ML24318C256
| ML24318C256 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 11/13/2024 |
| From: | Mahesh Chawla NRC/NRR/DORL/LPL4 |
| To: | Elwood T Ameren Missouri |
| References | |
| L-2024-LRO-0009 | |
| Download: ML24318C256 (5) | |
Text
From:
Mahesh Chawla Sent:
Wednesday, November 13, 2024 9:29 AM To:
Elwood, Thomas B Cc:
Greg Makar; David Rudland; Tony Nakanishi; Steven Bloom; Paul Klein; Lauren Gibson; Andrew Siwy (He/Him); Chris Tyree (He/Him); William Orders; Nathan Brown; Scott Schwind (He/Him); Ami Agrawal; Michael Bloodgood
Subject:
FINAL - Request for Confirmation of Information - Callaway License Renewal Commitments 34 & 35 - EPID: L-2024-LRO-0009 Attachments:
RCI-10428-R1-FINAL.docx
Dear Mr. Elwood,
By letter dated December 20, 2023, (Agencywide Documents Access and Management Systems (ADAMS) Package Accession No. ML23354A244), Ameren Missouri (the licensee),
submitted to the U.S. Nuclear Regulatory Commission (NRC or staff) a response to Commitment Nos. 34 and 35 of the Callaway, Unit 1 (Callaway) license renewal safety evaluation report. Commitment No. 34 is related to a concern regarding potential failure at the divider plate welds to primary head and tubesheet cladding. Commitment No. 35 is related to a concern regarding potential failure of primary-to-secondary pressure boundary due to PWSCC cracking of tube-to-tubesheet welds. To address both commitments, the licensee selected Option 2: Analysis. The December 20, 2023, letter included Enclosure 1, Cracking Assessment for Framatome RSG Channel Head Assembly (ML23354A246), which describes the analyses. An audit plan was issued on May 7, 2024 (ML24122A150). On September 11, 2024, the NRC staff issued audit questions for the subject commitments. The licensee provided draft information via an electronic portal. The NRC staff conducted an audit of license renewal commitments 34 and 35, and discussed on October 22, 2024, the audit information provided by the licensee via portal.
As a follow up to the audit discussion, the NRC staff transmitted a draft request for confirmation of information (RCI), which was sent to you on November 8, 2024. A clarification teleconference was held with the NRC staff on November 12, 2024, to discuss the subject draft RCI. The discussion led to a minor revision in the write up of the RCI. A revised Final RCI is attached to this email for your review and response. The licensee agreed to provide response on the docket prior to December 6, 2024. In case of any questions, please contact me. Thanks 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
Hearing Identifier:
NRR_DRMA Email Number:
2642 Mail Envelope Properties (SJ0PR09MB10405BCDFDE174884DCCBE704F15A2)
Subject:
FINAL - Request for Confirmation of Information - Callaway License Renewal Commitments 34 & 35 - EPID L-2024-LRO-0009 Sent Date:
11/13/2024 9:29:15 AM Received Date:
11/13/2024 9:29:00 AM From:
Mahesh Chawla Created By:
Mahesh.Chawla@nrc.gov Recipients:
"Greg Makar" <Gregory.Makar@nrc.gov>
Tracking Status: None "David Rudland" <David.Rudland@nrc.gov>
Tracking Status: None "Tony Nakanishi" <Tony.Nakanishi@nrc.gov>
Tracking Status: None "Steven Bloom" <Steven.Bloom@nrc.gov>
Tracking Status: None "Paul Klein" <Paul.Klein@nrc.gov>
Tracking Status: None "Lauren Gibson" <Lauren.Gibson@nrc.gov>
Tracking Status: None "Andrew Siwy (He/Him)" <Andrew.Siwy@nrc.gov>
Tracking Status: None "Chris Tyree (He/Him)" <Christopher.Tyree@nrc.gov>
Tracking Status: None "William Orders" <William.Orders@nrc.gov>
Tracking Status: None "Nathan Brown" <Nathan.Brown@nrc.gov>
Tracking Status: None "Scott Schwind (He/Him)" <Scott.Schwind@nrc.gov>
Tracking Status: None "Ami Agrawal" <ami.agrawal@nrc.gov>
Tracking Status: None "Michael Bloodgood" <Michael.Bloodgood@nrc.gov>
Tracking Status: None "Elwood, Thomas B" <TElwood@ameren.com>
Tracking Status: None Post Office:
SJ0PR09MB10405.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 2073 11/13/2024 9:29:00 AM RCI-10428-R1-FINAL.docx 25681 Options Priority:
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1 REQUEST FOR CONFIRMATION OF INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION CALLAWAY LICENSE RENEWAL COMMITMENTS 34 & 35 UNION ELECTRIC COMPANY CALLAWAY, UNIT 1 DOCKET NO. 05000483 ISSUE DATE: N/A Question 1
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Background===
