PNO-III-23-002, Prairie Island Nuclear Power Station Declaration of an Unusual Event Following a Turbine Generator and Reactor Trip Due to Fault on Unit 2 Generator Main Transformer

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PNO-III-23-002 - Prairie Island Nuclear Power Station Declaration of an Unusual Event Following a Turbine Generator and Reactor Trip Due to Fault on Unit 2 Generator Main Transformer
ML23151A685
Person / Time
Site: Prairie Island Xcel Energy icon.png
Issue date: 06/01/2023
From: Hironori Peterson
NRC/RGN-III/DORS/RPB3
To:
References
PNO-III-23-002
Download: ML23151A685 (1)


PRELIMINARY NOTIFICATION - REGION III June 1, 2023 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE - PNO-III-23-002 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. Some of the information may not yet be fully verified or evaluated by the Region III staff.

Facility Licensee Emergency Classification Xcel Energy X Notification of Unusual Event Prairie Island Nuclear Generating Plant Alert Welch, MN Site Area Emergency Docket: 05000306 General Emergency Not Applicable

SUBJECT:

PRAIRIE ISLAND NUCLEAR POWER STATION DECLARATION OF AN UNUSUAL EVENT FOLLOWING A TURBINE GENERATOR AND REACTOR TRIP DUE TO FAULT ON UNIT 2 GENERATOR MAIN TRANSFORMER On Saturday, May 27, at 6:44 p.m. CDT, the Prairie Island Nuclear Generating Plant notified the NRC of a Notification of Unusual Event (NOUE) due to indications of a potential fire in the containment building. At 6:19 p.m. CDT the Unit 2 turbine and reactor had automatically tripped due to a fault on the Unit 2 generator main transformer. At the same time as the trip, two fire alarms were received from the Unit 2 containment building. Personnel were unable to enter the Unit 2 containment to validate the fire alarms within 15 minutes; therefore, Shift Manager declared an NOUE at 6:34 p.m. CDT (EN 56543 completed at 7:20 p.m. CDT). After entry into the Unit 2 containment building, plant operators verified that there was no smoke, fire, steam, acrid odors, or elevated temperatures within the building. At 6:45 p.m. CDT, the licensee determined there was no fire. The licensee terminated the NOUE at 11:04 p.m. CDT. The licensee determined that the alarms were caused by the electrical transient which occurred due to the fault on the Unit 2 main transformer.

Following the trip, all safety systems operated as designed. Station personnel maintained the plant in a safe condition and troubleshooting is in progress to determine the cause of the main generator transformer fault and initiate any necessary repairs.

NRC Resident Inspectors responded to the site and verified that the plant was in a safe condition and that plant personnel were operating in a manner consistent with protecting the health and safety of the public.

The State of Minnesota was notified by the licensee. Region III Government Liaison Officer contacted the States of Minnesota and Wisconsin to inform them of the situation and answer questions.

The NRC resident inspectors will continue to monitor the licensees investigation and repair efforts. The resident inspectors are scheduled to observe and monitor the reactor plant restart following completion of repair activities.

OFFICIAL RECORD COPY

NRC Region III, located in Lisle, IL, received initial notification of this occurrence by telephone call at 7:28 p.m. CDT via official event notification of the NOUE on Saturday May 27, 2023, with updates being provided daily. The information presented herein has been discussed with the licensee and is current as of 4:10 p.m. CDT, May 31, 2023.

ADAMS Accession Number: ML23151A685 CONTACT: Hironori Peterson 630-829-9707 Hironori.Peterson@nrc.gov OFFICIAL RECORD COPY