ML25063A143
| ML25063A143 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 03/04/2025 |
| From: | Mahesh Chawla Plant Licensing Branch IV |
| To: | Elwood T Ameren Missouri, Union Electric Co |
| Chawla M | |
| References | |
| EPID L-2024-LLR-0084 | |
| Download: ML25063A143 (1) | |
Text
From:
Mahesh Chawla To:
Elwood, Thomas B Cc:
Smith, Erin S; Tony Nakanishi; Matthew Mitchell; John Honcharik; William Orders; Ami Agrawal; Scott Schwind; Nathan Brown; Michael Bloodgood
Subject:
Callaway Plant, Unit 1 - Verbal Authorization of Relief Requests IWE-01 and IWE EPID: L-2024-LLR-0084 Date:
Tuesday, March 4, 2025 10:13:00 AM Attachments:
VERBAL AUTHORIZATION for Callawya non compliance weld repair on metal containment - rev B_030425.docx
Dear Mr. Elwood,
By telephone conversation on March 3, 2025, the U.S. Nuclear Regulatory Commission (NRC) staff provided a verbal authorization to Union Electric Company (dba Ameren Missouri)(the licensee) for the Requests for relief from Inservice Inspection Requirements of American Society of Mechanical Engineers Boiler Pressure Vessel Code (ASME Code),
Section XI. By letter dated December 19, 2024 and supplemented by letters dated February24,2025 and March 3, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML24354A196 (Package), ML25055A152 and ML25062A125 (package), respectively, Union Electric Company (Ameren Missouri, the licensee), proposed an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, paragraph IWE-5221(a) that requires a leakage test, and to paragraph IWA-4412 that requires defects be removed in accordance with the requirements of IWA-4420, for Callaway Plant, Unit 1.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee submitted Alternative Requests, IWE-01 and IWE-02, requesting NRC approval of:
- 1. a proposed alternative, IWE-01, to demonstrate that the Instrument Tunnel Sump (Incore Pit) Liner (SUMPLF07DRWIT) of the metal containment liner will maintain its leak tight integrity without repair in accordance with ASME Code, SectionXI until the units Spring 2025 refueling outage. This alternative will also defer the leakage test until the Spring 2025 refueling outage.
- 2. a proposed alternative, IWE-02, that would require additional examinations to be performed during the Spring 2025 refueling outage to verify the containment is structurally sound and leak tight for the remaining life of the plant.
The NRC staffs evaluation and verbal authorization is repeated in the attachment to this e-mail. The following NRC and licensee personnel participated in the conference call.
NRC
Tony Nakanishi - Chief, Plant Licensing Branch IV (LPL4)
Matthew Mitchell - Chief, Piping and Head Penetrations Branch (NPHP)
John Honcharik - Senior Materials Engineer, NPHP Mahesh Chawla - Project Manager, LPL4 Hannah McLatchie - Project Manager, LPL4
UNION ELECTRIC COMPANY (dba AMEREN MISSOURI)
Kuhlenberg, Jacob P -Director, Nuclear Plant Engineering Hutchison, Jesse J - Manager, Engineering Perry, Greg J - Manager, Nuclear Oversight Elwood, Thomas B - Manager, Regulatory Affairs Sellers, J.C. - Manager, Nuclear Project Management Richardson, Carissa - Supervising Engineer, Engineering Programs Davis, Rigel - Consulting Engineer, Regulatory Initiatives Erin Smith - Consulting Engineer, Licensing and Regulatory Affairs Wunderlich, Nolan - Engineer, Engineering Design
Please contact me if you have any questions.
