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LLC Submittal of Supplemental Topical Report Entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601-P, Revision 3
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Issue date:	10/12/2023
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LO-151253 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Docket No.52-050 October 12, 2023 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738

SUBJECT:

NuScale Power, LLC Submittal of Supplemental Topical Report Entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601-P, Revision 3

REFERENCES:

1.

NuScale letter to NRC, NuScale Power, LLC Submittal of Topical Report Supplement Entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, TR-108601, Revision 1, dated April 25, 2022 (ML22115A223) 2.

NRC letter to NuScale, Audit Plan for the Regulatory Audit of NuScale Power Topical Report Supplement Entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2. TR-108601, Revision 1, dated June 21, 2022 (ML22168A086) 3.

NuScale letter to NRC, NuScale Power, LLC Submittal of Supplemental Topical Report Entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601, Revision 2, dated December 13, 2022 (ML22347A315)

NuScale Power, LLC (NuScale) hereby submits Revision 3 of the supplemental topical report entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601. The purpose of this submittal is to provide an updated revision of the statistical subchannel analysis methodology topical report. The content of the revision is consistent with descriptions provided to the NRC during audit of previous revisions of the topical report (Reference 2). Revision 3 supsersedes previously submitted revisions of this topical report (Reference 1 and Reference 3). contains the proprietary version of the report entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601, Revision 3. NuScale requests that the proprietary version be withheld from public disclosure in accordance with the requirements of 10 CFR § 2.390. The enclosed affidavit (Enclosure 3) supports this request. Enclosure 1 has also been determined to contain Export Controlled Information. This information must be protected from disclosure per the requirements of 10 CFR § 810. Enclosure 2 contains the nonproprietary version of the report.

LO-151253 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Page 2 of 2 10/12/23 This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.

If you have any questions, please contact Wren Fowler at 541-452-7183 or at sfowler@nuscalepower.com.

Sincerely, Thomas Griffith Manager, Licensing NuScale Power, LLC Distribution: Matthew Mitchell, NRC Getachew Tesfaye, NRC Stacy Joseph, NRC : Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601-P, Revision 3, proprietary version : Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601-NP, Revision 3, nonproprietary version : Affidavit of Carrie Fosaaen, AF-151254

LO-151253 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com :

Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601-P, Revision 3, proprietary version

LO-151253 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601-NP, Revision 3, nonproprietary version

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology Licensing Topical Report

Statistical Subchannel Analysis Methodology Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology October 2023 Revision 3 Docket: 52-050 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 www.nuscalepower.com

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology Licensing Topical Report

© Copyright 2023 by NuScale Power, LLC ii COPYRIGHT NOTICE This report has been prepared by NuScale Power, LLC and bears a NuScale Power, LLC, copyright notice. No right to disclose, use, or copy any of the information in this report, other than by the U.S. Nuclear Regulatory Commission (NRC), is authorized without the express, written permission of NuScale Power, LLC.

The NRC is permitted to make the number of copies of the information contained in this report that is necessary for its internal use in connection with generic and plant-specific reviews and approvals, as well as the issuance, denial, amendment, transfer, renewal, modification, suspension, revocation, or violation of a license, permit, order, or regulation subject to the requirements of 10 CFR 2.390 regarding restrictions on public disclosure to the extent such information has been identified as proprietary by NuScale Power, LLC, copyright protection notwithstanding. Regarding nonproprietary versions of these reports, the NRC is permitted to make the number of copies necessary for public viewing in appropriate docket files in public document rooms in Washington, DC, and elsewhere as may be required by NRC regulations.

Copies made by the NRC must include this copyright notice and contain the proprietary marking if the original was identified as proprietary.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology Licensing Topical Report

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology Licensing Topical Report

All Initial Issue 1

All Reissued to address NRC Request for Supplemental Information (RSI) 2 All Reissued to reintroduce modeling removed in Revision 1 with additional supporting justification as discussed during NRC audit.

3 All Incorporated changes in response to NRC audit questions.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology Table of Contents

1.0 Introduction.......................................................... 3 1.1 Purpose.............................................................. 3 1.2 Scope................................................................ 3 1.3 Abbreviations and Definitions.............................................. 3 1.4 Topical Report Supplement Format and Layout............................... 3 2.0 Background.......................................................... 4 2.1 VIPRE-01............................................................. 4 2.2 As-Approved Use....................................................... 4 2.3 VIPRE-01 Safety Evaluation Report Requirements............................. 4 2.4 Regulatory Requirements................................................ 4 3.0 General Application Methodology........................................ 5 3.1 Nuclear Safety Engineering Disciplines...................................... 5 3.2 Core Design Limits...................................................... 5 3.3 Critical Heat Flux Correlation.............................................. 5 3.4 Thermal Margin Results Reporting......................................... 6 3.5 Geometry Design Input.................................................. 7 3.6 Fuel Design Specific Inputs............................................... 8 3.7 Basemodel............................................................ 8 3.7.1 Radial Nodalization............................................... 9 3.7.2 Axial Nodalization................................................ 10 3.7.3 Review of Changes to Basemodel................................... 11 3.8 Boundary Conditions................................................... 15 3.9 Turbulent Mixing....................................................... 15 3.10 Radial Power Distribution................................................ 15 3.10.1 Static Standard Review Plan Section 15.4 Analyses..................... 15 3.10.2 Time-Dependent Standard Review Plan Section 15.4 Analyses............ 16 3.10.3 Enthalpy Rise Hot Channel Factor................................... 16 3.10.4 Radial Flux Tilt.................................................. 17 3.10.5 All Rods Out Power Dependent Insertion Limit Enthalpy Rise Hot Channel Factor......................................................... 17 3.10.6 Determining the Bounding Radial Power Distribution.................... 17 3.10.7 Deterministic Radial Power Distribution............................... 20

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology Table of Contents

© Copyright 2023 by NuScale Power, LLC vi 3.10.8 Axial Power Distribution........................................... 21 3.10.9 Standard Review Plan Section 15.4 Analyses.......................... 21 3.11 Numerical Solution..................................................... 21 3.12 Statistical Method and Treatment of Uncertainties............................ 21 3.12.1 Uncertainty in Analysis Method..................................... 21 3.12.2 Uncertainty in Operating Conditions.................................. 23 3.12.3 Uncertainty in Physical Data Inputs.................................. 27 3.12.4 Enthalpy Rise Engineering Uncertainty............................... 27 3.12.5 Heat Flux Engineering Uncertainty................................... 28 3.12.6 Linear Heat Generation Rate Engineering Uncertainty................... 29 3.12.7 Radial Power Distribution (SIMULATE5) Uncertainty.................... 29 3.12.8 Fuel Rod and Assembly Bow Uncertainty............................. 29 3.12.9 Core Inlet Flow Distribution Uncertainty............................... 30 3.12.10 Core Exit Pressure Distribution Uncertainty........................... 30 3.13 Bias and Uncertainty Application within Analysis Methodology................... 30 3.13.1 Statistical Methods............................................... 30 3.13.2 Statistical CHF Analysis Limit....................................... 33 3.13.3 MCHFR Calculation Process...................................... 39 3.13.4 Calculating the Statistical CHF Analysis Limit.......................... 40 3.13.5 Summary of Bias and Uncertainty Treatment.......................... 40 3.14 Mixed Core Analysis................................................... 42 3.15 Methodology-Specific Acceptance Criteria.................................. 42 4.0 Transient-Specific Applications Methodologies............................ 43 5.0 VIPRE-01 Qualification................................................ 44 6.0 Example Calculation Results........................................... 45 6.4 Sensitivity Analysis..................................................... 45 6.4.1 Radial Geometry Nodalization...................................... 45 6.4.3 Axial Geometry Nodalization....................................... 51 6.4.4 Inlet Flow Distribution............................................. 52 7.0 Summary and Conclusions............................................. 55 7.1 VIPRE-01 Safety Evaluation Report Requirements............................ 55 7.2 Criteria for Establishing Applicability of Methodology.......................... 55

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology Table of Contents

© Copyright 2023 by NuScale Power, LLC vii 7.2.1 General Criteria................................................. 55 7.2.2 Critical Heat Flux Correlation....................................... 56 7.2.3 Nuclear Analysis Discipline Interface................................. 56 7.2.4 Transients Discipline Interface...................................... 57 7.3 Cycle-Specific Confirmations............................................. 57 7.4 Key Fuel Design Interface Requirements................................... 57 7.5 Unique Features of the NuScale Design.................................... 58 8.0 References.......................................................... 59 8.1 Referenced Documents................................................. 59

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology List of Tables

© Copyright 2023 by NuScale Power, LLC viii Table 1-1 Abbreviations.................................................... 3 Table 3-3 Sample Size versus Number of Allowable Failures...................... 33 Table 3-4 Summary of Example Subchannel Methodology Parameter Treatment...... 41 Table 6-17 Radial Nodalization Sensitivities.................................... 45 Table 6-18 Radial Geometry Nodalization Linear Heat Generation Rate Sensitivity Results........................................................ 51 Table 6-19 Axial Nodalization Sensitivities...................................... 51 Table 6-20 Axial Geometry Nodalization Linear Heat Generation Rate Sensitivity Results........................................................ 52 Table 6-21 Description of Inlet Flow Distribution Sensitivities....................... 53 Table 6-22 Results Summary of Inlet Flow Distribution Sensitivities.................. 54 Table 7-2 Comparison of NuScale Reactor Core Design to Conventional PWR........ 58

