05000328/LER-2024-001, Reactor Trip Due to an Electrical Trouble Turbine Trip

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Reactor Trip Due to an Electrical Trouble Turbine Trip
ML24269A161
Person / Time
Site: Sequoyah Tennessee Valley Authority icon.png
Issue date: 09/25/2024
From: Marshall T
Tennessee Valley Authority
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
LER 2024-001-00
Download: ML24269A161 (1)


LER-2024-001, Reactor Trip Due to an Electrical Trouble Turbine Trip
Event date:
Report date:
3282024001R00 - NRC Website

text

Sequoyah Nuclear Plant, Post Office Box 2000, Soddy Daisy, Tennessee 37384

September 25, 2024 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 50-328/2024-001-00, Reactor Trip due to an Electrical Trouble Turbine Trip

The enclosed licensee event report provides details concerning an automatic reactor trip due to an electrical trouble 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 50-328/2024-001-00 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 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).

I. Plant Operating Conditions before the Event

At the time of the event, Sequoyah Nuclear Plant (SQN) Unit 2 was in Mode 1 at approximately 94 percent rated thermal power and increasing after a forced outage.

II. Description of Event

A. Event Summary

On July 30, 2024, at 1640 eastern daylight time (EDT), SQN Unit 2 experienced an automatic reactor [EIIS: RCT] trip due to an electrical trouble turbine [EIIS: TRB] trip. The turbine tripped as a result of a generator [EIIS: GEN] neutral resistor overvoltage relay [EIIS: 87] actuation.

Operators performed the appropriate actions in response to the reactor trip. All plant safety systems responded as designed.

The event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an event that resulted in an automatic actuation of the Reactor Protection System [EIIS: JC] and the Auxiliary Feedwater (AFW) System [EIIS: BA].

B. Status of structures, components, or systems that were inoperable at the start of the event and that contributed to the event

No inoperable structures, components, or systems contributed to this event.

C. Dates and approximate times of occurrences

Date/Time (EDT) Description

07/30/24, 1640 SQN Unit 2 experienced an automatic reactor trip due to an electrical trouble turbine trip. The unit entered Mode 3.

D. Manufacturer and model number of each component that failed during the event

The root cause for this event is still under investigation. When the final investigation is complete a supplement will be provided.

E. Other systems or secondary functions affected

No other systems or secondary functions were affected.

F. Method of discovery of each component or system failure or procedural error

Main control room (MCR) alarms and annunciators provided indication to the operators during the reactor trip.

G. The failure mode, mechanism, and effect of each failed component

The root cause for this event is still under investigation. When the final investigation is complete a supplement will be provided.

H. Operator actions

MCR operators responded to the reactor trip, as required, and then transitioned to post-trip response procedures.

I. Automatically and manually initiated safety system responses

The reactor protection system, including feedwater isolation and AFW start, responded to the trip, as designed.

III. Cause of the event

A. Cause of each component or system failure or personnel error

The root cause for this event is still under investigation. When the final investigation is complete a supplement will be provided.

B. Cause(s) and circumstances for each human performance related root cause

The root cause for this event is still under investigation. When the final investigation is complete a supplement will be provided.

IV. Analysis of the event

The reactor trip was not complex with all plant safety systems responded as designed. This event did not adversely affect the health and safety of plant personnel or the general public.

V. Assessment of Safety Consequences

There were no actual safety consequences as a result of this event.

A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event

None.

B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident

The event did not occur when the reactor was shut down.

C. For failure that rendered a train of a safety system inoperable, estimate of the elapsed time from discovery of the failure until the train was returned to service

There was no failure that rendered a train of a safety system inoperable.

VI. Corrective Actions

This event was entered into the Tennessee Valley Authority Corrective Action Program under condition report number 1947208.

A. Immediate Corrective Actions

A work order for troubleshooting the cause of the event was created.

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

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.