05000366/LER-2025-001, Primary Containment Inoperable Due to Exceeding Technical Specification Allowable Leakage Limits
| ML25107A275 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 04/17/2025 |
| From: | Busch M Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-25-0075 LER 2025-001-00 | |
| Download: ML25107A275 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3662025001R00 - NRC Website | |
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,>-,, Southern Nuclear Matt Busch Vice President - Plant Hatch April 17,2025 Hatch Nuclear Plant I I 028 Hatch Paricway No11h Baxley.GA 31513 912 537 5859 tel 912 366 2077 fax Docket Nos.: 50-366 NL-25-0075 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant Licensee Event Report 2025-001-00 Unit 2 Primary Containment Penetration Exceeded Maximum Allowable Leakage Rate (La)
Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73 (a)(2)(i)(B), 10 CFR 50.73 (a)(2)(ii)(A), and 10 CFR 50.73(a)(2)(v)(C), Southern Nuclear Operating Company hereby submits the enclosed Licensee Event Report.
This letter contains no NRC commitments. If you have any questions, please contact the Hatch Licensing Manager, Jimmy Collins, at 912.453.2342.
Respectfully submitted, Matt Busch Vice President - Hatch MSB/CJC Enclosure: LER 2025-001-00 Cc:
Regional Administrator, Region II NRR Project Manager - Hatch Senior Resident Inspector - Hatch RTYPE: CHA02.004
Enclosure to NL-25-0075 LER 2025-001-00 Edwin I. Hatch Nuclear Plant Licensee Event Report 2025-001-00 Unit 2 Primary Containment Penetration Exceeded Maximum Allowable Leakage Rate (La)
Enclosure LER 2025-001-00
Abstract
PRIMARY CONTAINMENT DEGRADED At 1111 EST on 02/22/2025, while in MODE 5 at 0% power, during planned Local Leak Rate Testing (LLRT) it was determined that the overall primary containment leakage rate exceeded the allowable limit, La, defined in 10CFR50, Appendix J, "Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors" and specified in the Technical Specifications. Two primary containment isolation valves (PCIVs) in a single penetration exceeded La during LLRT which represented a failure to maintain primary containment integrity.
Preliminarily causal analysis indicates the T-Ring to Disc interface has an excessive clearance which requires increased compression stresses in the T-ring to provide a proper seal. Over time, this results in T-ring relaxation, causing separation between T-Ring and Disc. Preliminary corrective actions included tightening T-ring bracket set screws to compensate for T-ring relaxation, and requiring a higher valve actuator closing torque. The repaired valves were leak rate tested successfully and primary containment was restored to operable status.
EVENT DESCRIPTION
I
- 2. DOCKET NUMBER 00366
- 3. LER NUMBER SEQUENTIAL NUMBER 001 REV NO.
1-G At 1111 EST on 02/22/2025, while in MODE 5 at 0% power, during planned Local Leak Rate Testing (LLRT} it was determined that the primary containment leakage rate exceeded the allowable limit, La, defined in 1 0CFR 50, Appendix J, "Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors" and specified in the Technical Specifications. Two primary containment isolation valves (PCIVs) (EIIS: ISV) in a single penetration exceeded La during LLRT which represents a failure to maintain primary containment integrity.
Failed Components Information
Master Parts List Number: 2T48F309 & 2T48F324 Manufacturer: Fisher Controls Company Model: Fisher Series 9200 Butterfly Valves Type: Isolation Valves
EVENT CAUSE ANALYSIS
A causal analysis is currently being performed to identify the root cause of the leakage. The preliminary cause is the T-Ring to Disc interface has an excessive clearance which requires increased compression stresses in the T-ring to provide a proper seal. This increased mechanical stress results in relaxation (creep, cold flow, compression set) with separation between T-Ring and Disc.
SAFETY ASSESSMENT
There were no actual safety consequences as a result of this event. Although the leakage rate through the degraded primary containment penetration for the as-found condition exceeded La, the primary containment leakage rate was below the level required to significantly impact the Core Damage Frequency and Large Early Release Frequency and was of low safety consequence. Additionally, any leakage past the degraded PCIVs during an actual event would have been filtered through Standby Gas Treatment and released through the main stack. The event was within the accident analysis of the UFSAR Chapter 15.
This event is reportable per 10 CFR 50.73 (a)(2)(ii)(A) because it resulted in one of the plant's principal safety barriers being seriously degraded. This event is also reportable per 10 CFR 50.73 (a)(2)(i)(B) because this is a condition prohibited by Technical Specifications because primary containment was inoperable in excess of the allotted Limited Condition of Operation (LCO) timeframe. Additionally, this event is reportable per 10 CFR 50.73 (a)(2)(v)(C) because it is an event that could have prevented fulfillment of a safety function that is needed to control the release of radioactive material.
CORRECTIVE ACTIONS
Preliminary corrective actions included tightening T-ring bracket set screws to compensate for T-ring relaxation, and requiring a higher valve actuator closing torque. The repaired valves were leak rate tested successfully and primary containment was restored to operable status.
PREVIOUS SIMILAR EVENTS
On February 7, 2023, it was determined that the primary containment leakage rate exceeded the allowable limit (La} under postulated accident conditions through two PCIVs in one penetration. Troubleshooting and investigation efforts identified the vendor supplied T-rings were manufactured incorrectly causing excessive leakage. As a corrective action, correctly manufactured T-rings were installed in the affected valves, LLRTs were performed satisfactorily, and primary containment was restored to operable status. Page 2
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