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology List of Figures

© Copyright 2023 by NuScale Power, LLC ix Figure 3-2 Example Thermal Margin Pictorial.................................... 7 Figure 3-3 VIPRE-01 Radial Nodalization....................................... 9 Figure 3-6 Axial Nodalization Diagram for Subchannel Basemodel (Not to Scale)....... 14 Figure 3-7 Example Radial Power Distribution for Core (Top) and Hot Assembly (Bottom)....................................................... 20 Figure 3-10 Density Function of the Uniform Distribution........................... 31 Figure 3-11 Density Function of the Normal Distribution............................ 32 Figure 3-12 CHF Analysis Limit Calculation Flow Chart............................ 37 Figure 3-13 Example Sample SCHFAL Domain.................................. 38 Figure 3-14

((2(a),(c),ECI......... 39 Figure 6-15 Single Fully Detailed Hot Assembly Model............................. 46 Figure 6-16 Nine Detailed Assemblies Model.................................... 47 Figure 6-17 Twenty-Five Detailed Assemblies Model.............................. 48 Figure 6-18 Fully Detailed Core Model......................................... 49 Figure 6-19 Full Core Lumped Model.......................................... 50

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 1 Abstract This report documents the NuScale statistical subchannel analysis methodology using the VIPRE-01 computer code. This methodology is used to calculate margin to fuel thermal limits, such as critical heat flux ratio and fuel centerline temperature. This report discusses how NuScale meets the NRC requirements for use of VIPRE-01, the modeling methodology for performing steady-state and transient subchannel analyses, and the qualification of the code for application to the NuScale design. NuScale intends to use this methodology for thermal-hydraulic analysis in support of future design work for NuScale reactors. NuScale requests NRC approval to utilize this methodology, with the noted limitations described herein, for the NuScale thermal-hydraulic design and supporting analysis.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 2 Executive Summary The purpose of this topical report supplement is to define and justify a statistical based methodology for steady-state and transient subchannel analysis applications. The bases for how the subchannel model is developed and utilized, as well as its application is discussed. This methodology will be utilized to evaluate thermal margin and demonstrate adequate heat removal capability in design applications of the NuScale Power Module (NPM). NuScale requests NRC review and approval of the statistical treatment of uncertainties presented in this supplement. The specific element of the requested approval is:

The methodology for treatment of uncertainties in the NuScale statistical subchannel methodology

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 3 1.0 Introduction 1.1 Purpose The purpose of this topical report supplement is to define and justify a statistical based methodology for steady-state and transient subchannel analysis applications. This methodology will be utilized to evaluate thermal margin and demonstrate adequate heat removal capability in design applications of the NuScale Power Module (NPM). NuScale requests NRC review and approval of the statistical treatment of uncertainties presented in this supplement to the Subchannel Analysis Methodology topical report TR-0915-17564-P-A, Revision 2 (Reference 8.1.1). The specific element of the requested approval is:

The treatment of uncertainties in the NuScale statistical subchannel methodology. 1.2 Scope This report describes the assumptions, codes, and methodology utilized to perform steady-state and transient subchannel analysis for design-basis accidents. This topical report focuses on the NuScale statistical subchannel methodology and is not intended to provide final detailed reactor core design or final values of any other associated accident evaluations. 1.3 Abbreviations and Definitions 1.4 Topical Report Supplement Format and Layout This topical report supplement provides an alternative methodology compared to Reference 8.1.1. The layout of this supplement follows the layout of the original topical report in Reference 8.1.1. Section titles and content are analogous to that presented in the base topical report, unless new content is provided, and then the new content is labeled with the next available section or subsection numbering. Figures, tables, and equations are numbered such that they use the corresponding figure, table, or equation number in Reference 8.1.1. Figures, tables, and equations that are new, in that there was not analogous content in Reference 8.1.1, are provided the next sequential number in that section, to avoid confusion with the table, figure, and equation numbering in Reference 8.1.1. Table 1-1 Abbreviations Term Definition A/Q assurance-to-quality CDF cumulative distribution function LHGR linear heat generation rate M/P measured-to-predicted NPM NuScale Power Module SCHFAL statistical critical heat flux analysis limit WRS Wilcoxon Rank Sum

Background

This section is unchanged relative to the corresponding section of Reference 8.1.1. The CHF correlations approved for use in VIPRE-01 are documented in Reference 8.1.2 and Reference 8.1.3. 2.1 VIPRE-01 This section is unchanged relative to the corresponding section of Reference 8.1.1. 2.2 As-Approved Use This section is unchanged relative to the corresponding section of Reference 8.1.1. The CHF correlations approved for use in VIPRE-01 are documented in Reference 8.1.2. Additionally, an extension of the range of applicability for the NSP4 CHF correlation has been submitted to the NRC for approval in Reference 8.1.3. Additional NRC approved CHF correlations may be used with the code in the future. 2.3 VIPRE-01 Safety Evaluation Report Requirements NuScale continues to fulfill the requirements of the VIPRE-01 Safety Evaluation Report requirements as detailed in the corresponding section of Reference 8.1.1. 2.4 Regulatory Requirements This section is unchanged relative to the corresponding section of Reference 8.1.1.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 5 3.0 General Application Methodology This section describes an overview of the statistical thermal design analysis methodology used for NuScale subchannel analysis. The bases for how the subchannel model is developed and utilized, as well as its application, is discussed. The core is modeled with a one-pass approach, meaning all the characteristics of the hot channel are captured, including inter-channel feedback. The one-pass approach allows the use of a fully-detailed model as well as lumped channel models to resolve the desired enthalpy and flow field. The uncertainty parameters included in the statistical method are independent and do not influence the other statistically treated parameters. 3.1 Nuclear Safety Engineering Disciplines This section is unchanged relative to the corresponding section of Reference 8.1.1. 3.2 Core Design Limits Section 3.7 provides details regarding changes to the basemodel relative to Reference 8.1.1. 3.3 Critical Heat Flux Correlation An NRC-approved CHF correlation is required for reporting thermal margin with the subchannel analysis methodology. The 5 conditions listed in Section 3.3 of Reference 8.1.1 remain applicable to the statistical subchannel analysis methodology. The NRC-approved subchannel analysis methodology LTR has an SER condition that any safety analysis referencing it is subject to referencing an approved CHF correlation. In review of the SER limitations of Reference 8.1.2, analyses using the NSP2 and NSP4 CHF correlations must be performed in accordance with Reference 8.1.1. Section 3.3.5.1 of the SER indicates the basis for the limitation is that the same computer code and models used in the data reduction are used when applying the CHF correlation. The CHF correlation performance, uncertainty, and 95/95 safety limit are dependent upon the local conditions simulated at the CHF location. Thus, the consistent use of the same computer code, same two-phase flow and heat transfer models, and same mixing model coefficients ensures the subchannel analysis methodology evaluates reactor core local conditions with the same underlying basis. The statistical subchannel analysis methodology continues to use the same two-phase flow and heat transfer models and correlations as those used in the NRC-approved methodology of Reference 8.1.1, Section 5.6. These models remain consistent with those listed in Tables 3-14 and 3-15 in Section 3.3.1 of Reference 8.1.2. Therefore, the statistical subchannel analysis methodology is applicable with the NRC-approved NSP4 correlation in Reference 8.1.2. However, in similar fashion to the NRC-approved subchannel analysis methodology, the statistical subchannel analysis methodology is not dependent upon a specific CHF correlation as long as the 5 conditions listed in Section 3.3 of Reference 8.1.1 are satisfied.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 6 3.4 Thermal Margin Results Reporting The corresponding section of Reference 8.1.1 is updated to provide additional clarification for the penalty fractions in Equation 3-4 of Reference 8.1.1. These penalty fractions may be determined either deterministically or statistically to calculate the CHF analysis limit. Additionally, Figure 3-2 shows the MCHFR limits and the example margins in the MCHFR calculation in the statistical subchannel analysis methodology.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 7 3.5 Geometry Design Input This section is unchanged relative to the corresponding section of Reference 8.1.1. Figure 3-2 Example Thermal Margin Pictorial 1.00 CHF Probabilistic UnFertainties 6CHFAL 1.35 Steady-state Initial MCHFR 2.40 Best-Estimate MCHFR > 5.00 Margin for Transients Bounding Model Biases: radial power distribution axial power distribution inlet flow distribution

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 8 3.6 Fuel Design Specific Inputs The application of form loss coefficients to the spacer grids is unchanged from the corresponding section of Reference 8.1.1. Changes to the axial model domain from that presented in Reference 8.1.1 are discussed in Section 3.7.2. With the change in the modeled axial domain, fuel assembly form loss coefficients are applied at the component centerline elevations. 3.7 Basemodel The NuScale core contains 37 fuel assemblies as shown in the red squares of Figure 3-3. The methodology for statistical subchannel analysis utilizes a radial nodalization that models the full core and contains at least one detailed subchannel surrounded by progressively-lumped channels. An example of this is shown in the red squares of Figure 3-3. The basemodel is developed in a conservative manner and it does not represent a cycle-specific core; it is constructed in a way to preserve the limiting core conditions along with the operational envelope specified in the Technical Specifications. It is established based on the design peaking factors in combination with the limiting reactor coolant system global parameters. With this method, an artificial and bounding subchannel analysis model is appropriate, because the methodology ensures the limiting conditions of the cycle-specific core are captured by the basemodel.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 9 3.7.1 Radial Nodalization The radial nodalization for the subchannel VIPRE-01 model represents the core at the level of detail required for the analysis. VIPRE-01 defines channels based on flow area, wetted perimeters, and heated perimeters, with subchannel communications modeled through gaps and centroid distances. The core radial nodalization must have at least one detailed subchannel with progression of lumped subchannels a few rod rows away from the hot subchannel, supported by sensitivity studies; these studies provide assurance that the hot rod and hot subchannel are able to resolve the local conditions while not significantly impacting MCHFR. Figure 3-3 VIPRE-01 Radial Nodalization B C D E F 6 7 G 1 2 3 4 5 A 34x34 3x3 1x1

