ML25325A172
| ML25325A172 | |
| Person / Time | |
|---|---|
| Site: | PROJ0728 |
| Issue date: | 12/15/2025 |
| From: | Ngola Otto Licensing Processes Branch |
| To: | |
| Shared Package | |
| ML25325A169 | List: |
| References | |
| EPID L-2025-TOP-0013 | |
| Download: ML25325A172 (0) | |
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OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION REPORT FOR SEPTEMBER 9-11, 2025, REGULATORY AUDIT REGARDING FRAMATOME, INC.
TOPICAL REPORT BAW-10247, REVISION 0, SUPPLEMENT 3P, REVISION 0 REALISTIC THERMAL - MECHANICAL FUEL ROD METHODOLOGY FOR BOILING WATER REACTORS SUPPLEMENT 3: EXTENSION TO HIGHER EXPOSURES PROJECT NO. 728 (EPID: 2025-TOP-0013)
1.0 BACKGROUND
On September 9-11, 2025, the U. S. Nuclear Regulatory Commission (NRC) staff conducted an in-person audit (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25212A128) to facilitate the review of Topical Report (TR) BAW-10247, Revision 0, Supplement 3P, Revision 0, Realistic Thermal-Mechanical Fuel Rod Methodology for Boiling Water Reactors Supplement 3: Extension to Higher Exposures. BAW-10247, Revision 0, Supplement 3P, Revision 0 was submitted by Framatome Inc. (Framatome), for NRC staff review by application dated April 7, 2025 (ML25094A181).
2.0 REGULATORY AUDIT OBJECTIVES The audit objectives were accomplished through discussions with Framatomes technical experts. The NRC and Framatome audit participants are provided below.
NRC Participants Name Affiliation Kevin Heller NRC River Rohrman NRC Richard Fu NRC (virtual)
Ngola Otto NRC Framatome Participants Name Affiliation Alam Meginnis Framatome Michael Anderson Framatome Paul Smith Framatome Sungje Hong Framatome Mustafa Siddiqi Framatome Chad King Framatome
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION Framatome Participants Name Affiliation Wesley Anderson Framatome Michael Harris Framatome Kevin Mon Framatome Ioan Arimescu Framatome Jeff Morris Framatome Sean Gray Framatome (virtual)
Dan Tinkler Framatome (virtual) 3.0 REGULATORY AUDIT BASES Applicable regulations are found in the following sections of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization Facilities:
10 CFR Part 50, Appendix A, General Design Criteria 10, which require the reactor core, coolant, and protection systems are designed to provide sufficient margin to the specified acceptable fuel design limits (SAFDLs) during normal operation and including anticipated operational occurrences (AOOs).
Additional review guidance is provided in NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition, Section 4.2, Fuel System Design.
The audit was performed in accordance with the NRC Office of Nuclear Reactor Regulation Office Instruction LIC-111, Revision 1, Regulatory Audits, dated October 31, 2019 (ML19226A274).
4.0 DISCUSSION In the audit plan, the NRC staff listed several topics, questions, and requests that needed clarification. The list is provided below. During the audit, Framatome representatives presented responses to the NRC audit plan questions as described below.
General (Question 1)
There does not appear to be discussion regarding the quantification of uncertainties associated with the new models presented for application to higher burnups or the existing models that are being extended to higher burnups. What is the quantification of associated uncertainties or the justification for the continued applicability of the existing uncertainty quantification?
Audit Discussion (Question 1)
Framatome discussed various justifications for the continued applicability of existing uncertainties. Many of the justifications were based on the ((
)) Framatomes justifications were responsive to the NRC staffs questions.
NRC staff noted the TR implies but does not directly state that the higher burnup fission gas release (FGR) database includes both steady state and transient data. Framatome confirmed
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION for NRC staff that the database does include both. The NRC staff examined associated calculation notes and verified this. The NRC staff indicated a potential Request for Additional Information (RAI) may be issued for this confirmation pending further internal discussion.
Section 2.1, Applicable Regulatory Guidance (Question 2)
((
)).
Audit Discussion (Question 2)
Framatome discussed ((
)) Framatome pointed to previous RODEX4 TR supplements to illustrate the ((
)) This was responsive to the NRC staffs questions.
NRC staff noted a reasonable likelihood of needing to issue an RAI (in conjunction with related material from Question 14) regarding the supportive database.
