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LLC, Submittal of Topical Report Extended Passive Cooling and Reactivity Control Methodology, TR-124587, Revision 0
	ML23005A308
Person / Time
Site:	99902078, 05200050
Issue date:	01/05/2023
From:	Shaver M; NuScale
To:	; Office of Nuclear Reactor Regulation, Document Control Desk
Shared Package
ML23005A307	List: ML23005A308;
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	LO-133393 TR-124587-NP, Rev 0
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LO-133393 January 5, 2023 Docket No.52-050 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 Topical Report Extended Passive Cooling and Reactivity Control Methodology, TR-124587, Revision 0 NuScale Power, LLC (NuScale) hereby submits Revision 0 of the Extended Passive Cooling and Reactivity Control Methodology, TR-124587. The purpose of this submittal is to request that the NRC review and approve the extended passive cooling and reactivity control methodology as described in the topical report. NuScale respectfully requests that the acceptance review be completed in 60 days from the date of transmittal. contains the proprietary version of the report entitled Extended Passive Cooling and Reactivity Control Methodology, TR-124587, Revision 0. 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.

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Sincerely, Mark W. Shaver Manager, Licensing NuScale Power, LLC Distribution: Michael Dudek, NRC Getachew Tesfaye, NRC Bruce Bavol, NRC NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com

LO-133393 Page 2 of 2 01/05/23 Enclosure 1: Extended Passive Cooling and Reactivity Control Methodology, TR-124587-P, Revision 0, Proprietary Version Enclosure 2: Extended Passive Cooling and Reactivity Control Methodology, TR-124587-NP, Revision 0, Nonproprietary Version Enclosure 3: Affidavit of Mark W. Shaver, AF-133396 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com

LO-133393 :

Extended Passive Cooling and Reactivity Control Methodology, TR-124587, Revision 0, Proprietary Version NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com

LO-133393 :

Extended Passive Cooling and Reactivity Control Methodology, TR-124587, Revision 0, Nonproprietary Version NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Licensing Topical Report Extended Passive Cooling and Reactivity Control Methodology December 2022 Revision 0 Docket: 52-050 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 www.nuscalepower.com

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Licensing Topical Report 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.

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Licensing Topical Report Department of Energy Acknowledgement and Disclaimer This material is based upon work supported by the Department of Energy under Award Number DE-NE0008928.

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.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table of Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Executive Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Abbreviations and Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.0 Regulatory Requirements and Roadmap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Regulatory Requirements and Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.1 Regulatory Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.2 Regulatory Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.3 Scope of Applicable Transients, Acceptance Criteria, and Transient Duration . . . . . . . 14 2.3.1 Scope of Applicable Transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.3.2 Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3.3 Transient Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.4 Extended Passive Cooling Evaluation Model Roadmap . . . . . . . . . . . . . . . . . . . . . . . . 15 3.0 Phenomena Identification and Ranking Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.1 Phenomena Identification and Ranking Table Process . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 NPM Plant Design Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2.1 General Design Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2.2 Key Design Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.2.3 Design Features for EM Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.3 PIRT Figures of Merit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 3.4 Highly Ranked Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.0 Extended Passive Cooling Evaluation Model Framework, Assessment Basis and Applicability Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.1 Extended Passive Cooling Evaluation Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.1.1 Evaluation Model Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4.1.2 Computational Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.2 NRELAP5 Assessment Basis for Extended Passive Cooling . . . . . . . . . . . . . . . . . . . . 41 4.2.1 Extended Passive Cooling Tests at the NIST-2 Facility . . . . . . . . . . . . . . . . . . . 44 4.2.2 Assessment of NIST-2 Extended ECCS Tests (LTC-01) . . . . . . . . . . . . . . . . . . 44

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table of Contents 4.2.3 Assessment of NIST-2 LOCA Test Extended ECCS Cooling Phase . . . . . . . . . 74 4.2.4 Conclusions from Extended ECCS Integral Test Assessments . . . . . . . . . . . . . 98 4.2.5 Conclusions from NIST-2 Non-LOCA SG/DHRS Testing and Assessments . . . 99 4.3 Boron Dissolution Testing Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.3.1 Facility Description and Test Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 4.3.2 Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 4.3.3 Dissolution Assessment Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 4.4 XPC EM Adequacy Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 4.4.1 Approach for Adequacy Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 4.4.2 Extended Passive Cooling Range of Conditions . . . . . . . . . . . . . . . . . . . . . . . 111 4.4.3 Bottom-up Assessments for XPC Phenomena . . . . . . . . . . . . . . . . . . . . . . . . 118 4.4.4 EM Top-Down Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 4.4.5 EM Adequacy Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 5.0 Extended Passive Cooling Thermal-Hydraulic Analysis Methodology . . . . . . . . 171 5.1 Extended Passive Cooling Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 5.1.1 Extended ECCS Passive Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 5.1.2 Extended DHRS Passive Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 5.2 NRELAP5 Models for Extended Passive Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 5.2.1 ECCS Long-Term Cooling Model Description . . . . . . . . . . . . . . . . . . . . . . . . . 188 5.2.2 Comparison of Simplified and Detailed Model Performance . . . . . . . . . . . . . . 194 5.2.3 Assessment of Lower Riser Hole Flow during ECCS Cooling . . . . . . . . . . . . . 199 5.3 Events Evaluated for Extended Passive Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 5.3.1 Extended ECCS Cooling Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 5.3.2 Extended DHRS Cooling Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 5.4 Initial Conditions and Biases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 5.4.1 Calculation Biases for ECCS Capacity - Minimum Collapsed Liquid Level . . . 211 5.4.2 Calculation Biases for ECCS/CNV Heat Transfer Capacity - Maximum Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 5.4.3 Calculation Biases for Boron Transport Analyses - Minimum Temperature. . . 217 5.4.4 Calculation Biases for Boron Transport Analysis - Sensitivities . . . . . . . . . . . . 219 5.4.5 Calculation Biases for DHRS Decay and Residual Heat Removal . . . . . . . . . 220 5.4.6 Calculation Biases for Boron Dilution Analyses . . . . . . . . . . . . . . . . . . . . . . . . 223

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table of Contents 5.5 Representative Thermal-Hydraulic Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 5.5.1 Minimum Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 5.5.2 Maximum Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 5.5.3 Minimum Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 5.5.4 State-point Evaluation to 72 Hours. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 6.0 Reactivity Control Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 6.1 General Approach and Acceptance Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 6.2 Boron Dilution Transport Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 6.2.1 Boron Dilution Method Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 6.2.2 Module Mixing Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 6.2.3 Boron Transport Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 6.2.4 Boron Loss Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 6.2.5 ESB Addition Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 6.3 Critical Boron Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 6.4 Assess Margin to Criticality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 6.5 Simplified Method to Demonstrate Adequate Reactivity Control during Extended DHRS Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 6.6 Representative Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 7.0 Boron Precipitation Evaluation and Analysis Results . . . . . . . . . . . . . . . . . . . . . . 279 7.1 General Approach and Acceptance Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 7.2 Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 7.2.1 Boron Precipitation Method Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 7.2.2 Module Mixing Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 7.2.3 Boron Transport Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 7.2.4 Boron Loss Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 7.2.5 ESB Addition Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 7.3 Boric Acid Solubility Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 7.4 Assess Margin to Boron Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 7.5 Representative Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 8.0 Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 9.0 Summary and Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 10.0 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table of Contents 10.1 Source Documents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 10.2 Referenced Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 List of Tables Table 1-1 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Table 1-2 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Table 2-1 Evaluation Model Development and Assessment Process Steps and Associated Application in the Extended Passive Cooling Evaluation Model . . . 18 Table 3-1 Importance Assessment Ranking Scale. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Table 3-2 Knowledge Assessment Ranking Scale. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Table 3-3 Summary of Design Features or Requirements for Applicability of the XPC EM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Table 3-4 List of Extended Passive Cooling High and Medium Importance Ranked Phenomena and Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Table 4-1 NIST and NRELAP5 Parameter Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Table 4-2 LTC-01 Characteristic State-Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Table 4-3 LTC-01 Run 1 Sequence of Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Table 4-4 LOCA Extended ECCS Cooling Characteristic State-Points . . . . . . . . . . . . . . . 77 Table 4-5 LOCA Run 1 Sequence of Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Table 4-6 LOCA Run 3 Sequence of Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Table 4-7 LOCA Run 4 Sequence of Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Table 4-8 Boron Oxide Dissolution Test Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Table 4-9 Boron Oxide Dissolution Test Data Summary . . . . . . . . . . . . . . . . . . . . . . . . . 105 Table 4-10 Pellet Batch Weight Summary Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Table 4-11 Pellet Batch Dimension Summary Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Table 4-12 Test Number to Evaluation Number Cross Reference . . . . . . . . . . . . . . . . . . . 108 Table 4-13 Approximate Sample Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Table 4-14 LOCA EM and XPC Extended ECCS Process Parameter Ranges . . . . . . . . . 111 Table 4-15 LOCA EM and XPC EM Extended DHRS Process Parameter Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Table 4-16 Non-LOCA EM and XPC EM Extended DHRS Process Parameter Ranges for SG/DHRS Boiling and Condensation Heat Transfer Phenomena . . . . . . . 117 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena . . . . . . . . . . . . . . . . 151 Table 4-18 Top-Down Assessment for Extended DHRS Cooling Phenomena . . . . . . . . . 162 Table 5-1 Range of Rod Bundle Data Conditions used to Develop Clark Drift Flux Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 Table 5-2 Range of Bundle Data Conditions used for Clark Model Comparison . . . . . . . 206 Table 5-3 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating Minimum Collapsed Liquid Level. . . . . . . . . . . 212

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 List of Tables Table 5-4 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating ECCS/CNV Heat transfer Capacity - Maximum Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 Table 5-5 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Evaluated for Boron Transport - Minimum Temperature . . . . . 217 Table 5-6 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Evaluated for Boron Transport - Sensitivities. . . . . . . . . . . . . . 219 Table 5-7 Initial and Boundary Condition Biases Evaluated for Extended DHRS Cooling Cases Demonstrating Decay Heat Removal. . . . . . . . . . . . . . . . . . . . 221 Table 5-8 Initial and Boundary Condition Biases Evaluated for Extended DHRS Cooling Cases Providing Input for Boron Dilution Analyses. . . . . . . . . . . . . . . 224 Table 5-9 Minimum Level State Point Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Table 5-10 Maximum Temperature State Point Results. . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Table 5-11 Minimum Temperature State Point Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Table 6-1 Example Results of Vapor and Liquid Flow during Extended DHRS Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 List of Figures Figure 1-1 Illustration of Core Event Progression and Extended Passive Cooling Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 2-1 Evaluation Model Development and Assessment Process (EMDAP) . . . . . . . . 17 Figure 3-1 NuScale Power Module Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 3-2 Simplified Diagram of ECCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 4-1 Schematic of XPC Calculation Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Figure 4-2 LTC-01 Run 1 Predicted PZR Pressure Comparison - Long Term . . . . . . . . . . 48 Figure 4-3 LTC-01 Run 1 Predicted CNV Pressure Comparison - Long Term . . . . . . . . . . 49 Figure 4-4 LTC-01 Run 1 Predicted RPV Downcomer Level Comparison - Long Term . . . 50 Figure 4-5 LTC-01 Run 1 Predicted CNV Level Comparison - Long Term . . . . . . . . . . . . . 50 Figure 4-6 LTC-01 Run 1 Predicted Core Exit Fluid Temperature Comparison . . . . . . . . . 51 Figure 4-7 LTC-01 Run 1 Predicted Core Inlet Fluid Temperature Comparison . . . . . . . . . 52 Figure 4-8 LTC-01 Run 1 Predicted Core Inlet Subcooling Comparison. . . . . . . . . . . . . . . 52 Figure 4-9 LTC-01 Run 1 Predicted Downcomer Fluid Temperature Comparison . . . . . . . 53 Figure 4-10 LTC-01 Run 1 Predicted Downcomer Fluid Temperature at RRV Elevation Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Figure 4-11 LTC-01 Run 1 Predicted CNV Level 1 Fluid Temperature Comparison. . . . . . . 55 Figure 4-12 LTC-01 Run 1 Predicted CNV Level 6 Fluid Temperature Comparison. . . . . . . 55 Figure 4-13 LTC-01 Run 1 Predicted CNV Level 7 Fluid Temperature Comparison. . . . . . . 56 Figure 4-14 LTC-01 Run 1 Predicted CNV Level 8 Fluid Temperature Comparison. . . . . . . 56 Figure 4-15 LTC-01 Run 1 Predicted CNV Level 2 Liquid Subcooling . . . . . . . . . . . . . . . . . 57 Figure 4-16 LTC-01 Run 1 Predicted CPV Fluid Temperature Comparison . . . . . . . . . . . . . 58 Figure 4-17 LTC-01 Run 1 Predicted CPV Fluid Level Comparison . . . . . . . . . . . . . . . . . . . 58 Figure 4-18 LTC-01 Run 1 Predicted Core Void Fraction Comparison . . . . . . . . . . . . . . . . . 59 Figure 4-19 LTC-01 Run 1 Predicted Lower Riser Void Fraction Comparison . . . . . . . . . . . 60 Figure 4-20 LTC-01 Run 2 Predicted PZR Pressure Comparison - Long Term . . . . . . . . . . 61 Figure 4-21 LTC-01 Run 2 Predicted CNV Pressure Comparison - Long Term . . . . . . . . . . 61 Figure 4-22 LTC-01 Run 2 Predicted RPV Downcomer Level Comparison - Long Term . . . 62 Figure 4-23 LTC-01 Run 2 Predicted CNV Level Comparison - Long Term . . . . . . . . . . . . . 63 Figure 4-24 LTC-01 Run 3 Predicted PZR Pressure Comparison - Long Term . . . . . . . . . . 64 Figure 4-25 LTC-01 Run 3 Predicted CNV Pressure Comparison - Long Term . . . . . . . . . . 64 Figure 4-26 LTC-01 Run 3 Predicted RPV Downcomer Level Comparison - Long Term . . . 65 Figure 4-27 LTC-01 Run 3 Predicted CNV Level Comparison - Long Term . . . . . . . . . . . . . 66 Figure 4-28 LTC-01 Run 5 Predicted PZR Pressure Comparison - Long Term . . . . . . . . . . 67

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 List of Figures Figure 4-29 LTC-01 Run 5 Predicted CNV Pressure Comparison - Long Term . . . . . . . . . . 67 Figure 4-30 LTC-01 Run 5 Predicted RPV Downcomer Level Comparison - Long Term . . . 68 Figure 4-31 LTC-01 Run 5 Predicted CNV Level Comparison - Long Term . . . . . . . . . . . . . 69 Figure 4-32 LTC-01 Run 5 Predicted CPV Fluid Temperature Comparison - Long Term. . . 70 Figure 4-33 LTC-01 Run 5 Predicted CPV Fluid Level Comparison - Long Term. . . . . . . . . 71 Figure 4-34 LTC-01 Run 6 Predicted PZR Pressure Comparison - Long Term . . . . . . . . . . 72 Figure 4-35 LTC-01 Run 6 Predicted CNV Pressure Comparison - Long Term . . . . . . . . . . 72 Figure 4-36 LTC-01 Run 6 Predicted RPV Downcomer Level Comparison - Long Term . . . 73 Figure 4-37 LTC-01 Run 6 Predicted CNV Level Comparison - Long Term . . . . . . . . . . . . . 74 Figure 4-38 LOCA Run 1 Predicted System Pressure Comparison - Full Test Duration . . . 79 Figure 4-39 LOCA Run 1 Predicted System Pressure Comparison - Long Term . . . . . . . . . 79 Figure 4-40 LOCA Run 1 Predicted System Level Comparison - Full Test Duration . . . . . . 80 Figure 4-41 LOCA Run 1 Predicted System Level Comparison - Long Term . . . . . . . . . . . . 81 Figure 4-42 LOCA Run 1 Comparison of RPV Pressure with Sensitivity Cases - Long Term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Figure 4-43 LOCA Run 1 Comparison of RPV Pressure with Sensitivity Cases - Full Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Figure 4-44 LOCA Run 1 Comparison of CNV Pressure with Sensitivity Cases - Long Term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Figure 4-45 LOCA Run 1 Comparison of CNV Pressure with Sensitivity Cases - Full Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Figure 4-46 LOCA Run 1 Comparison of RPV Downcomer Level with Sensitivity Cases

- Long Term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Figure 4-47 LOCA Run 1 Comparison of RPV Downcomer Level with Sensitivity Cases

- Full Duration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Figure 4-48 LOCA Run 1 Comparison of CNV Level with Sensitivity Cases - Long Term . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Figure 4-49 LOCA Run 1 Comparison of CNV Level with Sensitivity Cases - Full Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Figure 4-50 LOCA Run 3 Predicted System Pressure Comparison - Full Test Duration . . . 91 Figure 4-51 LOCA Run 3 Predicted System Pressure Comparison - Long Term . . . . . . . . . 91 Figure 4-52 LOCA Run 3 Predicted System Level Comparison - Full Test Duration . . . . . . 92 Figure 4-53 LOCA Run 3 Predicted System Level Comparison - Long Term . . . . . . . . . . . . 93 Figure 4-54 LOCA Run 4 Predicted System Pressure Comparison - Full Test Duration . . . 94 Figure 4-55 LOCA Run 4 Predicted System Pressure Comparison - Long Term . . . . . . . . . 95