Mahesh(Mac) Chawla, Project Manager Licensing Branch LPL4 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Phone: (301) 415-8371 Email: Mahesh.Chawla@nrc.gov
OFFICE NRR/DORL/LPL4/PM NRR/DNRL/NPHP/BC NRR/DORL/LPL4/BC NAME MChawla MMitchell TNakanishi DATE 3/4/2025 3/4/2025 3/4/2025
1 VERBAL AUTHORIZATION BY THE OFFICE NUCLEAR REACTOR REGULATION REQUEST TO DEFER INSPECTIONS AND TO DEMONSTRATE LEAK TIGHT INTEGRITY OF METAL CONTAINMENT LINER UNION ELECTRIC COMPANY (AMEREN MISSOURI)
CALLAWAY PLANT, UNIT 1 DOCKET NO. 50-483 March 3, 2025 Technical Evaluation read by Matthew Mitchell, Chief of the Piping and Head Penetration Branch, Office of Nuclear Reactor Regulation By letter dated December 19, 2024 and supplemented by letters dated February 24, 2025 and March 3, 2025 (Agencywide Documents Access and Management System (ADAMS)
Accession Nos. ML24354A196 (Package), ML25055A152 and ML25062A125 (package),
respectively), Union Electric Company (Ameren Missouri, the licensee), proposed an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, paragraph IWE-5221(a) that requires a leakage test, and to paragraph IWA-4412 that requires defects be removed in accordance with the requirements of IWA-4420, for Callaway Plant, Unit 1.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee submitted Alternative Requests, IWE-01 and IWE-02, requesting NRC approval of:
- 1. a proposed alternative, IWE-01, to demonstrate that the Instrument Tunnel Sump (Incore Pit) Liner (SUMPLF07DRWIT) of the metal containment liner will maintain its leak tight integrity without repair in accordance with ASME Code,Section XI until the units Spring 2025 refueling outage. This alternative will also defer the leakage test until the Spring 2025 refueling outage.
- 2. a proposed alternative, IWE-02, that would require additional examinations to be performed during the Spring 2025 refueling outage to verify the containment is structurally sound and leak tight for the remaining life of the plant.
The Instrument Tunnel Sump is a collection point for reactor coolant leakage in containment and is open to containment atmospheric pressure and temperature. The metal liner plate of the Instrument Tunnel Sump is an ASME Code,Section XI, Class CC component, consisting of 1/4" thick carbon steel material (material specification SA-285). The primary function of the metal containment liner is to ensure the structure is leak tight. The post-tensioned concrete containment structure behind the containment liner supports all structural loads, and no credit is taken for the liner for the pressure design of the containment structure. As such, if no concrete voids exist behind the liner plate, the liner is able to perform its leak tight design function with only a few mils of thickness.
During an internal audit in the Fall of 2024, the licensee discovered that a non-ASME Code compliant weld repair was performed to the liner plate of the Instrument Tunnel Sump during
2 the units Fall 2023 refueling outage. The weld repair was not in compliance with Section XI of the ASME Code because:
a pre-weld surface examination per IWA-4422.2.2(a) prior to performing the weld repairs to verify defect removal was not performed and a pneumatic leakage test per IWE-5223 or, alternatively, a bubble test-vacuum box technique per IWE-5224, following the performance of the weld repair was not performed.
To restore compliance with the ASME Code, the plant would have to be shutdown, and the Fall 2023 base metal repair welds would have to be excavated and repaired in accordance with paragraph IWA-4412 which requires defects be removed in accordance with the requirements of IWA-4420.
The licensee has concluded that immediately complying with the specified ASME Code requirement to repair the metal containment liner would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety, noting that unnecessary plant shutdown activities result in additional plant risk, and an unscheduled weld repair may cause additional damage. Additionally, plant personnel would be exposed to higher radiological dose due to performing the pneumatic leakage test in a cold shutdown, rather than refueling, mode. The licensee requested approval of proposed alternative IWE-01 for the duration from the staffs authorization of the alternative through the next refueling outage scheduled for Spring 2025. The licensee requested approval of proposed alternative IWE-02 for the duration from the staffs authorization of the alternative until Callaway's end of plant life or until such a time when base metal repairs on the Instrument Tunnel Sump liner are needed at the previously repaired locations.
To demonstrate that there is reasonable assurance that the containment liner will be able to perform its leak tight design function until the next refueling outage, the licensee provided the following in alternative IWE-01:
Concerning design margin, if no concrete voids exist behind the liner plate, the liner is able to perform its leak tight design function with only a few mils of thickness. The metal liner is located on the base slab of the containment concrete structure which is not in an area where tight rebar lattices exist that may hinder placement of concrete which could result in small voids. However, if a localized 5 diameter concrete void is behind the liner plate, the calculated the minimum wall thickness required for the containment liner is 1/8" (or 0.125"). All of the weld repaired areas were less than 5 in diameter.
The 2023 weld repairs were performed by qualified welders, using qualified procedures and with ASME Code compliant weld filler material.