Section 2.4, Exposure Distributions in Part-length Fuel Rods (Question 3)
In Table 2-4, Data Gaps Identified in PNNL [Pacific Northwest National Laboratory] Report, provides the justifications for assessing ((
)) for approval of ((
)) for the following parameters for which significant data is only available up to 70 GWd/MTU: Fuel Centerline Temperature, Power Ramp Tests, Fission Gas Release, Cladding Corrosion, and Hydriding Cladding Mechanical Properties.
Audit Discussion (Question 3)
Framatome discussed the justifications for the conclusions presented in Table 2-4 and identified where additional information to support the positions are readily available. The discussion was responsive to the NRC staffs questions.
Section 3.0, RODEX4 Thermal-Mechanical Applicability to Extended Exposure Range (Question 4)
Provide more details and data updates on extending Supplement 2 Safety Evaluation Report to allow modeling of boiling water reactor (BWR) fuel assemblies from a fuel assembly-average exposure of ((
)) to ((
)).
Audit Discussion (Question 4)
After clarifying the intent of this audit question, NRC staff concluded the scope of this question is more appropriately addressed via Audit Question 17 and Audit Question 20.
Section 3.1.1, G1-Fuel Centerline Temperature (Question 5)
The range of chromium doped (Cr-doped) fuel temperatures tested does not include an extended burnup range. Provide further explanation of how the Chromium (Cr)-doped fuel was treated for extended burnup past 62 megawatt-days per kilogram of uranium (MWD/kgU).
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION Audit Discussion (Question 5)
Framatome provided justification and supportive documentation that Cr-doped fuel acts substantially like UO2 fuel, particularly with respect to thermal conductivity degradation. NRC staff examined calculation notes to further assess the similarities. The discussion was responsive to NRC staffs questions.
Section 3.1.2.2, High-Exposure FGR [Fission Gas Release] Dataset (Question 6)
The discussions provided in Section 3.1.2.1, Summary of RODEX4 FGR Model, and Section 3.1.2.2, High-Exposure FGR Dataset, suggest that the database included in the original RODEX4 TR submittal for validation of the FGR model contains higher burnup data.
This database contains both steady state and transient (power ramp) data. However, its unclear from these discussions if the higher burnup portion of the data contained transient FGR. Has the FGR model been benchmarked or validated at extended burnup against the increased release of fission gases that can occur during rapid fuel pellet temperature redistribution that can occur during some transients?
Audit Discussion (Question 6)
Framatome confirmed for NRC staff that the database for FGR does include both steady state and transient data. NRC staff examined associated calculation notes and verified this. With regard to rapid thermal redistribution, Framatome indicated that such an event is typical for LOCA or rod ejection, which are not covered by RODEX4. The discussions were responsive to NRC staff questions.
Section 3.1.2.3, V&V [Validation and Verification] of RODEX4 for the High-Exposure FGR (Question 7)
((
)).
Audit Discussion (Question 7)
Framatome clarified that the subsets of data in the associated plot consist of fuel rods irradiated in the same bundle and discharged at different cycles. Thus, the data consist of the same fuel and cladding manufacturing and similar power histories. ((
)) is a bundle for which FGR kinetics data was collected due to its operating history. A full discussion of this history and the bundles characteristics were made available to the staff via a research paper. Framatome also indicated the available data demonstrate good agreement with calculations because of
((
)) The discussions and research paper were responsive to the NRC staffs questions.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION Section 3.1.2.4, Application of RODEX4 FGR Model to Cr-doped Fuel (Question 8)
Provide an explanation to accompany Figure 3-6, Exposure Range for Cr-doped Fission Gas Release Dataset, as there are no references to it throughout the TR. ((
)).
Audit Discussion (Question 8)
Framatome identified there is a typo in the TR; the figure referenced in Section 3.1.2.4 of the TR should be to Figure 3-6 instead of 3-4 (hence, Section 3.1.2.4 contains the pertinent discussion for Figure 3-6). The NRC staff noted Figure 3-6 appears to ((
))
Framatome indicated that the pertinent data is available in RAI-8.b of the Cr-doped TR.
However, after examining the response to this RAI, NRC staff had additional questions regarding the range of data provided and indicated that an RAI would likely be needed.
Section 3.2.1.1, Uniform Zircaloy-2 BWR Corrosion/HPU [Hydrogen Pick-up] Model (Question 9)
Would the approval of the new Uniform Zircaloy-2 BWR Corrosion/HPU model supersede the previous HPU model approved in BAW-10247, Supplement 1P? Are there any differences between the model in this TR versus Supplement 1P other than the new data that are considered? With the oxide layers no longer being overestimated due to a new measurement methodology that is not impacted by crud, will crud still be taken into consideration in a conservative manner?
