05000382/LER-2024-004-01, Automatic Reactor Trip Due to Lightning Strike
| ML25226A260 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 08/14/2025 |
| From: | Twarog J Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| W3F1-2025-0037 LER 2024-004-01 | |
| Download: ML25226A260 (1) | |
| 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 |
| 3822024004R01 - NRC Website | |
text
John Twarog Manager Regulatory Assurance 504-739-6747 Entergy Operations, Inc., 17265 River Road, Killona, LA 70057 W3F1-2025-0037 10 CFR 50.73 August 14, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-382/2024-004-01, Automatic Reactor Trip Due to Lightning Strike Waterford Steam Electric Station, Unit 3 NRC Docket No. 50-382 Renewed Facility Operating License No. NPF-38 Entergy Operations, Inc. (Entergy) submits the enclosed Licensee Event Report (LER) 50-382/2024-004-01 for Waterford Steam Electric Station, Unit 3 (Waterford 3). The events reported herein are reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A), Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B); Reactor protection system (RPS) including: reactor scram or reactor trip, general containment isolation signals, emergency core cooling systems (ECCS),
emergency feedwater system and emergency ac electrical power systems.
The supplemental report describes an automatic RPS reactor trip due to a lightning strike and revised corrective actions based on the results from a ground grid integrity test.
This letter contains no new commitments.
Should you have any questions concerning this issue, please contact me at 504-739-6747.
Respectfully, John Twarog JRT/rrp Digitally signed by John R. Twarog DN: cn=John R. Twarog, o=Waterford 3 Regulatory Assurance Manager, ou=Waterford 3 Regulatory Assurance,
email=jtwarog@entergy.com Date: 2025.08.14 11:27:24 -05'00' John R.
Twarog
- ) entergy
W3F1-2025-0037 Page 2 of 2 Enclosure: Licensee Event Report 50-382/2024-004-01 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Waterford Steam Electric Station, Unit 3 NRC Project Manager - Waterford Steam Electric Station, Unit 3 Louisiana Department of Environmental Quality
Enclosure W3F1-2025-0037 Licensee Event Report 50-382/2024-004-01
Abstract
On June 16, 2024, at 1233 CDT, Waterford Steam Electric, Unit 3 (WF3) experienced an automatic actuation of the reactor protection system (RPS) due to B channel and D channel Core Protection Calculator (CPC) auxiliary trip signals. Post trip analysis of the CPC revealed that the trip signals were generated by both an Asymmetrical Steam Generator Transient (ASGT) and a Variable Overpower Trip (VOPT). CPC trips were not received on channels A and C.
Prior to the trip, it was noted that multiple lightning strikes had occurred near WF3's grounding grid, with eight strikes recorded between 1232 CDT and 1234 CDT, coinciding closely with the time of the reactor trip.
The analysis of the event concluded that the plant trip was most likely due to multiple lightning strikes in the Waterford 3 area. These lightning strikes introduced a voltage transient to instrumentation that provides input to B and D CPC.
Corrective actions included the performance of an electrical grid ground study to evaluate if reinforcements are required.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50.73(a)(2)(iv)(B).
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Event Description
On June 16, 2024, at 1233 CDT, Waterford Steam Electric, Unit 3 (WF3) experienced an automatic actuation of the reactor protection system (RPS) [JC] due to B and D Core Protection Calculator (CPC) auxiliary trip signals. Post trip analysis of the CPC revealed that the sequence was triggered by both an Asymmetrical Steam Generator Transient (ASGT) and a Variable Overpower Trip. CPC data indicated an intermittent temperature drop on two Reactor Coolant System (RCS) [AB] cold leg Resistance Temperature Detectors (RTDs) [AB:DET] and one RCS hot leg RTD which resulted in calculated reactor power perturbations ranging from 93.72% to 103.28%.
Engineering performed an investigation of the RTDs, the Static Uninterruptible Power Supplies (SUPS) [UJX] which supply power to CPC Channels B and D, and the Process Analog Control cabinets that feed input data to the CPCs from the field. No faults were identified.
Prior to the automatic trip, it was noted that multiple lightning strikes had occurred near WF3's grounding grid, with eight strikes recorded between 1232 CDT and 1234 CDT, coinciding closely with the reactor trip. The motor control centers [MCC] that power the SUPS were evaluated for potential voltage transients induced by lightning strikes, but the Plant Indication (PI) data refresh rate is not fast enough to capture short transients.
This event was reported on June 16, 2024, at 1641 EDT in accordance with 10 CFR 50.72(b)(2)(iv)(B) for an RPS Actuation and 10 CFR 50.72(b)(3)(iv)(A) as a valid actuation of the Emergency Feedwater System (EN 57175). Licensee Event Report, 2024-004, was reported on August 15, 2024 in accordance with 50.73(a)(2)(iv)(A).
Event Cause
Based on industry operating experience, plant data, the lightning strike timing, the Ground Grid Integrity Test, and the Sequence of Events log at WF3, the plant trip was most likely due to the multiple lightning strikes that occurred in the area.
Safety Assessment
The actual consequence of the event was an uncomplicated reactor trip. Following the reactor trip, plant equipment performed as designed. There were no other structures, systems, or components out of service that contributed to this event. The event did not affect the availability of systems needed to maintain safe shutdown conditions, control the release of radioactivity, or mitigate the consequences of an accident.
The potential consequence to general safety of the public, nuclear safety, industrial safety, and radiological safety of this event if the automatic reactor trip was removed are very low. Operators are trained in the recognition and response to Anticipated Transients Without Scram and would initiate steps to manually trip the reactor.
Corrective Actions
(1) Performed a Ground Grid Integrity Test per Institute of Electrical and Electronics Engineers (IEEE) Standard 81, Section 10.2. Results indicated that the existing grounds are adequate for the WF3 grid.
(2) Implement a Core Protection Calculator time delay associated with auxiliary trips to aid in preventing spurious plant trips.
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Page 3 of 3 (04-02-2024)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 04/30/2027 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 1.
FACILITY NAME Waterford Steam Electric Station, Unit 3 050
- 2. DOCKET NUMBER 00382
- 3. LER NUMBER YEAR 2024 SEQUENTIAL NUMBER 004 REV. NO.
01 052 Previous Similar Occurrences None
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