05000260/LER-2021-001-01, Inoperability of a TS-required Main Steam Isolation Valve
| ML21232A618 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 08/20/2021 |
| From: | Rasmussen M Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2021-001-01 | |
| Download: ML21232A618 (9) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2602021001R01 - NRC Website | |
text
Post Office Box 2000, Decatur, Alabama 35609-2000 August 20, 2021 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 2 Renewed Facility Operating License No. DPR-52 NRC Docket No. 50-260
Subject:
Licensee Event Report 50-260/2021-001-01
Reference:
Letter from TVA to NRC, Licensee Event Report 50-260/2021-001-00, dated June 21, 2021 (ML21172A305).
The enclosed Licensee Event Report (LER) provides additional details of a Main Steam Isolation Valve that was inoperable for longer than allowed by plant Technical Specifications (TS) Limiting Conditions of Operability. The Tennessee Valley Authority is submitting this report in accordance with Title 10 of the Code of Federal Regulations 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plants Technical Specifications.
There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Christopher L. Vaughn, Nuclear Site Licensing Manager, at (256) 729-2636.
Respectfully, Matthew Rasmussen Site Vice President Enclosure: Licensee Event Report 50-260/2021-001 Inoperability of a TS-required Main Steam Isolation Valve
U.S. Nuclear Regulatory Commission Page 2 August 20, 2021 cc (w/ Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant NRC Project Manager - Browns Ferry Nuclear Plant
ENCLOSURE Browns Ferry Nuclear Plant Unit 2 Licensee Event Report 50-260/2021-001-01 Inoperability of a TS-required Main Steam Isolation Valve See Enclosed
Abstract
On June 5, 2021, Control Room Operators closed the Main Steam Line C Valves to support the installation of a Temporary Modification. However, the C Inboard Main Steam Isolation Valve (MSIV) [FCV; JM] unexpectedly re-opened after closure. The C Inboard MSIV was declared inoperable upon discovering this condition, since the valve would be unable to close upon receiving a valid PCIS signal. Troubleshooting identified a ground on the C Inboard MSIVs DC solenoid/wiring [FSV] which caused the DC solenoid to remain energized. The wiring to the valve was modified, and the valve was subsequently declared operable.
A Past Operability Evaluation (POE) initially identified an earlier time-of-failure on April 22, 2021, when an Assistant Unit Operator identified a -150 VDC ground on Battery Board [BYBD] 3 [EI] during one of their rounds.
The cause of this event was a grounding issue which prevented the de-energization of the DC solenoid which maintains C Inboard MSIV in an open position. This condition persisted because troubleshooting personnel did not fully understand and address the impact of DC grounds and their effects on DC coils. The DC solenoid input wires were lifted and a tagout/clearance was placed to maintain the solenoid in a de-energized state, so that the C Inboard MSIV would close on demand. Although removal of the 250 VDC control power from the solenoid does not conform with BFN UFSAR Chapter 4.6, all TS functions are maintained, and the C Inboard MSIV is capable of meeting all of its required safety functions. The installed TMOD will mitigate adverse effects until the condition can be permanently addressed during the next refueling or maintenance outage.
Page 6 of 6 C. For failure that rendered a train of a safety system inoperable, estimate of the elapsed time from discovery of the failure until the train was returned to service The C Inboard MSIV was inoperable for forty-four (44) days, from April 22, 2021 to June 5, 2021.
VI.
Corrective Actions
Corrective Actions for this event are being managed under Condition Reports (CRs) 1689113, 1699014, and 1699015.
A. Immediate Corrective Actions
The DC solenoid input wires were lifted and a tagout/clearance was placed to maintain the solenoid in a de-energized state, so that the C Inboard MSIV would close on demand.
Although removal of the 250 VDC control power from the solenoid does not conform with BFN UFSAR Chapter 4.6, all TS functions are maintained, and the C Inboard MSIV is capable of meeting all of its required safety functions.
B. Corrective Actions to Prevent Recurrence or to reduce the probability of similar events occurring in the future The installed TMOD will mitigate adverse effects until the condition can be permanently addressed during the next refueling or maintenance outage.
VII. Previous Similar Events at the Same Site
A search of BFN LERs and CRs found no previous examples of similar events.
VIII. Additional Information
There is no additional information.
IX.
Commitments
There are no new commitments.