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 10 As an example, in Figure 3-3 the core is modeled with one fully detailed assembly, where all fuel rods and subchannels are modeled explicitly, and the remaining fuel assemblies progressively lump several subchannels into a single lumped channel. Specifically, assemblies directly adjacent to a fully detailed assembly are represented by nine lumped flow channels while all other assemblies are lumped into a single flow channel. This allows VIPRE-01 to be efficient in performing calculations, while the limiting subchannel local conditions fidelity is maintained. In addition to the nodalization described, as well as that of Reference 8.1.1, limited flexibility is allowed. The following items must be satisfied in order for the radial nodalization to be acceptable:

Reliable and converged solution

Sufficient detail to resolve the dependent variables of CHF and CHF location (i.e., local flow, enthalpy, quality, and power)

Hot rod and immediately adjacent fuel rods must be explicitly modeled in full detail

At locations of node size changes, the relative difference in size (aspect ratio) must be sized in order to preserve fundamental assumptions of the numerical method (Reference 8.1.8)

Each unique nodalization requires a set of sensitivity studies comparing it to more detailed nodalizations with no significant non-conservative impacts on calculated MCHFR Justification for this example progressive-lumping approach is provided in Section 6.4.1. 3.7.1.1 Peripheral Assembly Geometry Modeling The area of the core that is beyond the assembly pitch boundaries is not considered core flow that is available for heat transfer. Therefore, any area that is outside of the assembly pitch boundary line is considered bypass flow. This bypass fraction is reduced from the total primary system flow rate. 3.7.2 Axial Nodalization The axial nodalization for the subchannel model is critical to capture the variance of the flow field throughout the height of the fuel assembly. Axial node size directly impacts the calculated MCHFR. The axial node size is selected to capture the flow field accurately. The following items must be considered and balanced in order to determine the axial nodalization:

Reliable and converged solution

Sufficient detail to resolve the dependent variables of CHF and CHF location (i.e., local flow, enthalpy, quality, and power)

Ensuring that losses are applied in the model consistent with their physical locations

At locations of node size changes, the relative difference in heights (aspect ratio) is roughly similar in order to preserve fundamental assumptions of the numerical method (Reference 8.1.8)

Smaller level heights in which flow diversions or asymmetric flow distributions may occur, such as just before the uppermost grid or at the core inlet, respectively The axial domain in the subchannel model spans from the bottom of the lower core plate to above the upper core plate. At each component, the form loss coefficients are applied at the centerline elevation. Since VIPRE-01 inherently applies drag losses for the entire model, it can over-account for frictional losses outside of the axially rodded regions. These additional frictional losses are acceptable to simplify the modeling. An alternate modeling approach is to adjust the form loss for components outside of the fuel assembly to compensate for the additional drag losses modeled by VIPRE-01. Figure 3-6 is a graphical representation of the axial nodalization scheme for the subchannel basemodel. The statistical subchannel basemodel axial nodalization is dependent upon having fuel design specific component losses as noted in Section 3.6. For implementing this methodology, component loss data from testing of fuel assembly components is required. The ability of the basemodel to properly resolve the flow distribution is ensured by utilizing pressure drop test data to define component losses. For example, the NuFuel-HTP2 fuel design underwent prototypic testing to characterize loss coefficients for each component of the fuel assembly, including spacer grids, bottom and top nozzles, and bare rod friction. The axial nodalization of approximatively 2 inches is justified based on a sensitivity analysis (Section 6.4.3) in which different axial node sizes in the active fuel region are assessed. This sensitivity analysis demonstrates that the nodalization is appropriate to calculate the core thermal-hydraulic conditions and the MCHFR. 3.7.3 Review of Changes to Basemodel The radial and axial modeling changes were evaluated relative to the basemodel described in Reference 8.1.1. A study examined the individual impacts of the

radial nodalization

axial nodalization

axial domain

application of the form losses for the upper and lower fuel nozzles at their respective locations

application of the form losses for the upper and lower core plates at their respective locations

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 12 The critical linear heat generation rate (LHGR) is used to incrementally evaluate the impact of each individual model change relative to the Reference 8.1.1 basemodel until the final model matches the basemodel described in Section 3.7 of this report. The impact of the modeling changes are quantified as follows:

(( }}2(a),(c),ECI The values reported above represent the percent difference from the reference model described in Reference 8.1.1. The results demonstrate that most of the changes to the basemodel have a negligible impact to the figures of merit. The most impactful difference between the Reference 8.1.1 basemodel and the basemodel described in Section 3.7 of this report is the extension of the axial domain as shown in Figure 3-6. The core inlet flow distribution (Section 3.12.9) is analytically defined at the bottom of the lower core plate consistent with the NPM design. The Reference 8.1.1 basemodel conservatively applied the flow distribution to the bottom of the fuel pins, which did not allow the flow to re-normalize before entering the limiting channel. Lateral flow within an assembly is appropriately modeled as there is no physical internal obstruction within the lower nozzle or lower core plate. Modeling the inlet flow distribution consistent with the NPM design provides a (( }}2(a),(c),ECI in the local mass flux entering the limiting channel, which in turn, reduces hot channel enthalpy and enables higher heat fluxes prior to CHF. Application of the flow distribution at the axial domain boundary is consistent with the design and interface for system boundary conditions. In addition, analysis (e.g., CFD) to evaluate the uncertainty distribution should be based on the same domain definition of the subchannel model. This ensures applicability of the applied penalty to account for the flow distribution uncertainty. If analysis shows that the penalty is insufficient it shall be increased. The impact of the magnitude of the flow distribution uncertainty for both top-and bottom-peaked axial power shapes was examined. The results of this examination (Section 6.4.4) show that inlet flow penalties of up to 10% from uniform flow have less than (( }}2(a),(c),ECI impact on MCHFR for both top and bottom-peaked power shapes. Therefore, it is appropriate to apply the inlet flow distribution of Section 3.12.9 to the extended axial domain boundary. The subchannel model utilizes a modeling simplification for the extended axial domain. This simplification applies (( }}2(a),(c),ECI The gap width of a subchannel multiplied by

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 13 the nodal height (x) defines the lateral flow area available for crossflow. The impacts of this modeling simplification were examined by considering (( }}2(a),(c),ECI These results demonstrate a lack of sensitivity to (( }}2(a),(c),ECI and confirm that the simplified modeling approach is acceptable. VIPRE-01 has been validated for resolving the flow and enthalpy distribution for the NuScale core in Reference 8.1.1. The axial and lateral flow equations are properly implemented such that flow redistribution benchmarks from a complete flow blockage show excellent agreement. The extension of the axial domain for the statistical subchannel basemodel is within the capability of VIPRE-01 such that local conditions can be accurately predicted when the component pressure drops are specified at their respective locations.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 14 Figure 3-6 Axial Nodalization Diagram for Subchannel Basemodel (Not to Scale) (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 15 3.8 Boundary Conditions This section and subsequent subsections are unchanged relative to the corresponding section of Reference 8.1.1. 3.9 Turbulent Mixing This section is unchanged relative to the corresponding section of Reference 8.1.1. 3.10 Radial Power Distribution The subchannel analysis uses a progressively-lumped basemodel as discussed in Section 3.7. To decouple the dependency of using a cycle-specific or time-in-life dependent radial power distribution, a conservative radial power distribution for a NuScale core that accounts for the worst distribution throughout the cycle is used. The limiting radial power distribution is bounding of the technical specifications limit on radial peaking factor. This must be confirmed for each fuel cycle loading pattern. The radial power distribution is held constant throughout the transient for subchannel analyses. 3.10.1 Static Standard Review Plan Section 15.4 Analyses For the Chapter 15 events where the radial power distribution can change during the event, particularly those that involve control rod movement, a modified radial distribution is used. An augmentation factor is utilized to address this modification to the power distribution. It is defined in Equation 3-6 as the ratio of the maximum FH during the event to the initial condition. The augmentation factor is applied to the limiting assembly while a lower power assembly far away is reduced to preserve normalization of core power. where:

= radial peaking augmentation factor
= maximum radial peaking at the beginning of the event Equation 3-6 F

Aug H F Max H F Initial H = F Aug H F Initial H

= maximum radial peaking during the event 3.10.2 Time-Dependent Standard Review Plan Section 15.4 Analyses This section is unchanged relative to the corresponding section of Reference 8.1.1.

3.10.3 Enthalpy Rise Hot Channel Factor The core design has imposed a design limitation on the peak value of FH, and therefore the highest value for any fuel rod throughout the full range of power, time in life, and allowed control rod positions. These values are defined in the development of the cycle design to allow the limiting peaking factor to increase for lower power level with the fit coefficients determined to bound the design peaking values as a function of power. This is inclusive of measurement uncertainties. The typical form of the equation is provided as example by Equation 3-8. where:

= Max. hot rod radial peaking analysis limit for safety analysis inclusive of the measurement uncertainties P = Fraction of rated thermal power A, B = Coefficients defined or confirmed during core cycle design to bound the design peaking values as a function of power The subchannel methodology bounds any radial power distribution that occurs in the core prior to any AOO, infrequent event, or accident. The hot rod for the radial power distribution is set to the core operating limit peaking factor (or design limit) dependent upon the initial condition.