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 List of Figures Figure 4-56 LOCA Run 4 Predicted System Level Comparison - Full Test Duration . . . . . . 96 Figure 4-57 LOCA Run 20 Predicted System Level Comparison - Long Term . . . . . . . . . . . 97 Figure 4-58 Boron Oxide Dissolution Facility Glass Reactor Vessel . . . . . . . . . . . . . . . . . . 101 Figure 4-59 Boron Oxide Dissolution Facility Feed Water Tank . . . . . . . . . . . . . . . . . . . . . 102 Figure 4-60 Boron Oxide Dissolution Facility Flow Path Elevation . . . . . . . . . . . . . . . . . . . 104 Figure 4-61 Data Comparison Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Figure 5-1 NPM LOCA Phases Resulting from a Typical Liquid-Space Break . . . . . . . . . 175 Figure 5-2 Simplified View of the Flow Paths through ECCS Valves between RPV and CNV. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 Figure 5-3 CNV Annular Region and Flow Area Restriction near RPV Flange, Relative Elevation of RRVs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Figure 5-4 Illustration of Major Primary Fluid Flow Paths during Extended ECCS Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Figure 5-5 Representative Behavior of Riser Void during Extended DHRS Operation with Riser Uncovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Figure 5-6 Representative Behavior of RCS Fluid Temperatures during Extended DHRS Operation with Riser Uncovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Figure 5-7 Representative Behavior of RCS Total Flow, and Riser Hole Flow during Extended DHRS Operation with Riser Uncovery . . . . . . . . . . . . . . . . . . . . . . . 184 Figure 5-8 Representative Behavior of RCS Riser Hole Flow during Leakage Conditions with Extended DHRS Operation and Riser Uncovery . . . . . . . . . . 185 Figure 5-9 Representative Behavior of RCS Riser Void Fraction during Leakage Conditions with Extended DHRS Operation and Riser Uncovery . . . . . . . . . . 186 Figure 5-10 Representative Behavior of RCS Fluid Temperatures with Extended DHRS Operation and Riser Uncovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Figure 5-11 Long-Term Cooling Model Nodalization Diagram . . . . . . . . . . . . . . . . . . . . . . 189 Figure 5-12 Decay Heat Comparison between LOCA and XPC Analytical Models . . . . . . 196 Figure 5-13 RCS Pressure Response Comparison between LOCA and XPC Analytical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Figure 5-14 Secondary Steam Pressure Response Comparison between LOCA and XPC Analytical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 Figure 5-15 Riser Collapsed Liquid Level Comparison between LOCA and XPC Analytical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 Figure 5-16 Riser Level above Top of Active Fuel at Minimum Level ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Figure 5-17 Containment Level above Top of Active Fuel at Minimum Level ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 List of Figures Figure 5-18 RCS Pressure at Minimum Level ECCS Transient Results . . . . . . . . . . . . . . . 229 Figure 5-19 CNV Pressure at Minimum Level ECCS Transient Results . . . . . . . . . . . . . . . 230 Figure 5-20 RVV Integrated Mass Release at Minimum Level ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Figure 5-21 Moderator Temperature at Minimum Level ECCS Transient Results . . . . . . . 232 Figure 5-22 Riser Level above Top of Active Fuel at Maximum Temperature ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Figure 5-23 Containment Level above Top of Active Fuel at Maximum Temperature ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 Figure 5-24 RCS Pressure at Maximum Temperature ECCS Transient Results . . . . . . . . 235 Figure 5-25 CNV Pressure at Maximum Temperature ECCS Transient Results . . . . . . . . 236 Figure 5-26 Moderator Temperature at Maximum Temperature ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Figure 5-27 Riser Level above Top of Active Fuel at Minimum Temperature ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Figure 5-28 Containment Level above Top of Active Fuel at Minimum Temperature ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Figure 5-29 RCS Pressure at Minimum Temperature ECCS Transient Results . . . . . . . . . 240 Figure 5-30 CNV Pressure at Minimum Temperature ECCS Transient Results . . . . . . . . . 241 Figure 5-31 Moderator Temperature at Minimum Temperature ECCS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Figure 5-32 Riser Level above Top of Active Fuel at Minimum Temperature DHRS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 Figure 5-33 Containment Level above Top of Active Fuel at Minimum Temperature DHRS Transient Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 Figure 5-34 RCS Pressure at Minimum Temperature DHRS Transient Results . . . . . . . . . 245 Figure 5-35 CNV Pressure at Minimum Temperature DHRS Transient Results . . . . . . . . . 246 Figure 5-36 Moderator at Minimum Temperature DHRS Transient Results . . . . . . . . . . . . 247 Figure 6-1 Boron Dilution Methodology Mixing Volumes. . . . . . . . . . . . . . . . . . . . . . . . . . 250 Figure 6-2 Porosity as a Function of Pellet Diameters from Wall . . . . . . . . . . . . . . . . . . . 257 Figure 6-3 Boric Acid Solubility Limit as a Function of Temperature . . . . . . . . . . . . . . . . . 258 Figure 6-4 Two-Volume Boron Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Figure 6-5 Ratio of Cold and Hot Region Concentrations for 2-Volume Transport, as a Function of Vapor, Liquid Mass Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Figure 6-6 Boron to Critical BOC (all cases) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 Figure 6-7 Boron to Critical MOC (all cases) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 List of Figures Figure 6-8 Boron to Critical EOC (all cases) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 Figure 6-9 Transient Boron Concentrations for Dilution Sensitivity . . . . . . . . . . . . . . . . . . 277 Figure 6-10 Transient Boron Mass for Dilution Sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . 278 Figure 7-1 Boron Precipitation Methodology Mixing Volumes . . . . . . . . . . . . . . . . . . . . . . 280 Figure 7-2 Boric Acid, Boron Solubility Limit as a Function of Temperature . . . . . . . . . . . 283 Figure 7-3 Transient Boron Concentrations for Example Precipitation Evaluation . . . . . . 284 Figure 7-4 Transient Boron Mass for Example Precipitation Evaluation . . . . . . . . . . . . . . 285

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Abstract This report presents the NuScale Power, LLC, methodology used to evaluate (1) the emergency core cooling system (ECCS) and decay heat removal system (DHRS) extended passive cooling of the NuScale Power Module (NPM) after a successful initial short-term response to a design basis event, (2) reactivity control during extended passive cooling of the NPM, and (3) margin to boron solubility limits to demonstrate coolable geometry is maintained in the NPM. The report includes discussion on the transition to extended passive cooling for events that assume the use of the DHRS, as well as those that actuate the ECCS early in a design basis event. This report is applicable to extended passive cooling capability following both loss-of-coolant accident (LOCA) and non-LOCA design basis events.

The extended passive cooling (XPC) methodology is an extension of the NuScale LOCA evaluation model (EM) (Reference 10.2.1) and NuScale non-LOCA EM (Reference 10.2.5), and thus uses a graded approach to the evaluation model development and assessment process (EMDAP) defined in Regulatory Guide 1.203. The important phenomena identified in the long-term cooling phenomena identification and ranking table (PIRT) analysis performed for the XPC EM are discussed in this report.

This methodology can be used to demonstrate ECCS conformance with the acceptance criteria in 10 CFR 50.46(b)(4) and 10 CFR 50.46(b)(5) for coolable geometry and long-term cooling for the long-term cooling phase when stable natural circulation develops through the ECCS configuration. This methodology can also be used as part of demonstrating conformance to NuScale Principal Design Criteria 34 and 35 along with compliance with relevant Acceptance Criteria given by the Design Specific Review Standard for NuScale Small Modular Reactor Design, Sections 5.4.7, 6.3, and 15.6.5 (Reference 10.2.8, Reference 10.2.3, and Reference 10.2.4, respectively).

The reactivity control methodology addresses boron transport during the design basis event progression. This methodology includes evaluation of boron transport in the reactor vessel through riser flow paths, addition of ECCS supplemental boron in the containment vessel (CNV) and recirculation into the reactor pressure vessel (RPV), and potential boron precipitation.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Executive Summary The NuScale Power Module (NPM) is designed to cool down after experiencing an initiated event and transition to extended passive cooling (XPC). This report defines the evaluation model (EM) for evaluating long-term cooling and demonstration of long-term DHRS and ECCS performance following a design-basis event. The XPC analyses demonstrate the NPM remains in a safe, stable condition with the DHRS or ECCS operating without credit for normal AC power, the nonsafety-related DC power system, or any operator action for 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months after event initiation.

The XPC EM is developed to ensure the long-term cooling (LTC) criteria of 10 CFR 50.46(b)(4) and 10 CFR 50.46(b)(5) are met.

In addition, analyses performed with this EM demonstrate conformance with the DHRS Principal Design Criterion (PDC) 34 and ECCS Principal Design Criterion 35, as described in the Final Safety Analysis Report (FSAR) Section 3.1.

Design-specific XPC EM acceptance criteria ensure that regulatory requirements of 10 CFR 50.46 are met:

collapsed liquid level in the reactor vessel remains above the top of active fuel, the core remains subcritical assuming the highest worth control rod stuck out, and boron concentrations in the core region remain below the boron solubility limit.

The XPC EM is developed using a graded approach to the evaluation model development and assessment process (EMDAP) defined in Regulatory Guide (RG) 1.203. The XPC EM uses the phenomena identification and ranking table (PIRT) process to identify the important parameters, which are specifically addressed. Each important parameter is discussed and evaluated as it relates to the XPC EM.

The XPC EM uses the NRELAP5 thermal-hydraulic code, CMS5 code suite, and boron transport calculation scripts as major computational devices. The non-LOCA NRELAP5 model is used to assess performance of extended DHRS cooling until transition to ECCS cooling. The detailed NPM NRELAP5 model is adapted, as described in this report, to evaluate long-term ECCS cooling. The models and correlations used by the NRELAP5 code were reviewed and determined to be appropriate for use within the extended passive cooling EM. The NRELAP5 model is validated through the assessment of the NuScale Integral System Test (NIST) facility tests and comparison of NRELAP5 predictions to test results.

The methodology for evaluating the NPM long-term cooling thermal-hydraulic response, reactivity control, and boron precipitation are presented in this report. Thermal-hydraulic responses are calculated for the following long-term ECCS cooling scenarios:

minimum collapsed liquid level above the core minimum cooldown to maximize module temperatures maximum cooldown to minimize core moderator temperature sensitivities to evaluate a range of boron dissolution and transport rates from containment into the RPV

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Thermal-hydraulic responses are calculated for the following extended DHRS cooling scenarios:

minimum cooldown to maximize module temperature sensitivities to evaluate potential for boron redistribution; the results of these scenarios are used to demonstrate acceptable system decay heat removal capacity and to provide input to reactivity control and boron precipitation analyses.

In order to evaluate the criterion for maintaining coolable geometry, the possibility of boron precipitation is evaluated. The maximum boron concentration is required to remain below the solubility limit for the minimum RCS temperatures reached within the 72-hour evaluation period for extended passive cooling.

The reactivity control methodology addresses boron transport during the transient progression.

This methodology includes evaluation of boron transport in the reactor vessel through flow paths in the riser, addition of ECCS supplemental boron in the CNV, and potential boron precipitation.

The EM includes methods to bias the supplemental boron dissolution rate to demonstrate conservative results for a range of transients. The dissolution methods are compared to separate effects test data.

For selected events, representative results are provided to demonstrate the application of the EM for the NPM. Design-basis event progressions analyzed with the XPC EM extend for 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months after event initiation. Results of representative calculations show that collapsed liquid level in the reactor vessel remains above the top of active fuel and subcriticality and boron precipitation acceptance criteria are met. Separate methodologies are used to analyze the short-term transient progression and demonstrate appropriate acceptance criteria are met.

NuScale requests U.S. Nuclear Regulatory Commission (NRC) approval to apply the EM to NPM plant designs meeting the criteria specified in Section 9.0. NuScale requests approval to use the EM described in this report for analyses of NPM design basis events that require extended passive cooling and reactivity control analyses. The specific scope of the events, for which the EM applies, is delineated in Section 1.2. NuScale is not seeking NRC approval of the representative calculations that are described in this report.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 1.0 Introduction 1.1 Purpose The evaluation model (EM) is used to evaluate the extended passive cooling (XPC)

NuScale Power Module (NPM) response during emergency core cooling system (ECCS) operation and decay heat removal system (DHRS) operation.

This topical report describes:

ECCS long-term cooling (LTC) and extended DHRS passive cooling analysis scope methodology acceptance criteria methodology for demonstrating that the acceptance criteria are met for the NPM The XPC EM addresses:

evaluation of extended passive cooling for decay and residual heat removal evaluation of boron transport phenomena evaluation of criticality during extended cooling with DHRS and ECCS evaluation of boron precipitation The XPC analysis scope is defined based on the applicable regulatory requirements, specific requirements for the design, and considering relevant aspects of the design that affect the transient progression.

1.2 Scope NuScale requests U.S. Nuclear Regulatory Commission (NRC) approval to use the XPC EM described in this report for analyses of NPM design basis events that require extended cooling and reactivity control analyses. Approval is requested for application of this EM to NPM designs as generally described in Section 3.2 and with the design features and requirements summarized in Section 3.2.3. Representative analysis results are provided in this report to illustrate results from application of the EM. These representative cases are not necessarily based on final NPM design inputs, and NRC approval of the representative results is not requested. The scope of this report includes the applicability and acceptability of this methodology to evaluate the acceptance criteria and regulatory requirements specified in this report.

In the NPM, the DHRS is designed to provide passive decay and residual heat removal following non-LOCA events where reactor coolant inventory is retained. The ECCS is designed to operate following a loss-of-coolant accident (LOCA) or after the inadvertent opening of a reactor valve that allows release of primary reactor coolant into containment.

The ECCS is also designed to actuate in scenarios where electrical power is lost, or if needed to maintain subcriticality. Due to the unique ECCS design, these different scenarios are considered in the analysis of the ECCS long-term cooling.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Consistent with the LOCA EM (Reference 10.2.1, Section 4.2), the ECCS long-term cooling phase of decay heat removal is defined as beginning when ECCS actuates to open the reactor vent valves (RVVs) and reactor recirculation valves (RRVs), the recirculation flow is established, and the pressures and levels in containment and the reactor pressure vessel (RPV) approach a stable condition. Consistent with the non-LOCA EM (Reference 10.2.5, Section 4.3.4), extended passive cooling with the DHRS starts after stable DHRS cooling is established with liquid convection heat transfer from primary coolant to the steam generators (SGs) such that steam is generated and condensed in the DHRS condensers, transferring decay and residual heat to the reactor pool.

This report summarizes the following:

NPM design-basis event progression following DHRS and ECCS actuation regulatory requirements and design-specific requirements applicable to XPC XPC acceptance criteria XPC phenomena identification and ranking table (PIRT) analysis tools, qualification of the tools, and methodology for demonstrating that the XPC acceptance criteria are met representative results of the XPC analyses The following XPC analysis areas are addressed in this report:

demonstration of long-term core cooling following ECCS actuation extended cooldown with DHRS boron transport, including dissolution of supplemental boron in containment, transport into the reactor pressure vessel, and transport through reactor pressure vessel riser flow paths criticality analysis during extended DHRS or ECCS cooling conditions evaluation for boron precipitation The XPC evaluation model is applicable to a nuclear power plant that follows the design features outlined in Section 3.2.3 and is within the ranges of conditions evaluated as part of the EM development.

The following areas are outside scope of this report.

The non-LOCA and LOCA evaluation models for the short-term time periods are covered in separate methodology reports. However the transition between short-term LOCA and non-LOCA initiating events is addressed as part of evaluating boron transport during events with extended DHRS cooling that transition to ECCS cooling.

The effects of debris on ECCS operation that are the subject of the NRC generic safety issue (GSI) 191 are outside scope of this report. The design and debris loads are assessed on a plant-specific basis to ensure that the system and its components

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 will operate as designed under long-term ECCS operating conditions. The XPC analyses are performed assuming a clean core condition without debris.

This EM does not assess seismic issues, which are covered in separate methodologies and assessments.

Critical heat flux (CHF) evaluation is only of interest in the short-term response of the events analyzed by this EM. Short-term LOCA CHF is addressed by the NuScale LOCA EM (Reference 10.2.1). Short-term non-LOCA CHF is addressed by the NuScale non-LOCA EM (Reference 10.2.5).For long-term cooling, demonstrating that subcriticality is maintained, collapsed liquid level calculated by NRELAP5 is above the top of active fuel (TAF), and boron precipitation does not occur are sufficient to demonstrate adequate decay and residual heat removal to maintain core cooling.

Control rod ejection accident analysis, performed to demonstrate acceptable short-term response to large, rapid reactivity insertions as required to meet General Design Criterion (GDC) 28, is addressed by a separate methodology and is not part of the XPC evaluation model.

Analysis of the peak containment pressure and temperature response is not part of the XPC evaluation model.

The EM provides the methodology for extended passive cooling analysis of the 72-hour design-basis event scope. The EM does not specifically address timeframes beyond 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months after event initiation.

The XPC EM for extended DHRS cooling analyses and long-term ECCS cooling analyses addresses extended passive cooling for the required design-basis events, as illustrated in Figure 1-1.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 1-1 Illustration of Core Event Progression and Extended Passive Cooling Scope

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 1.3 Abbreviations and Definitions Table 1-1 Abbreviations Term Definition AC alternating current ANS American Nuclear Society ARI all rods in BC boron coefficient BOC beginning of cycle ASME American Society of Mechanical Engineers CBC critical boron concentration CCFL counter current flow limitation CFR Code of Federal Regulations CHF critical heat flux CLL collapsed liquid level CNV containment vessel CPV cooling pool vessel CRA control rod assembly CVCS chemical and volume control system DC direct current DCA Design Certification Application DHR decay heat removal DHRS decay heat removal system DL discharge line dP differential pressure DSRS Design Specific Review Standard ECCS emergency core cooling system EM evaluation model EMDAP evaluation model development and assessment process EOC end of cycle EPRI Electric Power Research Institute ESB ECCS supplemental boron ESDU Engineering Sciences Data Unit FOM figure of merit FSAR Final Safety Analysis Report FW feedwater FWIV feedwater isolation valve GDC Generic Design Criterion GSI generic safety issue HPV high point vent (line)

HT heat transfer HTP heat transfer plate IAB inadvertent actuation block IEL integral effects test IL injection line

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 1-1 Abbreviations (Continued)

Term Definition IORV inadvertent opening of reactor valve ISA International Society of Automation LOCA loss-of-coolant accident LR lower riser LTC long-term cooling M&E mass and energy MOC middle of cycle MPS module protection system MSIV main steam isolation valve MTC moderator temperature coefficient NC natural circulation NIST NuScale Integral System Test NPM NuScale Power Module NPP NuScale Power Plant NRC Nuclear Regulatory Commission NRF nuclear reliability factor PDC principal design criteria PIRT phenomena identification and ranking table PS pressurizer supply (line)

PWR pressurized water reactor PZR pressurizer RCS reactor coolant system RG Regulatory Guide RPV reactor pressure vessel RRV reactor recirculation valve RSV reactor safety valve RVV reactor vent valve SAFDL specified acceptable fuel design limit SG steam generator SGTF steam generator tube failure SSC systems, structures, and components TAF top of active fuel UHS ultimate heat sink US460 baseline plant product design producing 460 MWt total US600 baseline plant product design producing 600 MWt total WRSO worst rod stuck out XPC extended passive cooling

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 1-2 Definitions Term Definition Cv Flow coefficient Excellent agreement One of the acceptance criteria defined in RG 1.203. Excellent agreement applies when the code exhibits no deficiencies in modeling a given behavior. Major and minor phenomena and trends are correctly predicted. The calculated results are judged to agree closely with the data. The calculation will, with few exceptions, lay within the specified or inferred uncertainty bands of the data. The code may be used with confidence in similar applications.

Figure of merit A parameter selected to characterize the plant long-term cooling response.

Loss-of-coolant accident Those postulated accidents that result in a loss of reactor coolant at a rate in excess of the capability of the reactor makeup system from breaks in the reactor coolant pressure boundary, up to and including a break equivalent in size to the double-ended rupture of the largest pipe in the reactor coolant system.

Non-LOCA transient Reactor coolant system transients described in the NUREG-0800 Standard Review Plan Sections 15.1, 15.2, 15.4, and 15.5, and other comparable transients that may be unique to the NuScale system. Other sections in the standard review plan are specific to events with reactor coolant pumps, LOCA, radiological analysis, anticipated transient without scram, or boiling water reactors, and are outside of the scope of non-LOCA transients.

