ML26015A117
| ML26015A117 | |
| Person / Time | |
|---|---|
| Site: | 99902041 |
| Issue date: | 02/03/2026 |
| From: | Ngola Otto Licensing Processes Branch |
| To: | |
| Otto N, NRR/DORL/LLPB | |
| Shared Package | |
| ML26015A112 | List: |
| References | |
| EPID L-2025-TOP-0018 | |
| Download: ML26015A117 (0) | |
Text
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION MARCH 4-5, 2026, REGULATORY AUDIT PLAN FOR FRAMATOME TOPICAL REPORT EMF-93-177, REVISION 1, SUPPLEMENT 1P, REVISION 0, MECHANICAL DESIGN FOR BWR FUEL CHANNELS: ATRIUM BWR ENHANCED ACCIDENT MODEL DOCKET NO. 99902041 EPID: 2025-TOP-0018
1.0 BACKGROUND
By letter dated May 16, 2025 (Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML25136A387), Framatome, Inc. (Framatome) submitted Topical Report (TR) EMF-93-177, Revision 1, Supplement 3P, Revision 0, Mechanical Design for BWR [Boiling Water Reactor] Fuel Channels: ATRIUM BWR Enhanced Accident Model, for U.S. Nuclear Regulatory Commission (NRC) staffs review and approval.
Based on the initial review of the TR, the NRC staff have determined that a regulatory audit would facilitate its review. Pacific Northwest National Laboratory (PNNL) staff will be supporting the NRC staff at the audit because PNNL is providing technical assistance for the review of EMF-93-177, Revision 1, Supplement 3P, Revision 0 (hereafter referred to as the TR). The audit will be conducted in-person from March 4-5, 2026, at Framatomes facility located in Richland, Washington (WA).
2.0 REGULATORY AUDIT BASES Regulatory guidance for the review of fuel system designs and adherence to Title 10 of the Code of Federal Regulations, Appendix A to Part 50, General Design Criteria-10, Reactor Design, is provided in NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants (SRP), Section 4.2, Fuel System Design. In accordance with SRP Section 4.2, the objectives of the fuel designs safety review is to provide reasonable assurance that: (1) the fuel system is not damaged as a result of normal operation and anticipated operational occurrence, (2) fuel system damage is never so severe as to prevent control rod insertion when it is required, (3) the number of fuel rod failures is not underestimated for postulated accidents, and (4) coolability is always maintained. The design bases include (1) fuel system damage, (2) fuel rod failure, and (3) fuel coolability. Dimensional changes of the fuel channel must be included in the design analysis to establish operational tolerances, which are part of the requirements in the design bases.
3.0 REGULATORY AUDIT SCOPE The audit will focus primarily on the TR, the enclosed audit information needs, all relevant supporting documentation (e.g., methodology, calculations), and questions identified in Section 8.0, Audit Questions and Requests, below. The purpose of this audit is to gain a more detailed understanding of the information supporting Framatomes proposed TR methodology and to address questions via in-person discussions.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION represented in the model, e.g., use of best-estimate, bounding, or 95/95 tolerance bounds.
Explain how this choice is justified in terms of the impact of uncertainty on design margin.
- 3. The TR and supporting documents describe model sensitivity to frequency and amplitude of excitation. However, sensitivity of the model to damping is not discussed. Please describe the sensitivity of the model to changes in damping?
- 4. Section 4.5, Amplitude, Frequency, and Time Step Sensitivity, of the TR describes sensitivity checks on model parameters including ((
)). The sensitivity of the model to the level of mesh discretization is not discussed. Has the effect of different mesh discretization besides that described in the documentation ((
)) been investigated, and how is the current discretization justified?
- 5. Provide a walkthrough of mass assignments in the model and explain and justify any simplifications made with respect to how the masses of fuel assembly components are represented in the model.
- 6. ((
)).
Explain and justify the assumptions underlying the fuel assembly ((
)) stress analysis.
- 7. Explain how damping is applied in the model. In reading ((
)), Section 8.3, it appears that the ((
))?
- 8. Explain how the moments in the time histories are synchronized/time-phased for the square root of the sum of the squares (SRSS) evaluation of the fuel assembly components.
- 9. Section 5.2, Loads, of the TR states that the Case 2 load scenario includes N+P+SSE+CHUGGING+SRV. Table 5-1, Fuel Channel ((
)) Results, in the same document states that the Case 2 load scenario includes
((
)). Confirm whether or not safe shutdown earthquake was included in the Case 2 load scenario.
- 10. Interaction between the grids, water channel and fuel channel is ((
)).
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION
- 11. Explain how the ((
)) were implemented into the finite element model data listed in ((
)).
- 12. Section 6.2 of ((
)), provides the spring stiffness values used in the sample problem, which has initial stiffness of ((
)).
Explain the use of ((
)).
- 13. Section 6.3 of ((
)), provides the spring stiffness values used in the sample problem, which has initial rotational stiffness of
((
)). Explain the use of ((
)).
- 14. An ((
)). Explain why this was done.
- 15. ((
)) provides the derived values for the moment of inertia of the fuel rod beam elements. The NRC staff determined that the derived value is ((
)).
Provide justification for the calculation method.
- 16. Explain the fuel assembly bottom geometry and how it is applied in the finite element model.
Explain and justify the lower tie plate and associated connections to the core plate, water channel, and fuel rods, and the applied boundary conditions to these components in this region.
- 17. Explain how the ((
)) Staff have discovered a potential discrepancy in the ((
))
- 18. Explain how the set of ((
)) are calculated and implemented into the finite element model.