05000443/LER-2023-001, Automatic Actuation of B Emergency Diesel Generator Emergency Power Sequencer

Automatic Actuation of B Emergency Diesel Generator Emergency Power Sequencer

ML23163A217
Person / Time
Site:	Seabrook
Issue date:	06/12/2023
From:	Strand D NextEra Energy Seabrook
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-2023-081 LER 2023-001-00
Download: ML23163A217 (1)

LER-2023-001, Automatic Actuation of B Emergency Diesel Generator Emergency Power Sequencer

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A)
4432023001R00 - NRC Website

text

NEXTera ENERGY ~

SEABROOK June 12, 2023 L-2023 -081 10 CFR 50.73

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

Re: Seabrook Station Docket No. 50 -443 Reportable Event: 2023-001-00 Date of Event: April 12, 2023

Automatic Actuation of 'B' Emergency Diesel Generator Emergency Power Sequencer

The attached Licensee Event Report 2023-001 is being submitted pursuant to the requirements of 10 CFR 50. 73 to provide notification of the subject event.

Respectfully,

Dianne Strand General Manager, Regulatory Affairs

Attachment

cc: Seabrook Station NRC Senior Resident Inspector Seabrook Station NRC Program Manager

NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874 NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)

Seabrook Station 05000443 1 of 3

4. Title Automatic Actuation of B Emergency Diesel Generator Emergency Power Sequencer

5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved Revision Facility Name Docket Number Month Day Year Year Sequential Number Number Month Day Year n/a05000 I I Facility Name Docket Number 4 12 2023 2023 - 001 -00 6 12 2023 n/a05000

9. Operating Mode 10. Power Level 6 I 0%

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

10 CFR Part 20 ~ 20.2203(a)(2)(vi) 50.36(c)(2) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2201(b) 20.2203(a)(3)(i) 50.46(a)(3)(ii) 50.73(a)(2)(v)(A) 10 CFR Part 73 20.2201(d) 20.2203(a)(3)(ii) 50.69(g) 50.73(a)(2)(v)(B) 73.71(a)(4) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C) 73.71(a)(5) 20.2203(a)(2)(i) 10 CFR Part 21 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D) 73.77(a)(1) 20.2203(a)(2)(ii) 21.2(c) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 73.77(a)(2)(i) 20.2203(a)(2)(iii) 10 CFR Part 50 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 73.77(a)(2)(ii) 20.2203(a)(2)(iv) 50.36(c)(1)(i)(A) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(v) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)

OTHER (Specify here, in abstract or in NRC 366A)

12. Licensee Contact for this LER Licensee Contact Telephone Number (Include area code)

Bob Murrell, Licensing Engineer I 319-651-9496

13. Complete One Line for each Component Failure Described in this Report

Cause System Component Manufacturer Reportable To IRIS Cause System Component Manufacturer Reportable To IRIS X JE PR W120 Y

14. Supplemental Report Expected 15. Expected Month Day Year YES (If yes, complete 15. Expected Submission Date) NO Submission

~ Date Abstract (Limit to 1560 spaces, i.e., approximately 15 single-spaced typewritten lines)

On April 12, 2023, at 11:07, while in Mode 6 at 0% power, a valid actuation of the B Emergency Diesel Generator (EDG) Emergency Power Sequencer (EPS) occurred due to a loss of power to the B train Emergency Bus E6. Troubleshooting determined that the loss of power resulted from spurious operation of EPS Remote Manual Override (RMO) relays that opene d the Unit Auxiliary Transformer (UAT) feeder breaker to Bus E6. Subsequently, the loss of power to Bus E6 resulted in a valid actuation of an EPS starting signal to the B EDG. On April 15, 2023, Emergency Bus E6 Remote Manual Override relays were tested and all functions were found to operate as designed. At the time of this event, the B EDG was removed from service for scheduled maintenance and therefore, did not start. There was minimal impact to the station due the unplanned actuation. However, based on the fact that the B EDG did not actually start, this event had no impact on to the health and safety of the public. In addition, there were no other Structure Systems or C omponents (SSCs) that contributed to this event.

Description

On April 12, 2023, at 11:07, while in Mode 6 at 0% power, a valid actuation of the B Emergency Diesel Generator (EDG) Emergency Power Sequencer (EPS) occurred due to a loss of power to the B train Emergency Bus E6.

Cause of the Event

Complex troubleshooting was performed in accordance with station processes. All potential faults were analyzed utilizing a Support Refute Matrix. Potential faul ts included:

1. Undervoltage Control Circuit Failures (refuted)

2. Actual undervoltage condition on Bus E6 (refuted)

3. Human Performance issues (refuted)

4. Faulty Bus E6 Breaker Protection (refuted)

5. EPS Power Supply Interactions (refuted)

6. Spurious Remote Manual Override Actuation (cause of event)

7. EPS Power Supplies (contributor to event)

Spurious actuation of the EPS Remote Manual Override (RMO) rela ys resulted in opening of the Unit Auxiliary Transformer feeder breaker to Bus E6. This caused a loss of power to Bus E6, which resulted in the valid actuation of the EPS. The spurious actuation of RMO was most likely caused by welding activities being performed in the B Train Essential Swi tchgear Room. A contributing cause is age related degradation of the B EPS Power Supplies. The electr olytic capacitors were at the end of their service life making the power supplies more susceptible t o conducted emissions that were introduced on ground as a result of a welding activity.

Analysis of the Event

This licensee event report is being submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A), Valid System Actuation.

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

Safety Significance

At the time of this event, the B EDG was removed from service for scheduled maintenance and therefore, did not start. The station was in a defueled condition with all fuel in the Spent Fuel Pool.

Spent fuel pool cooling was not impacted by the event. The unex pected actuation did result in minimal impact to the station. However, since the EDG was removed from service and did not acuate, this event had no impact on the health and safety of the public. In addition, there were no other Structures Systems or Components (SSCs) that contributed to this event.

Corrective Actions

On April 15, 2023, testing of the EPS RMO relays was performed, and all components were found to operate as designed. In addition, the EPS power supplies were r eplaced on April 17, 2023.

Similar Events

A review of reportable events dating back 10 years, did not identify any previous events or conditions that involved the same underlying cause as this event.