05000335/LER-2024-001, Unplanned Reactor Scram

Unplanned Reactor Scram

ML24269A205
Person / Time
Site:	Saint Lucie
Issue date:	09/25/2024
From:	Mack K Florida Power & Light Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-2024-155 LER 2024-001-00
Download: ML24269A205 (1)

LER-2024-001, Unplanned Reactor Scram

Event date:
Report date:
3352024001R00 - NRC Website

text

September 25, 2024 L-2024 - 155 10 CFR 50.73

U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

Re: St. Lucie Unit 1 Docket No. 50-335 Reportable Event: 2024-01-00 Date of Event: July 28, 2024

Unplanned Reactor Scram

The attached Licensee Event Report, 2024-01, is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.

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,

Ken Mack Director, Regulatory Affairs Florida Power & Light Company

Attachment

cc: St. Lucie NRC Senior Resident Inspector St. Lucie Station NRC Program Manager

Florid a Pow er & Li g h t Company

6501 S. Oc e an Dr iv e, Je n se n Bea ch, FL 3 4957

Abstract

On July 28, 2024, at 1837 EDT, while in Mode 1 with Unit 1 at 100 percent power, the reactor was automatically tripped due to an inadvertent closure of 'A' Main Steam Isolation Valve (MSIV) and both Main Feedwater Isolation Valves (MFIV). The cause of MSIV and MFIV valve closures was due to the failure of a normally energized relay in the Engineered Safety Features Actuation System (ESFAS). The failed relay had not previously been identified as a Single Point Vulnerability and therefore This event was caused by the failure to identify the failed ESFAS relay as a Single Point Vulnerability (SPV). This resulted in an ineffective component replacement strategy. There were no Systems, Structures, or Components that were inoperable at the start of the event that contributed to the event. This event is being reported pursuant of 10 CFR S0.73(a)(2)(iv)(A), System Actuation.

Description of Event

On July 28, 2024, at 1837 EDT, while in Mode 1 with Unit 1 at 100 percent power, the reactor was automatically tripped due to an automatic closure of 'A' Main Steam Isolation Valve (MSIV) and both Main Feedwater Isolation Valves (MFIV).

The cause of MSIV and MFIV valve closures was due to the failure of a normally energized relay in the ESFAS.

Cause of Event

This event was caused by the failure to identify the failed ESFAS relay as a Single Point Vulnerability (SPV). This resulted in an ineffective component replacement strategy.

Safety Significance

This event resulted in an extended unit shutdown and an NRC reportable event. During the trip, auxiliary feedwater actuated as expected. All other systems responded normally post trip with the exception MFIVs. Specifically, due to the MSIV closure signal being initiated, the MFIVs were not able to be repositioned (manually or automatically) within 30 minutes of the event. Therefore, this event meets the NEI 99-02 criteria as an Unplanned Scram with Complications.

This Licensee Event Report is being reported pursuant of 10 CFR 50.73(a)(2)(iv)(A), System Actuation.

This event did not result in a Safety System Functional Failure.

Corrective Actions

The failed relay and the associated ESFAS relays in Unit 1 were replaced prior to startup. ESFAS subcomponents for Unit 1 and Unit 2 will be evaluated to identify any latent SPVs in accordance with site processes.

Similar Events

A review of events over the past 5 years did not identify any unplanned reactor scrams as a result of a failed ESFAS relay.