Reasonable agreement One of the acceptance criteria defined in RG 1.203. Reasonable agreement applies when the code exhibits minor deficiencies. Overall, the code provides an acceptable prediction. All major trends and phenomena are correctly predicted. Differences between calculation and data are greater than deemed necessary for excellent agreement. The calculation will frequently lie outside but near the specified or inferred uncertainty bands of the data. However, the correct conclusions about trends and phenomena are reached if the code is used in similar applications.

xT Valve pressure differential ratio

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 2.0 Regulatory Requirements and Roadmap 2.1 Background In the NPM design, two systems perform the safety-related functions of decay heat and residual heat removal. The DHRS provides decay and residual heat removal while reactor coolant system (RCS) inventory is retained inside the reactor pressure vessel. If RCS inventory is redistributed between the RPV and the containment vessel (CNV), due to a pipe break LOCA or RPV valve opening event, or opening of the ECCS valves, the ECCS provides decay and residual heat removal.

In the NPM design, the safety-related systems provide decay and residual heat removal, without operator actions, for at least 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months for design-basis events.

2.2 Regulatory Requirements and Guidance The NRC regulations and regulatory guidance applicable to the XPC methodology are described in this section. The elements of the XPC methodology that address each of these regulations and guidance documents, including ECCS long-term cooling, are discussed.

2.2.1 Regulatory Requirements Title 10 Code of Federal Regulations (CFR) 50.46 (a) provides two options for an acceptable LOCA EM. Paragraph 50.46(a)(i) allows for a best-estimate approach to be followed and Paragraph 50.46(a)(ii) allows for the conservative deterministic approach detailed in 10 CFR 50 Appendix K. As the XPC EM is an extension of the NuScale LOCA EM (Reference 10.2.1), the disposition of the 10 CFR 50 Appendix K requirements that apply to the long-term cooling phase are applied in the same manner as for the LOCA EM. Because the NuScale LOCA EM (Reference 10.2.1) and the XPC EM are equivalent with regard to all Appendix K requirements, no further exemptions to the Appendix K requirements are required for the XPC EM beyond those identified in Reference 10.2.1.

The NuScale Principal Design Criterion (PDC) 35, based on GDC 35, establishes the required safety function of the ECCS, as described in NPM licensing applications. The portion of the PDC of interest to the LTC methodology is identical to 10 CFR 50, Appendix A, General Design Criterion 35, and states:

A system to provide abundant emergency core cooling shall be provided. The system safety function shall be to transfer heat from the reactor core following any loss of reactor coolant at a rate such that (1) fuel and clad damage that could interfere with continued effective core cooling is prevented and (2) clad metal-water reaction is limited to negligible amounts.

Suitable redundancy in components and features, and suitable interconnections, leak detection, isolation, and containment capabilities shall be provided to ensure that the system safety function can be accomplished, assuming a single failure.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 10 CFR 50.46(b) implements GDC 35, and thus NuScale PDC 35, by establishing specific acceptance criteria for ECCS cooling performance. The applicable regulatory criteria from 10 CFR 50.46(b) regarding long-term ECCS performance (Reference 10.2.2) include the following:

(4) Coolable geometry.

Calculated changes in core geometry shall be such that the core remains amenable to cooling.

(5) Long-term cooling.

After any calculated successful initial operation of the ECCS, the calculated core temperature shall be maintained at an acceptably low value and decay heat shall be removed for the extended period of time required by the long-lived radioactivity remaining in the core.

10 CFR 50.46 applies to ECCS performance following a LOCA. For the NPM, the long-term core cooling ECCS requirements following a LOCA are fulfilled through the actuation of the passive ECCS. The relevant requirement from 10 CFR 50 Appendix K for extended ECCS operation is a requirement for conservatively high decay heat assumed following a pipe break LOCA.

While 10 CFR 50.46 does not address ECCS performance associated with non-LOCA events for long-term core cooling, the ECCS removes residual and core decay heat whenever the NPM transitions to the ECCS configuration.

The NuScale PDC 34, based on GDC 34, establishes the required safety function of the DHRS, as described in NPM licensing applications. PDC 34 states:

A system to remove residual heat shall be provided. The system safety function shall be to transfer fission product decay heat and other residual heat from the reactor core at a rate such that specified acceptable fuel design limits and the design conditions of the reactor coolant pressure boundary are not exceeded.

Suitable redundancy in components and features, and suitable interconnections, leak detection, and isolation capabilities shall be provided to ensure that the system safety function can be accomplished, assuming a single failure.

The decay and residual heat removal safety function is performed by the DHRS actuation, and secondary side isolation functions performed by the main steam isolation valves (MSIVs), the main steam isolation bypass valves, and feedwater isolation valves, and their associated backup isolation valves.

The NPM design does not include any system with a safety function to supply reactor coolant makeup for protection against small breaks in the reactor coolant pressure boundary. As part of supporting exemption to GDC 33, the XPC EM can be used to

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 demonstrate that reactivity control is maintained during leakage conditions, and that DHRS and ECCS provide adequate decay heat removal.

GDC 26 and GDC 27 together address reactivity control system redundancy and capability during normal operation, anticipated operational events, and postulated accident conditions. To support demonstration of compliance with these GDC, the XPC EM can be used to demonstrate subcriticality during extended DHRS or ECCS operation.

2.2.2 Regulatory Guidance NRC review guidance regarding the ECCS requirements in Design Specific Review Standard (DSRS) Section 6.3 (Reference 10.2.3) includes the following from page 6.3-2.

For advanced passive reactors that rely on gravitational head to provide ECCS injection to the reactor coolant system (RCS), the RCS should be designed such that the available gravitational head is sufficient to provide adequate core cooling when depressurized.

For advanced reactors which rely on passive safety-related systems and equipment to automatically establish and maintain safe-shutdown conditions for the plant, these passive safety systems must be designed with sufficient capability to maintain safe shutdown conditions for 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months , without operator actions and without nonsafety-related onsite or offsite power.

The following review guidance from DSRS Section 15.6.5 (Reference 10.2.4) refers to the evaluation of post-LOCA long-term cooling for decay heat removal, and for assessment of boric acid precipitation.

An evaluation of post-LOCA long-term cooling should also be performed to identify the operator actions to successfully control and prevent boric acid precipitation. Analyses of small break LOCAs should be performed to identify the timing for boric acid precipitation. A spectrum of small breaks should also be analyzed to identify other means to control boric acid precipitation when RCS pressure remains too high to enable flushing of the core. All equipment and operator action times should also be clearly identified in the analyses.

From the DSRS page 15.6.5-4, the reactor systems review of this section includes the following.

F. The results of the post-LOCA long-term cooling analyses to assure that an acceptable model has been employed to identify the timing of boric acid precipitation for all break locations and sizes. The review will also verify that an

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 adequate procedure has been devised to control boric acid precipitation for all breaks to assure long-term cooling.

and, Steam generator tube rupture events shall also be reviewed as part of the LOCA break spectrum analysis. The reviewer shall review the potential coolant inventory loss from reactor vessel to the secondary side.

Steam generator tube failure and small pipe breaks carrying RCS coolant outside containment are non-LOCA events resulting in a decrease in RCS inventory. In the NPM design, these events are designed to be mitigated without actuation of ECCS. If power to the module protection system (MPS) is available, then in the short-term event progression the MPS will detect the RCS inventory reduction and mitigate the event by reactor trip, isolation of the leak with appropriate containment isolation valves, and actuation of DHRS to ensure decay heat removal. The short-term event progression of a steam generator tube failure (SGTF) or a pipe break carrying reactor coolant outside containment is analyzed using the non-LOCA analysis methodology (Reference 10.2.5). ECCS will be actuated during these events if the normal power supply is lost or if ECCS is actuated to assure sufficient boron is present in the RCS to maintain subcriticality. These initiating events could result in lower RCS inventory during ECCS cooling compared to LOCA pipe breaks inside containment, and therefore they are included in the scope of minimum level calculations.

NRC review guidance regarding the DHRS requirements in DSRS Section 5.4.7 (Reference 10.2.3) includes the following from page 5.4.7-3.

The organization responsible for the review of reactor thermal hydraulic systems reviews the design and operating characteristics of the DHR with respect to its shutdown and long-term cooling function.

2.3 Scope of Applicable Transients, Acceptance Criteria, and Transient Duration 2.3.1 Scope of Applicable Transients The XPC EM is developed for analysis of extended passive cooling design basis event progressions in a NuScale small modular reactor with key design characteristics described in Section 3.2.3.

As shown in Figure 1-1, the extended passive cooling design-basis event progressions are:

extended ECCS operation transition from DHRS to ECCS operation after an initial extended period of DHRS operation extended DHRS operation

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 2.3.2 Acceptance Criteria The XPC EM is used to demonstrate margin to the following acceptance criteria, consistent with the figures of merit (FOM) identified for the PIRT development described in Section 3.3.

Collapsed liquid level remains above the top of active fuel, demonstrating adequate decay heat removal for at least 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months after event initiation.

Collapsed liquid level is the coolant level that would be achieved if all vapor-phase coolant in a two-phase mixture were completely collapsed. During extended passive cooling conditions, when subcriticality and coolable geometry are maintained, demonstrating that coolant collapsed level remains above the core region is a surrogate to demonstrating successful decay and residual heat removal.

The core remains subcritical (keff < 1) assuming the highest worth control rod stuck out (WRSO), for at least 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months after event initiation.

Subcriticality is evaluated based on the core fluid temperatures, core void fraction, core fuel reactivity, negative reactivity from control rods, and core boron concentration.

Boron concentration remains below precipitation limits, supporting demonstration that coolable geometry is maintained.

Maintaining coolable geometry following a LOCA is a requirement of 10 CFR 50.46 and requires that calculated changes in core geometry shall be accounted for to demonstrate that the core remains amenable to cooling. In the context of the XPC EM for the NPM design, coolable geometry refers to demonstration that boron concentrations remain below precipitation limits.

2.3.3 Transient Duration The design-basis event progressions analyzed with the XPC EM extend for 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months after event initiation. Separate methodologies are used to analyze the short-term transient progression and demonstrate appropriate acceptance criteria are met. The XPC transient analyses are typically performed starting from event initiation in order to support model initiation and to assess boron transport. Statepoint analyses are used for extended time points.

2.4 Extended Passive Cooling Evaluation Model Roadmap Analyses are performed to demonstrate that a nuclear power plant can meet applicable NRC regulatory acceptance criteria for a limiting set of anticipated operational occurrences, infrequent events, and accidents. The evaluation model development and assessment process (EMDAP) as defined in Regulatory Guide (RG) 1.203 (Reference 10.2.6) provides a structured process to establish the adequacy of a methodology for evaluating complex events that are postulated to occur in nuclear power

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 plant systems. The XPC EM is developed for simulating the passive cooling capability and reactivity control of the NPM during long-term ECCS or DHRS operation.

NRELAP5 is the thermal-hydraulics code used to assess the performance of the NPM during XPC. The NuScale LOCA EM (Reference 10.2.1) and non-LOCA EM (Reference 10.2.5) are developed following the EMDAP guidelines of RG 1.203 (Reference 10.2.6). Phenomena identified as high-ranked for extended ECCS and DHRS passive cooling were evaluated with respect to the high-ranked phenomena identified as part of the LOCA and non-LOCA EM development. Considering the overlap in high-ranked phenomena and conservatism applied to input and boundary conditions in the XPC calculations, a graded approach to the EMDAP is applied for development of the XPC evaluation model.

Figure 2-1 shows various elements of the EMDAP as defined in RG 1.203 (Reference 10.2.6). The elements of the EMDAP and sections of this report that relate to the elements and steps of the EMDAP are summarized in Table 2-1. The focus of the XPC EM development is on the thermal-hydraulic analysis and boron transport analysis scope. The critical boron concentration is evaluated using the approved Studsvik Scandpower Core Management Software (CMS5) code suite, as described in the Nuclear Analysis Codes and Methods topical report (Reference 10.2.14).

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 2-1 Evaluation Model Development and Assessment Process (EMDAP)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 2-1 Evaluation Model Development and Assessment Process Steps and Associated Application in the Extended Passive Cooling Evaluation Model EMDAP Description EM Section Step Element 1, Establish Requirements for Evaluation Model Capability 1 Specify analysis The purpose of the XPC methodology is described in Section 1.1.

purpose, transient class Section 3.2 provides an overview of the NPM and a description of and power plant class.

design features related to the EM. The EM is applicable to NPM designs with characteristics described in Section 3.2.3.

The regulatory requirements that the methodology is designed to comply with are described in Section 2.2.

2 Specify FOMs. The design-specific acceptance criteria for XPC are identified in Section 2.3. Section 3.0 describes the XPC PIRT, including FOMs that are used to develop the PIRT.

3 Identify systems, Systems, components, phases and processes are identified as a part components, phases, of the XPC PIRT discussed in Section 3.0.

geometries, fields, and processes that should be modeled.

4 Identify and rank Section 3.0 describes the XPC PIRT.

phenomena and processes.

Element 2, Develop Assessment Base 5 Specify objectives for Objectives for the assessment base were identified as differences assessment base. with the existing assessment bases for NRELAP5, and needs for justification of boron oxide dissolution and transport.

6 Perform scaling Scaling analyses have been performed for LOCA and non-LOCA analysis and identify events as part of their respective short-term EM developments, to similarity criteria. identify dominant PI groups and define NuScale Integral System Test (NIST) test conditions. Insights from the LOCA scaling were used in development of the NIST-2 ECCS long-term cooling test program.

7 Identify existing data The NRELAP5 validation basis described in the LOCA EM and perform integral (Reference 10.2.1), and non-LOCA EM (Reference 10.2.5) includes effects tests (IETs) and a range of legacy test data, and NuScale-specific SETs and IETs.

separate effects tests To complete the database necessary for the XPC EM, a set of (SETs) to complete extended ECCS tests were performed at the NIST-2 facility, as database.

described in Section 4.2.

As described in Section 4.3, testing was performed to measure boron oxide dissolution rate to demonstrate that the XPC EM can simulate a conservatively low dissolution rate.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 2-1 Evaluation Model Development and Assessment Process Steps and Associated Application in the Extended Passive Cooling Evaluation Model (Continued)

EMDAP Description EM Section Step 8 Evaluate effects of IET IET distortions and SET scale-up capability have been evaluated as distortions and SET necessary as part of the LOCA and non-LOCA EM development. In scaleup capability. addition, ECCS long-term cooling tests performed at the NIST-2 facility are used to assess the NRELAP5 capability to predict trends in the measured data. It is concluded that given appropriate initial and boundary conditions to simulate the tests, NRELAP5 calculations demonstrate reasonable to excellent agreement for important phenomena, or the phenomena are bounded in the XPC EM.

9 Determine experimental Experimental uncertainties are captured with the measured data and uncertainties. used in assessment calculations to demonstrate level of agreement.

Element 3, Develop Evaluation Model 10 Establish EM The LOCA EM (Reference 10.2.1) provides information on the development plan. NRELAP5 development plan. NuScale procedures implementing the quality assurance program govern requirements for documentation and verification of the EM as described in Section 8.0.

11 Establish EM structure. The EM structure is summarized in Section 4.1.

12 Develop or incorporate NRELAP5 incorporates models and correlations adequate for the closure models. scope of calculations performed in the XPC EM, which are confirmed as part of the bottom-up assessment discussed in Step 13.

To address phenomena associated with lower riser hole flow during extended ECCS operation, ((2(a),(c) as described in Section 5.2.3. As discussed in Section 6.2, closure models were identified for different aspects of the boron transport methodology. In addition, models for volatilized steam concentration and for droplet entrainment were identified. First principles models were also incorporated as needed to address other aspects of boron dissolution and transport. Element 4, Assess Evaluation Model Adequacy Closure Relations (Bottom-up) 13 Determine model A bottom-up assessment is performed to assess model pedigree and pedigree and applicability to simulate physical processes of high importance and applicability to simulate medium importance phenomena identified in the extended passive physical processes. cooling PIRT. The bottom-up assessment is discussed in Section 4.4.3. It is concluded that models and correlations are adequate to simulate the important physical processes. © Copyright 2022 by NuScale Power, LLC 19

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 2-1 Evaluation Model Development and Assessment Process Steps and Associated Application in the Extended Passive Cooling Evaluation Model (Continued) EMDAP Description EM Section Step 14 Prepare input and As part of the LOCA EM and the non-LOCA EM development, perform calculations to NRELAP5 input is developed and calculations performed to assess assess model fidelity the code performance against separate effects test data. and accuracy. Conclusions related to the XPC EM are summarized in Section 4.2. Additional assessments were performed as necessary to support the EM adequacy evaluation. Assessment of the boron dissolution model against the dissolution test results is summarized in Section 4.3. 15 Assess scalability of No significant model scalability issues were identified as part of the models. bottom-up assessment discussed in Section 4.4.3. Element 4, Assess Evaluation Model Adequacy Integrated EM (Top-down) 16 Determine capability of NRELAP5 field equations and numeric solutions are discussed in field equations and Section 4.4.4.1. NRELAP5 is capable of predicting the system numeric solutions to energy balance and hydrostatic head above the RRVs even under represent processes sub-atmospheric conditions. (( and phenomena.

                                                                     }}2(a),(c) 17       Determine applicability Based on the results of the bottom-up and top-down assessments in of EM to simulate         Section 4.4, the EM is applicable to simulate the system system components.        components.

18 Prepare input and As part of the LOCA EM and the non-LOCA EM development, perform calculations to NRELAP5 input is developed and calculations performed to assess assess system the code performance against integral effects test data. In addition, interactions and global NRELAP5 input is developed and calculations performed to assess capability. code performance against NIST-2 extended ECCS integral effects test data. Sensitivity calculations were performed to assess system interactions during extended ECCS cooling. NPM sensitivity calculations were performed to evaluate impacts of coarser NPM nodalization used in extended ECCS cooling analyses. NPM calculations were performed to inform understanding of system interactions during extended DHRS cooling. A range of NPM transient scenarios and boron dissolution rates were evaluated to assess system interactions related to boron transport. 19 Assess scalability of Results of NRELAP5 validation calculations did not exhibit otherwise integrated calculations unexplained differences between calculated and measured data that and data for distortions. may indicate previously-unidentified experimental or code scaling distortions. 20 Determine EM biases The EM provides realistic or conservative models and correlations to and uncertainties. simulate important phenomena. Conservative initial and boundary conditions are specified as part of the EM to assure an overall conservative analysis result for comparison to acceptance criteria. © Copyright 2022 by NuScale Power, LLC 20

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 3.0 Phenomena Identification and Ranking Table 3.1 Phenomena Identification and Ranking Table Process The PIRT developed for the XPC EM is an extension of the PIRT for extended DHRS and ECCS operation from the previously approved US600 design. Considering relevant design changes of the US460 design, the extended cooling phases and the figures of merit for the PIRT were evaluated and adapted for the XPC EM, as described in this section. The extended ECCS and extended DHRS phases evaluated in the PIRT are as follows. ECCS Phase 2: Long-term recirculation with liquid flow from containment into the RPV through the recirculation valves, and vapor flow from the RPV into containment through the vent valves. DHRS Phase 3: Extended stable natural circulation. Primary system power and flow rates reflect decay power levels. DHRS is actuated and secondary side flow rates and pressures decrease with primary side pressure and temperature decrease. During extended DHRS operation, depending on integral DHRS heat removal and RPV fluid mass, the mixture level can decrease from the pressurizer (PZR) to the riser outlet region, and below the top of the riser. These sub-phases were considered during the PIRT evaluation but no separate phenomena identification or importance ranking associated with the sub-phases were identified. The FOMs specified for the PIRT are subcriticality, coolable geometry, and coolant collapsed liquid level as described in Section 3.3. Each phenomenon identified in the PIRT is assigned an importance ranking and knowledge level ranking as summarized in Table 3-1 and Table 3-2. Table 3-1 Importance Assessment Ranking Scale Importance Ranking Definition high (H) significant or controlling impact on a primary figure of merit medium (M) moderate impact on a primary figure of merit low (L) small impact on a primary figure of merit inactive (I) no or insignificant impact on a primary figure of merit Table 3-2 Knowledge Assessment Ranking Scale Knowledge Level Definition 4 fully known / small uncertainty 3 known / moderate uncertainty 2 partially known / large uncertainty 1 very limited knowledge / uncertainty cannot be characterized © Copyright 2022 by NuScale Power, LLC 21

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 With respect to the PIRT evaluation and the subcriticality figure of merit, the PIRT development focused on the following thermal-hydraulic parameters provided as interface to detailed criticality calculations: core fluid temperature distribution (affected by inlet temperature, liquid flow rate, decay heat source) core void fraction distribution (zero void fraction results in higher keff) core boron concentration ((

                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                          }}2(a),(c) 3.2      NPM Plant Design Features 3.2.1         General Design Description An NPM is a small, light water cooled, pressurized water reactor (PWR) consisting of a nuclear core, two helical coil steam generators (SGs), and a pressurizer, all contained within a single CNV (Figure 3-1). Power conversion occurs via a standard secondary system that includes the steam turbine-generator, the main condenser, and the plant components necessary to provide feedwater.

