ML25174A258
| ML25174A258 | |
| Person / Time | |
|---|---|
| Site: | 99902041 |
| Issue date: | 06/25/2025 |
| From: | Ngola Otto Licensing Processes Branch |
| To: | |
| Shared Package | |
| ML25174A239 | List: |
| References | |
| ANP-10354P, Rev. 0 | |
| Download: ML25174A258 (1) | |
Text
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FRAMATOME TOPICAL REPORT, ANP-10354P, "SINGLE-PHASE CFD FOR FUEL ASSEMBLY CHARACTERIZATION" FRAMATOME INC.
DOCKET NO. 99902041 ISSUE DATE: 06/25/2025
=
Background===
By letter dated May 22, 2024 (Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML24143A171), Framatome, Inc. submitted Topical Report (TR) ANP-10354P, Revision 0, Single-phase CFD for Fuel Assembly Characterization, for U.S. Nuclear Regulatory Commission (NRC) staffs review and approval. The NRC staff has reviewed the proposed TR, conducted an audit on October 21-24, 2024 (ADAMS Accession Nos. ML24291A118 and ML24352A156), and determined that additional information is needed to complete the review. The NRC staffs request for additional information (RAI)-10679-R1 is provided below.
Regulatory Basis The regulatory basis for this RAI can be found in Title 10 of the Code of Federal Regulations, Appendix A to Part 50, General Design Criteria (GDC)-10, Reactor Design, that is provided in NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants (SRP), Section 4.4, Thermal and Hydraulic Design. In accordance with SRP Section 4.4, the objectives of the thermal and hydraulic designs safety review are to provide reasonable assurance that there should be a 95-percent probability at the 95-percent confidence level that a hot fuel rod in the reactor core will not experience a departure from nucleate boiling or a transition condition during normal operation or anticipated operational occurrences.
Question 1
- a. The Phenomena Identification and Ranking Table (PIRT) analysis is of primary importance to Framatomes Computational Fluid Dynamics (CFD) methodology. In its review of the PIRT provided by Framatome in the TR, ANP-10354P, Revision 0, the NRC staff did not find evidence which justifies the PIRT conclusions. Therefore, the NRC staff requests that Framatome provide evidence which demonstrates the credibility of the results of the PIRT analysis and justifies the rationale for the assigned ranking of each parameter. This may include:
Definitions and justification for assigning High (H), Medium (M), or Low (L) importance across operational, manufacturing, numerical, modeling, and measurement parameters.
Discussions on how rankings were determined - whether through expert elicitation, structured scoring methods, or quantitative analyses - and specify the criteria or thresholds used to differentiate between rankings.
Explanations of how consistency across parameter types was ensured.
Discussions of the role of expert judgment versus data-driven analysis.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION Discussions of how local versus global system influence was considered in assigning importance.
- b. The dimensionless distance from the wall (y+) [
))
- c. Given the large number of possible test cases, the NRC staff is unsure of why data were presented for specific cases, and not others. Therefore, the NRC staff requests Framatome to elaborate on the criteria and methodology used to select the specific cases presented for each modeling feature. Specifically, clarify whether these cases represent bounding scenarios (e.g., best-case, worst-case, or nominal operating conditions) and how they were determined to be representative of the sensitivity behavior. Additionally, provide clarification on how the sensitivity of each key modeling parameter varies across the different evaluated assembly designs.
Question 2 As defined in the TR, ANP-10354P, Revision 0, Table 7-2, "Methodology Applicability," the current proposed methodology applicability would allow for an almost limitless number of possible fuel design changes. The NRC staff believes that, for its associated risk significance, the Framatomes CFD methodology would likely result in a reasonable estimate of the single-phase pressure drop for many future designs. However, given the very large number of possible future designs, the NRC staff cannot confirm that the methodology would result in a reasonable estimate of the single-phase pressure drop for all future designs. For example, ((
))
Therefore, the NRC staff requests that Framatome provide either a more detailed applicability section which clearly limits all future applications of the CFD methodology to only those designs which the methodologys validation domain supports, or develop an approach of confirming, with the NRC technical staff, that the CFD methodology is appropriate for a given future design.
Question 3 In review of Equation 23 in the TR, the NRC staff has identified a potential error. Specifically, the term would not equal the Right Hand Side, but zero. To perform this analysis,
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION the NRC used the definition of Reynolds number
, rearranged this to solve for the velocity
, substituted in the hydraulic diameter for the characteristic length
, and then substituted this term into the Bernoulli equation for the velocity. This results in a modified form of Equation 23.
The NRC staff requests Framatome to confirm that the equation derived using the above substitutions matches the results of Equation 23 or justify the difference.
Question 4 In its review of Section 9.1.2, "Experimental Uncertainty," of the TR, ANP-10354P, Revision 0, the NRC staff could not determine how Framatome calculated the uncertainty. Therefore, the NRC staff requests that Framatome provide further details clarifying the data and the procedure used to generate this uncertainty.
Question 5 In its review of the TR, ANP-10354P, Revision 0, the NRC staff found that the ((
)) was discussed, but no analysis was given. Therefore, the NRC staff requests that Framatome describe how this approach was used to determine the
((
))
Question 6 Framatome has well characterized the channel width uncertainty, and [
)) The NRC staff requests that Framatome explain why the ((
))
ADAMS Accession Nos.:
ML25174A239 (Package)
ML25174A194 (RAI - Proprietary)
ML25174A258 (RAI - Non-proprietary)
OFFICE NRR/DSS/D NRR/DORL/LLPB/BC NRR/DORL/LLPB/PM NAME JWhitman JRankin NOtto DATE 6/18/2025 6/23/2025 6/23/2025 OFFICE NRR/DORL/LLPB/LA NRR/DORL/LLPB/PM NAME DHarrison NOtto DATE 6/23/2025 6/25/2025