05000352/LER-2024-001, Leakage for the Unit 1 `B Outboard Main Steam Isolation Valve Exceeded Technical Specification Limit
| ML24162A324 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 06/10/2024 |
| From: | Gillin M Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LG-24-065 LER 2024-001-00 | |
| Download: ML24162A324 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3522024001R00 - NRC Website | |
text
~ :.~ Constellation
LG-24-065
June 10, 2024
U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Limerick Generating Station, Unit 1 Renewed Facility Operating License No. NPF-39 NRC Docket No. 50-352
Subject: LER 2024-001-00 Unit 1 'B' Main Steam Isolation Valve Exceeded the Technical Specification Allowable Leak Rate
In accordance with the requirements of 10 CFR 50.73(a)(2)(i)(B), Limerick Generating Station hereby submits the enclosed Licensee Event Report.
There are no commitments contained in this letter.
If you have any questions, please contact Jordan Rajan at (610) 718-3400.
Respectfully,
Michael F. Gillin Vice President - Limerick Generating Station Constellation Energy Company, LLC
cc: Administrator Region I, USNRC USNRC Senior Resident Inspector, Limerick Generating Station
Abstract
On April 9, 2024, during Local Leak Rate Testing (LLRT) conducted during the Unit 1 refueling outage (1R20), as-found leakage for the `B' Outboard Main Steam Isolation Valve (MSIV) HV-041-1F028B was 208.9 standard cubic feet per hour (scfh), which exceeded the Technical Specification (TS) 3.6.1.2.c limit of 100 scfh for individual MSIV leakage. The affected MSIV was declared inoperable, and the valve was disassembled to perform internal repairs.
The as-left leak rate following this maintenance was 1.7 scfh.
Based on the preliminary cause, there is evidence that the condition existed during the last operating cycle for longer than allowed by Technical Specification (TS) 3.6.3.a. This condition is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
Unit Conditions Prior To The Event
Limerick Generating Station (LGS) Unit 1 was at 0 percent Rated Thermal Power (RTP) in Operating Condition (OPCON) 5 when the condition was discovered.
Event Description
On April 9, 2024, during Local Leak Rate Testing (LLRT) conducted during the Unit 1 refueling outage (1R20), as-found leakage for the B Outboard Main Steam Isolation Valve (MSIV) HV-041-1F028B [EIIS System / Component Code: SB /
ISV] was 208.9 standard cubic feet per hour (scfh), which exceeded the Technical Specification (TS) 3.6.1.2.c limit of 100 scfh for individual MSIV leakage. The affected MSIV was declared inoperable, and the valve was disassembled to perform internal repairs. The as-left leak rate following this maintenance was 1.7 scfh.
The as-found inspection of HV-041-1F028B identified that the pilot poppet to poppet seat interface was the primary source of the leakage path for the LLRT failure due to several linear indications. The poppet seat was machined to remove the linear indications to reestablish acceptable sealing surface contact with the pilot poppet. The main seat and poppet were also reworked in accordance with station procedures to improve sealing surface contact, and the spring and stem were replaced due to normal wear. Based on the as-found condition, there is evidence that the linear indications existed during the last operating cycle for longer than allowed by Technical Specification (TS) 3.6.3.a. This condition is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
Analysis of the Event
This event was determined to be reportable in accordance with 10CFR50.73(a)(2)(i)(B), Any operation or condition which was prohibited by the plants Technical Specifications. Specifically, TS 3.6.1.2.c requires the leak rate for each individual MSIV to be less than or equal to 100 scfh and the leak rate for all four Main Steam lines to be less than or equal to 200 scfh. Based on the as-found condition and valve leakage history, the leakage rate for HV-041-1F028B was likely above 100 scfh during the last operating cycle; therefore, the valve was inoperable as a primary containment isolation valve.
With one or more of the primary containment isolation valves inoperable, TS 3.6.3.a requires the affected penetration to be isolated by use of at least one de-activated automatic valve secured in the closed position within four hours or be in at least Hot Shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and Cold Shutdown in the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. This action was not met.
This event is not classified as a safety system functional failure since the primary containment isolation capability of the B Main Steam line remained operable.
Safety Consequences
There were no actual consequences to the health and safety of the public for this event. As-found leakage and stroke time testing of the redundant B Inboard MSIV (HV-041-1F022B) was completed in the April 2024 Unit 1 refuel outage with the leak rate below the TS allowable value; thus, the primary containment isolation capability of the B Main Steam line remained operable. Additionally, the as-found minimum path leakage for all four Main Steam lines for the April 2024 Unit 1 refuel outage was below the TS 3.6.1.2 limit of 200 scfh.
Corrective Actions Completed
Corrective maintenance was completed for HV-041-1F028 in accordance with station procedures. The as-left leak rate following this maintenance was 1.7 scfh, which is consistent with historical as left MSIV leak rates following inbody maintenance.
Corrective Actions Planned
Complete a corrective action program investigation to determine the cause of the LLRT failure and any required
corrective actions
Evaluate submitting a license amendment request to change the Limerick TS requirement for MSIV leakage from a
single valve leakage and total valve allowed leakage limit to a steam line leakage and total valve leakage limit consistent
with the requirements of NUREG-1433 Standard Technical Specifications - General Electric BWR/4 Plants
Previous Similar Occurrences
There have been no previous similar licensee event reports in the past ten years.
Component Data
System: SB (Main/Reheat Steam System)
Component: ISV (Valve, Isolation)
Manufacturer: A585 (Attwood & Morrill Company, Inc.)