Each NPM is covered by a reinforced concrete biological shield and enclosed in a Reactor Building, and has a dedicated chemical and volume control system (CVCS), ECCS, and DHRS. An NPM is designed to operate efficiently at full power conditions using natural circulation as the means of providing core coolant flow, eliminating the need for reactor coolant pumps. Unique features of an NPM include: a reduced core size relative to operating PWRs, natural circulation reactor coolant flow (i.e., no reactor coolant pumps), integrated SGs and pressurizer inside the RPV (i.e., there is no piping connecting the SGs or pressurizer with the reactor), simplified passive safety systems that do not rely on ECCS pumps, accumulators, tanks, or connected piping, a high-pressure stainless steel containment, and containment partially immersed in a water-filled pool providing an effective passive heat sink for emergency cooling and decay heat removal. An NPP consists of one or more NPMs, each in its own bay of the common reactor pool. Each bay has a reinforced concrete cover that serves as a biological shield. The cover also serves to prevent deposition of foreign materials onto an NPM. The reactor pool is located in a Seismic Category I building designed to withstand postulated adverse natural conditions and aircraft impact. © Copyright 2022 by NuScale Power, LLC 23

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 3-1 NuScale Power Module Schematic main feedwater lines main steam lines main feedwater main steam isolation valves isolation valves RCCWS supply line RCCWS return line CVCS injection line CVCS discharge line CVCS spray line CVCS spray isolation valves CVCS discharge isolation valves CVCS injection isolation valves DHRS actuation valves containment vessel control rod drive reactor pool mechanisms ECCS reactor vent valves reactor safety valves CVCS spray nozzles reactor pressure vessel pressurizer main steam headers upper plenum DHRS heat exchangers steam generators riser main feedwater headers CVCS injection nozzle CVCS discharge nozzle ECCS control rods reactor recirculation valves downcomer reactor core lower plenum NOT TO SCALE © Copyright 2022 by NuScale Power, LLC 24

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 3.2.2 Key Design Features Systems and functions important to the plant response during extended passive cooling are discussed below. Reactor Coolant System The RCS consists of the RPV, reactor core, riser, upper plenum, SGs (shell side), downcomer, lower plenum, and pressurizer. The arrangement of the RCS and the relative locations of the thermal centers in the core and the SGs promote buoyancy driven natural circulation flow. The RPV consists of a steel cylinder with an inside diameter of approximately 10 feet and an overall height of approximately 60 feet and is designed for a normal operating pressure of approximately 2000 psia. Nozzles on the upper head provide connections for reactor safety valves (RSVs) and RVVs. The core configuration for an NPM consists of 37 fuel assemblies and 16 control rod assemblies (CRAs). The fuel assembly design is modeled from a standard 17x17 PWR fuel assembly with 24 guide tube locations for control rod fingers and a central instrument tube. The assembly is nominally half the height of standard plant fuel and is supported by five spacer grids. The U-235 enrichment is up to 4.95 weight percent. Each NPM uses two once-through helical coil SGs for steam production. The SGs, which produce superheated steam, are located in the annular space between the RCS riser and the reactor vessel inside diameter wall. Each SG is designed to remove 50 percent of the rated core thermal power. The PZR provides the primary means for controlling RCS pressure. PZR heaters and spray maintain a constant reactor coolant pressure during operation. A steel PZR baffle plate, integral with the SG tube sheets and the RPV, acts as a RCS flow and thermal barrier and allows for surge flow between the PZR and the RCS. Decay Heat Removal System The DHRS is a closed-loop, two-phase natural circulation cooling system. Two trains of decay heat removal equipment are provided, one attached to each SG loop. Each train is capable of removing 100 percent of the long-term decay heat load and cooling the RCS. Each train has a passive condenser immersed in the reactor pool. Upon receipt of an actuation signal, the MSIVs and the feedwater isolation valves close, and the decay heat removal actuation valves open, allowing heat removal via the SGs. The decay heat removal actuation valves open upon the loss of power, thus enabling reliable long-term cooling. During operation, liquid water enters the SG through the feedwater line and is boiled by heat from the RCS. The vapor exits the SG through the steam line and is directed to the DHRS condenser where it condenses back to © Copyright 2022 by NuScale Power, LLC 25

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 liquid to return to the SG. Thus, the loop transfers heat from the RCS to the DHRS fluid using the SG and then from the DHRS to the reactor pool water. Emergency Core Cooling System The ECCS consists of multiple independent RVVs and multiple independent RRVs. The ECCS is initiated by actuating the RVVs on the top of the RPV in the pressurizer region and the RRVs on the side of the RPV in the downcomer region. Opening the ECCS valves allows a natural circulation path to be established - water is vaporized in the core, leaves as steam through the RVVs, condenses and collects in the containment, and returns to the downcomer region inside the RPV through the RRVs. During normal operation, each ECCS valve is held closed by the hydraulic pressure across the valve main disc. ECCS valves may include an inadvertent actuation block (IAB) consisting of a spring loaded arming valve in the vent port path from the main disc chamber to the vent line. If the differential pressure across this arming valve is greater than a threshold value, the arming valve closes, preventing the main disc chamber from discharging through the vent line, blocking the main valve from opening. The main valve will not open until the arming valve differential pressure decreases below the release pressure. Provided the IAB device setpoint is reached, if applicable, the RVV and RRV components fail to the open (safe) position upon the loss of power, thus enabling reliable long-term cooling without operator actions, alternating current (AC) or direct current (DC) power, or make-up water. Successful operation of the ECCS requires isolation of the containment, such that the coolant inventory of the RCS is preserved. Containment Vessel The major safety functions of the CNV are to contain the release of radioactivity following postulated accidents, protect the RPV and its contents from external hazards, and retain an acceptable level of RCS inventory to provide heat rejection to the reactor pool following ECCS actuation. Following an actuation of the ECCS, heat removal through the CNV reduces the containment pressure and temperature and maintains them at less than design conditions for extended periods of time. Steam is condensed on the inside surface of the CNV, which is passively cooled by conduction and convection heat transfer to the reactor pool water. Reactor Pool The reactor pool is located below the plant ground level in the Reactor Building. During normal plant operations, heat is removed from the pool through a cooling system and ultimately rejected into the atmosphere through a cooling tower or other external heat sink. In an event where AC power is lost, heat is removed from an NPM by allowing the pool to heat up and boil. Water inventory in the reactor pool is maintained at a level that is sufficient to provide at least three days of DHRS operation. © Copyright 2022 by NuScale Power, LLC 26

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 3.2.2.1 Upper Riser Flow Paths For extended DHRS cooling, the upper riser flow paths are designed to maintain a substantial amount of liquid flow over the steam generator after the top of the riser uncovers. ((

                                                                                }}2(a),(c) 3.2.2.2            Lower Riser Flow Paths The lower riser holes are located in the lower riser near the top of the core and are designed to allow recirculation of liquid between the riser and downcomer during ECCS long-term cooling, to maintain a mixed boron concentration in the RPV.

During ECCS cooling when natural circulation flow is interrupted, two-phase mixture in the riser can generate more hydrostatic head at the lower riser hole elevation compared to colder liquid in the downcomer, depending on the relative levels and fluid densities. If the core/riser mixture level is above the lower riser holes, and differential pressure across the holes is from riser to downcomer, the liquid will recirculate from the riser to the downcomer region. In the quasi-steady ECCS long-term cooling phase, the core inlet flow rate is the combination of riser hole flow, boil-off flow rate (reflected in the liquid flow from containment to downcomer through the recirculation valves), and any internal recirculation in the core/riser region (e.g., through the reflector bypass holes). 3.2.2.3 ECCS Supplemental Boron (ESB) The ECCS supplemental boron design feature is designed to provide additional soluble boron for recirculation into the RPV during ECCS operation. Dry boron oxide pellets in containment are dissolved by condensate, or primary fluid discharged into the CNV, and released to mix with other liquid in containment and recirculate in the RPV. This boron addition increases the total boron mass available to recirculate into the RPV to maintain subcriticality during ECCS long-term cooling. Boron oxide pellets are loaded into baskets inside containment, attached to the containment wall, during outages. Condensate channels direct condensate from parts of the containment walls into the top of the baskets to supply sufficient and adequately distributed liquid for dissolution during ECCS operation. The borated liquid discharges from the dissolver baskets into the annular space between the CNV and RPV, above the reactor vessel flange. The hopper for loading the ESB © Copyright 2022 by NuScale Power, LLC 27

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 and the dissolver basket are shown on Figure 3-2; the condensate channels to the dissolver basket are not pictured. 3.2.2.4 Mixing Tubes in Containment As part of the ECCS supplemental boron function, mixing tubes are located in containment. Each mixing tube extends above the equilibrium water level in containment, and each mixing tube has dedicated condensate channels to collect and direct condensate into the tube. The purpose of the mixing tubes is to transport unborated condensate to the bottom of containment to displace liquid mass in the bottom of the CNV which may be borated due to discharge from the RPV into the CNV, or from supplemental boron dissolved early in the transient. ((

                                                                                            }}2(a),(c) The mixing tubes are shown in Figure 3-2; the condensate channels feeding the mixing tubes are not pictured.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 3.2.3 Design Features for EM Applicability Table 3-3 summarizes key features of the plant design or plant design requirements that must be met in order to apply the XPC EM. Table 3-3 includes an example assessment for the US460 standard design. The design requirements are met for the US460 standard design or are part of detailed design finalization. Table 3-3 Summary of Design Features or Requirements for Applicability of the XPC EM Feature or Design Requirement Additional Comment US460 design Light water cooled PWR composed of Yes reactor core, helical coil SGs, integral PZR in RPV, housed in compact steel CNV. Fuel assembly modeled from a standard Required for applicability of Appendix K Yes PWR fuel assembly, with U-235 decay heat enrichment below 4.95w/o. Primary side natural circulation during Yes normal operation. Steam generator produces superheated Affects range of secondary side operating Yes steam during normal operation. conditions to evaluate for extended DHRS conditions. Module partially immersed in reactor pool Yes ultimate heat sink. ECCS comprised of recirculation valves Valve flow path may include venturi Yes and vent valves between RPV and CNV nozzles; ECCS valves may include IABs. DHRS passive isolation condenser Yes connected SG secondary side, immersed in reactor pool Reactor pool inventory maintained at Reactor pool inventory evaluation for Yes appropriate level during normal operation DHRS operation must consider all NPMs such that DHRS condenser tubes remain simultaneously rejecting decay heat to covered for at least 3 days or is designed pool. to transition to ECCS prior to DHRS condenser uncovery. Safety systems credited for mitigation of Affects scope of analyses required to Yes design-basis events are module-specific address multi-module effects. except for the shared reactor pool portion of the ultimate heat sink (UHS). Upper riser flow paths between riser and Upper riser flow paths must be sized to Yes downcomer sustain liquid flow over the SG/DHRS for decay heat removal after riser uncovery. Lower riser flow paths between riser and Sized to maintain boron distribution in Yes downcomer RCS during ECCS cooling. ESB mixing tubes in containment Yes © Copyright 2022 by NuScale Power, LLC 30

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 3-3 Summary of Design Features or Requirements for Applicability of the XPC EM (Continued) Feature or Design Requirement Additional Comment US460 design ECCS supplemental boron Current methodology limited to Yes dissolution of boron oxide pellets that are equilateral cylinders. The dissolver basket diameter is at least 10x greater than boron oxide pellet diameter. ECCS supplemental boron systems, Required for analytical evaluation of Defined in detailed structures, and components (SSC) boron dissolution. design work. distribute condensate over top of the packed bed. Core remains subcritical during Affects PIRT applicability. Yes design-basis event progression ECCS actuation design such that when Method is not designed to evaluate a Yes ECCS is actuated, initial flow through rapid in-flux of potentially unborated RRVs is from downcomer into condensate from containment into containment. downcomer through the RRVs, at rates higher than those driven by long-term recirculation. Automatic ECCS actuation to assure Affects scope of extended DHRS cooling Yes subcriticality is maintained. events to evaluate. ECCS valves passively open due to low Affects limiting single failure assessment. Yes differential pressure across the valve. Reactor vessel flange limits annular flow Identified for consistency with volumes Yes area in containment. RRVs are located specified in boron transport methodology above the reactor vessel flange elevation. for dilution analyses. However, a different containment volume configuration could be accounted for by appropriately connecting boron transport flow volumes. The following evaluations are required for the plant design to support applicability of the EM: Primary containment isolation valve leakage has a negligible effect on RPV collapsed level over the analysis timeframe of interest, or leakage is accounted for. Secondary containment isolation valve leakage has a negligible effect on DHRS heat removal capacity over the analysis timeframe of interest, or leakage is accounted for. ((

                                                                                                          }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                }}2(a),(c) 3.3      PIRT Figures of Merit During extended passive cooling, including post-LOCA long-term cooling, the identified phenomena are compared to three FOMs:

Subcriticality: The condition of a nuclear reactor system in which nuclear fuel no longer sustains a fission chain reaction. A reactor becomes subcritical when its fission events fail to release a sufficient number of neutrons to sustain an ongoing series of reactions. Coolable geometry: For the NPM XPC EM, coolable geometry is maintained if boron concentration levels remain below the solubility limit, demonstrating the core remains amenable to cooling. Coolant collapsed level: The coolant level that results if all voids in the two-phase coolant are collapsed. During extended passive cooling conditions, when subcriticality and coolable geometry are maintained, demonstrating coolant collapsed level remains above the core region is a surrogate figure of merit to demonstrate successful decay and residual heat removal. 3.4 Highly Ranked Phenomena The important phenomena examined in the EM development are the phenomena with high- and medium- importance ranking in the PIRT. ((

                         }}2(a),(c)

The high-ranked and medium-ranked phenomena identified for extended passive cooling conditions are summarized in Table 3-4. The importance ranking and uncertainty ranking for each phenomenon, and the applicable components are identified. A description of the phenomena and how they are addressed in the XPC evaluation model are described in © Copyright 2022 by NuScale Power, LLC 32

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Section 4.4.3 in the bottom-up assessment performed for extended ECCS and DHRS cooling. Table 3-4 List of Extended Passive Cooling High and Medium Importance Ranked Phenomena and Components ((

                                                                                                       }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 3-4 List of Extended Passive Cooling High and Medium Importance Ranked Phenomena and Components (Continued) ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 3-4 List of Extended Passive Cooling High and Medium Importance Ranked Phenomena and Components (Continued) ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 3-4 List of Extended Passive Cooling High and Medium Importance Ranked Phenomena and Components (Continued) ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.0 Extended Passive Cooling Evaluation Model Framework, Assessment Basis and Applicability Evaluation Section 4.1 describes the XPC EM framework and calculational devices to provide context for the scope of assessments presented in Section 4.2 and Section 4.3 and the adequacy assessment presented in Section 4.4. Section 4.2 summarizes the NRELAP5 validation basis for the XPC EM. Section 4.3 describes boron dissolution testing and assessment of the XPC dissolution calculation methods against the test data. Section 4.4 summarizes the approach for the XPC EM adequacy assessment, bottom-up and top-down assessments of important phenomena identified in the PIRT, and overall conclusions. Refer to Section 5.1 for characterization of NPM extended ECCS and DHRS transient progressions. 4.1 Extended Passive Cooling Evaluation Framework 4.1.1 Evaluation Model Overview The XPC PIRT figures of merit are collapsed liquid level, subcriticality, and coolable geometry. In the scope of the XPC EM, these correspond to the following acceptance criteria.

1. Demonstrate that collapsed liquid level in the RPV riser remains above the top of the active fuel region.

2. Demonstrate that after reactor trip the reactor core remains subcritical with keff < 1.

3. Demonstrate that the boron concentration in the RPV remains below the solubility limit for precipitation.

As discussed in Section 1.2, Figure 1-1 illustrates the scope of design basis event progressions addressed in the XPC EM. As discussed in Section 3.0, evaluation of subcriticality and evaluation of boron precipitation limits require analysis of boron transport during extended passive cooling. Several calculational devices are used in the XPC EM to simulate the fluid mass, momentum and energy transport, boron mass transport, and core reactivity response necessary to demonstrate margin to the specified acceptance criteria. The XPC EM calculational framework is shown schematically in Figure 4-1 and summarized below. The EM framework is applicable for extended ECCS cooling and extended DHRS cooling, unless specified as applicable to only one transient progression. Note that transition from DHRS to ECCS cooling is evaluated to assure reactivity control during the transition; this is accomplished by evaluation of the subcriticality © Copyright 2022 by NuScale Power, LLC 37

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 acceptance criterion, specifically demonstration that the module boron concentration remains above the critical concentration prior to ECCS actuation. Collapsed Liquid Level Acceptance Criterion

                  -   The NRELAP5 code is used to calculate the collapsed liquid level during XPC conditions and demonstrate successful decay heat removal. Continuous calculations are performed from event initiation through establishing quasi-steady XPC conditions. After quasi-steady conditions are established in the module, statepoint calculations with appropriate boundary conditions are used for calculational efficiency to demonstrate margin over the remaining design basis timeframe.
                  -   In conjunction with demonstration that subcriticality and coolable geometry are maintained, demonstrating that collapsed liquid level is above top of the core demonstrates successful decay and residual heat removal.

