05000280/LER-2025-001, Failed Relay Caused Reactor Trip
| ML25275A606 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 10/02/2025 |
| From: | Denise Wilson Virginia Electric & Power Co (VEPCO) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 25-250 LER 2025-001-00 | |
| Download: ML25275A606 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2802025001R00 - NRC Website | |
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Abstract
At 18:47 on August 6, 2025, while operating at 100% power, Surry Power Station Unit 1 experienced a spurious Train "B" high consequence limiting safeguards (HI CLS) signal, resulting in a spurious HI CLS initiation, which caused safety injection initiation and subsequent Reactor Trip. Troubleshooting identified that the pick-up coil of the 01-CLS-RLY-3/4-1 B-RELAY (HI CLS TRAIN 1 B RELAY) had failed due to a defective soldered joint made up during manufacturing; this was the cause of the event. All safety systems responded as designed, given the spurious signal.
The relay was replaced, and the unit restored to critical on August 10, 2025. The relay failure would not have prevented any safety system from performing its normal function. The health and safety of the public were not affected by this event. This report is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A).
1.0 Description of the Event
- 2. DOCKET NUMBER
- 3. LER NUMBER I
00280 r::::7 NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 001 1-L On Wednesday, August 6, 2025, at 1847 hours0.0214 days <br />0.513 hours <br />0.00305 weeks <br />7.027835e-4 months <br />, Unit 1 reactor automatically tripped from 100% power due to a (spurious)
"B" Train high consequence limiting safeguards (HI CLS) [EIIS: JE] signal. "B" Train Safety Injection (SI) initiated, and a Reactor Trip signal was generated. All engineered safeguards function (ESF) systems responded as designed, all plant systems responded as expected, and no equipment malfunctions were noted at the time of the trip. The team proceeded through the Emergency Procedure network to restore normal parameters and systems. Off-site power remained available during the event. Unit 2 was at 100% power, 883 MWe and remained unaffected by the Unit 1 event.
The HI CLS actuation signal is "de-energize to function", ensuring that a de-energization of the relays associated with the initiation signal of 3 out of 4 containment pressure channel indications> 17.7 psia will generate a Safety Injection signal and selected containment isolation signal on the affected train(s) to provide protection for a Loss of Coolant Accident (LOCA) and/or a Steam Line Break inside containment. The plant parameters associated with the initiation signal for HI CLS were normal; all containment pressure protection channels indicated approximately 10 psia. No other component or instrument failures are attributed to this event.
The relay de-energization is attributed to a relay coil failure of 1-CLS-RLY-3/4-18 [EIIS: JE, RLY]. Upon investigation, 135 VDC was being supplied to the coil which is normal power supply for the coil to be energized. With power available and the relay coil in the deenergized state, coil failure is indicated. The relay is an NBFD65NR model relay, supplied by Westinghouse, most recently inspected in 2022, and most recently replaced in 2021. The relay was replaced and tested under normal work management processes, and completed on August 8, 2025.
The reactor was restored to critical operations on August 10, 2025, four days after the trip. There were no inoperable structures, systems or components that contributed to this event.
2.0 Significant Safety Consequences and Implications
The failure of this relay did not prevent any safety systems from performing their normal function.
3.0 Cause of the Event
The Unit 1 Reactor Trip was the result of the pick-up coil failure on 01-CLS-RL Y-3/4-18-RELA Y, resulting in a spurious HI CLS initiation, which caused a safety injection initiation and subsequent Reactor Trip. The relay failed due to a defective cold soldered joint, which occurred during manufacturing and was inaccessible for visual inspection upon receipt without disassembly of the relay.
4.0 Immediate Corrective Action
Operators used the appropriate emergency operating procedures to stabilize the plant.
The relay was replaced and tested under normal work management processes, completed on August 8, 2025.
The unit was restored to critical operations on August 10, 2025.
5.0 Actions to Prevent Recurrence I
- 2. DOCKET NUMBER
- 3. LER NUMBER IB SEQUENTIAL REV NUMBER NO.
00280
- - I 1-LJ 001 The station intends to modify the purchasing process to require manufacturers to provide documentation to prove adequacy of internal solder joints on single point vulnerability components.
6.0 Similar Events
The station found that over the last 15 years there was only one instance of an NBFD65NR relay failure. For the one event, Robinson number 2 in 2015 (IRIS number 320473), the failure was a random failure based on the relay being in service for twenty-six months at the time of failure. This is the only record of a failure of this type of relay. The NBFD65NR relay used in that application did not result in a Reactor Trip because it was not in a single point vulnerability configuration.
The relay is a normally energized control relay connected in parallel with an identical relay that, when both relays are de-energized, initiates a Reactor Trip for the Reactor Protection Train "A".
7.0 Additional Information
The health and safety of the public were not affected by this event. There was no impact to Unit 2. Page 3
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