ML25003A165
| ML25003A165 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 02/10/2025 |
| From: | Mahesh Chawla Plant Licensing Branch IV |
| To: | Diya F Callaway Energy Center |
| Chawla M | |
| References | |
| EPID L-2024-LRO-0009 | |
| Download: ML25003A165 (1) | |
Text
February 10, 2025 Fadi Diya Senior Vice President and Chief Nuclear Officer Ameren Missouri Callaway Energy Center 8315 County Road 459 Steedman, MO 65077
SUBJECT:
CALLAWAY PLANT, UNIT NO. 1 - AUDIT REPORT REGARDING THE RESPONSE TO STEAM GENERATOR LICENSE RENEWAL COMMITMENT NOS. 34 AND 35 (EPID L-2024-LRO-0009)
Dear Fadi Diya:
By letter dated December 20, 2023 (Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML23354A244), Union Electric Company, doing business as Ameren Missouri (the licensee), submitted to the U.S. Nuclear Regulatory Commission (NRC) a response to license renewal Commitment Nos. 34 and 35 for the Callaway Plant, Unit No. 1 (Callaway). In March 2015, the NRC published NUREG-2172, Safety Evaluation Report Related to the License Renewal of Callaway Plant, Unit 1, which documents the technical review of the Callaway license renewal application (ML15068A342).
The NRC staff reviewed the Callaway submittal regarding the license renewal resolution for Commitment Nos. 34 and 35 and determined that a regulatory audit was necessary to support its review of the submittal. A regulatory audit is a planned activity that includes the examination and evaluation of primarily non-docketed information. The audit increased the staffs understanding of the submittal and identified information that needed to be docketed to support staffs regulatory findings.
The NRC staff performed its audit from May 20, 2024 - December 13, 2024, in accordance with the audit plan (ML22265A013). The audit report is enclosed.
If you have any questions, please contact me at 301-415-8371 or via email at Mahesh.Chawla@nrc.gov.
Sincerely,
/RA/
Mahesh L. Chawla, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-483
Enclosure:
As stated cc: Listserv
U.S. NUCLEAR REGULATORY COMMISSION AUDIT REPORT REGARDING CALLAWAY PLANT, UNIT 1 STEAM GENERATOR, LICENSE RENEWAL RESPONSE TO COMMITMENT NOS. 34 AND 35 List of Participants NRC David Rudland, Senior Technical Advisor Gregory Makar, Materials Engineer Paul Klein, Senior Materials Engineer Steven Bloom, Branch Chief Mahesh Chawla, Project Manager Ameren Missouri Tom Elwood Erin Smith Craig Wicker Andrew Burgess Framatome Kaihong Wang Stacy Yoder Tim Wiger
Enclosure U.S. NUCLEAR REGULATORY COMMISSION AUDIT REPORT REGARDING UNION ELECTRIC COMPANY, CALLAWAY PLANT, UNIT 1 DOCKET NO. 50-483 STEAM GENERATOR, LICENSE RENEWAL RESPONSE TO COMMITMENT NOS. 34 AND 35 I.
BACKGROUND By letter dated December 20, 2023 (Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML23354A244), Union Electric Company, doing business as Ameren Missouri (the licensee), submitted to the U.S. Nuclear Regulatory Commission (NRC) a response to license renewal Commitment Nos. 34 and 35 for the Callaway Plant, Unit No. 1 (Callaway). In March 2015, the NRC published NUREG-2172, Safety Evaluation Report Related to the License Renewal of Callaway Plant, Unit 1, which documents the technical review of the Callaway license renewal application (ML15068A342).
II.
AUDIT ACTIVITIES AND DOCUMENTS REVIEWED On May 20, 2024 - December 13, 2024, the NRC staff performed an audit to gain a better understanding of the licensees technical basis for concluding that (1) the reactor coolant system pressure boundary will be adequately maintained in the presence of steam generator (SG) divider plate assembly cracking, and (2) the chromium content of the SG tube-to-tubesheet welds is at least 22 weight percent.
During its audit, the NRC staff interviewed licensee staff and reviewed documentation contained in the December 20, 2023, letter and provided by the licensee via the ePortal.
The table below lists documents that were reviewed by the NRC staff and were found relevant to the staffs review. The staff will document its review of this information in its safety evaluation.
Document Title Revision / Date 32-9055891-007 Fatigue and PWSCC Crack Growth Evaluation Tool AREVACGC 7/Aug 2019 32-9055891-005 Fatigue and PWSCC Crack Growth Evaluation Tool AREVACGC 5/Jan 2010 32-9360111-000 Framatome RSG Channel Head and Tubesheet Stress Analysis for Flaw Evaluation 0/May 2023 32-9364633-000 Framatome RSG Channel Head and Tubesheet Flaw Tolerance Evaluation 0/Jun 2023 51-9268036-000 EPRI SGMP for Channel Head Aging of Framatome RSG Designs 0/Aug 2019 Document Title Revision / Date DI-TS-2023.023 Chromium content of tubesheet cladding and tubes of Replacement steam generators for CALLAWAY Plant Unit 1 A/Oct 2023 N/A EPRI Research and Development Project Agreement 10012545, Divider Plate Cracking Assessment for Framatome Replacement Steam Generators May 2020 N/A Lidbury, D. P. G., The Significance of Residual Stress in Relation to the Integrity of LWR Pressure Vessels, International Journal of Pressure Vessels and Piping, 17 (1984), 197-328.1 1984 1Paper reviewed because it was used as a reference for the approach to residual stress in the crack growth analysis.
III.
AUDIT QUESTIONS PROVIDED TO THE LICENSEE To facilitate audit discussions, the NRC staff provided audit questions to the licensee, and they are available in ADAMS Accession No. ML24318C256.
IV.
AUDIT OBSERVATIONS During the audit, the NRC staff made the following observations:
Dimensions are not all specifically from Callaway. The geometry in the model is representative of all four units, which have insignificant variations.
The amount of residual stress assumed in the channel head cladding was conservative based on the cladding being a small percentage (approximately 5 percent) of the base metal thickness, the post-weld heat treatment, the pre-service hydrostatic testing, and inservice temperature changes.
No residual stress was included in the channel head base material because (1) the nearest circumferential welds are at least 13 inches away from any postulated crack in the triple point region, and (2) there are no longitudinal seam welds in the tubesheet rings.
The heat transfer coefficient units presented in the commitment response are incorrect; however, this was a typographical error in the report. There was not impact on the results because the correct values were used in the calculations.
The paths analyzed for crack growth were defined as those with the maximum stress magnitude and/or maximum stress variations.
ML25003A165 OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA NRR/DNRL/NCSG/BC NAME MChawla PBlechman (KZeleznock for)
SBloom DATE 1/2/2025 01/10/2025 1/13/2025 OFFICE NRR/DORL/LPL/BC NRR/DORL/LPL4/PM NAME TNakanishi MChawla DATE 1/13/2025 2/10/2025