05000325/LER-2021-001, Automatic Specified System Actuation Due to Loss of Power to Emergency Bus E3
| ML22020A402 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 01/20/2022 |
| From: | Krakuszeski J Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-21-0344 LER 2021-001-00 | |
| Download: ML22020A402 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3252021001R00 - NRC Website | |
text
(-, DUKE
~ ENERGY January 20, 2022 Serial: RA-21-0344 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Brunswick Steam Electric Plant, Unit Nos. 1 and 2 Renewed Facility Operating License Nos. DPR-71 and DPR-62 Docket Nos. 50-325 and 50-324 Licensee Event Report 1-2021-001 John A. Krakuszeski Vice President Brunswick Nuclear Plant 8470 River Rd SE Southport, NC 28461 o: 910.832.3698 10 CFR 50.73 In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Duke Energy Progress, LLC, is submitting the enclosed Licensee Event Report (LER). This report fulfills the requirement for a written report within sixty (60) days of a reportable occurrence.
This document contains no regulatory commitments.
Please refer any questions regarding this submittal to Mr. Mark DeWire, Manager - Nuclear Support Services, at (910) 832-6641.
Sincerely, John A. Krakuszeski SBY/sby
Enclosure:
Licensee Event Report
U.S. Nuclear Regulatory Commission Page 2 of 2 cc (with enclosure):
Ms. Laura Dudes, NRC Regional Administrator, Region II Mr. Luke Haeg, NRC Project Manager Mr. Gale Smith, NRC Senior Resident Inspector Chair - North Carolina Utilities Commission
Abstract
At 11:25 Eastern Standard Time (EST) on December 6, 2021, during a planned Emergency Diesel Generator (EDG) 3 maintenance outage, with Unit 1 and 2 in Mode 1 at approximately 100% power, electrical power was lost to 4160V emergency bus E-3. By design this resulted in automatic isolation of various Unit 2 Primary Containment Isolation System (PCIS) Group 2, 3, 6, and 10 isolation valves, and Unit 1 PCIS Group 6 isolation valves. EDG 3 received an automatic start signal by design but was under clearance for planned maintenance and therefore did not start.
Electrical power to emergency bus E-3 was lost due to an inadvertent undervoltage signal generated during a planned relay replacement as part of the EDG 3 maintenance outage. During removal of a support bar to facilitate relay replacement, a washer was released contacting terminals directly below the bolt being removed causing control power fuses to blow. This resulted in an undervoltage signal and the loss of electrical power to emergency bus E-3. The washer that was released was not on any design drawings and its location, behind the support bar, precluded viewing and establishment of preventative measures.
Emergency bus E-3 was re-energized on December 6, 2021, at 13:12 EST via its normal power source (i.e., Unit Auxiliary Transformer). There was no impact on the health and safety of the public or plant personnel. The safety significance of this event is minimal.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) due to actuation of the PCIS and EDG 3.
(See Page 3 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
Page 3 of 3 The cause of this event was insufficient rigor in documenting the as-built configuration of the equipment with the washer located behind the support bar. This condition has existed since original plant construction and is considered a historical condition.
Safety Assessment
There was no impact on the health and safety of the public or plant personnel as a result of this event. The safety significance of this event is minimal. The automatic system actuations occurred as expected, and all safety related systems operated as designed.
Corrective Actions
Emergency bus E-3 was re-energized on December 6, 2021, at 13:12 EST via its normal power source (i.e., Unit Auxiliary Transformer [EA]) following replacement of the associated control power fuses. The modified relay support bar was reinstalled on December 7, 2021.
In addition, on December 16, 2021, signs were installed inside the Sync Check Relay cabinets associated with emergency bus E-3 and E-4 identifying the potential for washers to be present behind relay support bars. Also, to prevent recurrence during the remaining Sync Check Relay replacements associated with emergency bus E-1 and E-2, work orders were updated on January 20, 2022, to install signs inside the cabinets identifying the potential for washers to be present behind relay support bars, and to place insulating material behind the terminals of the adjacent relays prior to removing hardware from the relay support bar.
Any revisions to corrective actions will be made in accordance with the sites corrective action program.
Previous Similar Events
A review of events for the past three years identified the following previous similar events related to automatic system actuations during planned maintenance activities.
Event Notification 54144, completed on July 3, 2019, reported an invalid actuation of EDG 1 during planned maintenance when the starting air clearance was being lifted while simultaneously performing a Post Maintenance Test (PMT) where an external DC power source was applied to a relay that provided continuity directly to the starting air solenoids resulting in the energization of the air start solenoids causing EDG 1 to start. The event resulted from insufficient risk recognition for a first time PMT and shortfalls in the scheduling process.
Event Notification 54675, completed on April 22, 2020, reported an invalid actuation of PCIS Group 6 isolation valves during a planned refueling outage. The invalid actuation occurred when power was lost as a result of removal of the inboard isolation logic fuse during a planned clearance hang to support maintenance. The event resulted from inadequate procedure use and adherence in clearance development.
The corrective actions associated with these previous similar events could not have reasonably been expected to prevent the condition reported herein.
Commitments
No regulatory commitments are contained in this report.