((
)). Please provide a comparison to data that demonstrates the predictive capability of the new model.
Audit Discussion (Question 9)
Framatome indicated the uniform corrosion model presented in the TR (Supplement 3) is identical to the one described and approved as part of Supplement 1 (BAW-10247(P)(A),
Supplement 1). Further, to be conservative, ((
)) (per BAW-10247(P)(A), Revision 0, Section 3.3).
Based on available data, ((
)) would bound any crud layer one would expect to see. The discussion was responsive to the NRC staffs questions.
Section 3.2.1.2, V&V of the Uniform Corrosion Model for BWR Zircaloy-2 Cladding (Question 10)
The full-length rod exposure for V&V of the Uniform Corrosion Model is stated to be ((
)). Please provide justification for the burnup values from plant A2 used for V&V for this new model.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION Audit Discussion (Question 10)
Framatome clarified that the Plant A2 data are a subset of the whole V&V data set, and it is representative with respect to residence time and validates ((
)) Framatome also indicated that additional data is available over the requested burnup range. This discussion was responsive to the NRC staffs questions.
Section 3.2.1.3, V&V of the HPU Model for BWR Zircaloy-2 Cladding (Question 11)
((
)).
Audit Discussion (Question 11)
Framatome provided pertinent calculation notes. NRC staff noted through examination of these documents and discussion with Framatome that the bracketed data in Figure 3-7 ((
)). The discussions with Framatome and the documentation provided were responsive to the NRC staffs questions.
Section 3.2.2, G6-Cladding Mechanical Properties (Question 12)
Please provide more information on the cladding mechanical properties and how they were determined. ((
)).
Audit Discussion (Question 12)
Framatome clarified that ((
)) the 1 percent strain criterion is defined as elastic strain plus permanent strain increment without radiation growth. Inclusion of ((
)). Framatome also clarified that fast fluence in a light water reactor is proportional to burnup ((
)). Framatomes clarification were responsive to the NRC staffs questions.
Section 3.3.1, HP1-Oxidation and Hydriding Irradiation Limits (Question 13)
The large margin to the HPU values provided are given based on an exposure of
((
)). Is this the full-length rod average or the fuel assembly average? The burnup range extension requested in this TR for a full-length rod average is ((
)). Please
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION provide the hydrogen update margin at the peak of the burnup range requested or explain why what is in the TR is acceptable.
Audit Clarification (Question 13)
Framatome clarified the database used for validation includes ((
)) Framatome and NRC staff also discussed the dependence of hydrogen pickup and oxidation on residency time as opposed to burnup, and NRC staff noted the ((
)) Framatomes discussions were responsive to NRC staff questions.
Section 3.3.3, HP3-Fission Gas Release and Fuel Rod Internal Pressure (Question 14)
While the percentage FGR results of Section 3.1.2 provide support rod internal pressure is being calculated appropriately, a direct comparison of rod internal pressures against measured data makes for a ready assessment of the continued applicability of the current rod internal pressure limit at higher burnups (as well as assurance that all phenomenological models that contribute to rod internal pressure are being modeled appropriately). Are there any comparisons available of computed rod internal pressure versus measured rod internal pressure at higher burnups? If so, please provide the relevant analyses.
Audit Discussion (Question 14)
The response to this question is subsumed by the response to Question 2. NRC staff noted a reasonable likelihood of needing to issue an RAI (in conjunction with related material from Question 2) regarding the supportive database.
Section 4.2, High Burnup Structure [HBS] (Question 15)
There does not appear to be any reference to the correlation between rim width and high burnup structure (HBS) in the initial RODEX4 TR or safety evaluation. Provide more details on how this correlation was developed, how RODEX4 implements it, and how it is acceptable at the burnup range requested in this TR.
Audit Discussion (Question 15)
The consideration of high burnup structure, or rim porosity effects, as it is described in the initial RODEX4 TR, was discussed. The NRC staff reviewed internal calculation documents and confirmed that the impacts of higher burnup structure were considered. The discussion was responsive to NRC staff questions.
