05000328/LER-2024-001-01, Reactor Trip Due to an Electrical Trouble Turbine Trip
| ML25182A055 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/01/2025 |
| From: | Michael K Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 2024-001-01 | |
| Download: ML25182A055 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3282024001R01 - NRC Website | |
text
Sequoyah Nuclear Plant, Post Office Box 2000, Soddy Daisy, Tennessee 37384 July 1, 2025 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Unit 2 Renewed Facility Operating License No. DPR-79 NRC Docket No. 50-328
Subject:
Licensee Event Report 50-328/2024-001-01, Reactor Trip due to an Electrical Trouble Turbine Trip
References:
1.
TVA letter submitted to NRC dated September 25, 2024, Licensee Event Report 50-328/2024-001-00, Reactor Trip due to an Electrical Trouble Turbine Trip.
2.
TVA letter submitted to NRC dated March 26, 2025, Licensee Event Report 50-328/2024-001-01, Reactor Trip due to an Electrical Trouble Turbine Trip, Update Letter.
3.
TVA letter submitted to NRC dated April 30, 2025, Licensee Event Report 50-328/2024-001-01, Reactor Trip due to Electrical Trouble Turbine Trip, Second Update Letter.
The enclosed licensee event report has been revised with supplemental information concerning an automatic reactor trip due to an electrical trouble turbine trip. This revised report reflects the results of the causal analysis and associated corrective actions. This event was previously reported 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. Changes to the Reference 1 report are indicated by revision bars on the right-side margin of the page.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Rick Medina, Site Compliance Manager, at (423) 843-8129 or rmedina4@tva.gov.
Respectfully, Kevin Michael Site Vice President Sequoyah Nuclear Plant Michael, Kevin Mckinley Digitally signed by Michael, Kevin Mckinley Date: 2025.07.01 07:47:54 -04'00'
U.S. Nuclear Regulatory Commission Page 2 July 1, 2025 Enclosure: Licensee Event Report 50-328/2024-001-01 cc:
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant
Abstract
On July 30, 2024, at 1640 eastern daylight time (EDT), SQN Unit 2 experienced an automatic reactor trip due to an electrical trouble turbine trip. The turbine tripped as a result of a generator neutral resistor overvoltage relay actuation.
Operators performed the appropriate actions in response to the reactor trip. All plant safety systems responded as designed. This event did not adversely affect the health and safety of plant personnel or the general public.
The event was caused by a hydrogen blower failure due to inadequate stationary blade screw staking.
Corrective actions for the event include modifying the Main Generator hydrogen blower shroud to change the natural resonance frequency away from 120 Hertz, this will reduce cyclic loading on the screws; revising Main Generator preventive maintenance instructions to provide guidance for thread staking of stationary blade screws; and revising the maintenance procedure providing guidance regarding assembling and tensioning threaded connections to add detailed guidance for screw staking.
Page 5 of 5 B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future Corrective actions for the event include modifying the main generator hydrogen blower shroud to change the natural resonance frequency away from 120 Hertz, this will reduce cyclic loading on the screws; revising Main Generator preventive maintenance instructions to provide guidance for thread staking of stationary blade screws; and revising the maintenance procedure providing guidance regarding assembling and tensioning threaded connections to add detailed guidance for screw staking.
To aid in earlier detection the following actions have been taken: (1) seismic vibration limits and associated actions have been established, (2) Main Generator Shaft Voltage monitoring has been installed to allow trending, and (3) the generator core monitoring configuration has been changed to allow automatic sampling during verified alarms and to provide operator guidance to remove the unit from service.
VII. Previous Similar Events at the Same Site
There were no previous similar events at SQN occurring within the last three years.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.