05000395/LER-2025-001, (Vcsns), Manual Reactor Trip Due to Unisolable EHC Leak
| ML25097A291 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 04/07/2025 |
| From: | Jenkins B Dominion Energy, Dominion Energy South Carolina |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 25-107 LER 2025-001-00 | |
| Download: ML25097A291 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3952025001R00 - NRC Website | |
text
Dominion Energy South Carolina, Inc Virgil C. Summer Nuclear Station Bradham Boulevard & Highway 215, Jenkinsville, SC 29065 Mailing Address:
P.O. Box 88, Jenkinsville, SC 29065 Dominion Energy.com April 7, 2025 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555 DOMINION ENERGY SOUTH CAROLINA, INC.
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Serial No.: 25-107 VCS-LIC/JB RO Docket No. 50-395 License No. NPF-12 VIRGIL C. SUMMER NUCLEAR STATION UNIT 1 (VCSNS)
LICENSEE EVENT REPORT 2025-001-00 MANUAL REACTOR TRIP DUE TO UNISOLABLE EHC LEAK Dominion Energy South Carolina, Inc. hereby submits VCSNS Licensee Event Report (LER) 2025-001-00. This report documents a manual reactor trip due to an unisolable electro-hydraulic control (EHC) power system leak on February 10, 2025.
Should you have any questions, please call Mr. Justin Bouknight at (803) 941-9828.
Sincerely,
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BethJe~-~
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 11 G. Miller - NRC Project Mgr.
NRC Resident Inspector J. N. Bassett-INPO Marsh USA, Inc.
Abstract
On February 10, 2025, at 1216 ET, V.C. Summer Nuclear Station manually tripped the reactor due to an unisolable electro-hydraulic control (EHC) power system leak. During performance of PTP-102.001, "Main Turbine Tests," a leak was identified in a pressure gauge line on the turbine EHC pump discharge header.
The leak was not able to be isolated and the main turbine load was immediately lowered, prior to manually tripping the reactor. The trip was not complex, with all systems responding normally post-trip. The 1/4" stainless steel tubing and fittings were replaced, prior to plant startup on February 12, 2025.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A).
1.0 DESCRIPTION OF THE EVENT
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395 YEAR SEQUENTIAL REV D
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~-I 001 1-0 On February 10, 2025, at 1216 ET, V.C. Summer Nuclear Station (VCSNS) identified an unisolable electro-hydraulic control (EHC) power system leak on the Main Turbine Control and Protection System. Operators immediately lowered Main Turbine load, prior to manually tripping the reactor from 67% power due to lowering fluid volume in the EHC reservoir. Emergency feedwater actuated and removed decay heat utilizing the condenser steam dump valves.
The leak occurred during scheduled turbine testing, in accordance with test procedure PTP 102.001, "Main Turbine Tests." A through-wall leak had developed in a section of 1/4" stainless steel tubing from the EHC fluid pump discharge header supplying a pressure indicator and transmitter.
Engineering evaluation determined the leak was caused by a loosening of a clamp over time. Normal vibration from the EHC fluid pumps caused movement between the tubing and clamp, leading to a loss of wall thickness until its failure on February 10, 2025. The line was replaced with new 1 /4" stainless steel tubing and fittings, prior to plant startup on February 12, 2025.
This event is being reported in accordance with 10 CFR 50. 73(a)(2)(iv)(A) due to actuation of the reactor protection and emergency feedwater systems.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS
The leak caused a loss of EHC fluid on the Turbine Control and Protection System. EHC fluid is used to operate the Main Turbine steam valves, which control speed/load during normal operation and protect the turbine during a trip.
3.0 CAUSE OF THE EVENT
Fretting and wall thinning of the tubing above the EHC skid top plate occurred due to loosening of the clamp over time.
Normal vibration of the EHC Fluid pumps caused relative movement between the tubing and clamp, which led to wear and loss of wall thickness to the point of failure.
4.0 CORRECTIVE ACTIONS
The affected section was replaced with new 1/4" stainless steel tubing/fittings and the remainder of the EHC system was inspected for similar fretting conditions.
Preventative maintenance practices will be updated to include routine physical inspection of the tubing, clamps, and supports on the EHC Skid.
Potential Consequential Event systems/components will be reviewed for high pressure fluid tubing exposed to vibration and corrective actions implemented, as required.
5.0 SIMILAR EVENTS
No similar events were identified within the last three years.
6.0 COMPONENT 1/4" Stainless Steel EHC Fluid Tubing and Tubing Clamp.
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