05000423/LER-2023-001, Automatic Reactor Trip Due to Main Generator Output Breaker Ground Fault

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Automatic Reactor Trip Due to Main Generator Output Breaker Ground Fault
ML23208A287
Person / Time
Site: Millstone Dominion icon.png
Issue date: 07/27/2023
From: O'Connor M
Dominion Energy Nuclear Connecticut
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
23-163 LER 2023-001-00
Download: ML23208A287 (1)


LER-2023-001, Automatic Reactor Trip Due to Main Generator Output Breaker Ground Fault
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation

10 CFR 50.73(a)(2)(iv)(B), System Actuation
4232023001R00 - NRC Website

text

Dominion Energy Nuclear Connecticut, Inc.

Millstone Power Station 314 Rope Ferry Road, Waterford, CT 06385 DominionEnergy.com U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 JUL 2 7 2023 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2023-001-00

'1;. Dominion ii a,, Energy SerialNo.:

23-163 MPS Lie/JP RO Docket No.: 50-423 License No.: NPF-49 AUTOMATIC REACTOR TRIP DUE TO MAIN GENERATOR OUTPUT BREAKER GROUND FAULT This letter forwards Licensee Event Report (LER) 2023-001-00, documenting an event that occurred at Millstone Power Station Unit 3, at 04:46 on May 30, 2023. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in manual or automatic actuation of systems listed in 10 CFR 50.73(a)(2)(iv)(B).

There are no regulatory commitments contained in this letter or its enclosure.

Should you have any questions, please contact Mr. Dean E. Rowe at (860) 444-5292.

Si~\\JL~~

Michael J. O'Connor Site Vice President - Millstone Enclosure: LER 423/2023-001-00

Serial No.23-163 Docket No. 50-423 Licensee Event Report 2023-001-00 Page 2 of 2 cc:

U.S. Nuclear Regulatory Commission Region I 475 Allendale Road, Suite 102 King of Prussia, PA 19406-1415.

R. V. Guzman NRC Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station

Serial No.23-163 Docket No. 50-423 Licensee Event Report 2023-001-00 ATTACHMENT LICENSEE EVENT REPORT 2023-001-00 AUTOMATIC REACTOR TRIP DUE TO MAIN GENERATOR OUTPUT BREAKER GROUND FAULT MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

Abstract

On May 30, 2023, at 04:46, Millstone Power Station Unit 3 was in Mode 1 at 100 percent reactor power when an automatic reactor trip occurred following a main generator turbine trip caused by a main generator ground fault. The direct cause of the trip was a ground fault on B phase of the main generator output breaker (MGOB) due to a flashover event that happened inside the B breaker pole fiberglass air supply tube. Air leaks in the breaker air system caused increased air compressor run time resulting in undesired moisture and oil accumulation in the air supply tube that led to flashover. The affected fiberglass air supply tube was replaced and air leaks were fixed in the air supply system. The actuation of the Reactor Protection System and the Auxiliary Feedwater System is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in a manual or automatic actuation of systems listed in 10 CFR 50.73(a)(2)(iv)(B).

07 27 2023Page of

3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.

052 050

CORRECTIVE ACTIONS

The affected fiberglass air supply tube from MGOB air compressor was replaced. The air supply system to the main generator output breaker was inspected, moisture and oil accumulation were cleaned, and leaks in the air system were repaired. Additional corrective actions will be taken in accordance with the station corrective action program.

PREVIOUS OCCURRENCES

On April 1, 2020, at Millstone Power Station Unit 3, an automatic reactor trip occurred following a main generator turbine trip caused by a main generator ground fault. The cause of reactor trip was a ground fault on the C phase of the normal station service transformer isolated phase bus duct due to water intrusion and buildup in an isolated phase bus duct transition section which caused a turbine generator trip, and subsequently a reactor trip. The root cause and faulted component of that event was different and therefore it is not a repeat event.

ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES EL - MAIN GENERATOR OUTPUT POWER SYSTEM BRK - BREAKER 3

3 Millstone Power Station Unit 3 423 2023 001 00