05000327/LER-2024-002, Reactor Trip Due to a Turbine Trip
| ML24325A507 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 11/20/2024 |
| From: | Marshall T Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 2024-002-00 | |
| Download: ML24325A507 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3272024002R00 - NRC Website | |
text
Sequoyah Nuclear Plant, Post Office Box 2000, Soddy Daisy, Tennessee 37384 November 20, 2024 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Unit 1 Renewed Facility Operating License No. DPR-77 NRC Docket No. 50-327
Subject:
Licensee Event Report 50-327/2024-002-00, Reactor Trip due to a Turbine Trip The enclosed licensee event report provides details concerning an automatic reactor trip due to a turbine trip. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(iv), as an event that resulted in an automatic actuation of the reactor protection system and the auxiliary feedwater system. A supplement to this LER will be submitted following completion of the associated root cause evaluation.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Rick Medina, Site Licensing Manager, at (423) 843-8129 or rmedina4@tva.gov.
Respectfully, Thomas Marshall Site Vice President Sequoyah Nuclear Plant Enclosure: Licensee Event Report 50-327/2024-002-00 cc:
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant
Abstract
On September 29, 2024, at 0556 eastern daylight time, SQN Unit 1 experienced a turbine trip and generator breaker trip while operating at full power. Two main generator protective relays actuated on Unit 1. This caused an automatic reactor trip. It was determined that generator exciter experienced a loss of excitation due to an open winding circuit from stator pole #4 to pole #5.
Operators performed the appropriate actions in response to the reactor trip. During post-trip actions, the motor driven auxiliary feedwater level control valve controller for Loop 1 failed to respond from the main control room. All other plant safety systems responded as expected. This event did not adversely affect the health and safety of plant personnel or the general public.
The root cause for this event is still under investigation. When the final investigation is complete a supplement will be provided with the identified cause and associated corrective action(s). Page 5 of 5 VI.
Corrective Actions
This event was entered into the Tennessee Valley Authority Corrective Action Program under condition report number 1962283.
A. Immediate Corrective Actions
Following complex troubleshooting and vendor input, the following actions were taken:
inspected, tested, and installed a fleet, spare exciter through an engineering change package; inspected, removed, and replaced deficient grout beneath the exciter and #11 bearing sole plate; inspected, chipped, and replaced voided concrete beneath the deficient grout; repaired exciter anchor bolt assembly; aligned the generator to exciter coupling gap to within acceptable tolerances; and performed an evaluation of the Unit 1 main generator health that determined it was acceptable with no challenges.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future The root cause for this event is still under investigation. When the final investigation is complete, a supplement will be provided.
VII. Previous Similar Events at the Same Site
LER 50-327/2024-001-00 was submitted for a similar event. The root cause and corrective actions to prevent recurrence had not been identified prior to this second Unit 1 trip.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.