05000250/LER-2025-001, Lightning Caused Turbine Control System Failures Resulting in Reactor Trip
| ML25274A076 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 10/01/2025 |
| From: | Mack K Florida Power & Light Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-2025-173 LER 2025-001-00 | |
| Download: ML25274A076 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2502025001R00 - NRC Website | |
text
U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington DC 20555-0001 RE: Turkey Point Nuclear Plant, Unit 03 Docket No. 50-250 Subsequent Renewed Facility Operating License DPR-31 Reportable Event: 2025-01-00 Date of Event: August 9, 2025 October 01, 2025 L-2025-173 10 CFR 50.73 Lightning Caused Turbine Control System Failures Resulting in Reactor Trip The attached Licensee Event Report (LER), Turkey Point Unit 03 LER 2025-01 -00, Lightning Caused Turbine Control System Failures Resulting in Reactor Trip, is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv)(A), System Actuation.
This event did not have an adverse effect on the health and safety of the public.
Should you have any questions regarding this submission, please contact Maribel Valdez, Fleet Licensing Manager, at 561-904-5164.
This letter contains no new or modified regulatory commitments.
Sincerely, Kenneth A. Mack Director, Licensing and Regulatory Compliance Florida Power and Light Company Attachment: Turkey Point Unit 3 LER 2025-01-00, Lightning Caused Turbine Control System Failures Resulting in Reactor Trip cc:
USNRC Regional Administrator, Region II USNRC Project Manager, Turkey Point Nuclear Plant USNRC Senior Resident Inspector, Turkey Point Nuclear Plant Mr. Clark Eldredge, Florida Department of Health Florida Power & Light Company 9760 SW 344th Street, Homestead, FL 33035
Attachment Turkey Point Unit 03 LER 2025-01-00 Lightning Caused Turbine Control System Failures Resulting in Reactor Trip (2 pages follow)
Abstract
At 1113 EDT on August 9, 2025, Turkey Point Unit 03 reactor automatically shut down while in Mode 1 at 100% power as the result of losing turbine trip header pressure inputs and the turbine tripping off-line. The event was analyzed as having low safety significance. The reactor shut down was uncomplicated with all safety systems responding as required. An actuation of the Auxiliary Feed Water (AFW) system occurred during the trip. The AFW System automatically started as designed. The turbine trip was most likely caused by a lightning induced voltage transient that resulted in the failure of three Turbine Control System (TCS) emergency trip solenoid valves and clearing of their respective fuses. The affected solenoid valve coils and fuses were replaced and tested satisfactorily. On August 11, 2025, Unit 03 was restarted and placed back on-line. Forensics analysis was performed on the solenoid valves and results are consistent with a large induced voltage. Due to the Unplanned Reactor Trip and Autostart of the AFW System, this event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A), System Actuation.
Description of Event
D 050 052
- 2. DOCKET NUMBER
- 3. LER NUMBER I
00250 D
NUMBER NO.
I YEAR SEQUENTIAL REV
~-I 001 1-0 At 1113 EDT on August 9, 2025, Turkey Point Unit 03 reactor automatically shut down while in Mode 1 at 100% power as the result of losing turbine trip header pressure inputs and the turbine [EIIS: TA] tripping offline. The reactor shut down was uncomplicated with all safety systems responding as required. An actuation of the Auxiliary Feed Water (AFW) system occurred during the trip. The AFW System automatically started as designed. The turbine trip was most likely caused by a lightning induced voltage transient that resulted in the failure of three Turbine Control System (TCS) emergency trip solenoid valves [EIIS: SOL], Parker Hannifin Co. [EIIS: P070] Part# HY15-3502/US and clearing of their respective fuses. The affected solenoid valve coils and fuses were replaced and tested satisfactorily. No Inoperable SSCs contributed to the event. On August 11, 2025, Unit 03 was restarted and placed back online.
Cause of the Event
Trip Block Emergency Trip Solenoid Valves SV-3-3451 Channel A (CH-A), SV-3-3452 Channel B (CH-B), SV-3-3453 (CH-B) de-energized resulting in PTN Unit 03 reactor trip by a turbine trip was most likely caused by a lightning induced voltage transient that shorted the solenoid coils.
Analysis of the event
The event was analyzed as having low safety significance. All safety systems functioned as designed during the reactor trip. The Reactor Protection System properly responded to the turbine trip signal by automatically shutting down the reactor. No safety systems were challenged beyond their design basis. The event did not result in any safety system functional failures or violate any Technical Specification limiting conditions for operation. The rapid identification and replacement of the failed solenoid valves restored normal plant configuration. Post-event testing confirmed proper operation of all affected systems. The Turbine Trip Block Solenoids are not safety related components and perform no SR function.
Corrective Actions
Replaced failed Trip Block Emergency Trip Solenoid Valve Coils SV-3-3451 (CH-A), SV-3-3452 (CH-B), SV-3-3453 (CH-B) and addressed the condition of the 3 failed shorted solenoid coil fuses.
Replaced fuses to outputs on Chassis 2 board 7 output 3; Chassis 3 board 7 outputs 2; and Chassis 3 board 7 output 3.
This addresses the condition of the 3 blown fuses.
Planned Actions:
Evaluate additional surge protection devices on critical solenoid circuits to address possible need to increase protection against voltage spikes that caused the solenoid failures.
Similar Events
The forensic analysis conducted on the failed solenoid components confirmed that the lightning-induced voltage transient was the most likely cause of the solenoid failures. No other similar events involving trip block solenoid failures have been identified at Turkey Point Nuclear Generating Station within the past three years. Page 2
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