Uncertainties associated with FH are accounted for in the subchannel analysis as an increase on the core operating limit value. The uncertainties accounted for are measurement uncertainty related to the instrumentation used for monitoring, which is detailed in Section 3.12.2, and engineering hot channel uncertainty, which is detailed in Section 3.12.4. Increases in FH peaking for rodded configurations are also included as detailed in Section 3.10.5. For cases evaluated at partial power levels, the FH distribution for the entire limiting assembly is scaled by Equation 3-8. The limiting assembly is peaked using Equation 3-8 and the lower power assembly is reduced by the necessary factor to maintain normalization of the core power. Equation 3-8 F Max H F SA H A [1 + B (1 - P)] = F SA H

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 17 3.10.3.1 Assembly Peripheral Row Peaking In the subchannel methodology in Reference 8.1.1, a requirement is imposed on the core design that the peak FH rod for any assembly is not allowed to occur on the peripheral row. This requirement forces the hot subchannel to not occur on the outer row, as the outer row would be influenced by direct crossflow from the annulus channel between assemblies. While this channel is not truly simulated in the CHF tests, it is consistent with the CHF testing basis, therefore it was conservatively chosen to impose this design constraint. However, for the statistical subchannel methodology described in this supplement, this restriction is no longer maintained. It is acceptable for the peak FH rod in an actual core design to occur on a peripheral fuel rod in the assembly. The ratio of the flow area to heated area associated with a peripheral fuel rod location is larger, which results in a higher calculated MCHFR as compared to the smaller flow area to heated area ratio of a fuel rod channel in the interior of the assembly. The radial power distribution is determined as described in Section 3.10.6, which conservatively forces the analyzed hot rod location to occur in the limiting interior fuel rod location. This occurs either in a channel surrounded by four fuel rods, or a smaller flow area of the channel surrounded by three fuel rods and one unpowered guide tube rod. 3.10.4 Radial Flux Tilt This section is unchanged relative to the corresponding section of Reference 8.1.1. 3.10.5 All Rods Out Power Dependent Insertion Limit Enthalpy Rise Hot Channel Factor As described in Section 3.10.3, the power dependent radial peaking factor analysis limit inherently includes allowed control rod insertions. The deterministic methods in Reference 8.1.1 did not account for this allowed operational flexibility in this manner, and thus a specific PDIL-ARO factor was defined and accounted for in the subchannel method. In the method defined in this supplement, this factor is no longer applicable. 3.10.6 Determining the Bounding Radial Power Distribution The radial power distribution for the subchannel basemodel is a bounding distribution expected to be used for future core designs that maintain a similar shuffle or loading pattern. This modeling method is justified from parametric sensitivity analysis in Section 6.4.2 of Reference 8.1.1, which confirms that the radial power distribution far removed from the hot subchannel has a negligible impact on the MCHFR results. Therefore, the use of a radial power distribution with the hot rod at the design peaking limit is sufficient for any distribution in a cycle-specific core.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 18 The bounding radial power distribution used in the basemodel and most transients is not representative of the actual core conditions, and as a result, the determination of MCHFR for meeting the acceptance criterion is only applicable for the hot rod and subchannel. Thus, the purpose of the bounding radial power distribution is to capture the hot subchannel flow conditions, which are dependent upon the surrounding crossflow neighbor channels. A "flat" power distribution is one in which nearly all the rods provide similar power, and therefore, flow conditions and this power distribution limit the amount of turbulent mixing and diversion crossflow in the hot subchannel. This is conservative for thermal margin calculations. The power distribution for an assembly may be characterized by its "peak-to-average" ratio, which is the maximum FH rod in an assembly divided by the average FH for the assembly. A value closer to unity denotes a flat power distribution. A spectrum of peak-to-average values for each assembly throughout the cycle burnup is utilized to determine a bounding distribution. For each core design, each rod has a unique radial peak-to-average assembly ratio. In evaluating these ratios, assembly average relative power fraction values below a reasonable threshold (~1.1) are filtered out because the hot rod power is too low to be considered limiting for MCHFR. For example, when a core loading pattern contains fresh fuel on the periphery of the core, assemblies with a high FH rod have a large peak-to-average ratio due to the average FH rod being reduced by core leakage. These assemblies are considered non-limiting because of the enhanced inner-assembly crossflow that will be induced. For higher average-powered assemblies, the ratio of the peak-to-average ratio is flatter, because all the FH values are not far from the mean. These configurations are of interest because they work to reduce inner-assembly crossflow. The flattest peak-to-average ratio for assemblies of interest occur at high burnup steps where the maximum FH is quite small and thus considered non-limiting. Thus, a FH is required to be above a threshold (i.e., 1.25) for consideration in the peak-to-average ratio. Maximum FH values below this threshold are far below the analysis limit described in Section 3.10.3 and are excluded. (( }}2(a),(c),ECI

3. ((

}}2(a),(c),ECI The process above ensures that the limiting subchannel and rod that experience the MCHFR are located near the center of the limiting assembly and not on the periphery of an assembly. An example radial power distribution utilizing the example values and implementing the defined steps is presented in Figure 3-7.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 20 3.10.7 Deterministic Radial Power Distribution This section is no longer applicable to the statistical subchannel analysis methodology as the F measurement uncertainty and F engineering uncertainty are applied in the determination of the statistical CHF analysis limit (SCHFAL) as described in Section 3.12. Figure 3-7 Example Radial Power Distribution for Core (Top) and Hot Assembly (Bottom) (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 21 3.10.8 Axial Power Distribution This section is unchanged relative to the corresponding section of Reference 8.1.1. 3.10.9 Standard Review Plan Section 15.4 Analyses This section is unchanged relative to the corresponding section of Reference 8.1.1. 3.11 Numerical Solution This section and associated subsections are unchanged relative to the corresponding section of Reference 8.1.1. 3.12 Statistical Method and Treatment of Uncertainties There are several biases and uncertainties that are accounted for in subchannel safety analysis calculations, including those from analysis method, physical manufacturing design inputs to the model, and operating conditions. Each of these will be discussed in more detail to inform what each is composed of and how each is accounted for within the subchannel analysis methodology. All of the uncertainties described in the sections below are summarized in Table 3-4 with a description of how each is applied and what distribution is recommended for use in generating random samples. The uncertainty distribution utilized in generating the statistical CHF analysis limit is justified in the implementing analysis. A normal distribution is applied when there are no firm bounds on the value or where the uncertainty is known to come from a stochastic process. For instance, measurement uncertainty for a thermocouple comes from the manufacturer and is generally based on sample testing, which naturally lends itself to a normal distribution. A uniform distribution is applied when well defined bounds are available and the probability of a particular value occurring is no greater than that of any other value (e.g., a measurement dead band or rod bow factor). There may be cases where neither of these distributions are ideal; engineering judgment will determine the most appropriate or conservative distribution. 3.12.1 Uncertainty in Analysis Method The uncertainties in the analysis method consist of computer code uncertainty and CHF correlation uncertainty. 3.12.1.1 Computer Code Uncertainty The computer code uncertainty pertains to the effects from using distinct discretization in axial and radial nodalization and also the approximations in the governing constitutive equations. Comparisons of code predictions to actual data for the condition ranges of application will usually eliminate the need for an explicit penalty on code and model uncertainties when the models used in the application are consistent with the models used in the development of the analysis limit. Most of this test validation work has been performed in VIPRE-01 already in

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 22 Reference 8.1.5. Additional validation work is performed in benchmarking VIPRE-01 to COBRA-FLX, an approved subchannel analysis code owned by Framatome with an approved SER, as described in Section 5.8 of Reference 8.1.1. The results of the benchmarks demonstrate that VIPRE-01 results are in good agreement with the AREVA COBRA-FLX code for conditions anticipated for NuScale applications. This includes various specific configurations of the NPM design concept at different powers, pressures, and temperatures, as well as axial and radial nodalizations that have been demonstrated to be acceptable. CHF correlations are developed from the local conditions derived from a simulated subchannel model of the CHF test, using the subchannel software. This means that the uncertainty in the VIPRE-01 computer code is included in the CHF correlation itself. This has been the conventional industry practice and is appropriate. For this reason, no additional penalties for uncertainty in analysis method are added to the subchannel calculations. 3.12.1.2 Critical Heat Flux Correlation Uncertainty The CHF correlation uncertainty is measureable and is included as part of the total CHF analysis limit. CHF correlations are developed from the local conditions derived from a simulated subchannel model of the CHF test, using the subchannel software. Generally, a CHF correlation limit is determined in the process of correlation development. This limit prevents the occurrence of CHF on the hot rod with 95% probability at the 95-percent confidence level (95/95 level). The CHF measured-to-predicted (M/P) samples used to set this limit have a distribution that may or may not be parametric. The 95/95 limit for the CHF correlation is utilized to create a normal distribution for sampling the CHF correlation uncertainty. The CHF correlation limit is based on a one-sided tolerance limit. For a normal distribution, the method for determining a one-sided upper tolerance limit is discussed in Section 9.12 of Ref. 8.1.4. The upper tolerance limit for CHF, LCHF, is determined with: where: is the sample mean, is the sample standard deviation, and is the one-sided tolerance factor based on the confidence level and the number of sample data. Equation 3-10 LCHF s k1s + = s s k1

