ML25069A668
| ML25069A668 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  (NPF-072, NPF-077) |
| Issue date: | 03/13/2025 |
| From: | Scott Wall Plant Licensing Branch III |
| To: | Rhoades D Constellation Energy Generation |
| Wall, S | |
| References | |
| EPID: L-2024-LRO-0047 | |
| Download: ML25069A668 (1) | |
Text
March 13, 2025 Mr. David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555
SUBJECT:
BRAIDWOOD STATION, UNITS 1 AND 2 - REVIEW OF THE UNIT 1 UPDATED FALL 2022 AND THE UNIT 2 SPRING 2023 STEAM GENERATOR TUBE INSPECTION REPORTS (EPID L-2024-LRO-0047)
Dear David Rhoades:
By letter dated July 26, 2023 (Agencywide Documents Access and Management System Accession No. ML23188A129), the U.S. Nuclear Regulatory Commission (NRC) issued Amendments 233 and 233 for Braidwood Station, Units 1 and 2, respectively, to revise the technical specifications (TS) to adopt Technical Specifications Task Force (TSTF)-577, Revised Frequencies for Steam Generator [SG] Tube Inspections. Constellation Energy Generation, LLC (CEG), stated in a letter dated May 22, 2023 (ML23143A136), that it will submit, 60 days after implementation of TSTF-577, SG tube inspection reports meeting the revised reporting requirements in TS 5.6.9, Steam Generator (SG) Tube Inspection Report.
On December 1, 2023 (ML23313A155), the NRC staff issued its review of the Braidwood Station, Unit 1, fall 2022 SG tube inspection report. By letter dated November 1, 2023 (ML23305A039 (Package)), CEG submitted the updated Braidwood Station Unit 1, fall 2022 SG tube inspection report and the Braidwood Station, Unit 2, spring 2023 SG tube inspection report meeting the revised TS 5.6.9 reporting requirements. By letter dated February 20, 2025 (ML25051A003), CEG provided additional information concerning the inspections.
Based on its review, the NRC staff concludes that the licensee has provided the information required by TS 5.6.9, and that no follow-up is required at this time. A summary of the NRC staffs review is enclosed.
Please feel free to contact me at (301) 415-2855 if you have any questions or concerns.
Sincerely,
/RA/
Scott P. Wall, Senior Project Manager Plant Licensing Branch III Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-456, STN 50-457
Enclosure:
Review of the Unit 1 Updated Fall 2022 and the Unit 2 Spring 2023 Steam Generator Tube Inspection Reports cc: Listserv
Enclosure REVIEW OF THE UNIT 1 UPDATED FALL 2022 AND THE UNIT 2 SPRING 2023 STEAM GENERATOR TUBE INSPECTION REPORTS CONSTELLATION ENERGY GENERATION, LLC BRAIDWOOD STATION, UNITS NO. 1 AND 2 DOCKET NOS. STN 50 456, STN 50 457 By letter dated July 26, 2023 (Agencywide Documents Access and Management System Accession No. ML23188A129), the U.S. Nuclear Regulatory Commission (NRC) issued Amendments 233 and 233 for Braidwood Station, Units 1 and 2, respectively, to revise the technical specifications (TS) to adopt Technical Specifications Task Force (TSTF)-577, Revised Frequencies for Steam Generator [SG] Tube Inspections. Constellation Energy Generation, LLC (CEG), stated in a letter dated May 22, 2023 (ML23143A136), that it will submit, 60 days after implementation of TSTF-577, SG tube inspection reports meeting the revised reporting requirements in TS 5.6.9, Steam Generator (SG) Tube Inspection Report.
On December 1, 2023 (ML23313A155), the NRC staff issued its review of the Braidwood Station, Unit 1, fall 2022 SG tube inspection report. By letter dated November 1, 2023 (ML23305A039 (Package)), CEG submitted the updated Braidwood Station Unit 1, fall 2022 SG tube inspection report and the Braidwood Station, Unit 2, spring 2023 SG tube inspection report meeting the revised TS 5.6.9 reporting requirements. By letter dated February 20, 2025 (ML25051A003), CEG provided additional information concerning the inspections.
TS 5.6.9 requires that a report be submitted within 180 days after the initial entry into hot shutdown (MODE 4) following completion of an inspection of the SGs performed in accordance with TS 5.5.9, which requires that a SG program be established and implemented to ensure SG tube integrity is maintained.
