ML25240B631
| ML25240B631 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/28/2025 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML25240B627 | List: |
| References | |
| Download: ML25240B631 (1) | |
Text
Table 2-2 (page 1 of 3)
Table 2-2: Additional Information Pertaining to Reactor Vessel Inspection for Calvert Cliffs Unit 2 Inspection methodology:
The latest RV ISI for Calvert Cliffs Unit 2 was conducted in accordance with the requirements of Appendix VIII of the ASME Code,Section XI, 2004 Edition with no Addenda, as modified by 10 CFR Part 50(b)(2)(xiv, xv, and xvi). Evaluation of recordable indications was performed to the acceptance standards of Section XI, 2004 Edition with no Addenda. Future inservice inspections will be performed to ASME Section XI, Appendix VIII requirements.
Number of past inspections:
All welds have been inspected at least three times with the exception of five lower head meridional welds which have been inspected two times.
Number of indications found:
There were sixteen total indications identified in the beltline and extended beltline regions during the most recently completed inservice inspection. These indications are located in the upper to intermediate shell circumferential weld seam (Item 10 in Table 3-2), the intermediate to lower shell circumferential weld seam (Item 11 in Table 3-2), and the longitudinal welds seams in the upper shell, intermediate shell, and lower shell (Items 12, 15 through 17 and 19 of Table 3-2). All sixteen indications are acceptable per Table IWB-3510-1 of Section XI of the ASME Code. Of the sixteen indications, there are eight indications within the inner 1/10th or inner 1 of the reactor vessel wall thickness. A disposition of the eight flaws against the limits of the Alternate PTS Rule is shown in the tables below. Eight flaws were located in the plate material. Of the eight indications, seven of these indications are acceptable per the requirements of the Alternate PTS Rule, 10 CFR 50.61a (Reference 9). One indication, in the plate material with a TWE greater than 0.325 inches, does not meet the requirements in the Alternate PTS Rule. Additional information regarding this indication is discussed further in later paragraphs.
Through-Wall Extent, TWE (in.)
Scaled Maximum number of flaws per 1,612 inches of weld length in the inspection volume that are greater than or equal to TWEMIN and less than TWEMAX.
Number of Calvert Cliffs Unit 2 Flaws Evaluated (Axial/Circ.)
TWEMIN TWEMAX 0
0.075 No Limit 0
0.075 0.475 268 0
0.125 0.475 146 0
0.175 0.475 36 0
0.225 0.475 13 0
0.275 0.475 6
0 0.325 0.475 4
0 0.375 0.475 2
0 0.425 0.475 1
0 0.475 Infinite 0
0
Table 2-2 (page 2 of 3)
For the eight flaws in the plate material:
Through-Wall Extent, TWE (in.)
Scaled Maximum number of flaws per 14,045 square-inches of inside surface area in the inspection volume that are greater than or equal to TWEMIN and less than TWEMAX.
Number of Calvert Cliffs Unit 2 Flaws Evaluated (Axial/Circ.)
TWEMIN TWEMAX 0
0.075 No Limit 0
0.075 0.375 113 8 (5/3) 0.125 0.375 44 8 (5/3) 0.175 0.375 11 3 (2/1) 0.225 0.375 4
2 (2/0) 0.275 0.375 1
1 (1/0) 0.325 0.375 0
1 (1/0) 0.375 Infinite 0
0 As discussed previously, one flaw was detected which exceeds the requirements in the Alternate PTS Rule. This flaw is located near the 30 degree intermediate shell longitudinal weld (Weld 2-203A) and has a through wall extent of 0.34 inches. Given the theta position of 30.9° and an x position of 217.2 inches, the flaw is located in the adjacent plate material. Weld 2-203 A was previously inspected in 1999 during the second ISI at Calvert Cliffs Unit 2 and had a recordable indication with a through-wall extent of 0.60 inches which exceeded the acceptance criteria. This flaw from the second 1999 ISI is larger than the flaw recorded in the 2019 ISI (discussed previously in this paragraph) and was previously dispositioned and determined to be acceptable by the U.S.
NRC in the Safety Evaluation for the Calvert Cliffs Unit 2 relief request (Reference 2). This approach of utilizing the previous experience of the larger flaw with through-wall extent of 0.60 inches was similarly completed and determined to be acceptable by the U.S. NRC in the Safety Evaluation for Farley Unit 1 relief request (Reference 10).
While this one flaw is outside the limits of the Alternate PTS Rule, it is not expected that this flaw would increase the Calvert Cliffs Unit 2 TWCF value in Table 3-2 above that of the pilot plant for the following reasons:
The plate which the flaw is located in has a maximum RTNDT + T30 of 161.75°F and is not the limiting material in the beltline region. Furthermore, the peak fluence was used to calculate the T30 shift for this plate; however, the fluence at the position of this flaw is approximately 60% of the peak fluence. This was determined using the fluence values reported in Table 6-13 of WCAP-18958-NP (Reference 12), since the location of the flaw is just slightly offset from the location of the intermediate shell 30 degree longitudinal weld.
Therefore, the actual RTNDT + T30 at the specific location of the flaw is less than 161.75°F.
The total number of flaws detected in the Calvert Cliffs Unit 2 beltline is far less than those allowed in the Alternate PTS Rule tables above.
The TWCF for the Calvert Cliffs Unit 2 RV is more than 3 orders of magnitude below that for the bounding pilot plant vessel.
Note that the plant-specific total length (1,612 inches) of reactor vessel beltline welds that were volumetrically inspected and the plant-specific total surface area (14,045 square-inches) of reactor vessel beltline plates that were volumetrically inspected are comprised of the upper-to-intermediate shell circumferential weld, the intermediate-to-lower shell circumferential weld, three longitudinal welds in the intermediate shell, and three longitudinal welds in the lower shell. While the three upper shell longitudinal welds were inspected and evaluated, the length and area associated with these
Table 2-2 (page 3 of 3) welds are conservatively excluded from the total inspected length and area. Weld length and area were also adjusted based on examination coverage of each weld as this is considered a conservative approach.
Proposed inspection schedule for balance of plant life:
The fourth inservice inspection is proposed to be performed in the sixth interval no later than Spring 2041. The proposed inspection date is within plus or minus one refueling outage of the date in the latest revised implementation plan, OG-10-238 (Reference 3), which reflects the next inspection being performed in 2039.