ULNRC-06849, License Renewal Resolution for Commitments 34 and 35 – Perform Evaluation of Crack Initiation and Propagation in Steam Generator Divider Plate and Tube-To-Tubesheet Welds
| ML23354A245 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 12/20/2023 |
| From: | Witt T Ameren Missouri, Union Electric Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| Shared Package | |
| ML23354A244 | List: |
| References | |
| ULNRC-06849 | |
| Download: ML23354A245 (1) | |
Text
.
.t
.t
.t Callaway Plant 8315 County Road 459 : Steedman, MO 65077 : AmerenMissouri.com
.t December 20, 2023 ULNRC-06849 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Ladies and Gentlemen:
DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.
RENEWED FACILITY OPERATING LICENSE NPF-30 CALLAWAY PLANT LICENSE RENEWAL RESOLUTION FOR COMMITMENTS 34 AND 35 - PERFORM EVALUATION OF CRACK INITIATION AND PROPOGATION IN STEAM GENERATOR DIVIDER PLATE AND TUBE-TO-TUBESHEET WELDS
References:
- 1. NUREG-2172, "Safety Evaluation Report Related to the License Renewal of Callaway Plant, Unit 1," dated March 2015 (ADAMS Accession No. ML15068A342)
- 2. EPRI Steam Generator Management Program Report 3002002850, Investigation of Crack Initiation and Propagation in the Steam Generator Channel Head Assembly, EPRI, Palo Alto, CA, 2014.
- 3. NRC License Renewal Interim Staff Guidance LR-ISG-2016-01, Changes to Aging Management Guidance for Various Steam Generator Components, 2016 (ADAMS Accession No. ML16237A383)
Callaway Plant License Renewal Commitments 34 and 35 are associated with steam generator divider plate and tube-to-tubesheet welds and address concerns regarding 1) potential failure at the divider plate welds to primary head and tubesheet cladding and 2) potential failure of primary-to-secondary pressure boundary due to primary water stress corrosion cracking (PWSCC) of tube-to-tubesheet welds. These license renewal commitments are acknowledged in Appendix A of Reference 1 and are identified in Callaway's FSAR Chapter 19.1.9, "Steam Generators," and FSAR Table 19.4-1 as Items 34 and 35.
ULNRC-06849 December 20, 2023 Page 2 of 6 Commitments 34 and 35 provide Ameren Missouri options to resolve the concerns associated with the steam generator divider plate and tube-to-tubesheet welds. Ameren Missouri has chosen to resolve these concerns using analysis (Option 2: Analysis). For Option 2: Analysis, Ameren Missouri must submit the analysis to the NRC for review by the fall of 2023. Therefore, Ameren Missouri is submitting this letter and supporting analytical evaluations in accordance with the noted commitments.
Each commitment and Ameren Missouri's resolution of the commitment is described below, with supporting technical information and analysis provided in Enclosures 1 and 2.
Callaway Plant License Renewal Commitment 34 FSAR Table 19.4-1, Item 34 states, in part:
Ameren Missouri replacement steam generator divider plate assemblies are fabricated of Alloy 690. The divider plate to primary head and tubesheet junctions are welded with Alloy 152 weld materials. The tubesheet cladding is Alloy 182, and the primary head cladding is stainless steel.
There is a concern regarding potential failure at the divider plate welds to primary head and tubesheet cladding and Ameren Missouri commits to perform one of three resolution options.
The three resolution options provided in FSAR Table 19.4-1, Item 34 are inspection, analysis, and industry/NRC studies. Ameren Missouri has chosen Option 2: Analysis. As documented in FSAR Table 19.4-1, Item 34, this option requires Ameren Missouri to do the following:
Perform an analytical evaluation of the steam generator divider plate welds in order to establish a technical basis which concludes that the steam generator reactor coolant system (RCS) pressure boundary is adequately maintained with the presence of steam generator divider plate weld cracking. The analytical evaluation will be submitted to the NRC for review and approval.
Commitment 34 Analytical Evaluation Summary The EPRI Steam Generator Management Program (SGMP) investigated crack initiation and propagation in the steam generator channel head assembly (i.e., divider plate to primary head and tubesheet junctions) for Westinghouse steam generators. However, since replacement steam generators at Callaway were supplied by Framatome, the results and conclusions presented in Reference 2 are not necessarily applicable to the Framatome replacement steam generators. Therefore, Framatome conducted a similar analysis (Enclosure 1) to demonstrate, by flaw tolerance assessment, that a postulated initial flaw in Framatome replacement steam generator channel heads meets the ASME Section XI, IWB-3612 acceptance criteria over the design life of the replacement steam generators.