Braidwood Station, Unit 1, is a 4-loop plant with Babcock and Wilcox Model 7720 replacement SGs. Each SG contains 6,633 thermally treated Alloy 690 tubes with a nominal outside diameter of 0.6875 inches and a nominal wall thickness of 0.040 inches. The tubes are supported by stainless steel lattice grid structures and fan bars (U-bend). The tubes were hydraulically expanded at both ends for the full depth of the tubesheet.
Braidwood Station, Unit 2, has four Westinghouse Model D5 SGs. There are 4,570 thermally treated Alloy 600 tubes in each SG, with a nominal outside diameter of 0.750 inches and a nominal wall thickness of 0.043 inches. The tubes were hydraulically expanded at both ends for the full depth of the tubesheet. The tubes are supported by stainless steel tube support plates (TSPs) with quatrefoil shaped holes and chrome plated Alloy 600 anti-vibration bars (AVBs).
The licensee provided the scope, extent, methods, and results, of its SG tube inspections in its November 1, 2023, letter, as supplemented by letter dated February 20, 2025. In addition, the licensee described corrective actions, such as tube plugging taken in response to the inspection findings.
Based on the review of the information provided, the NRC staff has the following observations:
Braidwood Station, Unit 1, Updated Fall 2022 SG Tube Inspection Report In the letter dated February 20, 2025 (ML25051A003), CEG clarified that (1) the bounding growth rate for fan bar wear used in the operational assessment calculations is 1.0 percent through wall (TW) per effective full power years; (2) the maximum depths predicted at the next inspection for fan bar wear and lattice grid wear are 30.4 percent TW and 25.6 percent TW, respectively; and (3) only 13 foreign objects (FOs), as shown in Table 10 of the Braidwood Station, Unit 1, updated fall 2022 SG tube inspection report, remain in SGs A, B, and C.
Braidwood Station, Unit 2, Spring 2023 SG Tube Inspection Report The licensee inspected 100 percent of the tubes in service in all four SGs with both bobbin and array probes, and the Rows 1 and 2 U-bend regions were inspected with rotating pancake coil probes from the 11th hot leg TSP to the 11th cold leg TSP. A total of 1,131 AVB wear indications, 10 TSP wear indications, and 26 FO wear indications were reported. The deepest AVB wear indication measured 40 percent TW, the deepest TSP wear indication measured 34 percent TW, and the deepest FO wear indication measured 38 percent TW.
One axial outside diameter stress corrosion cracking (ODSCC) indication in Tube Row 49, Column 59 in SG 2C was detected with bobbin and array probes and confirmed with
+Point' probe. The indication was coincident to a low-level freespan ding and measured 64 percent TW with a total length of 0.18 inches. CEG stated that a history review revealed that a bobbin signal has been present and first detectable in 2006.
One volumetric indication was detected above 8th hot leg TSP in Tube Row 41, Column 82 in SG 2A with bobbin and array probes and confirmed with +Point' probe. The indication measured 49 percent TW with a total length of 0.26 inches. CEG stated that history review confirmed the flaw was present during the 2021 SG tube inspections.
CEG plugged a total of 4 tubes: 2 in SG 2A and 2 in SG 2C. The tubes plugged in SG 2A were one AVB wear indication greater than the 40 percent TS plugging criterion and the volumetric indication in Tube Row 41, Column 82. The tubes plugged in SG 2C were one AVB wear indication greater than the 40 percent TS plugging criterion and the axial ODSCC indication in Tube Row 49, Column 59.
CEG confirmed in the letter dated February 20, 2025 (ML25051A003), that the 14 potentially high residual stress tubes will be treated as a sub-population in subsequent degradation assessments such that they will be more likely to be inspected with enhanced probes in subsequent SG inspections.
Based on a review of the information provided, the NRC staff concludes that the licensee provided the information required by the TSs. In addition, the staff concludes that there are no
current technical issues that warrant additional follow-up action. The inspections appear to be consistent with the objective of detecting potential tube degradation and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.
Reviewer: L. Terry, NRR Date: March 13, 2025
- via memo OFFICE NRR/DORL/LPL3/PM NRR/DORL/LPL3/LA NRR/DNRL/NCSG/BC*
NAME SWall SRohrer SBloom DATE 03/10/2025 03/11/2025 03/03/2025 OFFICE NRR/DORL/LPL3/BC(A)
NRR/DORL/LPL3/PM NAME IBerrios SWall DATE 03/12/2025 03/13/2025