05000382/LER-2022-005, Engineered Safety Features Actuation System Relay Failure Results in Reactor Trip and Emergency Feedwater Actuation
| ML22361A050 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 08/23/2022 |
| From: | Milster L Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| W3F1-2022-0053 LER 2022-005-00 | |
| Download: ML22361A050 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3822022005R00 - NRC Website | |
text
- ) entergy W3F1-2022-0053 August23,2022 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Leia Milster Manager Regulatory Assurance 504-739-6250 10 CFR 50.73
Subject:
Licensee Event Report 50-382/2022-005-00, Engineered Safety Features Actuation System Relay Failure results in Reactor Trip and Emergency Feedwater Actuation 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) 50-382/2022-005-00 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 Leia Milster, Manager, Regulatory Assurance, at 504-739-6250.
Respectfully, Leia Milster LEM/mrp Entergy Operations, Inc., 17265 River Road, Killona, LA 70057
W3F1-2022-0053 Page 2 of 2 Enclosure: Licensee Event Report 50-382/2022-005-00 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 W3F1-2022-0053 Licensee Event Report 50-382/2022-005-00
Abstract
On June 24, 2022, at 2012 CDT, while Waterford Steam Electric Station Unit 3 was operating in Mode 1 at 100% power, Main Steam Isolation Valve (MSIV) #2 (B train) and Main Feedwater Isolation Valve (MFIV) #2 (B train) closed due to an Engineered Safety Features Actuation Signal (ESFAS) relay failure. This resulted in an uncomplicated, automatic reactor trip and Emergency Feedwater (EFW) system actuation. All reactor control element assemblies properly inserted into the core and the plant was stabilized in Mode 3. The condition was reported on June 24, 2022, at 2344 CDT (Event Number 55963) 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.
This condition is reportable in accordance with 10 CFR 50. 73(a)(2)(iv)(A) as a condition that resulted in a valid actuation of the RPS and EFW.
The direct cause of the relay failure was determined to be a short in the ESFAS relay coil. Corrective actions were taken to replace the relay for both MSIV and MFIV trains A and B prior to returning to power operations.
Plant Conditions
YEAR SEQUENTIAL NUMBER 2022 005 REV NO.
00 At the time of the event, Waterford Steam Electric Station Unit 3 (Waterford 3) was operating in Mode 1 at 100% reactor power. There were no other structures, systems, or components out of service that contributed to this event.
Event Description
On June 24, 2022, at 2012 CDT, the Main Steam Isolation Valve (MSIV) B [ISV] closed, Main Feedwater Isolation Valve (MFIV) B [ISV] closed, MFIV [ISV] A closed. The Control Room Supervisor directed the operators to perform a manual reactor trip, however the reactor automatically tripped before the manual trip could be initiated.
All reactor control element assemblies properly inserted into the core, and all equipment required for shutdown functioned as designed. There were no complications.
The Post Transient Response and Review indicated Emergency Feedwater Actuation Signal (EFAS) 1 & 2 [Channels A, B, C & D] and Emergency Feedwater (EFW) [SJ] A, AB and B actuated at 2012 CDT. Manual control of the EFW Flow Control Valves [FCV] was taken to prevent full flow initiation. Operations noted that Steam Generator (SG) [SG] B pressure met the Technical Specification Steam Line Safety Valve lift setpoints, causing two relief valves to lift as designed. The Reactor Coolant System (RCS) [AB] pressure reached 2300 PSIA due to MSIV B closure. The plant was stabilized in Mode 3.
After the reactor trip, Startup Feedwater Regulating Valve (SUFRV) A and Main Feedwater Regulating Valve (MFRV) A went to Reactor Trip Override position and then to manual. Main Feedwater Pump [Pl A controller went to manual.
However, due to the inadvertent Main Steam Isolation Signal (MSIS), SUFRV Band MFRV B went closed. Later, MFIV A was manually opened when the Auxiliary Feedwater Pump [Pl was started.
The cause of the relay failure was determined to be a short in the relay coil. Voltage readings across the coil were approximately 30 VDC and the relay coil had a high resistance indicating the coil had failed open. The relay is normally energized and closes MSIV Band MFIV B following initiation of a MSIS from the Engineered Safety Features Actuation System (ESFAS). Open-circuit failure of the coil results in de-energizing the relay allowing contacts to return to shelf state. For this relay, the contact closure caused the inadvertent actuation and closure of MSIV Band MFIV B. The valve closure ultimately resulted in the Core Protection Calculators generating a reactor trip signal to the Plant Protection System for the asymmetric steam generator auxiliary trip.
The relay was previously identified as a Single Point Vulnerability (SPV) component where component failure will directly result in a reactor trip. All four relays were replaced for both MSIV and MFIV trains (A and B) with new relays prior to plant start up on June 27, 2022.
Safety Assessment
The actual consequence for the failure of the relay is a reactor trip. The failure of the relay challenges the ESFAS and RPS to automatically trip the reactor. The automatic reactor trip occurred as expected for a failure of the ESFAS relay.
Following the 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 SGs such that there were no actual consequences to general safety of the public, nuclear safety, industrial safety, and radiological safety for this event.
NRG rQRM 366A (08-2020)
Page 2 of 3 U.S. NUCLEAR REGULATORY COMMISSION (08-2020)
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LICENSEE EVENT REPORT (LER)
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CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-<:ollections/nuregs/staff/sr1 022/r~
APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023
- 3. LER NUMBER Waterford Steam Electric Station, YEAR Unit 3 05000- 382 SEQUENTIAL NUMBER REV NO.
2022 005 00 The potential consequence to general safety of the public, nuclear safety, industrial safety, and radiological safety of this event if the automatic reactor trip was removed are very low. Operators are trained in the recognition and response to Anticipated Transients Without Scram and had already initiated steps to manually trip the reactor when the automatic reactor trip occurred.
Event Cause(s):
The direct cause of relay failure was a short in the relay coil. At the time of the event, the preventative maintenance frequency at Waterford 3 was 10 years and the relay had been installed for 8 years.
Corrective Actions
- 1.
Relays were replaced for MSIV and MFIV trains (A and B) with new relays with a manufacturing date of 2019.
- 2.
Reduce preventative maintenance replacement frequency for all SPV ESFAS relays from 10 years to 6 years (or for 4 refueling outages).
- 3.
Validate ESFAS relay SPV elimination modification is scoped into refueling outage 25.
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