ML23137A078

Public -Byron and Braidwood Commitment 10 Audit Call Questions

ML23137A078
Person / Time
Site:	Byron, Braidwood
Issue date:	02/01/2023
From:	Lauren Gibson NRC/NRR/DNRL/NLRP
To:	Rhoades D Constellation Energy Generation
References
EPID L-2022-RNW-0010, EPID L-2022-RNW-0011
Download: ML23137A078 (1)

Text

Braidwood Unit 1 and Byron Unit 1 L-2022-RNW-0010/0011 License Renewal Commitment 10 Response Steam Generator Divider Plate Assembly and Tube-to-Tubesheet Welds QUESTIONS FOR AUDIT DISCUSSION No. Topic Question Outcome 1 Material Properties What is the basis for using an upper-shelf fracture toughness value of (( ))

rather than the value of 200 ksi-in used in EPRI Report 3002002850? While not explicitly called out in ASME Code Section XI, the de facto value used is typically 220 MPA-m (200 ksi-in), but as illustrated in PVP2011-57173, this can sometime be non-conservative, especially at higher temperatures.

2 Material Properties Please discuss the test data that demonstrate

(( )) was achieved. This value was assumed in the analyses and required in the material specification in CDS 18-1229648.

3 Material Properties For transients for which the total stress is above the yield strength, the procedure in

(( )) was used for stress modification.

Was the critical crack size (and thus the allowable K) also adjusted per ((

)), and if so, what was the correction?

4 Materials Properties Please provide a summary of the yield and tensile strength values, and associated temperature dependencies, used in the analyses. Most of the documents refer to ASME Code Section III, Division 1, Appendices (1986), but some refer to other calculations for material properties, and M2004-SR-01 and EPRI Report 3002002850 refer to ASME Code Section II, Part D. If there are differences, please explain the significance.

5 Finite Element Model Please clarify the assumed flaw length and how it is a bounding value for prediction of stresses ahead of the crack tip. BWXT Report No.

M2004-SR-01, Revision 1, discusses a postulated (( )) through crack included between the divider plate and tubesheet.

However, M2004-B001 states that this flaw is

(( )) long.

6 Finite Element Model Please explain the boundary condition of a

((

)) in Figure 11 of M2004-SR-01, Revision 1. This appears to be an ((

1

)), but it is unclear to the staff how it is added to the model.

7 Finite Element Model BWXT Report No. M2004-B002, Section 9.2, suggests the transients were ((

)).

Please explain the rationale and impact of this approach compared to the thermal boundary conditions described in Figure 8 of M2004-SR-01.

8 Finite Element Model Please clarify if the mesh density ahead of the postulated crack in the finite element model is sufficient to capture the stresses at the crack tip and the large stress gradient ahead of the crack. For numerical elastic fracture analyses, typically the mesh is biased toward the crack tip.

9 Transients Please clarify how the conditions used in the analyses are bounding for the current uprated power of 3645 MWt. For example, the Abstract of the transient analysis report, 222-7720-SR-2, states that the report was prepared for ((

)), while the Summary of the ASME Code and fatigue calculation, 236R-B02, states that it is for an uprate power of

(( )).

10 Transients Please discuss how the modification of the

(( )) for these analyses reduces conservatism and how this impacts the overall conservatism of the analyses.

11 Transients Please discuss the final size of the flaw and whether it is conservative. In conducting the transient analysis, the ((

)).

12 Transients Item 4 of Section 3.3 in Attachment 7 of the LAR explains that ((

)). The staff recognizes similar discussions are in Section 4.1 of EPRI Report 3002002850 and the Discussion section of LR-ISG-2016-01.

However, please discuss how the analyses may have addressed the period of extended operation directly, including analyzed transients.

13 Fatigue Analysis and Please expand on the discussion of how the Acceptance Criteria cladding is in compression and how the 2

((

)). BWXT Report No.

M2004-SR-01 suggests the cladding is in compression and refers to EPRI Report 3002002850. However, the EPRI report refers to compressive stresses in the tubesheet cladding, not the primary head cladding. In addition, Figure 3-23 of EPRI TR-100251 (White Paper on Reactor Vessel Integrity Requirements for Level A and B Conditions) shows the ((

)).

14 Fatigue Analysis and Regarding the ((

Acceptance Criteria )) developed to conduct these analyses: (a) What is the quality assurance pedigree for this code, beyond the verification at the end of M2004-B004-R0? (b)

How was the remainder of the code verified?

(c) Was verification done by a third party?

15 Limit Analysis Please confirm that (( )) is considered the lower-bound collapse load. Per ASME Code Section III, NB-3213.29, Collapse Load Lower Bound, ((

)). In this case, the ((

)). Figure 9.2 of M2004-B005-R0 suggests the ((

)).

16 Minimum Channel The Byron Unit 1 and Braidwood Unit 1 Head Thickness checklist in Appendix A of Revision 2 of M1702-LR-01 states that the minimum channel head thickness is (( )). However, the documents on the portal do not appear to use this thickness value. For example, Revision 0 of M2004-B001 and Revision 4 of 222-7720-SR-1 use (( )), Revision 1 of M2004-B003 states (( )) at Paths 4 and 8, and Revision 0 of M2004-B004 uses ((

)). Please discuss the different thickness values and their impact on the analyses.

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