Through this analysis, Framatome concluded that the replacement steam generator channel heads are not compromised by the postulated circumferential or axial flaw initiating from the divider plate over the design life of the replacement steam generators. As a result, the analysis in Enclosure 1 establishes the technical basis that the steam generator RCS pressure boundary is adequately maintained with the presence of steam generator divider plate weld cracking.
ULNRC-06849 December 20, 2023 Page 3 of 6 Callaway Plant License Renewal Commitment 35 FSAR Table 19.4-1, Item 35 states, in part:
The material of the steam generator tubesheet cladding is Alloy 182. The tubes are made of Alloy 690 and are secured to the tubesheet by means of tube-to-tubesheet leaktight weld and tube expansion. There is a concern regarding potential failure of primary-to-secondary pressure boundary due to PWSCC cracking of tube-to-tubesheet welds. Ameren Missouri commits to perform one of two resolution options.
The two resolution options stated in FSAR Table 19.4-1, Item 35 are inspection and analysis. Ameren Missouri has chosen Option 2: Analysis. As stated in FSAR Table 19.4-1, Item 35, this option requires Ameren Missouri to do the following:
Perform an analytical evaluation of the steam generator tube-to-tubesheet welds either determining that the welds are not susceptible to PWSCC or redefining the reactor coolant pressure boundary of the tubes, where the steam generator tube-to-tubesheet welds are not required to perform a reactor coolant pressure boundary function. The redefinition of the reactor coolant pressure boundary will be submitted as part of a license amendment request requiring approval from the NRC. The evaluation for determination that the welds are not susceptible to PWSCC and do not require inspection will be submitted to the NRC for review.
Commitment 35 Analytical Evaluation Summary The approach taken to resolve this commitment was to perform the analytical evaluation for determining that the welds are not susceptible to PWSCC. Specifically, the Framatome replacement steam generators were evaluated for the chromium content in the tube-to-tubesheet welds to determine if the welds are susceptible to PWSCC. Enclosure 1 includes a materials assessment (Section 6.3) to determine whether the tube-to-tubesheet welds have a chromium content of at least 22% weight content (22 wt%), consistent with the requirements of Reference 2 and Reference 3. Based the on the initial assessment, it could not be determined that the tube-to-tubesheet welds meet the 22 wt%
chromium requirement. However, as documented in Enclosure 2, manufacturing completion records were searched for Ameren Missouri's replacement steam generators. This search yielded, in greater detail, the tube-to-tubesheet weld chromium content. Subsequently, as documented in Enclosure 2, when inputting this manufacturing data into the same weld dilution equation from Section 6.3 of, it was confirmed the tube-to-tubesheet welds have a chromium content of at least 22 wt%. As a result, the tube-to-tubesheet welds were validated to not be susceptible to PWSCC and do not require inspection.
ULNRC-06849 December 20, 2023 Page 4 of 6 Ameren Missouri respectfully requests review and approval of the analytical evaluations provided in and Enclosure 2 by June 20, 2025 to support the resolution of Callaway Plant License Renewal Commitments 34 and 35.
This letter does not contain new commitments. If there are any questions, please contact Tom Elwood at 314-225-1905.
Sincerely, Todd A. Witt Manager, Regulatory Affairs
- Cracking Assessment for Framatome RSG Channel Head Assembly : Callaway Tube to Tubesheet Welding Report
ULNRC-06849 December 20, 2023 Page 5 of 6 cc:
Mr. John Monninger Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. M. Chawla Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop O8B1A Washington, DC 20555-0001
ULNRC-06849 December 20, 2023 Page 6 of 6 Index and send hardcopy to QA File A160.0761 Hardcopy:
Certrec Corporation 6500 West Freeway, Suite 400 Fort Worth, TX 76116 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)
Electronic distribution for the following can be made via Other Situations ULNRC Distribution:
F. M. Diya K. C. Scott J. G. Beck W. A. Witt T. A. Witt B. L. Jungmann T. B. Elwood NSRB Secretary STARS Regulatory Affairs Mr. Jay Silberg (Pillsbury Winthrop Shaw Pittman LLP)
Ms. Kathleen McNelis (Public Service Commission)
Ms. Claire Eubanks (Public Service Commission)