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 23 The one-sided tolerance factor is determined using tables found in various statistical references such as Table T-11b of Ref. 8.1.4. To create a bounding normal distribution for the CHF M/P data, the one-sided upper tolerance limit sets the CHF correlation limit. A standard deviation based on the CHF correlation limit, , is determined based on a rearrangement of Equation 3-10 to calculate where: is the CHF correlation limit, is the mean of the sample data, and is the tolerance factor. 3.12.2 Uncertainty in Operating Conditions The operating boundary conditions that are input into the subchannel analysis must account for all sources of margin and uncertainties related to them. Operating uncertainties account for process variable uncertainty, sensor accuracy and drift, and control deviation. The values for these uncertainties will be based on the instrumentation used for monitoring, and therefore are plant specific. Engineering judgement is made to incorporate reasonable uncertainties for the measured parameters. The measurement uncertainties consist of those related to

core thermal power (CAL)

core inlet flow (G)

core inlet temperature (T)

core exit pressure (P)

enthalpy rise measurement uncertainty ( ) The correct accounting for uncertainties will be consistent between the system code and subchannel methodology, and care is taken to ensure the uncertainty is applied once to either the systems or subchannel calculations. Additional information on each of the operating boundary conditions and how they are applied in the statistical subchannel methodology is described in the following subsections. The nominal Equation 3-11 lim lim lim LCHF s ( ) k1 = LCHF s k1 F U H

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 24 values for operating boundary conditions used in the calculation of the statistical analysis limit shall match the nominal values used in performing subchannel safety analysis calculations. 3.12.2.1 Core Thermal Power Core thermal power is a function of the core calorimetric calculation and uncertainty. The core calorimetric calculation deduces core power from the temperature differential between cold-side and hot-side temperatures, the flow rate, and core fluid properties. The core thermal power QC is expressed as: where: is the calorimetric calculation of core power, and is the calorimetric measurement and calculation uncertainty (%). The core thermal power uncertainty is accounted for either as a deterministic uncertainty or as part of the SCHFAL. When treated deterministically, the core thermal power uncertainty can be included in the system analysis that provides boundary condition input to the subchannel analysis or applied to nominal boundary conditions at the analysis interface. When incorporated into the SCHFAL, this uncertainty is included as part of the uncertainty distributions for the probabilistic parameters (Section 3.13.2). The calorimetric measurement and calculation uncertainty value is design specific. 3.12.2.2 Core Inlet Flow The core inlet flow boundary condition must account for the appropriate bypass flow that is not available for heat transfer. The system-code transmitted flow boundary condition information will be that of RCS system flow to maintain compatibility with the systems transient methodology. The type of bypass mechanisms applicable for NuScale core subchannel analyses are described throughout Section 3.8.4 of Reference 8.1.1, with exact values defined in the core parameters report for a given core design. Core inlet flow is a function of the system flow and bypass flows, as well as flow measurement uncertainty. The core inlet flow GIN is expressed as: Equation 3-12 Equation 3-13 QC QCAL 1 CAL 100 +

= QCAL CAL GIN GSYS 1 G GRB 100 GGT 100 +

=

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 25 where: is system flow, is reflector bypass (%), is bypass (%) in the fuel assembly guide thimbles/tubes, and is flow measurement uncertainty. Core inlet flow uncertainty is accounted for either as a deterministic uncertainty or as part of the SCHFAL. When treated deterministically, the core inlet flow uncertainty can be included in the system analysis that provides boundary condition input to the subchannel analysis or applied to nominal boundary conditions at the analysis interface. When incorporated into the SCHFAL, this uncertainty is included as part of the uncertainty distributions for the probabilistic parameters (Section 3.13.2). The values for components of the uncertainty are design specific. 3.12.2.3 Core Inlet Temperature Core inlet temperature uncertainty is a function of the cold-side temperature, temperature control dead band, and measurement uncertainty. The core inlet temperature TIN is expressed as: where: is cold-side temperature, is the temperature controller dead band, and is the temperature measurement uncertainty. The temperature dead band may be applied to a temperature other than TCOLD depending on the control system (i.e., THOT or TAVE) and core inlet temperature distribution is considered to be flat per Section 3.8.6 of Reference 8.1.1. Core inlet temperature uncertainty is accounted for either as a deterministic uncertainty or as part of the SCHFAL. When treated deterministically, the core inlet temperature uncertainty can be included in the system analysis that provides boundary condition input to the subchannel analysis or applied to nominal boundary conditions at the analysis interface. When incorporated into the Equation 3-14 GSYS GRB GGT G TIN TCOLD T TDB + + = TCOLD TDB T

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 26 SCHFAL, this uncertainty is included as part of the uncertainty distributions for the probabilistic parameters (Section 3.13.2). The values for components of the uncertainty are design specific. 3.12.2.4 Core Exit Pressure Core exit pressure is a function of the pressurizer pressure, pressure control dead band, measurement uncertainty, and the static head pressure drop between the pressurizer and the core exit. The core exit pressure POUT is expressed as: where: is pressurizer pressure, is the pressure controller dead band, and is the pressure measurement uncertainty. The hydrostatic head from the core exit to the pressurizer should be determined and provided as a boundary condition from a systems code such as NRELAP5. Core exit pressure uncertainty is accounted for either as a deterministic uncertainty or as part of the SCHFAL. When treated deterministically, the core exit pressure uncertainty can be included in the system analysis that provides boundary condition input to the subchannel analysis or applied to nominal boundary conditions at the analysis interface. When incorporated into the SCHFAL, this uncertainty is included as part of the uncertainty distributions for the probabilistic parameters (Section 3.13.2). The values for components of the uncertainty are design specific. 3.12.2.5 Enthalpy Rise Measurement Uncertainty The FH measurement uncertainty ( ) accounts for uncertainties in the instrumentation for protecting Technical Specification limits. The default method accounts for this in the SCHFAL, but when the radial peaking factor is defined as an analytical limit (as opposed to an operating limit), no additional uncertainty is incorporated (Section 3.10.3). The enthalpy rise measurement uncertainty is applied to the SCHFAL (Section 3.13.2). Equation 3-15 POUT PPRZ P PDB + + = PPRZ PDB P F U H

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 27 3.12.3 Uncertainty in Physical Data Inputs Physical data that is used in the VIPRE-01 subchannel analysis has an uncertainty and must be accounted for in thermal margins analysis because small deviations from nominal are allowed. The items that are generally applicable to VIPRE-01 and subchannel calculation methods are related to initial manufacturing tolerances and changes to dimensions throughout the life of fuel:

enthalpy rise engineering uncertainty ( )

heat flux engineering uncertainty ( )

LHGR engineering uncertainty ( )

radial power distribution uncertainty ( )

fuel rod bowing and assembly bowing uncertainties ( )

core inlet flow distribution uncertainty

core exit pressure distribution uncertainty The treatment, in the VIPRE-01 inputs or post-processing thermal margin determination, for each above uncertainties is described in the follow sections. Values for these uncertainties are design specific. 3.12.4 Enthalpy Rise Engineering Uncertainty The enthalpy rise engineering uncertainty ( ) is a penalty factor that is applied on the hot channel to account for fabrication uncertainties related to allowable manufacturing tolerances. This factor is also referred to as the enthalpy rise hot channel factor. The enthalpy rise hot channel factor accounts for variations in pellet diameter, pellet density, enrichment, fuel rod diameter, fuel rod pitch, rod bowing, inlet flow distribution, flow redistribution, and flow mixing. The fuel vendor divides this into two factors, , referred to as the pin power effect, and , which is the flow area factor impact on enthalpy rise. The fuel vendor provides the channel factor while is dependent upon the subchannel modeling and methodology applied. FE H FE Q FE LHGR F NRF H F RB H FE H F E H1 F E H2 F E H1 F E H2

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 28 The rod power part of the hot channel factor, , accounts for fuel stack length and uranium loading uncertainties. The hot channel factor is dependent upon the VIPRE-01 modeling and two phase flow correlations when used in combination with accounting for uncertainties in the subchannel flow area due to fuel rod pitch and outer diameter variations. Both sources of enthalpy rise engineering uncertainty are applied to the SCHFAL (Section 3.13.2). 3.12.5 Heat Flux Engineering Uncertainty The heat flux engineering uncertainty factor ( ) is a penalty factor that accounts for the small manufacturing uncertainties that affect the local heat flux. This factor is often referred to as the heat flux hot channel factor. The heat flux hot channel factor is affected by variations in fuel enrichment, pellet density, pellet diameter, and fuel rod surface area. The value of this uncertainty parameter is provided by the fuel vendor. The use of a non-uniform axial factor on the critical heat flux value is sufficient to account for any reasonable non-uniformities that develop in the heat flux distribution. NuScale CHF correlations use a non-uniform axial factor, referred to as the F-Factor, to account for non-uniform axial heating. However, the heat flux engineering uncertainty is included in the SCHFAL for conservatism. The heat flux is intended to be penalized so that the local heat flux uncertainty does not affect the channel enthalpy rise. There is no method to directly account for this in VIPRE-01, therefore this uncertainty is applied to the CHFAL in the SCHFAL methodology. Heat flux engineering uncertainty samples, PHF (i), are taken on the range of 0% to the maximum heat flux engineering factor for a one-sided distribution. Using a one-sided distribution is appropriate because the heat flux engineering factor always provides a CHF penalty. The sample heat flux engineering penalty factor, (i), is calculated with: where: is sample heat flux engineering penalty in %. The heat flux engineering uncertainty is sampled and applied to the SCHFAL (Section 3.13.2). Equation 3-16 F E H1 F E H2 FE Q FE Q FE Q i( ) 1 PHF i( ) 100 + = PHF i( )

