05000395/LER-2022-001-01, (Vcsn), Unit 1, Manual Reactor Trip Due to Main Transformer Fault

(Vcsn), Unit 1, Manual Reactor Trip Due to Main Transformer Fault

ML22349A700
Person / Time
Site:	Summer
Issue date:	12/15/2022
From:	Lippard G Dominion Energy South Carolina
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
22-001A LER 2022-001-01
Download: ML22349A700 (1)

LER-2022-001, (Vcsn), Unit 1, Manual Reactor Trip Due to Main Transformer Fault

Event date:
Report date:
3952022001R01 - NRC Website

text

V.C. Summer Nuclear Station ~ Dominion Bradham Blvd & Hwy 215, Jenkinsville, SC 29065 Mailing Address: ~ Energy P.O. Box 88, Jen kinsville, SC 29065 DominionEnergy.com December 15, 2022

Document Control Desk Serial No. : 22-001A U.S. Nuclear Regulatory Commission VCS-LIC/HK RO Washington, DC 20555 Docket No. 50-395 License No. NPF-12

DOMINION ENERGY SOUTH CAROLINA (DESC)

VIRGIL C. SUMMER NUCLEAR STATION (VCSNS) UNIT 1 LICENSEE EVENT REPORT 2022-001-01 MANUAL REACTOR TRIP DUE TO MAIN TRANSFORMER FAULT

Dominion Energy South Carolina hereby submits Licensee Event Report (LER) 2022-001-01, for VCSNS. This report provides updated details concerning a manual reactor trip due to a main transformer fault and is submitted in accordance with 10 CFR 50. 73(a)(2)(iv)(A).

Should you have any questions, please call Mr. Michael Moore at (803) 345-4752.

Sincerely,

~~

George A. Lippard Site Vice President V.C. Summer Nuclear Station

Enclosure

Commitments contained in this letter: None

cc:

G. J. Lindamood - Santee Cooper L. Dudes - NRC Region II G. Miller - NRC Project Mgr.

NRC Resident Inspector J. N. Bassett-INPO Marsh USA, Inc.

Abstract

On November 15, 2021, at approximately 1728 EST with Unit 1 in Mode 1 at 47 percent power, the reactor was manually tripped due to a fault on the 8-phase of the main transformer. The turbine tripped automatically based on the reactor trip signal.

Emergency Feedwater (EFW) actuation occurred as expected due to the low-low steam generator water levels which occurred as a result of the reactor trip. The reactor trip was not complex with all systems responding normally post trip. Operations stabilized the plant in Mode 3. Decay heat was removed by the steam generators, utilizing the steam dump system.

Due to the manual Reactor Protection System (RPS) actuation and the automatic actuation of the EFW system, this event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A).

1.0 DESCRIPTION OF THE EVENT

On November 14, 2021, at approximately 1141 EST, VCSNS closed the main generator breaker, conclud ing refueling outage 26. Normal startup was in progress. On November 15, 2021, at approximately 1728 EST with Unit 1 in Mode 1 at 47 percent power, the reactor was manually tripped due to a fault on the 8 -phase of the main transformer (XTF0001). The turbine tripped automatically based on the reactor trip signal. Eme rgency Feedwater (EFW) actuation occurred as expected due to the low - low steam generator water levels which occurred as a result of the reactor trip. The reactor trip was not complex with all systems responding normally post trip. Operations stabilized the plant in Mode 3. Decay he at was removed by the steam gen e rators, utilizing the steam dump system.

There were no other structures, system s, or components (SSCs) tha t were inoperable at the beginning of the even t o r contributed to the event.

Due to the manual Reactor Protection System (RPS) actuation and the automatic actuation of the EFW system, this e vent is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A).

2.0 SIGNIFICANT SAF ETY CONSEQUENCES AND IMPLICATIONS

XTF0001 serves no safety related purpose for the unit. When the transfo rmer failed, all of the appropriate safety systems responded as designed. The main generator, turbine, reactor, and EFW system operated as expected ; and all the control rods fully inserted into the core. The operating crew performed as expected. The event was with in the analysis of the Updated Final Safety Analysis Report Chapter 15. This event did not pose a threat to the health and safety of the public.

Therefore, the safety significance of this issue is very low.

3.0 CAUSE OF THE EVENT

The fault was caused by a failure of the center phase high-voltage bushing. Substantial evidence supports that an electrical failure occurred inside the bushing itself. Failure analysis indicates that it is most probable that the H2 bushing failed due to one or mo re manufacturing defects. Specifically, erroneous layers of paper insulation and a large surface defect on the conductor.

4.0 IMMEDIATE CORRECTIVE ACTIONS

The faulted transformer was removed from service and replaced with the spare ma in transformer. The unit was placed back online with breakers closed on December 10, 2021.

5.0 ADDITIONAL CORRECTIVE ACTIONS

None

6.0 ACTIONS TO PREVENT RECURRENCE

A new high voltage composite bushing design was selected to be utilized in the new replacement transformer design.

A vendor surveillance plan for the manufacturing and testing of the high voltage bushings for the replacement transformer is being developed and will be implemented to provide confidence that manufacturing defects are identified and addressed prior to installation.

7.0 SIMILAR EVENTS

On August 28, 2017, VCSNS Unit 1 automatically tripped due to a turbine trip. The turbine trip was caused by the Main Generator Differential Lockout due to a fault on the center phase, 230 kV lightning arrester, on the main transformer. This is described in LER 2017-003-01 (ML17347A216).

8.0 MANUFACTURER/PURCHASE ORDER NUMBER

The failed center phase high-voltage bushing was manufactured by ABB and is an ABB O+C 230kV 900kV BIL 4000A oil impregnated bushing.

The main transformer was manufactured by Mitsubishi Electric Corporation. The Mitsubishi Design Number is HE11343.

The transformer was purchased under P.O. Number NU-02NN728893.

9.0 ADDITIONAL INFORMATION

None