Subcriticality Acceptance Criterion

                  -   Evaluation of the core reactivity balance as a function of time after reactor trip is performed using the reactor core simulator code SIMULATE5, part of the CMS5 code suite, an approved software package to perform nuclear analysis for the NPM design (Reference 10.2.9).
                  -   Critical transient parameters needed to evaluate the core reactivity balance are xenon reactivity, core (moderator) fluid temperature and density (accounting for void fraction if necessary), and core boron concentration.

Xenon reactivity is determined using approved core design methods. Moderator fluid temperature and density are provided based on XPC system thermal-hydraulic calculations with the NRELAP5 code. Appropriate margins or bounding low temperatures or void fractions may be applied to account for uncertainty in the code temperature prediction or for analysis simplification. In the SIMULATE5 calculations, the critical boron concentration is calculated for an appropriate range of time in cycle, and time after reactor trip. The negative reactivity from control rod insertion assumes the highest worth control rod remains stuck out of the core.

                  -   The core boron concentration is calculated using the methodology described in Section 6.2, biased for dilution analysis.

The boron transport calculations are performed with MATLAB or other appropriate computational script for efficiency in the calculation process. ((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                           }}2(a),(c)

Boron Precipitation Acceptance Criterion

                  -   Critical transient parameters needed to evaluate the margin to the boron precipitation limit are core fluid temperature and core boron concentration.

((

                                           }}2(a),(c)
                  -   The solubility limit for boric acid as a function of temperature is shown in Section 7.3.
                  -   The core boron concentration is calculated using the methodology described in Section 7.2, biased for precipitation analysis.

The boron transport calculations are performed with MATLAB or other appropriate computational script for efficiency in the calculation process. ((

                                                                                                       }}2(a),(c) by alternate calculation as described in Section 5.2.3.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-1 Schematic of XPC Calculation Framework ((

                                                                                                          }}2(a),(c) 4.1.2         Computational Tools There are three major computational devices used in the XPC EM:

1. NRELAP5 system thermal-hydraulic code

2. CMS5 code suite comprising the lattice physics code CASMO5, linkage code CMSLINK5 for nuclear data library generation, and core simulator code SIMULATE5

3. boron transport calculation scripts implemented in MATLAB or other appropriate computational script for efficiency in the calculation process NRELAP5 Code NRELAP5 is NuScales system thermal-hydraulics code used to simulate the NPM system response to design basis events, including anticipated operational occurrences and postulated accidents.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 CMS5 Code Suite Design and nuclear analysis of the NPM reactor core is performed with the Studsvik Scandpower CMS5 suite of reactor simulation tools. The CMS5 code suite comprises the lattice physics code CASMO5, linkage code CMSLINK5 for nuclear data library generation, and core simulator code SIMULATE5. The CMS5 is described in the nuclear analysis methodology topical report (Reference 10.2.9). Therefore the CMS5 code suite is not further discussed in this report. Boron Transport Calculation Scripts Boron transport calculation scripts implement the boron transport analysis methodology, with appropriate bias options for dilution and precipitation analysis, in MATLAB or another appropriate computational script to assure consistent, verifiable implementation and for efficiency in the calculation process. ((

                                                                                                     }}2(a),(c)

The output is boron concentration in the defined module regions as a function of time, which is compared to the critical boron concentration or solubility limit, for dilution and precipitation analyses, respectively. As part of the boron transport method, the boron dissolution rate in the ESB components in containment is calculated. Section 4.4.3.37 and Section 6.2.5 provide additional discussion of the dissolution rate calculation, including spatial discretization of the dissolver basket. 4.2 NRELAP5 Assessment Basis for Extended Passive Cooling As part of LOCA EM development, NRELAP5 was validated against a range of legacy test data, NuScale-specific tests performed to validate prediction of separate effects phenomena including helical coil steam generator pressure drop and heat transfer phenomena, and high pressure condensation phenomena, and NuScale-specific integral effects testing performed to assess code prediction of integral effects during the short-term LOCA transient. NRELAP5 validation results against legacy test data, NuScale-specific separate effects testing for helical coil steam generator phenomena and high pressure condensation phenomena, and NuScale-specific integral effects testing for LOCA are summarized in the LOCA topical report (Reference 10.2.1). The LOCA topical report (Reference 10.2.1) summarizes tests performed at the NIST-2 facility to support the LOCA EM. It is noted that while these tests were designed as LOCA tests primarily to assess the short-term transient response, the tests were executed for © Copyright 2022 by NuScale Power, LLC 41

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 24 hours to measure data during the extended ECCS cooling phase as well. Focused NRELAP5 assessment of the extended ECCS cooling phase of selected tests is performed and key conclusions are discussed below. As part of non-LOCA EM development, NRELAP5 was validated against additional NuScale-specific tests performed to validate high pressure tube condensation phenomena and NuScale-specific integral effects testing performed to assess code prediction of integral effects during the short-term non-LOCA transient, while primary side mixture level remains above the top of the riser. NRELAP5 validation results against NuScale-specific separate effects testing for high pressure tube condensation phenomena and NuScale-specific integral effects testing are summarized in the non-LOCA topical report (Reference 10.2.5). NuScale-specific integral effects tests performed at the NIST-2 facility to support NRELAP5 code validation during extended ECCS cooling are summarized in the following sections. Table 4-1 defines NIST and NRELAP5 identifiers for parameters shown in the following sections. © Copyright 2022 by NuScale Power, LLC 42

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-1 NIST and NRELAP5 Parameter Definitions ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.2.1 Extended Passive Cooling Tests at the NIST-2 Facility The NIST facility is a scaled, non-nuclear reactor that uses electric heater rods to represent the heat produced from fission. It is designed to produce experimental data in support of verification and validation of thermal-hydraulic codes. The NIST facility has been modified to test specific NPM configurations. The NIST-1 configuration was utilized from 2015 to 2018 and the NIST-2 configuration was used from 2019 to 2022. A schematic and description of the NIST facility is provided in Reference 10.2.1. 4.2.2 Assessment of NIST-2 Extended ECCS Tests (LTC-01) Six test runs make up the test data gathered during the LTC-01 testing program. Five of the runs were initiated with a broken CVCS discharge line break, and a sixth test run simulated an inadvertent opening of an RVV. Run 1 is the base case and the other cases are variations in the initial conditions. An additional seventh run was performed as a repeat of Run 1, and it is not included in this report. The six NIST-2 LTC-01 tests cases (referred to herein as runs) are summarized below. ((

                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.2.2.1 Facility Description for LTC-01 The entirety of the NIST facility (except for the DHRS) was utilized for these tests, including ((

                                                                                        }}2(a),(c) 4.2.2.2            Phenomena Addressed by LTC-01 The pertinent phenomena addressed with the NIST-2 LTC-01 assessment are

((

                                           }}2(a),(c)

Parameters to assess agreement included direct measurements of the CNV pressure, RPV pressure, CNV level, RPV level, primary flowrate, pressurizer level, CPV temperature, CNV temperature, and HTP temperature. 4.2.2.3 Experimental Procedure for LTC-01 ((

                          }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                               }}2(a),(c) 4.2.2.4            Parameter Ranges Assessed for LTC-01 Table 4-2 summarizes the characteristic state-points of the NIST-2 tests considered for the LTC-01 assessment. ((
                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-2 LTC-01 Characteristic State-Points ((

                                                                                                      }}2(a),(c),ECI 4.2.2.5            Assessment Results: LTC-01 Run 1 (CVCS Discharge Line Break Base Case)

Run 1 is the base LTC-01 case, representing a liquid space break that utilizes the CVCS discharge line. Table 4-3 provides the sequence of events for Run 1. Overall, the sequence timings between the data and the simulation match well. For the other break cases, the sequence of events are similar because they are sensitivity tests of Run 1, and they are not included herein. Table 4-3 LTC-01 Run 1 Sequence of Events ((

                                                                                                   }}2(a),(b),(c),ECI Figure 4-2 and Figure 4-3 compares the predicted RPV and CNV pressures with the data, respectively, for the long-term cooling portion of the transient (i.e., after 20,000 seconds). ((
                                                       }}2(a),(c) During the long-term cooling period

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 (time greater than 20,000 seconds) the simulation shows reasonable agreement with the measured data. Figure 4-2 LTC-01 Run 1 Predicted PZR Pressure Comparison - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-3 LTC-01 Run 1 Predicted CNV Pressure Comparison - Long Term ((

                                                                                                 }}2(a),(b),(c),ECI The simulated RPV downcomer level is compared to the data in Figure 4-4. The overall trend of the simulated RPV level shows reasonable agreement with the data. For the long-term cooling phase, Figure 4-4, the predicted RPV level is

((

                           }}2(a),(c)

Figure 4-5 is a comparison of the predicted and measured CNV level. After ECCS initiation, the simulation shows excellent agreement with the measured data, remaining mostly within the bounds of the uncertainty. Assessment of the momentum balance between the RPV and CNV (via comparison of the NRELAP5 prediction of the static head difference between the two vessels) was also performed with reasonable comparison to the measured data. © Copyright 2022 by NuScale Power, LLC 49

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-4 LTC-01 Run 1 Predicted RPV Downcomer Level Comparison - Long Term ((

                                                                                         }}2(a),(b),(c),ECI Figure 4-5 LTC-01 Run 1 Predicted CNV Level Comparison - Long Term

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-6 compares the predicted core exit fluid temperature with the measured data for the full test duration. ((

                                  }}2(a),(c)

Figure 4-7 compares the predicted and measured fluid temperature at the core inlet (lower plenum). ((

                                   }}2(a),(c)

Figure 4-6 LTC-01 Run 1 Predicted Core Exit Fluid Temperature Comparison ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-7 LTC-01 Run 1 Predicted Core Inlet Fluid Temperature Comparison ((

                                                                                         }}2(a),(b),(c),ECI Figure 4-8 LTC-01 Run 1 Predicted Core Inlet Subcooling Comparison

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 A comparison of the fluid temperature just below the steam generator tube coil is given in Figure 4-9. ((

                                    }}2(a),(c)

Figure 4-9 LTC-01 Run 1 Predicted Downcomer Fluid Temperature Comparison ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-10 LTC-01 Run 1 Predicted Downcomer Fluid Temperature at RRV Elevation Comparison ((

                                                                                               }}2(a),(b),(c),ECI A comparison of the fluid temperatures in the CNV are shown in Figure 4-11 through Figure 4-14. ((
                                           }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-11 LTC-01 Run 1 Predicted CNV Level 1 Fluid Temperature Comparison ((

                                                                                      }}2(a),(b),(c),ECI Figure 4-12 LTC-01 Run 1 Predicted CNV Level 6 Fluid Temperature Comparison

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-13 LTC-01 Run 1 Predicted CNV Level 7 Fluid Temperature Comparison ((

                                                                                      }}2(a),(b),(c),ECI Figure 4-14 LTC-01 Run 1 Predicted CNV Level 8 Fluid Temperature Comparison

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-15 LTC-01 Run 1 Predicted CNV Level 2 Liquid Subcooling ((

                                                                                             }}2(a),(b),(c),ECI Figure 4-16 compares the CPV fluid temperatures that lie below the water level.

((

                                                            }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-16 LTC-01 Run 1 Predicted CPV Fluid Temperature Comparison ((

                                                                                          }}2(a),(b),(c),ECI Figure 4-17 LTC-01 Run 1 Predicted CPV Fluid Level Comparison

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-18 shows the comparison of the core void fraction. ((

                              }}2(a),(c)

Figure 4-18 LTC-01 Run 1 Predicted Core Void Fraction Comparison ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-19 LTC-01 Run 1 Predicted Lower Riser Void Fraction Comparison ((

                                                                                                  }}2(a),(b),(c),ECI 4.2.2.6            Assessment Results: LTC-01 Run 2 ((                                            }}2(a),(c)

Run 2 is a sensitivity of the base LTC-01 case, representing a liquid space break that utilizes the CVCS discharge line with a larger RVV capacity. Figure 4-20 and Figure 4-21 compares the predicted RPV and CNV pressures with the data, respectively, for the long-term cooling portion of the transient (i.e., after 20,000 seconds). ((

                                                                        }}2(a),(c) During the long-term cooling period (time greater than 20,000 seconds) the simulation shows reasonable agreement with the measured data.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-20 LTC-01 Run 2 Predicted PZR Pressure Comparison - Long Term ((

                                                                                       }}2(a),(b),(c),ECI Figure 4-21 LTC-01 Run 2 Predicted CNV Pressure Comparison - Long Term

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The simulated RPV downcomer level is compared to the data in Figure 4-22. The overall trend of the simulated RPV level shows reasonable agreement with the data. For the long-term cooling phase, Figure 4-22, the predicted RPV level is ((

                          }}2(a),(c)

Figure 4-23 is a comparison of the predicted and measured CNV level. After ECCS initiation, the simulation shows excellent agreement with the measured data, remaining mostly within the bounds of the uncertainty. Figure 4-22 LTC-01 Run 2 Predicted RPV Downcomer Level Comparison - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-23 LTC-01 Run 2 Predicted CNV Level Comparison - Long Term ((

                                                                                                  }}2(a),(b),(c),ECI 4.2.2.7            Assessment Results: LTC-01 Run 3 ((
                                                     }}2(a),(c)

Run 3 is a sensitivity of the base LTC-01 case, representing a liquid space break that utilizes the CVCS discharge line with ((

                                                     }}2(a),(c)

Figure 4-24 and Figure 4-25 compares the predicted RPV and CNV pressures with the data, respectively, for the long-term cooling portion of the transient (i.e., after 20,000 seconds). During the long -term cooling period (time greater than 20,000 seconds) the simulation shows reasonable agreement with the measured data. For the following pressure and level figures, Run 3 is also compared against the base case data and simulation results, Run 1. © Copyright 2022 by NuScale Power, LLC 63

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-24 LTC-01 Run 3 Predicted PZR Pressure Comparison - Long Term ((

                                                                                       }}2(a),(b),(c),ECI Figure 4-25 LTC-01 Run 3 Predicted CNV Pressure Comparison - Long Term

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The simulated RPV downcomer level is compared to the data in Figure 4-26. The overall trend of the simulated RPV level shows reasonable agreement with the data. For the long-term cooling phase, Figure 4-26, the predicted RPV level is ((

                          }}2(a),(c)

Figure 4-27 is a comparison of the predicted and measured CNV level. After ECCS initiation, the simulation shows excellent agreement with the measured data, remaining mostly within the bounds of the uncertainty. Figure 4-26 LTC-01 Run 3 Predicted RPV Downcomer Level Comparison - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-27 LTC-01 Run 3 Predicted CNV Level Comparison - Long Term ((

                                                                                                  }}2(a),(b),(c),ECI 4.2.2.8            Assessment Results: LTC-01 Run 4

((

                            }}2(a),(c) Assessment comparisons are not included in this section.

4.2.2.9 Assessment Results: LTC-01 Run 5 ((

                                    }}2(a),(c)

Run 5 is a sensitivity of the base LTC-01 case, representing a liquid space break that utilizes the CVCS discharge line with ((

                                  }}2(a),(c)

Figure 4-28 and Figure 4-29 compares the predicted RPV and CNV pressures with the data, respectively, for the long-term cooling portion of the transient (i.e., after 20,000 seconds). During the long -term cooling period (time greater than 20,000 seconds) the simulation shows reasonable agreement with the measured data. For the following pressure and level figures, Run 5 is also compared against the base case data and simulation results, Run 1. © Copyright 2022 by NuScale Power, LLC 66

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-28 LTC-01 Run 5 Predicted PZR Pressure Comparison - Long Term ((

                                                                                       }}2(a),(b),(c),ECI Figure 4-29 LTC-01 Run 5 Predicted CNV Pressure Comparison - Long Term

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The simulated RPV downcomer level is compared to the data in Figure 4-30. The overall trend of the simulated RPV level shows reasonable agreement with the data. For the long-term cooling phase, Figure 4-30, the predicted RPV level is ((

                          }}2(a),(c)

Figure 4-31 is a comparison of the predicted and measured CNV level. After ECCS initiation, the simulation shows reasonable agreement with the measured data. Figure 4-30 LTC-01 Run 5 Predicted RPV Downcomer Level Comparison - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-31 LTC-01 Run 5 Predicted CNV Level Comparison - Long Term ((

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

((

                                                                              }}2(a),(c) The fluid temperature in the CPV is influenced by heat loss out the CPV wall and evaporation of the fluid at the water surface.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-32 LTC-01 Run 5 Predicted CPV Fluid Temperature Comparison - Long Term ((

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

((

                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-33 LTC-01 Run 5 Predicted CPV Fluid Level Comparison - Long Term ((

                                                                                                  }}2(a),(b),(c),ECI 4.2.2.10           Assessment Results: LTC-01 Run 6 ((
                           }}2(a),(c)

Run 6 is a sensitivity of the base LTC-01 case, ((

                                                     }}2(a),(c)

Figure 4-34 and Figure 4-35 compares the predicted RPV and CNV pressures with the data, respectively, for the long-term cooling portion of the transient (i.e., after 20,000 seconds). During the long -term cooling period (time greater than 20,000 seconds) the simulation shows reasonable agreement with the measured data. For the following pressure and level figures, Run 6 is also compared against the base case data and simulation results, Run 1. © Copyright 2022 by NuScale Power, LLC 71

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-34 LTC-01 Run 6 Predicted PZR Pressure Comparison - Long Term ((

                                                                                       }}2(a),(b),(c),ECI Figure 4-35 LTC-01 Run 6 Predicted CNV Pressure Comparison - Long Term

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The simulated RPV downcomer level is compared to the data in Figure 4-36. The overall trend of the simulated RPV level shows reasonable agreement with the data. For the long-term cooling phase, Figure 4-36, the predicted RPV level is ((

                       . }}2(a),(c)

Figure 4-37 is a comparison of the predicted and measured CNV level. After ECCS initiation, the simulation shows excellent agreement with the measured data, remaining mostly within the bounds of the uncertainty. Figure 4-36 LTC-01 Run 6 Predicted RPV Downcomer Level Comparison - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-37 LTC-01 Run 6 Predicted CNV Level Comparison - Long Term ((

                                                                                                }}2(a),(b),(c),ECI 4.2.3         Assessment of NIST-2 LOCA Test Extended ECCS Cooling Phase Seven unique tests were performed using data collected from the NIST-2 LOCA tests.

Four of these tests were performed to replicate NIST-1 HP-06, HP-07, HP-09, and HP-49 transient scenarios ((

                                                            }}2(a),(c) Assessment results for Run 1, Run 3 and Run 4 are presented here as they are representative of the range of test conditions and validation results in the long-term phase.