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 29 3.12.6 Linear Heat Generation Rate Engineering Uncertainty The hot channel factor remains applicable for PLHGR FCM calculations. This is not applied to the CHFR calculations because it is accounted for in the heat flux hot channel factor ( ). The linear heat generation rate engineering uncertainty factor is applied as a penalty on the peak LHGR (Section 4.5.1 of Reference 8.1.1). 3.12.7 Radial Power Distribution (SIMULATE5) Uncertainty The radial power distribution uncertainty is related to the neutronics code that is used for the radial power distribution inputs. A sensitivity study for different power distributions of the NuScale core in Section 6.0 of Reference 8.1.1 showed that rod powers a few rod rows beyond the limiting hot rod/channel have a negligible impact on the MCHFR. The hot rod in the subchannel model is placed at the radial peaking analysis limit (see Section 3.10.3) and the neutronic code uncertainty is accounted for in the check of the core design to the analysis limit. No radial power distribution penalty is applied to the subchannel analysis evaluation model or SCHFAL. 3.12.8 Fuel Rod and Assembly Bow Uncertainty 3.12.8.1 Fuel Rod Bow Uncertainty Rod bow penalty samples, PRB (i), are taken from a uniform distribution on the range of 0% to the maximum rod bow penalty. The rod bow penalty is conservatively assumed to only provide a CHF penalty. The sample rod bow penalty factor, , is calculated with: where PRB (i) is sample rod bow penalty in %. The fuel rod bow uncertainty is applied to the SCHFAL (Section 3.13.2). 3.12.8.2 Assembly Bow Uncertainty Assembly bow is a complex phenomenon that results in axial distortions of the fuel assembly. The large flux gradients along the outer assemblies, if higher reactivity fuel is loaded there, increases the potential for assembly bow to occur. As defined in Reference 8.1.6, CHF penalties are only applied for rod bow and not Equation 3-17 FE LHGR FE Q F RB H i( ) F RB H i( ) 1 PRB i( ) 100 + =

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 30 assembly bowing because bowing of a full assembly will preserve the flow area. No penalties for assembly bowing are considered in CHF calculations. 3.12.9 Core Inlet Flow Distribution Uncertainty This section is unchanged relative to the corresponding section of Reference 8.1.1. The core inlet flow distribution uncertainty is applied to the limiting channels in the basemodel. 3.12.10 Core Exit Pressure Distribution Uncertainty This section is unchanged relative to the corresponding section of Reference 8.1.1. No uncertainty for core exit pressure distribution is applied. 3.13 Bias and Uncertainty Application within Analysis Methodology In the NuScale statistical subchannel methodology, random uncertainties are combined together statistically and accounted for within the statistical CHF analysis limit (SCHFAL). A summary of the uncertainties discussed throughout this section is provided in Table 3-4. Figure 3-2 visually represents the MCHF limits and presents a pictorial meaning to the margins. 3.13.1 Statistical Methods The statistical methods utilized are predominantly based on Reference 8.1.4, which include, but are not limited to non-parametric confidence intervals and assurance-to-quality (A/Q) of 95/95. For all statistical tests and processes the level of significance,, is 0.05. For all parameters used, a justification must be provided for the distribution used. Evidence or theoretical reasoning must be provided for parameters that sample from a uniform distribution. Parameters that are directly measured will typically utilize a normal distribution with proper justification. 3.13.1.1 Uniform Distribution A uniform distribution models situations where a random variable takes on a value from a specified interval with equal probability. The density function for a uniform distribution is illustrated in Figure 3-10. This demonstrates that on the range a to b, all points have the same probability of occurring. More information regarding the uniform distribution may be found in Section 7.2 of Reference 8.1.4. A randomly generated value from a uniform distribution on the range a to b, U(a,b), is determined with: Equation 3-18 U(a,b) RND(0,1) b a ( ) a +

=

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 31 where: RND(0,1) is a randomly generated value on the range 0 to 1, a is the lower bound of the range, and b is the upper bound of the range. 3.13.1.2 Normal Distribution The use of the normal distribution is ubiquitous in statistics as it provides a model for many natural phenomena. The density function for the normal distribution is illustrated in Figure 3-11 below. Two randomly generated values from a normal distribution, Z1 and Z2, are determined with the Box-Muller transformation (Section 27.5 of Reference 8.1.4). where U1 and U2 are randomly generated values from a uniform distribution, U(0,1), using Equation 3-18 above. The two z values calculated with the Box-Muller transformation can both be shown to belong to the normal distribution given enough samples. Uncertainty values N1 and N2 may be determined from the two samples above with: Figure 3-10 Density Function of the Uniform Distribution Equation 3-19 f(y) 1/(b - a) a b Z1 -2ln U1 ( )cos 2U2 ( ) = Z2 -2ln U1 ( )sin 2U2 ( ) =

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 32 where: is standard deviation, and is the mean value. In most cases is considered to be 0, unless some bias is noted. 3.13.1.3 Quality Assurance Sampling The specific criteria necessary to meet the requirements of GDC 10 are that "there should be a 95-percent probability at the 95-percent confidence level that the hot rod in the core does not experience a boiling crisis during normal operation or AOOs." This amounts to a quality assurance statement equivalent to an A/Q of 95/95. Quality assurance is discussed in detail in Section 24.8, 24.9, 24.10, and 24.11 of Reference 8.1.4. Some general rules for A/Q sampling are:

Sample size shall be determined before sampling begins and the entire set will be either accepted or rejected

The set shall be unequivocally defined before sampling begins

The set is made up of similar items that are treated alike

If the set is comprised of several sub-sets, each sub-set must be addressed separately While A/Q sampling is more generally used in manufacturing to determine whether a lot is acceptable based on statistically sampling of the lot, the concept Equation 3-20 Figure 3-11 Density Function of the Normal Distribution N1, ( ) Z1

+ = N2, ( ) Z2

+ = f(y) 0

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 33 may be extended to the determination of data bounds. For instance, if the lot is considered to be all occurrences of CHF then statistical sampling is performed on a subset of CHF, namely the CHF test results. Once a CHF correlation is developed it is imperative to create a limit that assures an A/Q of 95/95 to meet GDC 10. In this example, the limit is set to be greater than or equal to 95% of the data with 95% confidence. This same principle can be applied to any data subset that is representative of a larger set. The sample size is fixed in advance, and should be informed by the number of failures, or in the CHF example above the number of data above the limit, that are deemed acceptable. Using the framework set forth in Section 24.10 of Reference 8.1.4 for determining the allowable number of failures for a given sample size n, utilizing a binomial distribution, Table 3-3 is created. This table provides the number of samples required to meet a particular number of allowable failures, up to 99. 3.13.2 Statistical CHF Analysis Limit When not considering uncertainties, a fuel rod is considered to fail when MCHFR reaches 1.0. (( }}2(a),(c),ECI Table 3-3 Sample Size versus Number of Allowable Failures fail n fail n fail n fail n 0 59 25 694 50 1260 75 1810 1 93 26 717 51 1282 76 1832 2 124 27 740 52 1305 77 1854 3 153 28 763 53 1326 78 1876 4 181 29 786 54 1348 79 1898 5 208 30 809 55 1371 80 1919 6 234 31 832 56 1393 81 1941 7 260 32 855 57 1415 82 1963 8 286 33 877 58 1437 83 1985 9 311 34 900 59 1460 84 2006 10 336 35 923 60 1481 85 2029 11 361 36 945 61 1503 86 2050 12 386 37 968 62 1525 87 2071 13 410 38 991 63 1547 88 2093 14 434 39 1013 64 1569 89 2115 15 458 40 1036 65 1591 90 2138 16 482 41 1058 66 1613 91 2158 17 506 42 1081 67 1635 92 2180 18 530 43 1103 68 1657 93 2202 19 554 44 1126 69 1679 94 2223 20 577 45 1148 70 1701 95 2245 21 601 46 1170 71 1723 96 2267 22 624 47 1193 72 1745 97 2288 23 647 48 1215 73 1766 98 2310 24 671 49 1237 74 1788 99 2331

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 34 (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 35 (( }}2(a),(c),ECI )

5. ((

}}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 37 3.13.2.1 Best-Estimate Model Reference State-Point Determining the overall uncertainty of the SCHFAL requires (( }}2(a),(c),ECI The range of the sampled state-points should be constructed such that it is ensured that the time of MCHFR and the associated state-point within a given transient are bounded by the domain of which the SCHFAL was developed. Figure 3-13 provides a sample of this for conceptual purposes. The red shaded regions represent the applicability domain for the current NSP4 CHF correlation. The red-hatched regions represent the domain that may be of interest for the transient space to which the SCHFAL may be appropriately applied. If the transient domain is discovered to go outside the SCHFAL applicability range then the limit must be re-derived considering the wider range. Figure 3-12 CHF Analysis Limit Calculation Flow Chart (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 38 (( }}2(a),(c),ECI Figure 3-13 Example Sample SCHFAL Domain (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 39 (( }}2(a),(c),ECI 3.13.3 MCHFR Calculation Process (( }}2(a),(c),ECI Figure 3-14 (( }}2(a),(c),ECI (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 40 (( 3.13.4 Calculating the Statistical CHF Analysis Limit The SCHFAL is a value determined to ensure that a sufficient number of probabilistic samples of the CHFAL fall below the SCHFAL at the 95/95 level. A single SCHFAL is calculated at the 95/95 level using the SCHFAL(i) values calculated with Equation 3-24. A non-parametric statistical method is used to determine the SCHFAL, so the CHFAL samples are ranked in ascending order and the number of allowable values above the SCHFAL are determined based on the number of overall converged CHFAL samples using Table 3-3. For a sample size of 500 CHFAL samples, the number of acceptable values above the SCHFAL would fall between 16 and 17 values. The lower (i.e., 16th) value is chosen to ensure compliance with the 95/95 criterion. From the 500 ordered samples the 484th (500-16) ordered value sets the SCHFAL. Assessments of the complete sample and subsets of the sample are performed to ensure that the SCHFAL is sufficient to cover all subregions of the data. Subsets of the CHFAL samples are created by binning the CHFAL samples. These bins are sized to achieve as close to an even distribution of data in each subset as possible. Each bin is processed with the non-parametric method described above and a SCHFAL for each bin is calculated. The maximum SCHFAL of the bins is considered the limiting SCHFAL because it covers all of the bins. This same process is performed for other relevant parameters. 3.13.5 Summary of Bias and Uncertainty Treatment To summarize the uncertainties and biases applied in the statistical subchannel methodology, Table 3-4 is provided. The uncertainty bias for the boundary conditions are listed as being accounted for either in the system transient analysis boundary conditions provided using systems transient methodology or in the statistical analysis limit. The table provides example distributions for the statistically treated parameters;