The completed weld repairs were examined by visual (VT-1) and magnetic particle (MT) surface examinations.
Less than month remains before the start of Callaway's next scheduled refueling outage in the Spring of 2025. Consequently, there is a very low probability of risk to the health and safety of the public during this short duration until compliance with ASME Code,Section XI is restored.
3 The NRC staff finds the licensees identified hardship meets the requirements of 10 CFR 50.55a(z)(2) and reviewed the proposed alternative to determine if it provided an adequate level of quality and safety given this hardship.
The NRC staff finds the licensee demonstrated that there is reasonable assurance that the containment liner will be able to perform its leak tight design function until the next refueling outage, scheduled for Spring 2025, based on the surface examination performed in Fall 2023, and the design margin wall thickness range from a few mils of thickness to a conservative calculated thickness of 1/8 inch. The NRC staff notes that the MT surface examination has some limited subsurface detection capabilities and therefore provides additional assurance of leak tightness, and that there is a very low probability of the liner being called upon for its design leak tightness function until the Spring 2025 refueling outage.
For the base metal repairs to be valid for the remaining plant life, the licensees alternatives, IWE-01 and IWE-02, propose to perform the ASME Code,Section XI, IWE-5221(a) pneumatic leakage test and to perform an ultrasonic examination of the base metal repairs during the Spring 2025 refueling outage. Performance of the leakage test would meet the requirements of Section XI to the ASME Code and restore compliance for this aspect.
Performance of the ultrasonic examination would be used to verify that defects were removed in the weld repair performed during the 2023 refueling outage. In alternative IWE-02, the licensees acceptance criteria using Subsection NE-5330 of Section III of the ASME Code for the ultrasonic examination is acceptable to verify that sound metal meeting the minimum wall thickness requirements calculated by the licensee is satisfied to maintain its leak tightness function. Therefore, the NRC staff finds that acceptable results from the proposed leakage test and ultrasonic examination to be performed in the Spring 2025 refueling outage will provide reasonable assurance that the base metal repairs are acceptable. Re-excavation of the base metal repairs would only be performed if the leakage test fails, or if the ultrasonic results exceed the acceptance criteria in alternative IWE-02 and would be entered into the correction action program of the plant for evaluation and disposition in accordance with the construction code or Section XI of the ASME Code.
In conclusion, given the licensees identified hardship and based on the review of the information provided above, the NRC staff finds that the licensees proposed alternatives to defer the leakage test will provide reasonable assurance that the leak tight integrity of the metal containment will be maintained until the next scheduled refueling outage in Spring 2025 when additional examinations of the containment weld repairs will be performed to demonstrate the leak tight integrity of the metal containment for the remaining life of the plant. The NRC staff also finds that unnecessary plant shutdown activities could result in increased plant risk given the short duration till the next refueling outage, performing repair during an unscheduled shutdown could increase radiological dose to personnel and that an unscheduled weld repair may cause additional damage.
Therefore, the NRC staff finds this is a valid basis for establishing hardship with respect to implementing an ASME Code repair or performing additional examinations prior to the Spring 2025 refueling outage.
Authorization read by Tony Nakanishi, Chief of the Plant Licensing Branch IV, Office of Nuclear Reactor Regulation As Chief of the Plant Licensing Branch IV, Office of Nuclear Reactor Regulation, I agree with the conclusions of the Piping and Head Penetration Branch.
4 The NRC staff concludes that the proposed alternatives, will provide reasonable assurance that the leak tight integrity of the metal containment liner will be maintained until the next scheduled refueling outage in Spring 2025 when additional examinations in the proposed alternatives will be performed to demonstrate the previous weld repair is acceptable for the life of the plant. The NRC staff finds that complying with the requirements of the ASME Code,Section XI would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
Therefore, effective March 3, 2025, the NRC authorizes the use of the proposed alternative IWE-01 at Callaway Plant, Unit 1, from the date of authorization up until completion of the next scheduled refueling outage, scheduled for Spring 2025 and authorizes the use of the proposed alternative IWE-02 from the date of authorization up until Callaway's end of plant life or until such a time when base metal repairs on the Instrument Tunnel Sump liner are needed at the previously repaired locations.
All other requirements in ASME Code,Section XI for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
This verbal authorization does not preclude the NRC staff from asking additional clarification questions regarding the proposed alternative while subsequently preparing the written safety evaluation.