The seven NIST-2 LOCA test cases (referred to herein as runs) are summarized below. ((

                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                }}2(a),(c) 4.2.3.1            Facility Description for LOCA Extended ECCS Cooling The entirety of the NIST facility (except for the DHRS) was utilized for these integral effects tests, including

((

                                                                                         }}2(a),(c) 4.2.3.2            Phenomenon Addressed for LOCA Extended ECCS Cooling The pertinent phenomena addressed with the NIST-2 LOCA assessment are

((

                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Parameters to assess agreement included direct measurements of the CNV pressure, RPV pressure, CNV level, RPV level, primary flowrate, pressurizer level, CPV temperature, CNV temperature, and HTP temperature. 4.2.3.3 Experimental Procedure for LOCA Extended ECCS Cooling The NIST-2 LOCA test procedure is as described in Section 4.2.2.3 for the NIST-2 LTC tests. 4.2.3.4 Parameter Ranges Assessed for LOCA Extended ECCS Cooling Table 4-4 summarizes the characteristic state-points of the NIST-2 tests considered for LOCA assessment. ((

                                }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0

                                                                                          }}2(a),(c),ECI Table 4-4 LOCA Extended ECCS Cooling Characteristic State-Points

((

  © Copyright 2022 by NuScale Power, LLC 77

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.2.3.5 Assessment Results: 100 Percent CVCS Discharge Line Break Case (Run 1) Run 1 of the NIST-2 LOCA test series represents a liquid space break that utilizes the CVCS discharge line (reminiscent of the NIST-1 HP-06 case). Table 4-5 provides the sequence of events for Run 1. Overall, the sequence timings between the data and the simulation match well. ((

                                                                            }}2(a),(c)

Table 4-5 LOCA Run 1 Sequence of Events ((

                                                                                                    }}2(a),(b),(c),ECI Figure 4-38 and Figure 4-39 compare the predicted RPV and CNV system pressures with the data for the full test duration and the long-term cooling portion of the transient (i.e., after 20,000 seconds), respectively. During the long-term cooling period (time greater than 20,000 seconds), the simulation shows reasonable-to-excellent agreement with the measured data.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-38 LOCA Run 1 Predicted System Pressure Comparison - Full Test Duration ((

                                                                                      }}2(a),(b),(c),ECI Figure 4-39 LOCA Run 1 Predicted System Pressure Comparison - Long Term

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The simulated RPV downcomer level and CNV level is compared to the data for the full test duration and long-term cooling portion of the transient (i.e., after 20,000 seconds) in Figure 4-40 and Figure 4-41, respectively. During the long-term cooling period (time greater than 20,000 seconds), the simulation shows reasonable-to-excellent agreement with the measured data. A Bernoulli check was performed to evaluate the pressure drop across the RVVs and the hydrostatic head of CNV liquid above the downcomer level. This check confirmed that the NRELAP5 prediction of the static head difference between the RPV and CNV (driving force for ECCS long-term cooling) was reasonable compared to the measured data. Figure 4-40 LOCA Run 1 Predicted System Level Comparison - Full Test Duration ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-41 LOCA Run 1 Predicted System Level Comparison - Long Term ((

                                                                                                 }}2(a),(b),(c),ECI For Run 1, additional sensitivity calculations were performed that compared the following:

((

                                                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                     }}2(a),(c) The sensitivity calculation results provide confidence that there is no significant bias in the code prediction of long-term pressures or levels, when appropriate test boundary conditions are accounted for.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-42 LOCA Run 1 Comparison of RPV Pressure with Sensitivity Cases - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-43 LOCA Run 1 Comparison of RPV Pressure with Sensitivity Cases - Full Duration ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-44 LOCA Run 1 Comparison of CNV Pressure with Sensitivity Cases - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-45 LOCA Run 1 Comparison of CNV Pressure with Sensitivity Cases - Full Duration ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-46 LOCA Run 1 Comparison of RPV Downcomer Level with Sensitivity Cases - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-47 LOCA Run 1 Comparison of RPV Downcomer Level with Sensitivity Cases - Full Duration ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-48 LOCA Run 1 Comparison of CNV Level with Sensitivity Cases - Long Term ((

                                                                                    }}2(a),(b),(c),ECI Figure 4-49 LOCA Run 1 Comparison of CNV Level with Sensitivity Cases - Full Duration

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.2.3.6 Assessment Results: Inadvertent RVV Opening Case (Run 3) Run 3 of the NIST-2 LOCA test series represents a steam space break that utilizes the RVV line (reminiscent of the NIST-1 HP-09 case). Table 4-6 provides the sequence of events for Run 3. Overall, the sequence timings between the data and the simulation match well. ((

                                                         }}2(a),(c)

Table 4-6 LOCA Run 3 Sequence of Events ((

                                                                                                     }}2(a),(b),(c),ECI Figure 4-50 and Figure 4-51 compare the predicted RPV and CNV system pressures with the data for the full test duration and the long-term cooling portion of the transient (i.e., after 20,000 seconds), respectively. During the long-term cooling period (time greater than 20,000 seconds), the simulation shows reasonable-to-excellent agreement with the measured data.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-50 LOCA Run 3 Predicted System Pressure Comparison - Full Test Duration ((

                                                                                      }}2(a),(b),(c),ECI Figure 4-51 LOCA Run 3 Predicted System Pressure Comparison - Long Term

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The simulated RPV downcomer level and CNV level is compared to the data for the full test duration and long-term cooling portion of the transient (i.e., after 20,000 seconds) in Figure 4-52 and Figure 4-53, respectively. During the long-term cooling period (time greater than 20,000 seconds), the simulation shows reasonable-to-excellent agreement with the measured data. Figure 4-52 LOCA Run 3 Predicted System Level Comparison - Full Test Duration ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-53 LOCA Run 3 Predicted System Level Comparison - Long Term ((

                                                                                               }}2(a),(b),(c),ECI 4.2.3.7            Assessment Results: Inadvertent RRV Opening Case (Run 4)

Run 4 of the NIST-2 LOCA test series represents a liquid space break that utilizes the RRV line (reminiscent of the NIST-1 HP-49 case). Table 4-7 provides the sequence of events for Run 4. Overall, the sequence timings between the data and the simulation are reasonable. ((

                                                     }}2(a),(c)

Table 4-7 LOCA Run 4 Sequence of Events ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-7 LOCA Run 4 Sequence of Events (Continued) ((

                                                                                                    }}2(a),(b),(c),ECI Figure 4-54 and Figure 4-55 compare the predicted RPV and CNV system pressures with the data for the full test duration and the long-term cooling portion of the transient (i.e., after 20,000 seconds), respectively. During the long-term cooling period (time greater than 20,000 seconds), the simulation shows reasonable agreement with the measured data. ((
                              }}2(a),(c)

Figure 4-54 LOCA Run 4 Predicted System Pressure Comparison - Full Test Duration ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-55 LOCA Run 4 Predicted System Pressure Comparison - Long Term ((

                                                                                                 }}2(a),(b),(c),ECI The simulated RPV downcomer level and CNV level is compared to the data for the full test duration and long-term cooling portion of the transient (i.e., after 20,000 seconds) in Figure 4-56 and Figure 4-57, respectively. During the long-term cooling period (time greater than 20,000 seconds), the simulation shows reasonable agreement with the measured data. ((
                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-56 LOCA Run 4 Predicted System Level Comparison - Full Test Duration ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-57 LOCA Run 20 Predicted System Level Comparison - Long Term ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.2.4 Conclusions from Extended ECCS Integral Test Assessments From the assessment observation, the following key conclusions from the NRELAP5 assessment basis are drawn. ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.2.5 Conclusions from NIST-2 Non-LOCA SG/DHRS Testing and Assessments The NIST-2 non-LOCA integral effects testing focused on SG/DHRS heat removal are presented in the non-LOCA topical report (Reference 10.2.5). Key conclusions from this testing relevant for the extended passive cooling phase are summarized here. ((

                                  }}2(a),(b),ECI 4.3      Boron Dissolution Testing Summary 4.3.1         Facility Description and Test Matrix

((

                                                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-58 Boron Oxide Dissolution Facility Glass Reactor Vessel ((

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

((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                       }}2(a),(c)

Figure 4-59 Boron Oxide Dissolution Facility Feed Water Tank ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                       }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-60 Boron Oxide Dissolution Facility Flow Path Elevation ((

                                                                                                  }}2(a),(c),ECI Various size tubing and connections are used to establish the flow paths between test equipment. Needle valves are sized so their flow coefficient ranges encompass the range necessary to achieve the required flow rates.

((

                                          }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                             }}2(a),(c)

Table 4-8 shows the tests used to support the assessment in Section 4.3.3. Table 4-8 Boron Oxide Dissolution Test Matrix ((

                                                                                                          }}2(a),(b),(c),ECI 4.3.2         Test Results Boron dissolution testing was performed at the Boron Oxide Dissolution Facility using

(( }}2,(a),(c) for the analyzed tests. Test results used in the assessment are summarized in Table 4-9. Measured pellet weights and dimensions are provided in Table 4-10 and Table 4-11. Table 4-9 Boron Oxide Dissolution Test Data Summary ((

                                                                                                       }}2(a),(b),(c),ECI
  © Copyright 2022 by NuScale Power, LLC 105

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-10 Pellet Batch Weight Summary Table ((

                                                                                                }}2(a),(b),(c),ECI Table 4-11 Pellet Batch Dimension Summary Table

((

                                                                                                }}2(a),(b),(c),ECI 4.3.3         Dissolution Assessment Results Assessment Method The dissolution test data are used to assess the boron dissolution computational methods that are part of the boron transport methodology. MATLAB is used to implement these computational methods, which are described in Section 4.4.3.37 and Section 6.2.5. ((
                                                                                                     }}2,(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                               }}2,(a),(c)

Assessment Figure 4-61 shows a plot of the ratios of (a) dissolution times predicted by computational methods, to (b) test data for measured dissolution times. Table 4-12 provides a cross-reference between test numbers used in Table 4-8 and evaluation numbers used in Figure 4-61. Table 4-13 shows approximate sample density compared to the density assumed in the boron dissolution methodology. © Copyright 2022 by NuScale Power, LLC 107

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 4-61 Data Comparison Results ((

                                                                                                        }}2(a),(c)

Table 4-12 Test Number to Evaluation Number Cross Reference ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-12 Test Number to Evaluation Number Cross Reference (Continued) ((

                                                                                                    }}2(a),(b),(c),ECI Table 4-13 Approximate Sample Density

((

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

((

                                             }}2,(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4 XPC EM Adequacy Assessment 4.4.1 Approach for Adequacy Assessment Assessment of EM adequacy involves both a bottom-up assessment and top-down assessment of the integrated EM. The bottom-up assessment addresses the model pedigree and applicability to simulate each physical process of interest identified in the PIRT. Calculations are performed to assess the ability of the as-implemented model to simulate separate effects test data. Scalability issues of the model are identified. The top-down assessment of the EM considers the capability of field equations and the numeric solution to represent the processes and phenomena in the integrated calculation for the necessary system components. Calculations are performed to assess system interactions and global capability with comparison against integrated effects test data. Scalability is evaluated to examine differences between assessment calculations and experiments, or between data from different facilities, that may indicate a scaling distortion in the experimental facility or computational model. The XPC EM builds on the LOCA and non-LOCA EMs and their applicability assessments for NRELAP5 where appropriate. The LOCA EM covers the initial blowdown (Phase 1a) and ECCS actuation (Phase 1b) phases of the transient, through the beginning of Phase 2 recirculation. The XPC EM covers the Phase 2 extended passive cooling, as well as addressing module boron transport and distribution throughout the transient. The non-LOCA EM covers the transient phases prior to reactor trip (Phase 1), DHRS actuation (Phase 2), and establishment of stable DHRS cooling while RPV mixture level remains above the riser (Phase 3). The XPC EM covers the Phase 3 extended passive cooling, where RPV mixture level may remain above the top of the riser or may decrease to below the top of the riser depending on the rate of cooling and coolant volume shrinkage. Therefore, first, the range of conditions for important transient parameters are compared between the XPC conditions and the LOCA or non-LOCA EM range of conditions. Then the bottom-up assessment of the model pedigree, applicability to simulate the physical process, and range of conditions for the XPC phase are discussed for each important phenomenon. This assessment builds on the LOCA and non-LOCA applicability assessments where appropriate. The important phenomena examined in the bottom-up assessment are the phenomena ranked high importance and medium importance in the PIRT as discussed in Section 3.4. Specific modeling techniques implemented in the XPC EM to address each phenomenon are summarized as necessary. A top-down assessment of the EM is performed considering the availability of integral effects test data to simulate important phenomena, results of code validation against the test data, conservatisms applied in the EM, and results of plant sensitivity calculations. © Copyright 2022 by NuScale Power, LLC 110

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.2 Extended Passive Cooling Range of Conditions Extended ECCS Cooling Range of Conditions Table 4-14 summarizes the process parameter ranges for the US460 design evaluated in justification of the LOCA EM applicability. The parameters and LOCA EM ranges are compared to the XPC ranges of conditions for extended ECCS operation. A graded approach is applied where ((

                                                                         }}2(a),(c)

Table 4-14 LOCA EM and XPC Extended ECCS Process Parameter Ranges ((

                                                                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-14 LOCA EM and XPC Extended ECCS Process Parameter Ranges (Continued) ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-14 LOCA EM and XPC Extended ECCS Process Parameter Ranges (Continued) ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-14 LOCA EM and XPC Extended ECCS Process Parameter Ranges (Continued) ((

                                                                                                        }}2(a),(c)

Extended DHRS Cooling Range of Conditions Table 4-15 summarizes the process parameter ranges for the US460 design evaluated in justification of the LOCA EM applicability. The parameters and LOCA EM ranges are compared to the XPC ranges of conditions for extended DHRS operation without or prior to ECCS actuation. ((

                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                             }}2(a),(c)

Table 4-15 LOCA EM and XPC EM Extended DHRS Process Parameter Ranges ((

                                                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-15 LOCA EM and XPC EM Extended DHRS Process Parameter Ranges (Continued) ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-15 LOCA EM and XPC EM Extended DHRS Process Parameter Ranges (Continued) ((

                                                                                                    }}2(a),(c)

Table 4-16 Non-LOCA EM and XPC EM Extended DHRS Process Parameter Ranges for SG/DHRS Boiling and Condensation Heat Transfer Phenomena ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3 Bottom-up Assessments for XPC Phenomena The high-ranked and medium-ranked phenomena identified by the XPC PIRT in Section 3.4 are assessed. The assessments are summarized in the following sections. The summaries describe the phenomena, the importance of the phenomena in parts of the EM calculation, and how the phenomena are addressed in the XPC evaluation method. 4.4.3.1 Fuel Decay Heat Source and Distribution ((

                                                                                         }}2(a),(c)

NRELAP5 includes appropriate decay heat and point kinetics models. It also includes the option for the user to specify the decay heat source as a tabulated input. These models and user input options are assessed and determined to be adequate. ((

                                                       }}2(a),(c) 4.4.3.2            Core Heat Removal

((

                         }}2(a),(c)

The dominant NRELAP5 models and correlations and their range of applicability are assessed and determined to be adequate. ((

                                                                                            }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.3 Axial Void Distribution, Level Swell ((

                               }}2(a),(c)

The dominant NRELAP5 model that determines void distribution is the interfacial friction model, which is intimately related to the flow regime map, as the interphase friction correlation used is flow regime dependent. Evaluation of the models and correlations for interfacial drag are focused on extended ECCS cooling, which also addresses the range of conditions during extended DHRS operation. ((

                                                                                       }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                    }}2(a),(c) 4.4.3.4            Flashing

((

                                                        }}2(a),(c) The flashing model in NRELAP5 covers the entire range of the water properties table, which encompasses the NPM extended ECCS cooling application. NRELAP5 physical models for simulation of flashing are adequate.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.5 Interfacial Drag / Phase Slip / Flow Regimes ((

                                                 }}2(a),(c) 4.4.3.6            Evaporation

((

                                      }}2(a),(c) 4.4.3.7            RPV Pressure Loss due to Friction and Form Losses

((

                                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                          }}2(a),(c) 4.4.3.8            Lower Riser Hole Form Loss

((

                              }}2(a),(c)

NRELAP5 models are capable of simulating single phase and two-phase form and friction losses. The lower riser holes are an orifice-type flow path in the lower riser metal structure. ((

                                  }}2(a),(c) 4.4.3.9            Pressure Drop across Lower Riser Holes

((

                                                                                                 }}2(a),(c)

The NRELAP5 models are capable of simulating pressure drop from single phase and two-phase form and friction losses. Section 4.4.3.8 discusses the lower riser hole form loss. © Copyright 2022 by NuScale Power, LLC 122

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                          }}2(a),(c) 4.4.3.10           Upper Riser Hole Form Loss

((

                                                                }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.11 Bypass Flow ((

                                                                                 }}2(a),(c) 4.4.3.12           3D Flow/Boron Distribution and Mixing in the RPV

((

                                                                                                      }}2(a),(c)

Boron transport and mixing methods are incorporated in the boron transport part of the XPC EM as described in Section 6.2. Extended ECCS Cooling ((

                                                                                                     }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                 }}2(a),(c)

Extended DHRS Cooling ((

                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.13 CVCS Break Flow ((

                                }}2(a),(c)

Therefore, NRELAP5 models for CVCS break flow are assessed and determined to be adequate. ((

                                                                                                 }}2(a),(c) 4.4.3.14           Reactor Vessel, Internals Heat Removal

((

                                                              }}2(a),(c)

The NRELAP5 models and evaluation discussed in Section 4.4.3.2 for the convective heat transfer coefficient at the inside surface of the RPV are applicable to this phenomenon. NRELAP5 models for reactor vessel and CNV metal heat transfer are assessed and determined to be adequate. © Copyright 2022 by NuScale Power, LLC 127

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                         }}2(a),(c) 4.4.3.15           Condensation on RPV Inside Walls

((

                                                                                            }}2(a),(c)

With respect to NRELAP5 calculations, condensation heat transfer is calculated on the RPV walls when appropriate to the conditions. The models and correlations are consistent with those applied to the CNV inside wall. However, the majority of decay heat removal is through condensation on the steam generator tubes and inside containment wall, which are continually cooled by the DHRS and the reactor pool, respectively. ((

                                                                                        }}2(a),(c) 4.4.3.16           Thermal Stratification

((

                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.17 Natural Circulation Flow ((

                                                                                                  }}2(a),(c)

With respect to the bottom-up assessment, NRELAP5 models for prediction of natural circulation flow are adequate. ((

                                                                                               }}2(a),(c) 4.4.3.18           Natural Circulation Flow Instability

((

                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.19 Flow Stagnation, Reversal, Recirculation ((

                                                                                             }}2(a),(c) 4.4.3.20           Liquid Droplet Entrainment

((

                                                           }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.21 Liquid Droplet De-Entrainment ((

                                                        }}2(a),(c) 4.4.3.22           Boron Precipitation/Plateout

((

                                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.23 Boric Acid Volatility ((

                                          }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.24 Steam Generator Shell-Side Heat Transfer ((

                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                 }}2(a),(c) 4.4.3.25           Steam Generator Tube-Side Heat Transfer

((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.26 DHRS Heat Transfer ((

                                           }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                           }}2(a),(c) 4.4.3.27           DHRS Loop Pressure Loss / Flow Resistance

((

                                                                                       }}2(a),(c)

Assessments of NRELAP5 for the LOCA EM and non-LOCA EM development demonstrated capacity of the code to model single phase flow conditions and loop flow resistance for boiling/condensing natural circulation conditions. While secondary side pressures and temperatures are lower during the XPC phase, the fundamental capability of NRELAP5 is maintained. Therefore it is concluded that the NRELAP5 models for DHRS loop pressure loss and flow resistance are adequate. ((

                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.28 SG/DHRS Boiling/Condensing Loop Flow ((

                                                                             }}2(a),(c) 4.4.3.29           Parallel Channel Instability

((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                   }}2(a),(c) 4.4.3.30           Mass and Energy Release through ECCS Valves

((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Therefore, it is concluded that from a bottom-up perspective, given appropriate user input, NRELAP5 is applicable to model flow through the ECCS valves during extended ECCS operation. ((

                                                                 }}2(a),(c) 4.4.3.31           Boiling/Condensation Instability

((

                          }}2(a),(c)

With respect to extended passive cooling, the importance of this phenomenon is due to potential effects on the integral heat removal capacity. Based on the assessments in Section 4.4.3.24, Section 4.4.3.25, Section 4.4.3.26, and Section 4.4.3.27, it is concluded that from a bottom-up perspective the NRELAP5 models are adequate for prediction of SG/DHRS heat removal. Top-down assessment of integral effects and phenomena are discussed in Section 4.4.4. ((

                                                                                           }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.32 RRV Flow Instability ((

                                }}2(a),(c) Therefore, it is concluded that from a bottom-up perspective, NRELAP5 models are capable of accounting for effects of RRV flow instability.

