

• * * UPDATE AT 0148 EDT ON 5/28/23 FROM CHRIS BAARTMAN TO BILL GOTT * * *

The following information was provided by the licensee via email: This update is being made to report the actuation of the auxiliary feedwater system following the reactor trip at 1819 CDT. This event is being reported as a specified system actuation in accordance with the reporting criteria of 10 CFR 50.72(b)(3)(iv)(A). This update is also being made for the termination of the notification of unusual event at 2304 CDT on 5/27/2023. The basis for the termination was that there was no indication of a fire. Upon lockout of 2GT transformer, main to reserve power transfer did not occur on 3 of 4 non-safeguards buses. Subsequently, operator action successfully restored power to all non-safeguards buses at 1925 CDT. There was no impact to the health and safety of the public or plant personnel. The NRC resident inspector has been notified of the update. Notified R3DO (Benjam¡n), NRR EO (Walker), IRMOC (Grant), DHS Senior Watch Officer, FEMA Operations Center, CISA Central watch officer, DOE Operations Center (email), HHS Operations Center (email), EPA Emergency Operations Center (email), USDA Operations Center (email), FDA EOC (email), FEMA NWC (email) and DHS Nuclear SSA (email), FEMA NRCC (email) and CWMD watch desk (email).

The following information was provided by the licensee via email: On 12/8/2022, Prairie Island Nuclear Generating Plant initiated a notification to the State of Minnesota due to a HVAC coolant leak reaching waters of the state. The estimated quantity is 5 gallons of NALCO LCS-60. The leak was due to a failed heat exchanger coil and has been isolated. This notification is being made solely as a four-hour, non-emergency notification for a Notification of Other Government Agency. This event is reportable in accordance with 10 CFR 50.72(b)(2)(xi). There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.

• * * RETRACTION ON 12/21/2022 AT 1115 EST FROM RAYMOND YORK TO JEFF WHITED * * *

The following information was provided by the licensee via email: At 0019 EST on 12/9/2022, the Prairie Island Nuclear Generating Plant (PINGP) made Event Notification 56266 notifying the NRC of an environmental report to the State of Minnesota due to an estimated 5 gallons of NALCO LCS-60 that leaked from a failed heat exchanger coil and reached the waters of the state. This event notification was made in accordance with 10 CFR 50.72(b)(2)(xi). During further review of NRC reporting guidance, PINGP has concluded that the reported quantity of NALCO LCS-60 that leaked during this event was below the reporting threshold outlined in NUREG 1022, Revision 3. The NRC Resident Inspector has been notified. Notified R3DO (Kozak)

EN Revision Text: BOTH EMERGENCY DIESEL GENERATORS INOPERABLE DUE TO LOW AIR TEMPERATURE At 0743 (CST) on 1/31/2019, both trains of Unit 2 Diesel Generators were declared INOPERABLE due to outside air temperature exceeding the low temperature design limit for the diesel engines; therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v) for an event or condition that could have prevented the fulfillment of a safety function. The Unit 2 Diesel Generators are still able to start if necessary to provide power. Additionally, multiple layers of defense in depth measures are in place to ensure safety. Prairie Island has five sources of offsite power; all of which are currently available. The Unit 1 Diesel Generators are OPERABLE and capable of being cross-connected to Unit 2. Additional equipment capable of responding to beyond design basis events is available on site providing another layer of defense in depth. Both Unit 2 Diesel Generators were returned to an OPERABLE status at 0810 on 1/31/2019 based on outside air temperature rising above the low temperature design limit with forecasted temperatures to remain above the low temperature design limit. There is no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified. The air temperature limit was -30 degrees Fahrenheit. Unit 1 was not affected. The EDGs were supplied by a different manufacturer with different air temperature limits.

• * * RETRACTION AT 1340 EDT ON 03/22/2019 FROM BRIAN JOHNSON TO JEFFREY WHITED * * *

Engineering analysis performed subsequent to the event notification has determined that both Unit 2 Diesel Generators would have been able to fulfill their safety function during the period of time when the outside air temperature had exceeded the low temperature design limit. Therefore, EN# 53853 is being retracted. The NRC Resident Inspector has been notified of the event notification retraction. Notified R3DO (McCraw).

This event is being reported pursuant to 10 CFR 50.72(b)(3)(xiii) for a major loss of emergency assessment capability at the Prairie Island Nuclear Generating Plant. At 1435 CDT on October 28, 2018, troubleshooting of the Seismic Monitoring Panel resulting from the receipt of Control Room annunciator 47023-0603 (Seismic Monitor Panel) determined that the '(Operational Basis Earthquake) OBE Exceedance' alarm on the Seismic Monitoring Panel will not alarm and determined the panel is non-functional. The Seismic Monitoring Panel system functions to provide indication that the OBE threshold has been exceeded following a seismic event and is used in the Prairie Island Nuclear Generating Plant Emergency Plan to perform classification of Initiating Condition 'Seismic event greater than OBE levels' and Emergency Action Level HU2.1. Station personnel are monitoring the seismic recorders for event alarms on a 15 minute frequency due to alarm function failure. The station is developing repair plans for restoration of the alarm function. This event does not adversely affect the safe operation of the plant or health and safety of the public.