}}2(a),(c),ECI Equation 3-28

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 41 however, the distribution applied for each shall be justified in the implementing analysis based on the source data for each parameter. When performing steady-state analyses for CHF evaluation or analyses that don't explicitly involve system transient methodology, these uncertainties should be applied explicitly in the subchannel application. Table 3-4 Summary of Example Subchannel Methodology Parameter Treatment (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 42 3.14 Mixed Core Analysis This section is unchanged relative to the corresponding section of Reference 8.1.1. 3.15 Methodology-Specific Acceptance Criteria This section is unchanged relative to the corresponding section of Reference 8.1.1, with one exception. The MCHFR may occur on a peripheral subchannel of the assembly, as discussed in Section 3.10.3.1. Table 3-4 Summary of Example Subchannel Methodology Parameter Treatment (Continued) (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 43 4.0 Transient-Specific Applications Methodologies This section is unchanged relative to the corresponding section of Reference 8.1.1. A criterion for ensuring fuel integrity is MCHFR. The SCHFAL calculated using the methodology in this supplemental topical report is used to evaluate transient margin by demonstrating the transient-specific MCHFR is larger than the SCHFAL.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 44 5.0 VIPRE-01 Qualification This section is unchanged relative to the corresponding section of Reference 8.1.1.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 45 6.0 Example Calculation Results The example calculation analyses and results presented in Reference 8.1.1 are provided to demonstrate the applicability of the subchannel methodology. This topical report supplement does not repeat the example calculations since the examples provided in Reference 8.1.1 continue to provide a suitable demonstration of subchannel analysis. Note that the sensitivity analysis presented in this topical report uses a different set of inputs than those presented in Reference 8.1.1 since neither methodology requires specific input values. It is further noted that Section 6.2 of Reference 8.1.1 examined multiple basemodel scenarios which are not applicable to this topical report; however, that section continues to provide an acceptable example of steady-state subchannel analysis. A subset of the sensitivity analysis has been reperformed for the updated radial nodalization (Section 6.4.1) and axial nodalization (Section 6.4.3) discussed in Section 3.7. Additionally, the inlet flow distribution sensitivity analysis (Section 6.4.4) has been reperformed. No additional changes are needed in the corresponding section of Reference 8.1.1. 6.4 Sensitivity Analysis The following sensitives are performed by comparing the critical linear heat generation rate to determine impacts of the revised model nodalization. Results from specific sensitivities are compared to a reference basemodel to quantify the impacts. 6.4.1 Radial Geometry Nodalization A sensitivity analysis is performed to demonstrate that the radial nodalization outside the hot channel does not have significant impact on the local hot channel results. To demonstrate this, the sensitives in Table 6-17 are performed considering various levels of resolution of the subchannels outside the modeled hot assembly. Table 6-17 Radial Nodalization Sensitivities (( Case Description }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 46 Figure 6-15 Single Fully Detailed Hot Assembly Model Table 6-17 Radial Nodalization Sensitivities (Continued) (( Case Description }}2(a),(c),ECI B C D E F 6 7 G 1 2 3 4 5 A 34x34 3x3 1x1

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 47 Figure 6-16 Nine Detailed Assemblies Model (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 48 Figure 6-17 Twenty-Five Detailed Assemblies Model (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 49 Figure 6-18 Fully Detailed Core Model (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 50 The results are presented in Table 6-18. (( }}2(a),(c),ECI Figure 6-19 Full Core Lumped Model (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 51 (( }}2(a),(c),ECI 6.4.3 Axial Geometry Nodalization A sensitivity analysis is performed (Table 6-19) to demonstrate a reasonable and consistent solution can be obtained considering both accuracy and performance. Sensitivities inform the appropriate axial nodalization resolution required to:

Ensure a reliable and converged solution

Ensure nodalization resolves the dependent variables of CHF and CHF location (i.e., local flow, enthalpy, quality, and power)

Ensure that losses are applied in the model near their appropriate locations Table 6-18 Radial Geometry Nodalization Linear Heat Generation Rate Sensitivity Results (( Case ID Critical LHGR (kW/ft) Axial Location (in) Local Heat Flux (Mbtu/(hr-ft2)) Mass Flux (Mlbm/(hr-ft2)) Equilibrium Quality (-) }}2(a),(c),ECI Table 6-19 Axial Nodalization Sensitivities (( Case Sensitivity }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 52 (( }}2(a),(c),ECI 6.4.4 Inlet Flow Distribution A sensitivity analysis is performed to examine the impact of inlet flow distributions on the figures of merit for the subchannel analysis. The sensitivities examined varying magnitudes of flow reduction to the hot assembly as well as varying the reduction of flow in assemblies surrounding the hot assembly. Each sensitivity case considered Table 6-20 Axial Geometry Nodalization Linear Heat Generation Rate Sensitivity Results (( Case ID Critical LHGR (kW/ft) Axial Location (in) Heat Flux (Mbtu/(hr-ft2)) Mass Flux (Mlbm/(hr-ft2)) Equilibrium Quality (-) }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 53 both bottom and top peaked power profiles. Table 6-21 summarizes the sensitivities performed. The results of the cases are provided in Table 6-22 and show (( }}2(a),(c) Table 6-21 Description of Inlet Flow Distribution Sensitivities (( Case Sensitivity }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 54 (( }}2(a),(c),ECI Table 6-22 Results Summary of Inlet Flow Distribution Sensitivities (( }}2(a),(c),ECI

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 55 7.0 Summary and Conclusions An overview of the statistical methodology utilized for steady-state and transient subchannel analysis has been presented. Design calculations will use this methodology for assessing thermal margin and to determine if fuel failure will occur due to inadequate heat removal capability through evaluation of the critical heat flux ratio and fuel centerline melt. The methodology is developed to meet relevant acceptance criteria of Section 4.4 and Chapter 15 of the SRP. The thermal design analysis methodology for NuScale subchannel analysis has been presented with the basis for the statistical application of uncertainties. A progressively lumped channel model is used to resolve the desired enthalpy and flow field, with focus on the hot channel. This methodology is applied as a standard technique for modeling steady-state calculations and transients. Sensitivity analysis is provided to demonstrate applicability of the methodology. Descriptions of the model nodalization, boundary conditions, radial power distributions, and uncertainties and biases are provided. 7.1 VIPRE-01 Safety Evaluation Report Requirements This section is unchanged relative to the corresponding section of Reference 8.1.1. The NuScale application of VIPRE-01 continues to fulfill the requirements specified in the generic VIPRE-01 SER (Reference 8.1.7). 7.2 Criteria for Establishing Applicability of Methodology The generalized methodology presented in this topical report supplement is based upon modeling assumptions. The following set of criteria for establishing the applicability of this methodology is provided. An applicant or licensee that uses the methodology of this supplement must satisfy these criteria in order to establish applicability. Any deviation from these criteria must be defined and justified. 7.2.1 General Criteria The following criteria are required for a valid MCHFR calculation:

The local mass flux, equilibrium quality, and pressure at the location and time of MCHFR must be within the correlation applicability range.

The hot rod from the VIPRE-01 MCHFR calculation must be the rod with the highest FH peaking factor.

The VIPRE-01 calculation must satisfy all selected convergence criteria for the results to be considered valid. If convergence cannot be met with the selected default values or methods, justification must be provided to ensure that the relaxed acceptance criterion does not result in incorrect or premature results. If the calculation still does not converge, an assessment of the calculated results needs to be provided to prove acceptability.

Axial nodalization within the region in which MCHFR is predicted to occur must be sufficiently small to resolve the flow field such that parametric sensitivity analysis results in a change of less than five CHF points for a halving of the nodalization size. Additionally, an aspect ratio (ratio of adjacent cell heights) of less than three must be maintained.

The RECIRC numerical solution must be used.

Heat transfer and two-phase flow correlation options defined in Table 5-7 of Reference 8.1.1 must be used.

Rate of depressurization must be below 20 psi/second.

Fast transients require that simulations are performed in sufficiently small time steps to capture the CHFR behavior adequately.

Water properties for temperature and specific volume must be valid within the VIPRE-01 application range.

Fuel pressure drop must be significantly less (by a factor of 10) than the minimum system pressure evaluated with the uniform pressure option or the local pressure drop option must be used. 7.2.2 Critical Heat Flux Correlation The methodology presented in this report is independent of a specific CHF correlation. However, any application of the subchannel methodology is limited by the following restrictions:

The application must explicitly state that an approved CHF correlation is used.

The CHF correlation must be used within its applicable parameter ranges.

Simulated local conditions in the subchannel analysis must be consistent with or bounded by the local conditions for CHF testing, CHF correlation development, and CHFR analysis limit development.

The same two-phase flow model options must be used for CHF correlation and analysis limit development.

CHF correlation and corresponding inputs must be those which are applicable to the fuel design (including spacer grids) being analyzed.