Section 5.3, Extension of NAF RPP [Radial Power Peaking] Correlations for Higher Enrichments (Question 16)
Please provide more detail on how the higher enrichment data from GALILEO was incorporated in RODEX4.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION TR Section 5.3, Extension of NAF RPP Correlations for Higher Enrichments, states that for AFM applications fuel enrichment must be increased above 5 weight-percent (wt%), and therefore, the Radial Power Peaking (RPP) tables have been extended to 10 wt% U-235 enrichment and 10 wt% gadolinia. However, it also states that laterafter the submittal of RODEX4 TRan updated versions of ((
)), namely ((
)) was used to extend the enrichment range to 10 wt% U-235, except for the gadolinia fuel, in which case the maximum U-235 enrichment remained at 5 wt% U-235. Please explain this apparent discrepancy in the range of uranium and gadolinia enrichments. Also, please provide detailed analyses of the extended enrichment range and gadolinia concentration.
Audit Discussion (Question 16)
Framatome provided clarification on the various RPP tables utilized within RODEX4 and their origin. Specifically, ((
- l.
)) NRC staff examined associated documentation and indicated to Framatome an RAI would likely be needed to ensure appropriate documentation of the RPP tables and their origin.
Section 6.1.1, Rod Bow (Question 17)
Since the rod bow correlation from Supplement 2P ((
)), how was the correlation extrapolated to the end-of-life burnup level requested? How is this different from the parameters that were assessed in Table 2-1, Standard Review Plan Section 4.2 Criteria, to
((
))? Is additional validation performed? If so, please provide a discussion and applicable data.
Audit Discussion (Question 17)
Framatome explained the process of extrapolating utilized for extending the rod bow correlation to the End-of-Life burnup level requested. A useful figure which outlines the data is provided in RAI Figure 1-1 in BAW-10247P-A Supplement 2 Q1P. The discussion was responsive to the NRC staffs questions.
Section 7.0, Update Process (Question 18)
Within the provided context, it is not clear how the word model is being used or how it should be interpreted, particularly with respect to replacing them. For example, changing the coefficients of an equation could be construed as a new model. Alternatively, changing coefficients could be considered the same model because the mathematical forms of the underlying equations remain unchanged, and only when the underlying mathematical forms of equations are changed would a model be considered new. In light of this, please further discuss the phrase the only change will be the replacement of the model or models in paragraph 3 of Section 7, specifically with respect to the intended interpretation of the word model.
Audit Discussion (Question 18)
Framatome explained their use of the word model and how it relates to the calibration parameters. A model is a mathematical expression of physical processes in RODEX4 methodology and includes the defining equations and calibration constants. This is consistent
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION with Limitation and Condition 4 of the RODEX4 TR. After discussion with the NRC staff, Framatome stated they would provide an update to the supplement to revise this section for clarification.
Appendix A, Sample Problem (Question 19)
((
))?
Audit Discussion (Question 19)
Framatome discussed the sample problem and provided explanation for the values used. The discussions were responsive to the NRC staffs questions.
Appendix B, BWR Fuel Rod to Fuel Assembly Differential Growth Correlation (Question 20)
((
))?
Audit Discussion (Question 20)
Framatome elaborated on the statistical procedure used to extrapolate the differential fuel rod/fuel assembly growth correlation to the burnup level requested. The discussion provided additional insight into the growth phenomena and trends that were used to justify the extrapolation to higher burnup levels. While the discussion was responsive to the NRC staffs questions, the NRC staff noted that additional information will likely need to be provided via RAI.
Additional Audit Discussion Notes During the audit, Framatome and NRC staff discussed the justification provided in the TR for meeting fuel system damage criteria of NUREG-800 Chapter 4.2 with regard to dimensional changes such as fuel rod growth. Some of the justification provided in the TR made generalized assertions that could potentially lead to NRC RAIs in future license amendment requests.
Specifically, line A.V of Table 2-1 states ((
)) The currently approved RODEX4 ((
)) were determined using MICROBURN-B2. The use of ((
)) After internal discussion, NRC staff indicated to Framatome that an RAI would likely be issued on the matter to resolve the potential concern generically (during the TR review). This would avoid potential complications on the subject during the review of future license amendment requests.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION 5.0 DOCUMENTS REVIEWED
6.0 CONCLUSION
The audit accomplished the objectives listed in Section 2.0 by allowing direct interaction with Framatomes technical experts. The NRC staff participants were able to obtain clarification on their questions and will issue requests for information needed on the docket. This audit supports the TR review and development of the NRC staffs safety evaluation. No regulatory decisions were made at the audit.