The licensee has notified the NRC Resident Inspector.

On 8/10/2018 at 1445 (CDT) both trains of Cooling Water (Cooling Water Pumps for Emergency Diesel Generators) were declared INOPERABLE and both units entered (Technical Specification) (TS) 3.0.3 due to corroded jacket cooling water plugs for (the) 12 and 22 cooling water pump motors; therefore this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v). At 1543 (CDT), 08/10/2018 the 121 Cooling Water pump was aligned to the "A" Cooling Water train and the TS 3.0.3 condition was exited for both units. (After restoring train A cooling water the site entered a seven day limiting condition for operations, TS 3.7.8 for one inoperable cooling water pump.) There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified.

• * * RETRACTION ON 09/29/2018 AT 2128 EDT FROM BRIAN JOHNSON TO OSSY FONT * * *

Testing and forensic analysis performed subsequent to the notification has determined the as-found condition would not have impacted either diesel-driven pumps' ability to start, run, and meet flow/pressure requirements to perform their required safety function. Therefore, EN# 53546 is being retracted. The NRC Resident Inspector has been notified of the Event Notification retraction. Notified R3DO (Kozak).

On February 3, 2017, Prairie Island staff performed maintenance on the transom above Battery Room Door 225. This activity resulted in the transom being unlatched for approximately five minutes. On February 6, 2017, a question from the NRC Resident Inspector resulted in an evaluation of this condition for past operability. On March 20, 2017, the past operability evaluation of Door 225 concluded that, in the event of a postulated HELB (High Energy Line Break), the transom being unlatched during the five minute maintenance period resulted in the inoperability of multiple systems in the Unit 1 and Unit 2 battery, auxiliary feedwater, and Unit 1 safeguards bus rooms that would be required to mitigate the postulated HELB. The loss of safety functions required to mitigate the postulated HELB make the condition reportable under 50.72(b)(3)(ii) for an unanalyzed condition that significantly degrades plant safety. Unlatching the transom above the Battery Room Door creates an opening not accounted for in design bases documents. This occurred due to an improperly prepared work permit. Corrective actions are in place to preclude recurrence. The licensee informed the NRC Resident Inspector.

• * * RETRACTION FROM MARK LOOSBROCK TO JEFF ROTTON AT 1559 EDT ON 04/10/2017 * * *

Further analysis determined that an unlatched transom would result in a relative humidity of 100 percent in 11 Battery Room for about 10 minutes following a postulated HELB. Since the equipment in the Battery Rooms is not qualified for a harsh environment, the components in 11 Battery Room would have been inoperable. Temperature and relative humidity in the other Battery Rooms, Auxiliary Feedwater Rooms, and the Unit 1 Safeguards Bus Rooms would have remained within the allowable limits. Therefore, for the five minutes the strike was removed from the transom, only equipment in 11 Battery Room and supported A Train components would have been inoperable. This event was not an Unanalyzed Condition that significantly degraded plant safety, under 10 CFR 50.72(b)(3)(ii), as no safety function would have been lost. The licensee notified the NRC Resident Inspector. Notified R3DO (Skokowski).

At 0935 (CST) on 12/21/2016, while performing the High Pressure Coolant Injection (HPCI) Comprehensive Pump and Valve Tests for post-maintenance testing following scheduled maintenance, the HPCI turbine did not start as expected due to the HPCI turbine stop valve failing to open. This issue is being reported under 10CFR50.72(b)(3)(v)(D) as a condition that could have prevented the fulfillment of a safety function at the time of discovery. Investigation into the failure of the HPCI system to start is in progress. The plant remains at 100% power with no challenges to the health and safety of the public. The NRC Resident Inspector has been notified. The plant is in a 14-day action statement under LCO 3.5.1, 'ECCS - Operating' due to the HPCI turbine stop valve failure. The licensee notified the Minnesota State Duty Officer.

• * * RETRACTION FROM KIM HOFFMAN TO JOHN SHOEMAKER AT 1303 EST ON 1/17/18/17 * * *

On December 21, 2016, the NRC Operations Center was notified of Event Number 52454 that described a failure of the High Pressure Coolant Injection (HPCI) turbine stop valve to open during post maintenance testing prior to being declared operable. The condition was reported in accordance with 10 CFR 50.72 (b)(3)(v)(D) as a condition that could have prevented the fulfillment of a safety function at the time of discovery. At the time, it was not readily apparent that the failure was due to the maintenance activities. Subsequent return-to-service testing showed the oil system vent and fill had been inadequate following the maintenance. This event occurred as a result of the maintenance process and would not have occurred during normal operation of the system. NUREG-1022, Revision 3 states, 'reports are not required when systems are declared inoperable as part of a planned evolution for maintenance or surveillance testing when done in accordance with an approved procedure and the plant's TS (unless a condition is discovered that would have resulted in the system being declared inoperable).' There was no discovered condition that would have resulted in the safety function of the system being declared inoperable under normal, non-maintenance conditions. Based on the above additional information, Monticello Nuclear Generating Plant is retracting this report. The plant was in a planned evolution and did not discover a condition that could have prevented performing a safety function. The licensee has notified the NRC Resident Inspector. Notified R3DO (McCraw).