05000382/LER-2024-001, Manual Reactor Trip Due to Engineered Safety Features Actuation System Relay Failure

Manual Reactor Trip Due to Engineered Safety Features Actuation System Relay Failure

ML24136A170
Person / Time
Site:	Waterford
Issue date:	05/15/2024
From:	Twarog J Entergy Operations
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
W3F1-2024-0013 LER 2024-001-00
Download: ML24136A170 (1)

LER-2024-001, Manual Reactor Trip Due to Engineered Safety Features Actuation System Relay Failure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
3822024001R00 - NRC Website

text

E) entergy John Twarog Manager Regulatory Assurance 504-739-67 4 7

W3F1-2024-0013 10 CFR 50.73

May 15, 2024

ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject: Licensee Event Report 50-382/2024-001-00, Manual Reactor Trip Due to Engineered Safety Features Actuation System Relay Failure 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) 50-382/2024-001-00 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 and PWR auxiliary or emergency feedwater system actuation.

The LER describes the Engineered Safety Features Actuation System relay failure and subsequent reactor trip and emergency feedwater actuation.

This letter contains no new commitments.

Should you have any questions concerning this issue, please contact me at 504-739-6747.

Respectfully,

John Twarog /1/

JRT/ahv

Entergy Operations, Inc., 17265 River Road, Killona, LA 70057 W3F1-2024-0013 Page 2 of 2

Enclosure: Licensee Event Report 50-382/2024-001-00

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

W3F1-2024-0013

Licensee Event Report 50-382/2024-001-00

Abstract

At 1449 CDT on March 16, 2024, with Waterford Steam Electric Station, Unit 3 (WF3), operating in Mode 1 at approximately 100% power, Main Feedwater Isolation Valve #2, FW-184B, and Main Steam Isolation Valve #2, MS-124B, began closing resulting in steam generator levels lowering. As a result of these indications, control room operators initiated a manual reactor trip. All control element assemblies properly inserted in response to the reactor trip. All safety systems, including the Emergency Feedwater System, performed as designed and there were no complications with the trip.

The cause of the event was a failure of the Steam Generator #2 and Main Steam Line #2 Valves Main Steam Isolation Signal Actuation Relay, K313-A, resulting in the unexpected closing of MS-124B and FW-184B. The relay has been sent to the vendor for analysis. The failed relay was replaced, and the remaining Engineered Safeguard Features Actuation System relays were verified to be from a different batch.

This event is being reported in accordance with 10 CFR 50. 73(a)(2)(iv)(A), as an actuation of the Reactor Protection System and Emergency Feedwater System.

Event Description

At 1449 CDT on March 16, 2024, with Waterford Steam Electric Station, Unit 3 (WF3), operating Mode 1 at 100% power,

Main Feedwater Isolation Valve #2 [SJ:ISV], FW-184B, and Main Steam Isolation Valve #2 [SB:ISV], MS-124B, began closing resulting in steam generator levels lowering. As a result of these indications, control room operators initiated a manual reactor trip. All control element assemblies properly inserted in response to the reactor trip. All safety systems, including the Emergency Feedwater System (EFW) [BAJ, performed as designed and there were no complications with the trip. The condition was reported on March 16, 2024, at 1836 EDT (Event Number 57032) in accordance with 10 CFR 50. 72 (b)(2)(iv)(B) and 10 CFR 50. 72(b)(3)(iv)(A) for a valid Reactor Protection System (RPS) actuation and EFW system actuation.

Following the reactor trip, an acrid odor was detected in the rear of relay cabinet, 3AS Bay 3. The investigation identified that the Tyco, MDR-7034, K313-A relay had failed.

Event Cause

The cause of FW-184B and MS-124B failing closed was due to a degraded relay coil. The K313-A relay, Steam Generator

1. 2 and Main Steam Line #2 Valves Main Steam Isolation Signal Actuation Relay, is part of the Engineered Safeguard Features Actuation System (ESFAS). The relay has been sent for vendor failure analysis. If the results from the vendor analysis indicate a different cause for the failure, then a supplement will be provided.

ESFAS relays were previously identified as Single Point Vulnerabilities (SPV). Elimination of this SPV was scheduled to be completed in WF3's most recent outage (Refuel Outage [RF] 25) however due to a design discrepancy with the Engineering Change the modification was removed from the RF-25 scope.

Safety Assessment

The actual consequence for the relay failure was a reactor trip. The relay failure challenged the ESFAS and Reactor Protection System. Following the manual reactor trip, plant equipment performed as designed. There were no other structures, systems, or components out of service that contributed to this event. EFW responded and provided normal post trip heat removal via the Steam Generators [SG] such that there were no actual consequences to general safety of the public, nuclear safety, industrial safety, or radiological safety for this event.

Corrective Actions

(1) K313-A relay was replaced, and post maintenance testing was completed.

(2) Validated the remaining ESFAS relays are not from the same batch as the failed K313-A relay.

(3) Determine if any ESFAS spare relays in stock are from the same batch as the failed K313-A relay. This action is scheduled for completion by May 31, 2024.

(4) Ensure the Engineering Modification to eliminate the ESFAS relays as SPVs is planned to be scoped for either RF-26 or RF-27. This action is scheduled for completion by September 30, 2024.

Previous Similar Events

LER-2022-005-00, documents of the opposite train failure ESFAS relay, K313-B that resulted in a reactor trip on June 24,2022. The direct cause of the relay failure was a short in the relay coil. After the failure of the relay on June 24, 2022, the site replaced all six Main Steam Isolation Valve and Main Feed Isolation Valve ESFAS relays. Vendor analysis determined the relay coil failed due to a manufacturing defect.