Top-down assessment of integral effects and phenomena are discussed in Section 4.4.4. 4.4.3.33 CNV Wall Heat Transfer ((

                                                                                }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                }}2(a),(c) It is concluded that NRELAP5 models are adequate to model heat transfer through the CNV wall.

((

                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.34 3D Flow, Boron Distribution and Mixing in the CNV ((

                                                             }}2(a),(c) Therefore, it is concluded that the boron transport method conservatively accounts for effects of 3D flow, boron distribution and mixing in the CNV, with appropriate methods specified for boron dilution analyses and boron precipitation analyses.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.35 Containment Isolation Valve Leakage Rate ((

                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.36 Condensate Collection ((

                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.37 Boron Dissolution ((

                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.38 Hydrostatic Head above CNV Liquid ((

                                                         }}2(a),(c) 4.4.3.39           Form and Friction Loss in ESB Mixing Tube

((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.40 Mixing Efficiency in CNV ((

                                              }}2(a),(c) 4.4.3.41           Boron Dilution in CNV

((

                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 4.4.3.42 3D Flow, Mixing in Reactor Pool ((

                                               }}2(a),(c) 4.4.4         EM Top-Down Assessment 4.4.4.1            NRELAP5 Top-Down Assessment for Extended ECCS Cooling Phenomena The first portion of the top-down assessment is focused on NRELAP5 prediction of extended ECCS cooling thermal-hydraulic phenomena. As the system analysis code, in the EM the calculation results are used to demonstrate margin in collapsed liquid level above the core and sustained decay heat removal. The code calculation results provide boundary condition input for boron transport analysis and subcriticality analysis. A summary of the NRELAP5 code governing equations and numerics is provided in the LOCA topical report (Reference 10.2.1) Section 6 and Section 8.3.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 NPM model nodalization and convergence was assessed as part of LOCA EM development. For extended ECCS cooling the NPM model nodalization is coarser, as described in Section 5.2. ((

                                                                             }}2(a),(c) In addition to the benchmark calculations, assessment of NRELAP5 against NIST-2 LTC tests demonstrate key capabilities of the code predictions of extended ECCS cooling phenomena for integral effects test data.

NRELAP5 provides reasonable to excellent prediction of the system energy balance and mass distribution, and therefore pressures and collapsed liquid levels, even during sub-atmospheric pressure conditions. Key conclusions from the NIST-2 LTC tests and NRELAP5 assessments include: ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                    }}2(a),(c)

Key conclusions from the NIST-2 SG/DHRS tests and NRELAP5 assessments are as follows. ((

                                      }}2(a),(c) 4.4.4.2            Extended ECCS Top-Down Assessment The high-ranked and medium-ranked phenomena for extended ECCS cooling are considered with respect to the overall EM treatment, as summarized in Table 4-17.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena ((

                                                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                              }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-17 Top-Down Assessment for Extended ECCS Phenomena (Continued) ((

                                                                                                          }}2(a),(c) 4.4.4.3            NRELAP5 Top-Down Assessment for Extended DHRS Cooling Phenomena The first portion of the top-down assessment is focused on NRELAP5 prediction of extended DHRS cooling thermal-hydraulic phenomena. As the system analysis code, in the EM the calculation results are used to demonstrate sustained decay heat removal. The code calculation results provide boundary condition input for boron transport analysis and subcriticality analysis.

This assessment builds on the extended ECCS applicability assessment described in Section 4.4.4, and the non-LOCA EM applicability evaluation. It is noted that extended ECCS cooling reaches more extreme ranges of low pressure and temperature conditions than extended DHRS cooling, because energy can also be transferred through the containment wall to the reactor pool. ((

                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The non-LOCA EM applicability evaluation demonstrated the applicability of NRELAP5 to predict SG/DHRS heat transfer for conditions with primary natural circulation sustained with flow over the top of the riser. Conditions unique for extended DHRS cooling, specifically cross-flow through the upper riser flow paths with the riser uncovered, and heat transfer to the secondary side with a partially uncovered steam generator, are considered further. ((

                                                           }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                            }}2(a),(c)

Therefore, considering NRELAP5 integral assessments for single-phase and two-phase natural circulation flow, incorporation of models for condensation heat transfer, and effectiveness of condensation heat transfer compared to single-phase natural convection, it is concluded that the scope of NRELAP5 integral assessments are adequate for the purpose of the XPC EM adequacy evaluation for extended DHRS cooling. 4.4.4.4 Extended DHRS Cooling Top-Down Assessment The high-ranked and medium-ranked phenomena for extended DHRS cooling are considered with respect to the overall EM treatment, as summarized in Table 4-18. Table 4-18 Top-Down Assessment for Extended DHRS Cooling Phenomena ((

                                                                                                           }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-18 Top-Down Assessment for Extended DHRS Cooling Phenomena (Continued) ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-18 Top-Down Assessment for Extended DHRS Cooling Phenomena (Continued) ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-18 Top-Down Assessment for Extended DHRS Cooling Phenomena (Continued) ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-18 Top-Down Assessment for Extended DHRS Cooling Phenomena (Continued) ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 4-18 Top-Down Assessment for Extended DHRS Cooling Phenomena (Continued) ((

                                                                                                        }}2(a),(c) 4.4.5         EM Adequacy Conclusion Overall EM Adequacy Assessment for Extended ECCS Cooling A bottom-up assessment was performed examining the models and correlations incorporated in the XPC EM, as part of NRELAP5 or in the boron transport method, for simulation of the high-ranked and medium-ranked phenomena for extended ECCS operation. Results of NRELAP5 assessments against NIST-2 integral test results are examined, and sensitivity calculations are performed to assess impacts of compensating effects on the integral performance. Considering these results, a top-down assessment was performed considering the prediction of the phenomena and biases observed when assessed in an integral manner with the EM. The overall approach used in the boron transport method, considering use of boundary conditions from NRELAP5, was also assessed.

The bottom up assessment demonstrates that models and correlations incorporated in the EM are adequate for the range of conditions to be evaluated during extended ECCS cooling. ((

                       }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                   }}2(a),(c)

Finally, the EM relies on qualified core design methods, as described in Reference 10.2.9, to evaluate the critical boron concentration. Considering these evaluations, it is concluded that the overall EM to simulate ECCS extended passive cooling is adequate. Overall EM Adequacy Assessment for Extended DHRS Cooling A bottom-up assessment was performed examining the models and correlations incorporated in the XPC EM, as part of NRELAP5 or in the boron transport method, for simulation of the high-ranked and medium-ranked phenomena for extended DHRS operation. Results of NRELAP5 assessments against NIST SET and IET are considered to evaluate adequacy of the code and modeling approach to simulate integral performance of the NPM. Considering these results, a top-down assessment was performed considering the prediction of the phenomena, biases incorporated into the methodology, and limiting conditions for the EM acceptance criteria. The overall approach used in the boron transport method, considering use of boundary conditions from NRELAP5, was also assessed. © Copyright 2022 by NuScale Power, LLC 169

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The bottom-up assessment demonstrates that models and correlations incorporated in the EM are adequate for the range of conditions to be evaluated during extended DHRS cooling. The top-down assessment considered the NRELAP5 validation against NIST testing, and ((

                                      }}2(a),(c) it is concluded that the scope of NRELAP5 integral assessments are adequate for the purpose of the XPC EM adequacy evaluation for extended DHRS cooling.

The summary of the boron transport method evaluation provided in Section 4.4.5 for long-term ECCS operation is applicable for extended DHRS operation. Finally, the EM relies on qualified core design methods, as described in Reference 10.2.9, to evaluate the critical boron concentration. Considering these evaluations, it is concluded that the overall EM to simulate DHRS extended passive cooling is adequate. © Copyright 2022 by NuScale Power, LLC 170

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 5.0 Extended Passive Cooling Thermal-Hydraulic Analysis Methodology Section 4.4 describes the important phenomena and parameters to evaluate the FOM, which are tied to the acceptance criteria delineated in Section 2.0. This section establishes the XPC methodology. Analysis of XPC credits long-term decay heat removal through the ECCS and the DHRS. Analysis demonstrates that the top of active fuel remains covered. XPC conditions are also evaluated to demonstrate maximum temperature cases remain within pressure and temperature limits for the RPV and CNV. Minimum temperature cases and other sensitivity calculations are included to provide boundary conditions for reactivity control and boron precipitation analyses described in Section 6.0 and Section 7.0. The methodology to address maintaining a coolable geometry by precluding boron precipitation is described in Section 7.0. The results presented in Section 5.5 for the minimum RCS temperatures will be considered in the Section 7.0 analyses for limiting boron solubility conditions. 5.1 Extended Passive Cooling Characteristics 5.1.1 Extended ECCS Passive Cooling As shown in Figure 1-1, in the NPM design, ECCS actuation may occur early in the transient progression, such as for LOCA pipe break or inadvertent ECCS operation events, or may occur later in the transient after several hours of DHRS cooling. For LOCA or inadvertent ECCS operating events, module behavior can be divided into three distinct phases: Phase 1a, blowdown (through the break or opened valve) Phase 1b, ECCS actuation Phase 2, flow reversal at RRVs These phases are shown schematically in Figure 5-1. For a non-LOCA or leakage event with extended DHRS operation prior to ECCS actuation, the module pressure and temperature decrease from normal operating conditions due to DHRS cooling, and any leakage, prior to ECCS actuation. Therefore, conditions in ECCS blowdown reflect lower RCS energy conditions compared to a LOCA event phase 1b conditions. In either case, when ECCS actuates, flow through the RRVs is initially outwards from the RPV into containment. After RPV and CNV pressures equalize, and sufficient hydrostatic head is developed in the CNV above the RRVs, flow reverses and recirculation from containment into the downcomer begins. © Copyright 2022 by NuScale Power, LLC 171

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 First, the system-level thermal-hydraulic response is considered in terms of the overall energy, momentum, and mass balances between the RPV and CNV. Then boron transport between regions in the module is considered. ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                       }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-1 NPM LOCA Phases Resulting from a Typical Liquid-Space Break ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-2 Simplified View of the Flow Paths through ECCS Valves between RPV and CNV ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-3 CNV Annular Region and Flow Area Restriction near RPV Flange, Relative Elevation of RRVs ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-4 Illustration of Major Primary Fluid Flow Paths during Extended ECCS Operation ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 5.1.2 Extended DHRS Passive Cooling For extended DHRS operation, driving forces (e.g., the temperature difference between RPV and pool) are smaller compared to the short-term DHRS operation phase addressed in the non-LOCA EM, but the extended DHRS response is reasonably similar to the short-term DHRS response. Primary natural circulation flow transfers decay and residual heat to the steam generator. Vapor generated in the steam generator is condensed in the DHRS heat exchanger and energy is transferred to the reactor pool ultimate heat sink. In the NPM design, extended DHRS operation is evaluated to demonstrate adequate decay heat removal, and to assess boron transport to demonstrate subcriticality is maintained. Boron transport during extended DHRS operation is evaluated to demonstrate that the core and downcomer boron concentrations remain above the critical concentration, in order to assure that ECCS actuation does not result in a rapid positive reactivity insertion to the core. ((

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-5 Representative Behavior of Riser Void during Extended DHRS Operation with Riser Uncovery ((

                                                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-6 Representative Behavior of RCS Fluid Temperatures during Extended DHRS Operation with Riser Uncovery ((

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-7 Representative Behavior of RCS Total Flow, and Riser Hole Flow during Extended DHRS Operation with Riser Uncovery ((

                                                                                                     }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-8 Representative Behavior of RCS Riser Hole Flow during Leakage Conditions with Extended DHRS Operation and Riser Uncovery ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-9 Representative Behavior of RCS Riser Void Fraction during Leakage Conditions with Extended DHRS Operation and Riser Uncovery ((

                                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-10 Representative Behavior of RCS Fluid Temperatures with Extended DHRS Operation and Riser Uncovery ((

                                                                                                        }}2(a),(c) 5.2      NRELAP5 Models for Extended Passive Cooling The NRELAP5 XPC model input file is developed based on engineering drawings, calculations, and reference documents. These sources of information provide the numerical information necessary to develop a complete thermal-hydraulic simulation model of the NPM. For extended ECCS operation, the NPM model is adapted from the detailed NRELAP5 model as described in Section 5.2.1. Section 5.2.2 provides representative comparison results of the more detailed model developed for short-term LOCA calculations, and coarser model long-term ECCS model, to demonstrate that the coarser model is adequate.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 5.2.1 ECCS Long-Term Cooling Model Description The NPM NRELAP5 analytical model for ECCS long-term cooling is developed from the detailed NRELAP5 basemodel. ((

                                 }}2(a),(c)

Reactor Coolant System Hydraulic Volume Basemodel Modifications The reactor coolant system is comprised of the lower plenum, core, riser, upper plenum, downcomer, and pressurizer. A description of the RCS is provided in Section 3.2.2. ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-11 Long-Term Cooling Model Nodalization Diagram ((

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Secondary System Hydraulic Volume Basemodel Modifications The secondary system is comprised of the feedwater lines, steam generator tubes, steam lines, DHRS condenser tubes, and DHRS condensate lines. A description of the secondary is provided in the non-LOCA EM (Reference 10.2.5). ((

                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Containment System Hydraulic Volume Basemodel Modifications The containment system is comprised of the containment volume, initialization volumes, and the containment evacuation system. A description of the containment is provided in Section 3.2.2. ((

                               }}2(a),(c)

Pool Hydraulic Volume Basemodel Modifications ((

                              }}2(a),(c)

CVCS and Reactor Valve Basemodel Modifications Key modifications to the CVCS and RPV valve components between the standard basemodel and the ECCS long-term cooling basemodel are described here. ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                }}2(a),(c)

Heat Structure Basemodel Modifications Key modifications to the heat structures between the standard basemodel and the XPC basemodel are described here. ((

                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Radiation Heat Transfer Modeling and Reactor Kinetics Modeling Modifications Modifications to the radiation modeling between the standard basemodel and the XPC basemodel are described here. ((

                                                         }}2(a),(c)

Control Variable and Trip Logic Modifications ((

                                      }}2(a),(c)

((

                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                  }}2(a),(c)

For extended DHRS calculations focused on demonstrating decay heat removal, the detailed non-LOCA model is used (Reference 10.2.5). 5.2.2 Comparison of Simplified and Detailed Model Performance A consistency evaluation was performed between the ECCS long-term cooling analytical model and the LOCA base model. (( }}2(a),(c) © Copyright 2022 by NuScale Power, LLC 194

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-12 Decay Heat Comparison between LOCA and XPC Analytical Models ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-13 RCS Pressure Response Comparison between LOCA and XPC Analytical Models ((

                                                                                             }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-14 Secondary Steam Pressure Response Comparison between LOCA and XPC Analytical Models ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-15 Riser Collapsed Liquid Level Comparison between LOCA and XPC Analytical Models ((

                                                                                                 }}2(a),(c) 5.2.3         Assessment of Lower Riser Hole Flow during ECCS Cooling

((

                                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Method to Evaluate Core and Riser Axial Void Distribution ((

                                                               )
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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

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Table 5-1 Range of Rod Bundle Data Conditions used to Develop Clark Drift Flux Model (Reference 10.2.11) Parameter Range Superficial liquid velocity, jf 0.0 - 1.0 m/s Superficial gas velocity, jg 0.03-10.0 m/s Void fraction 0.05 - 0.93 Pressure 14.7 psia © Copyright 2022 by NuScale Power, LLC 205

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-2 Range of Bundle Data Conditions used for Clark Model Comparison (Reference 10.2.11) Parameter Range Superficial liquid velocity, jf 0.0 - 1.4 m/s Superficial gas velocity, jg 0.03 - 8.33 m/s Void fraction 0.04 - 0.92 Pressure 0.1-17 MPa (14.5 -2466 psia) Rod diameter 9.5-10.5 mm (0.374-0.413 in) Rod pitch 12.6-16.0 mm (0.496-0.630 in) 5.3 Events Evaluated for Extended Passive Cooling 5.3.1 Extended ECCS Cooling Events During extended ECCS cooling, boiling/condensing recirculation of RCS inventory between the RPV and CNV can challenge the acceptance criteria of maintaining collapsed liquid level over top of the core. It is necessary to demonstrate that ECCS recirculation and heat removal to the reactor pool provide adequate decay heat removal. Effective ECCS and DHRS cooling decreases RPV liquid temperatures; boron transport in the module must be assessed for dilution and precipitation evaluations. Therefore, in the XPC EM, extended ECCS cooling calculations are performed for the following scenarios.

1. Demonstrate ECCS capacity to maintain collapsed liquid level above the core for up to 72 hours under conditions challenging minimum liquid level.

2. Demonstrate the system decay heat capacity for up to 72 hours under conditions challenging ECCS/CNV heat removal.

3. Provide input to boron transport analyses for dilution (subcriticality analysis) and precipitation with conditions biased to minimize core moderator temperature.

4. Provide input to boron transport analyses for dilution (subcriticality analysis) and precipitation with conditions biased to evaluate a range of boron dissolution and transport rates from containment into the RPV.