In March 2015, the NRC published the final Safety Evaluation Report Related to the License Renewal of Callaway Plant, Unit 1, as NUREG-2172 (ML15068A342). In NUREG-2172, Appendix A, Callaway Plant Unit 1 License Renewal Commitments, Commitment No. 34 provides for three options to fulfill the commitment, and Commitment No. 35 provides for two options to fulfill the commitment. By letter dated December 20, 2023, (Agencywide Documents Access and Management Systems (ADAMS) Package Accession No. ML23354A244), Ameren Missouri (the licensee), submitted to the U.S. Nuclear Regulatory Commission (NRC or staff) a response to Commitment Nos. 34 and 35 of the Callaway, Unit 1 (Callaway) license renewal safety evaluation report. Commitment No. 34 is related to a concern regarding potential failure at the divider plate welds to primary head and tubesheet cladding. Commitment No. 35 is related to a concern regarding potential failure of primary-to-secondary pressure boundary due to PWSCC cracking of tube-to-tubesheet welds. To address both commitments, the licensee selected Option 2: Analysis. The December 20, 2023 letter included Enclosure 1, Cracking Assessment for Framatome RSG Channel Head Assembly (ML23354A246), which describes the analyses.
Regulatory Basis Section 54.21(a)(3) of Title 10 of the Code of Federal Regulations (10 CFR) requires an applicant to demonstrate that the effects of aging for structures and components will be adequately managed so that the intended function(s) will be maintained consistent with the current licensing basis for the period of extended operation. One of the findings that the NRC staff must make to issue a renewed license (10 CFR 54.29(a)) is that actions have been identified and have been or will be taken with respect to managing the effects of aging during the period of extended operation on the functionality of structures and components that have been identified to require review under 10 CFR 54.21, such that there is reasonable assurance that the activities authorized by the renewed license will continue to be conducted in accordance with the current licensing basis.
Issue
- a. Section 4.2, Justified Assumptions and Modeling Simplifications, of Enclosure 1 states that a residual stress of +2 ksi was conservatively assumed to exist through the thickness of the channel head cladding based on the project agreement between Framatome and EPRI.
During the audit, the licensee clarified that 2 ksi is identified as a residual stress uncertainty in the EPRI source documents, not residual stress magnitude, and this was misstated in. Citing a technical reference, the licensee stated that +2 ksi in the cladding was a conservative value based on the small thickness of the cladding relative to the base metal
2 (about 5%), the post-weld heat treatment, pre-service hydrostatic testing, and inservice temperature changes.
- b. Section 4.2 of Enclosure 1 also states that no residual stress was assigned to the low alloy steel channel head material. Industry studies used a base metal residual stress of +8 ksi due to uncertainty about the location of seam welds. In the audit the licensee stated that the circumferential welds will not affect crack growth because they are too distant from the postulated fatigue crack location. The licensee also noted that there are no longitudinal welds in the tubesheet ring. The licensee provided a stress analysis example with dimensions similar to those of the Callaway SGs to show that residual stress decreases sharply from the weld location and therefore would not affect growth of the postulated fatigue crack.
Request Please confirm the following about the cracking assessment for the Callaway steam generator channel head assemblies.
- a. For cladding residual stress, please confirm the following:
- The cracking assessment for the Callaway steam generators concluded residual stress in the channel head cladding is insignificant based on the cladding thickness being a small percentage (about 5 percent) of the base metal thickness, the post-weld heat treatment, the pre-service hydrostatic testing, and inservice temperature changes.
- The conclusion was informed by the survey documented in D. P. G. Lidbury, The Significance of Residual Stress in Relation to the Integrity of LWR Pressure Vessels, International Journal of Pressure Vessels and Piping, 17 (1984) 197-328.
- b. For base metal residual stress, please confirm the following:
- Circumferential welds in the tubesheet ring are at least 13 inches from any postulated crack in the triple point region.
- Finite element analysis for weld geometry approximating the Callaway SG configuration shows that a weld residual stress of approximately 8 ksi attenuates to near zero within 5-6 inches of the weld.
- There are no longitudinal welds in the Callaway steam generator tubesheet rings.
OFFICE NRR/DORL/LPL4/BC NRR/DORL/LPL4/PM NRR/DNRL/NCSG/BC NAME TNakanishi MChawla SBloom DATE 11/07/2024 11/06/2024 11/05/2024