Fuel design and CHF correlation dependent (or bounding) turbulent mixing coefficient (ABETA) must be defined and utilized in the analysis. 7.2.3 Nuclear Analysis Discipline Interface The nuclear analysis interfaces are:

Cycle-specific confirmations of all bounding analysis limits must be defined in the core parameter report for a specific core design.

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 57 7.2.4 Transients Discipline Interface The transient analysis interfaces are:

For events in which one or more parameters are outside the CHF correlation range applicability, such as low flow rate after reactor trip, the transients discipline calculation must ensure all SAFDLs are satisfied via long term cooling methodology.

Either the system transients analysis or the subchannel analysis must account for operating parameter measurement uncertainties in core power, system flow, inlet temperature, and core exit pressure.

The flow boundary condition must be provided as system flow (as opposed to core flow) such that the subchannel analysis accounts for all components of bypass flow consistent with methodology. 7.3 Cycle-Specific Confirmations In general, the subchannel method presented is generic to a given core design (i.e., not cycle-specific) and specific analyses utilizing the methods do not need to be repeated each cycle if the cycle remains within evaluated bounds. However, each unique core design is checked to ensure the subchannel analysis remains applicable. As a result, the following cycle-specific confirmations with respect to subchannel analysis only (i.e., other confirmations may be required) are performed for each cycle:

Cycle-specific axial power shapes are bounded by those used in the generic bounding analysis

Radial nodalization appropriately treats the symmetry of the core design

Hot full power FH at all exposures is less than analysis limit FH

Changes to radial peaking as a result of allowed control rod insertion is appropriately treated in an analysis limit or subchannel input

Fission product (i.e., xenon) transients that disturb symmetric power peaking preserve radial tilt less than allowed by Technical Specifications

Asymmetric reactivity anomaly events analyses confirm that the maximum cycle-specific augmentation factor calculated is bounded by that used in the generic bounding analysis 7.4 Key Fuel Design Interface Requirements The subchannel analysis methodology presented is generic to a given fuel design, and does not need to be reformulated for a different design. However, each unique fuel design requires significant inputs into the subchannel analysis. The following is a minimum list of required fuel design inputs that must be provided for each fuel design evaluated with this methodology:

An approved CHF correlation valid for the fuel design

Basic geometry, flow loss coefficients, and friction factors

Guide tube bypass flow

Heat flux engineering uncertainty factor

Linear heat generation rate engineering uncertainty factor

Assembly and rod bow uncertainty factors

Calibration of the VIPRE-01 fuel rod conduction model to a fuel performance code

Melting temperature equation to calculate fast transient FCM safety limit 7.5 Unique Features of the NuScale Design This section is unchanged relative to the corresponding section of Reference 8.1.1, with the exception of Table 7-2, which is updated. Table 7-2 Comparison of NuScale Reactor Core Design to Conventional PWR Parameter Units NuScale Typical 4-Loop PWR (Ref. 8.2.39) Core Thermal Output MW 160-250 3565 System pressure psia 1850-2000 2250 Thermal design flow rate Mlbm/hr 5-6 139.4 Core average coolant mass velocity Mlbm/hr-ft2 0.5-0.6 2.41 Core inlet coolant temperature °F 470-500 556.8 Core average rise in reactor core °F 90-125 63.2 Core average heat flux MBtu/hr-ft2 0.02-0.03 0.206 Local peak heat flux MBtu/hr-ft2 0.03-0.05 0.515 Min. CHFR at nominal conditions Ratio >5 2.47

Statistical Subchannel Analysis Methodology TR-108601-NP Revision 3 Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology © Copyright 2023 by NuScale Power, LLC 59 8.0 References 8.1 Referenced Documents 8.1.1 NuScale Power, LLC, Subchannel Analysis Methodology, TR-0915-17564-P-A, Revision 2. 8.1.2 NuScale Power, LLC, NuScale Power Critical Heat Flux Correlations, TR-0116-21012-P-A, Revision 1. 8.1.3 NuScale Power, LLC, Applicability Range Extension of NSP4 Critical Heat Flux Correlation, Supplement 1 to TR-0116-21012-P-A, Revision 1, TR-107522-P-A, Revision 1. 8.1.4 U.S. Nuclear Regulatory Commission, Applying Statistics, NUREG-1475, Revision 1, March 2011. 8.1.5 C.W. Stewart et al., NP-2511-CCM-A, Volume 2, User's Manual, Revision 4.5, VIPRE-01 A Thermal-Hydraulic Code for Reactor Cores, Computer Code Manual, February 2014. 8.1.6 NuScale Power, LLC, Applicability of AREVA Fuel Methodology for the NuScale Design, TR-0116-20825-P-A, Revision 1. 8.1.7 Safety Evaluation by the Office of Nuclear Reactor Regulation Relating to VIPRE-01 Mod 02 for PWR and BWR Applications, EPRI-NP-2511-CCM-A, Revision 3, October 30, 1993. 8.1.8 C.W. Stewart et al., NP-2551-CCM-A, Volume 1, Mathematical Modeling, Revision 4.5, VIPRE-01 A Thermal-Hydraulic Code for Reactor Cores, Computer Code Manual, February 2014.

LO-151253 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Affidavit of Carrie Fosaaen, AF-151254

AF-151254 Page 1 of 2

NuScale Power, LLC AFFIDAVIT of Carrie Fosaaen I, Carrie Fosaaen, state as follows: (1) I am the Vice President of Regulatory Affairs of NuScale Power, LLC (NuScale), and as such, I have been specifically delegated the function of reviewing the information described in this Affidavit that NuScale seeks to have withheld from public disclosure, and am authorized to apply for its withholding on behalf of NuScale (2) I am knowledgeable of the criteria and procedures used by NuScale in designating information as a trade secret, privileged, or as confidential commercial or financial information. This request to withhold information from public disclosure is driven by one or more of the following: (a) The information requested to be withheld reveals distinguishing aspects of a process (or component, structure, tool, method, etc.) whose use by NuScale competitors, without a license from NuScale, would constitute a competitive economic disadvantage to NuScale. (b) The information requested to be withheld consists of supporting data, including test data, relative to a process (or component, structure, tool, method, etc.), and the application of the data secures a competitive economic advantage, as described more fully in paragraph 3 of this Affidavit. (c) Use by a competitor of the information requested to be withheld would reduce the competitors expenditure of resources, or improve its competitive position, in the design, manufacture, shipment, installation, assurance of quality, or licensing of a similar product. (d) The information requested to be withheld reveals cost or price information, production capabilities, budget levels, or commercial strategies of NuScale. (e) The information requested to be withheld consists of patentable ideas. (3) Public disclosure of the information sought to be withheld is likely to cause substantial harm to NuScales competitive position and foreclose or reduce the availability of profit-making opportunities. The accompanying report reveals distinguishing aspects about the process by which NuScale develops its statistical subchannel analysis methodology. NuScale has performed significant research and evaluation to develop a basis for this methodology and has invested significant resources, including the expenditure of a considerable sum of money. The precise financial value of the information is difficult to quantify, but it is a key element of the design basis for a NuScale plant and, therefore, has substantial value to NuScale. If the information were disclosed to the public, NuScale's competitors would have access to the information without purchasing the right to use it or having been required to undertake a similar expenditure of resources. Such disclosure would constitute a misappropriation of NuScale's intellectual property, and would deprive NuScale of the opportunity to exercise its competitive advantage to seek an adequate return on its investment. (4) The information sought to be withheld is in the enclosed report entitled Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, TR-108601, Revision 3.The enclosure contains the designation Proprietary at the top of each page containing proprietary information. The information considered by NuScale to be proprietary is identified within double braces, (( }} in the document.

AF-151254 Page 2 of 2 (5) The basis for proposing that the information be withheld is that NuScale treats the information as a trade secret, privileged, or as confidential commercial or financial information. NuScale relies upon the exemption from disclosure set forth in the Freedom of Information Act (FOIA), 5 USC § 552(b)(4), as well as exemptions applicable to the NRC under 10 CFR §§ 2.390(a)(4) and 9.17(a)(4). (6) Pursuant to the provisions set forth in 10 CFR § 2.390(b)(4), the following is provided for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld: (a) The information sought to be withheld is owned and has been held in confidence by NuScale. (b) The information is of a sort customarily held in confidence by NuScale and, to the best of my knowledge and belief, consistently has been held in confidence by NuScale. The procedure for approval of external release of such information typically requires review by the staff manager, project manager, chief technology officer or other equivalent authority, or the manager of the cognizant marketing function (or his delegate), for technical content, competitive effect, and determination of the accuracy of the proprietary designation. Disclosures outside NuScale are limited to regulatory bodies, customers and potential customers and their agents, suppliers, licensees, and others with a legitimate need for the information, and then only in accordance with appropriate regulatory provisions or contractual agreements to maintain confidentiality. (c) The information is being transmitted to and received by the NRC in confidence. (d) No public disclosure of the information has been made, and it is not available in public sources. All disclosures to third parties, including any required transmittals to NRC, have been made, or must be made, pursuant to regulatory provisions or contractual agreements that provide for maintenance of the information in confidence. (e) Public disclosure of the information is likely to cause substantial harm to the competitive position of NuScale, taking into account the value of the information to NuScale, the amount of effort and money expended by NuScale in developing the information, and the difficulty others would have in acquiring or duplicating the information. The information sought to be withheld is part of NuScale's technology that provides NuScale with a competitive advantage over other firms in the industry. NuScale has invested significant human and financial capital in developing this technology and NuScale believes it would be difficult for others to duplicate the technology without access to the information sought to be withheld. I declare under penalty of perjury that the foregoing is true and correct. Executed on October 12, 2023. Carrie Fosaaen}}

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