05000325/LER-2020-002-01, Technical Specification Required Shutdown Due to Unidentified Leakage
| ML20322A021 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 11/17/2020 |
| From: | Krakuszeski J Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RA-20-0326 LER 2020-002-01 | |
| Download: ML20322A021 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3252020002R01 - NRC Website | |
text
November 17, 2020 d_~ DUKE
~ ENERGY Serial: RA-20-0326 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Brunswick Steam Electric Plant, Unit No. 1 Renewed Facility Operating License No. DPR-71 Docket No. 50-325 Licensee Event Report 1-2020-002, Revision 1 John A. Krakuszeski Vice President Brunswick Nuclear Plant 8470 River Rd SE Southport, NC 28461 o: 910.832.3698 10 CFR 50.73
Reference:
Brunswick, Unit 1, LER 1-2020-002, "Technical Specification Required Shutdown due to Unidentified Leakage," Revision 0, May 18, 2020, ADAMS Accession Number ML20140A004 In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Duke Energy Progress, LLC, is submitting the enclosed Revision 1 to Licensee Event Report (LER) 1-2020-002 (i.e., Reference). This revision provides the results of the completed cause evaluation.
This document contains no regulatory commitments.
Please refer any questions regarding this submittal to Ms. Sabrina Salazar, Manager - Nuclear Support Services, at (910) 832-3207.
Sincerely, John A. Krakuszeski SBY/sby
Enclosure:
Licensee Event Report 1-2020-002, Revision 1
U.S. Nuclear Regulatory Commission Page 2 of 2 cc (with enclosure):
Ms. Laura Dudes, NRC Regional Administrator, Region II Mr. Andrew Hon, NRC Project Manager Mr. Gale Smith, NRC Senior Resident Inspector Chair - North Carolina Utilities Commission
Abstract
At 12:05 Eastern Daylight Time on March 24, 2020, with Unit 1 in Mode 1, at approximately 22% power, coming out of a refueling outage, a Technical Specification required shutdown was initiated due to increased drywell leakage. The reactor was shutdown in accordance with normal shutdown procedures. Reactor water level reached low level 1 (LL1) following the shutdown. Per design, the LL1 signal resulted in automatic actuation of the Primary Containment Isolation System with closure of Group 2, 6, and 8 isolation valves. The shutdown was uncomplicated and all control rods inserted as expected.
The increased drywell leakage was a result of an intermediate-position failure of Safety Relief Valve 1F in conjunction with opening of the associated vacuum breaker. The cause of this failure was determined to be susceptibility of the Target Rock two stage Safety Relief Valve design to fretting wear of the main disc stem to piston connection when the associated main body is subjected to a high number of cycles during testing, resulting in displacement of the piston and galling in the main body piston guide. Safety Relief Valve 1F pilot and main valve were replaced and retested upon restart from the reactor shutdown.
There was no impact on the health and safety of the public or plant personnel. This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(A) due to the completion of a Technical Specification required shutdown, and 10 CFR 50.73(a)(2)(iv)(A) due to valid actuation of the Primary Containment Isolation System.
(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/)
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Safety Assessment
There was no adverse impact on the health and safety of the public. The safety significance of this event is minimal. The reactor was shutdown in accordance with plant procedures and all safety related systems operated as designed.
Corrective Actions
The vacuum breaker associated with SRV 1F was inspected and confirmed to be operating properly. SRV 1F pilot and main valve were replaced and retested upon restart from the reactor shutdown.
While there is no specified design limit provided by Target Rock for the number of cycles of a two stage SRV main body, and no consistent industry standard for limiting main body cycles, engineering judgement was applied to vendor information for a similar Target Rock SRV design, and a threshold of 24 cycles was established for considering an SRV at risk for damage by this failure mode. All other Unit 1 SRVs were confirmed to be below this threshold.
In addition to the aforementioned completed corrective actions, the following corrective actions are currently planned.
- Five SRVs on Unit 2 have been identified with main bodies that have been cycled during testing 24 or more times.
The four SRVs with the most cycles will be replaced in the 2021 refueling outage.
The other SRV with greater than 24 cycles will be replaced in the 2023 refueling outage.
All five of these SRVs were lifted with no issues as part of testing during startup from the 2019 refueling outage, thereby providing confidence in their continued operation. Regarding the SRV that will remain installed until the 2023 refueling outage, additional confidence in its acceptability is provided based on it having an improved flex piston design and being replaced on an accelerated schedule.
Any changes to corrective actions or completion schedules will be made in accordance with the sites corrective action program.
Previous Similar Events
No events have occurred within the past three years in which increased drywell leakage from an SRV failure resulted in a LER.
Commitments
No regulatory commitments are contained in this report.