ML25051A005
| ML25051A005 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 02/20/2025 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25051A003 | List: |
| References | |
| BW250007 | |
| Download: ML25051A005 (1) | |
Text
ATTACHMENT Response to Request for Additional Information NRC Request for Additional Information:
By letter dated July 26, 2023 (Agencywide Documents Access and Management System (ADAMS) 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 the letter dated May 22, 2023, that it will submit, 60 days after implementation of TSTF-577, SG tube inspection reports meeting the revised reporting requirements in TS Section 5.6.9. 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 Section 5.6.9 reporting requirements. The SG tube inspections were performed at Braidwood Station, Units 1 and 2, during refueling outage 23 (A 1 R23 (Unit 1) and A2R23 (Unit 2)).
TS Section 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 Section 5.5.9, which requires that a SG Program be established and implemented to ensure SG tube integrity is maintained. To complete its review of the inspections, the NRC staff requests the following additional information:
Braidwood Station, Unit 1, Updated Fall 2022 SG Tube Inspection Report
- 1. In the discussion of the forward-looking tube integrity assessment in the updated fall 2022 Braidwood Station, Unit 1, SG tube inspection report, there are some inconsistencies with regards to the values for total Effective Full Power Years (EFPY) in five fuel cycles (7.3 or 7.5 EFPY), the growth rate per EFPY for fan bar wear (1.0 percent through wall (TW) per EFPY or 1.5 percent TW per EFPY), and the maximum depth predicted at the next inspection for fan bar and lattice grid wear. For example, The updated report states that the operational assessment for wear at support structures was evaluated for five fuel cycles of 1.5 EFPY each (1.5 x 5 = 7.5 EFPY).
However, for both fan bar and lattice grid wear, it appears that 7.3 EFPY was used.
The updated report states that a growth rate of 1.5 percent TW per EFPY was used for fan bar wear. However, the report appears to use a growth rate of 1.0 percent TW per EFPY ("Applying a growth rate of 7.3%TW (1.0 x 7.3)").
For fan bar wear, the updated report states, "Applying a growth of 7.3% TW (1.0 x 7.3) gives a bounding real depth at the end of the upcoming inspection interval of 34.1% TW (23.1 + 7.3)." However, a projected depth of 30.4 percent TW is reported elsewhere in the report, consistent with the (23.1 + 7.3) value.
ATTACHMENT Response to Request for Additional Information Please clarify which values were used in the degradation projections for the following:
- 1. The total EFPY used for five fuel cycles.
Response
The total Effective Full Power Years (EFPY) utilized during the fall 2022 Operational Assessment (OA) was 7.3 EFPY, which conservatively bounds the 7.25 EFPY identified for the five-cycle Degradation Assessment.
- a. The growth rate per EFPY for fan bar wear.
Response
The Unit 1 Braidwood Station, Unit 1 Updated Steam Generator Tube Inspection Report incorrectly states 1.5% TW/EFPY as the bounding value. A bounding growth rate of 1.0% TW/EFPY was used in the fan bar wear OA calculations. The 1.5% TW/EFPY was a typographical error.
- b. Based on the total EFPY in five cycles and the growth rate per EFPY, please confirm the maximum depths predicted at the next inspection for fan bar wear and lattice grid wear.
Response
For fan bar wear the maximum depth predicted at the next inspection is 30.4%
through wall (TW). The 34.1 % value was a typographical error. For lattice grid the wear maximum expected depth predicted at the next inspection is 25.6% TW.
- 2. The updated fall 2022 Braidwood Station, Unit 1, SG tube inspection report states 14 foreign objects in SGs A, B, and C were not removed during A 1 R23 and are included in Table 10. However, Table 10 appears to only include 13 foreign objects with a status of "Remains." Therefore, it is unclear how many total foreign objects remain in the three SGs. Please confirm how many total foreign objects remain in SGs A, 8, and C.
Response
Foreign object logs from outage documentation were reviewed and compared to the fall 2022 condition monitoring and operational assessment (CMOA) and Table 10 of the Braidwood Station Unit 1 Updated Steam Generator Tube Inspection Report and confirmed that there are only 13 foreign objects that remain in the SGs. The 13 foreign objects listed in Table 10 are the only foreign objects that remain in SGs A, 8, and C.
ATTACHMENT Response to Request for Additional Information Braidwood Station, Unit 2, Spring 2023 SG Tube Inspection Report
- 1. Table 1 in the spring 2023 Braidwood Station, Unit 2, SG tube inspection report states, "A sub-population of 14 potentially high residual stress tubes has been identified from eddy current U-bend offset signals and are currently designated as a sub population potentially more susceptible to ODSCC [outside diameter stress corrosion cracking] in the A2R23 degradation assessment [DA]." In addition, the report states, "During A2R23, all tube-to-TSP intersections received a bobbin and array exam, so tubes with potentially higher residual stresses no longer need to be treated differently for OA [Operational Assessment] purposes since all tube-to-TSP intersections received the same baseline examinations." Please clarify if the 14 potentially high residual stress tubes will be treated as a sub-population in subsequent DAs such that they will be more likely to be inspected with enhanced probes in subsequent SG inspections.
Response
Constellation confirms the 14 potentially high residual stress tubes will continue to be treated as a sub population in subsequent degradation assessments (DAs) such that they will be more likely to be inspected with enhanced probes in subsequent SG inspections. That section of the report applies to the spring 2023 operational assessment for Unit 2, not all operational assessments in the future.