For XPC thermal-hydraulic analyses, NRELAP5 calculations are typically performed starting from event initiation to minimize user effort for model initiation and to assess boron transport over the event duration. The transient calculations are run for a number of hours (e.g.12-24) to demonstrate that quasi-steady conditions are reached. Then statepoint analyses are used to evaluate the later time periods. Statepoint analyses specify constant boundary conditions (e.g. for decay heat and pool level/temperature) and then an NRELAP5 transient is executed for sufficient time to reach quasi-steady conditions. The statepoint results are the results at the end of © Copyright 2022 by NuScale Power, LLC 206

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 the calculation and they reflect the event time of the boundary conditions specified, not the transient calculation time. Minimum Collapsed Level Extended ECCS operation justifying sufficient ECCS capacity to maintain level above the top of the reactor core must address the range of transient and accident initiating events that could result in sustained ECCS heat removal. Minimum level above the top of the core is affected by the RCS inventory and timing of ECCS actuation. Therefore, the following initiating events resulting in a decrease in RCS inventory are specifically evaluated to determine bounding conditions for the range of NPM design-basis initiating events: Small pipe breaks outside containment Steam generator tube failure Loss of coolant accidents from pipe breaks inside containment Inadvertent operation of the ECCS For the pipe breaks inside and outside containment, the spectrum of liquid and vapor pipe break locations and a range of break areas is evaluated. In the NPM design, steam generator tube failure and small pipe breaks carrying RCS coolant outside containment (non-LOCA events resulting in a decrease in RCS inventory) are designed to be mitigated without actuation of ECCS. If power to the MPS is available, then with or without normal AC power supply the MPS is designed to detect the inventory reduction and mitigate the event by reactor trip, isolation of the leak with appropriate containment isolation valves, and actuation of DHRS to assure decay heat removal. The short-term event progression of an SGTF or a pipe break carrying reactor coolant outside containment is analyzed using the non-LOCA analysis methodology (Reference 10.2.5). ECCS is actuated in these events if normal power supply is assumed to be lost, or if ECCS is actuated to assure sufficient boron is present in the RCS to maintain subcriticality. These initiating events could result in lower RCS inventory during ECCS cooling compared to LOCA pipe breaks inside containment, and therefore they are included in the scope of minimum level calculations. © Copyright 2022 by NuScale Power, LLC 207

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Maximum Temperature Analysis of extended ECCS operation is performed to justify sufficient ECCS capacity to maintain level above the top of the reactor core, and reactor pressure vessel and containment vessel integrity, during conditions biased to minimize decay heat removal and maximize module temperatures. The scope of analysis must address the range of transient and accident initiating events that could result in sustained ECCS heat removal. ((

                      }}2(a),(c)

Minimum Temperature Analysis of extended ECCS operation is performed with conditions biased to evaluate effective decay heat removal and the coolest moderator conditions that may arise in the module in the 72 hours following a design basis event. Thermal-hydraulic results from these calculations are used in downstream boron transport analyses to assess margin to subcriticality and to boron precipitation. The scope of analysis must address the range of transient and accident initiating events that could result in sustained ECCS heat removal. Module heat transfer capacity is affected by decay heat, ECCS capacity, and cooling pool conditions. ((

                                                                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                              }}2(a),(c)

Boron Transport Sensitivities Analysis of extended ECCS operation is performed with conditions biased to generate transient conditions for sensitivity cases evaluated for downstream boron transport analysis. Lower temperatures and pressures in the RCS and CNV are limiting for both subcriticality (lower temperatures improve moderator feedback) and boron precipitation (lower temperature decrease solubility limits). Thermal-hydraulic results from these calculations are used in downstream boron transport analyses to assess margin to subcriticality and to boron precipitation. The scope of analysis must address the range of transient and accident initiating events that could result in sustained ECCS heat removal. Module heat transfer capacity and boron transport are affected by module inventory, decay heat, ECCS capacity, ECCS actuation time, RCS energy at time of ECCS actuation, cooling pool conditions, and break location. Therefore, the following initiating events are specifically evaluated to provide an appropriate range of sensitivity results for downstream boron transport analysis. ((

                                             }}2(a),(c) 5.3.2         Extended DHRS Cooling Events During extended DHRS cooling, RCS inventory is retained inside the RPV such that maintaining collapsed liquid level over top of the core is not challenged. RPV liquid reaches cooler temperatures, with higher boron concentration during ECCS cooling compared to extended DHRS cooling. Therefore, DHRS cooling conditions are non-limiting for boron precipitation analysis. Therefore, demonstration that decay heat removal is sustained, subcriticality is maintained, and downcomer concentration

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 remains higher than the critical concentration prior to ECCS actuation, are sufficient to demonstrate acceptance criteria are met during extended DHRS cooling. Therefore, in the XPC EM, extended DHRS cooling calculations are performed to for the following scenarios,

1. Demonstrate the system decay heat capacity for up to 72 hours under conditions challenging DHRS heat removal.

2. Provide input to boron dilution calculations with conditions biased to maximize potential for boron redistribution.

DHRS Heat Removal Extended DHRS operation justifying sufficiently decay and residual heat removal for 72 hours must address the range of transient and accident initiating events that could result in sustained DHRS heat removal. The DHRS heat transfer capacity is limited in cases with a single DHRS train or a high secondary side inventory. Therefore, the following initiating events are specifically evaluated because they are bounding for the range of NPM design-basis initiating events: Initiating event increases secondary side inventory:

                  -    Increase in feedwater flow Initiating event disables one train of DHRS:
                  -    Main steam line break
                  -    Feedwater line break
                  -    Steam generator tube failure Boron Redistribution Extended DHRS cases biased to provide input for boron dilution analyses must address the range of transient and accident initiating events that could result in sustained DHRS heat removal. In addition, leakage conditions are assessed to evaluate conditions prior to ECCS actuation. As discussed in Section 5.1.2, during extended DHRS operation, boron redistribution occurs if there is sustained condensation in the upper portion of the steam generator after there is sufficient primary volume shrinkage to uncover part of the steam generator. The purpose of the boron transport analyses biased for dilution is to quantify the core and downcomer boron concentration versus time as input to subcriticality calculations during extended DHRS operation. The subcriticality calculations demonstrate that subcriticality is maintained during extended DHRS operation, and that the downcomer concentration remains above the critical concentration prior to ECCS actuation.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Therefore, the following initiating events are specifically evaluated because they are bounding for the range of NPM design-basis initiating events: ((

                                                                                    }}2(a),(c) 5.4      Initial Conditions and Biases The following sections describe key initial and boundary condition biases for extended ECCS cooling and extended DHRS cooling event NRELAP5 analysis.

Multi-module Consideration Thermal-hydraulic analyses are performed for a single module. In the NPM design, components performing safety-related functions during the transient are module-specific with the exception of the shared portion of the reactor pool ultimate heat sink. Therefore, multi-module effects are accounted for, as necessary, through specification of the pool temperature and level boundary conditions. 5.4.1 Calculation Biases for ECCS Capacity - Minimum Collapsed Liquid Level Table 5-3 summarizes the key initial and boundary condition biases applied or evaluated for the extended ECCS cooling cases. For these initiating events, the transient response is evaluated for at least 12 hours or until quasi-steady conditions are reached. Then statepoint evaluations with the same biasing factors are performed to assess later time periods, out to 72 hours. © Copyright 2022 by NuScale Power, LLC 211

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-3 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating Minimum Collapsed Liquid Level Key Parameter Bias Basis for Bias / Comment (( Single failures Power availability Normal control system response Operator action Decay heat Initial RCS Temperature Pressurizer Level, Pressurizer Pressure

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-3 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating Minimum Collapsed Liquid Level (Continued) Key Parameter Bias Basis for Bias / Comment (( Reactor pool level Reactor pool temperature Non-condensable gas effects Riser hole elevations and form loss ECCS valve capacity

                                                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-3 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating Minimum Collapsed Liquid Level (Continued) Key Parameter Bias Basis for Bias / Comment (( Steam generator operating parameters

                                                                                                         }}2(a),(c) 5.4.2         Calculation Biases for ECCS/CNV Heat Transfer Capacity - Maximum Temperature Table 5-4 summarizes the key initial and boundary condition biases applied or evaluated for the extended ECCS cooling cases. For these initiating events, the transient response is evaluated for at least 12 hours or until quasi-steady conditions are reached. Statepoint evaluations with the same biasing factors are performed to assess later time periods, out to 72 hours.

Table 5-4 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating ECCS/CNV Heat transfer Capacity - Maximum Temperature Key Parameter Bias Basis for Bias / Comment (( Single failures Power availability Normal control system response

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-4 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating ECCS/CNV Heat transfer Capacity - Maximum Temperature (Continued) Key Parameter Bias Basis for Bias / Comment (( Operator action Decay heat Initial RCS Temperature Pressurizer Level, Pressurizer Pressure Reactor pool level Reactor pool temperature

                                                                                                       }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-4 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Demonstrating ECCS/CNV Heat transfer Capacity - Maximum Temperature (Continued) Key Parameter Bias Basis for Bias / Comment (( Non-condensable gas effects Riser hole elevations and form loss ECCS valve capacity Steam generator operating parameters

                                                                                                       }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 5.4.3 Calculation Biases for Boron Transport Analyses - Minimum Temperature Table 5-5 summarizes the key initial and boundary condition biases applied or evaluated for the extended ECCS cooling cases. For these initiating events, the transient response is evaluated for at least 12 hours or until quasi-steady conditions are reached. Statepoint evaluations with the same biasing factors are performed to assess later time periods extending to 72 hours. Table 5-5 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Evaluated for Boron Transport - Minimum Temperature Key Parameter Bias Basis for Bias / Comment (( Single failures Power availability Normal control system response Operator action Decay heat Initial RCS Temperature Pressurizer Level, Pressurizer Pressure Reactor pool level

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-5 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Evaluated for Boron Transport - Minimum Temperature (Continued) Key Parameter Bias Basis for Bias / Comment (( Reactor pool temperature Non-condensable gas effects Riser hole elevations and form loss ECCS valve capacity Steam generator operating parameters

                                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 5.4.4 Calculation Biases for Boron Transport Analysis - Sensitivities Table 5-6 summarizes the key initial and boundary condition biases applied or evaluated for the extended ECCS cooling cases. For these initiating events, the transient response is evaluated for at least 12 hours or until quasi-steady conditions are reached. Statepoint evaluations with the same biasing factors are performed to assess later time periods, out to 72 hours. Table 5-6 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Evaluated for Boron Transport - Sensitivities Key Parameter Bias Basis for Bias / Comment (( Single failures Power availability Normal control system response Operator action Decay heat Initial RCS Temperature Pressurizer Level Pressurizer Pressure Reactor pool level Reactor pool temperature

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-6 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Evaluated for Boron Transport - Sensitivities (Continued) Key Parameter Bias Basis for Bias / Comment (( Non-condensable gas effects Riser hole elevations and form loss ECCS valve capacity Steam generator operating parameters

                                                                                                       }}2(a),(c) 5.4.5         Calculation Biases for DHRS Decay and Residual Heat Removal Table 5-7 summarizes the key initial and boundary condition biases applied or evaluated for extended DHRS cooling cases. For these initiating events, transient conditions are evaluated until DHRS heat removal exceeds decay heat. As summarized in Table 5-7, adequate pool level is maintained during operation and the pool temperature heatup effects are bounded. Because pool conditions are bounded, after DHRS capacity exceeds decay heat, cooling will be sustained and it can be concluded that DHRS heat removal is adequately demonstrated.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 The detailed NRELAP5 model developed as part of the non-LOCA EM is used for extended DHRS calculations biased to demonstrate adequate decay heat removal. Table 5-7 Initial and Boundary Condition Biases Evaluated for Extended DHRS Cooling Cases Demonstrating Decay Heat Removal Key Parameter Bias Basis for Bias / Comment (( Single failures Power availability Normal control system response Operator action RCS inventory Decay heat Reactor pool level

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-7 Initial and Boundary Condition Biases Evaluated for Extended DHRS Cooling Cases Demonstrating Decay Heat Removal (Continued) Key Parameter Bias Basis for Bias / Comment (( Reactor pool temperature Non-condensable gas effects Riser hole elevations Riser hole form loss

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

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-7 Initial and Boundary Condition Biases Evaluated for Extended DHRS Cooling Cases Demonstrating Decay Heat Removal (Continued) Key Parameter Bias Basis for Bias / Comment (( Steam generator operating parameters

                                                                                                      }}2(a),(c),ECI 5.4.6         Calculation Biases for Boron Dilution Analyses Table 5-8 summarizes the key initial and boundary condition biases applied or evaluated for extended DHRS cooling cases. For these initiating events, transient conditions are evaluated until ECCS actuation occurs or until calculation duration is sufficient to justify that quasi-steady conditions have been reached and adequately bound conditions out to 72 hours. Statepoint calculations may be used to assess conditions at later time periods, rather than continuous calculations.

((

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                 }}2(a),(c)

Table 5-8 Initial and Boundary Condition Biases Evaluated for Extended DHRS Cooling Cases Providing Input for Boron Dilution Analyses Key Parameter Bias Basis for Bias / Comment (( Single failures Power availability Normal control system response Operator action RCS inventory Decay heat Reactor pool level Reactor pool temperature

                                                                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-8 Initial and Boundary Condition Biases Evaluated for Extended DHRS Cooling Cases Providing Input for Boron Dilution Analyses (Continued) Key Parameter Bias Basis for Bias / Comment (( Non-condensable gas effects Riser hole elevations Riser hole form loss Steam generator operating parameters Leakage rate

                                                                                                       }}2(a),(c) 5.5      Representative Thermal-Hydraulic Results The XPC methodology is used to provide representative transient results. The transients noted below are selected to demonstrate the application of the NuScale XPC methodology for analysis of the plant responses to the events identified in Section 5.3.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 maximum temperature with inadvertent opening of an RVV with loss of AC and DC minimum temperature with inadvertent opening of an RVV with loss of AC and DC minimum temperature with small liquid break outside containment coincident with loss of AC The information included for each representative transient includes an event description, the results for the acceptance criteria of interest, and conclusions regarding the acceptance criteria of interest. These results are presented to demonstrate the application of the XPC methodology to the NPM. 5.5.1 Minimum Level The minimum level scenario evaluates the combined impact of biased conditions, provided in Section 5.4.1, that are applied to produce transients that result in the lowest collapsed liquid levels in the riser. The level depression phenomenon is driven by high differential pressure between the RPV and CNV during ECCS conditions, resulting in accumulation of liquid in the CNV. This biasing is focused on maximizing the differential pressure across the ECCS valves during ECCS conditions, and minimizing the initial RCS inventory. Results are presented for a range of break sizes for a discharge line break outside of containment, with power available and considering loss of AC power or loss of AC and DC power at event initiation (actuating a reactor trip, containment isolation, and ECCS coincident with break initiation). Of these selected cases, the 100 percent break size with power available case (plot minlevel-dlo-a) represents the minimum collapsed level during ECCS long-term cooling. Figure 5-16 through Figure 5-21 show the long-term transient behavior of key parameters for the discharge line breaks. The minimum collapsed level for the 100 percent discharge line break outside of containment is 1.6 feet above TAF and occurs approximately 8.6 hours after ECCS initiates. Figure 5-21 demonstrates that stable ECCS cooling is established and maintained through the analyzed LTC phase. For the minimum collapsed level representative cases, the core remains covered at all times and acceptance criteria are satisfied. State point conditions at 24, 48, and 72 hours are presented in Section 5.5.4 for a minimum level case. © Copyright 2022 by NuScale Power, LLC 226

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-16 Riser Level above Top of Active Fuel at Minimum Level ECCS Transient Results ((

                                                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-17 Containment Level above Top of Active Fuel at Minimum Level ECCS Transient Results ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-18 RCS Pressure at Minimum Level ECCS Transient Results ((

                                                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-19 CNV Pressure at Minimum Level ECCS Transient Results ((

                                                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-20 RVV Integrated Mass Release at Minimum Level ECCS Transient Results ((

                                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-21 Moderator Temperature at Minimum Level ECCS Transient Results ((

                                                                                                            }}2(a),(c) 5.5.2         Maximum Temperature The maximum temperature scenario evaluates the combined impact of biased conditions that result in the highest temperatures and pressures in the system. In general, conditions are biased to maximize RCS energy and minimize heat transfer to the UHS.

During the 72 hour evaluation period, the reactor pool may heat up and begin to boil-off. As it boils the effective heat transfer area from the CNV to the pool is reduced. The maximum temperature cases demonstrate that under extended ECCS conditions that vessel integrity is maintained, and pressures and temperatures stabilize at an acceptably low value after initial pressurization. In this case, the exact initiating event and short term transient effects have a negligible impact on the long-term ECCS conditions in the NPM. Results are presented in Figure 5-22 through Figure 5-26 for an inadvertent opening of an RVV with a loss of AC and DC power as © Copyright 2022 by NuScale Power, LLC 232

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 a representative transient. The transient results for the first 12 hours are shown (plot maxtemp-rvv-LoACDC) with statepoint results at 12, 24, 48, and 72 hours. The statepoint results are the quasi-steady conditions reached at the end of the calculation. The results demonstrate that CNV pressure and temperature decrease following the initial blowdown and stabilize at quasi-steady conditions at an acceptably low value. The module pressure continues decreasing as decay heat decreases over the 72-hour timeframe. Figure 5-22 Riser Level above Top of Active Fuel at Maximum Temperature ECCS Transient Results ((

                                                                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-23 Containment Level above Top of Active Fuel at Maximum Temperature ECCS Transient Results ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-24 RCS Pressure at Maximum Temperature ECCS Transient Results ((

                                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-25 CNV Pressure at Maximum Temperature ECCS Transient Results ((

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Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-26 Moderator Temperature at Maximum Temperature ECCS Transient Results ((

                                                                                                        }}2(a),(c) 5.5.3         Minimum Temperature The minimum temperature scenarios evaluate the combined impact of biased conditions that result in the lowest temperatures and pressures in the system, with a specific focus on core moderator temperature. Minimum temperature cases are used to assess core subcriticality and coolable geometry in the reactivity control and boron precipitation calculations presented in Section 6.0 and Section 7.0. In general, conditions are biased to minimize RCS energy and maximize heat transfer to the UHS.

The minimum moderator temperature and pressure conditions occur late in the transient when the decay heat is lowest, and the system has the most time to remove stored energy. In these cases, the exact initiating event and short term transient effects have a negligible impact on the long-term ECCS conditions in the NPM. Results are presented for an inadvertent opening of an RVV with loss of AC and DC © Copyright 2022 by NuScale Power, LLC 237

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 power (plot mintemp-rvv-LoACDC) as a representative ECCS transient. The transient results for the first 12 hours are shown (plot maxtemp-rvv-LoACDC) with statepoint results at 12, 24, 48, and 72 hours. The statepoint results are the quasi-steady conditions reached at the end of the calculation. Results are also presented for a small liquid break outside containment coincident with loss of AC power, from full power (plot mintemp-dhrs) or low power initial conditions (plot mintemp-nn-dhrs), as representative DHRS transients. Figure 5-27 through Figure 5-31 show the transient behavior of key parameters for the inadvertent opening of an RVV with loss of AC and DC power. Figure 5-32 through Figure 5-36 show the transient behavior of key parameters for a small liquid break outside containment coincident with loss of AC power. Early ECCS actuation results in the most effective heat removal condition and bounds non-LOCA or leakage cases that transition to ECCS after a period of time with only DHRS cooling. Figure 5-27 Riser Level above Top of Active Fuel at Minimum Temperature ECCS Transient Results ((

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-28 Containment Level above Top of Active Fuel at Minimum Temperature ECCS Transient Results ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-29 RCS Pressure at Minimum Temperature ECCS Transient Results ((

                                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-30 CNV Pressure at Minimum Temperature ECCS Transient Results ((

                                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-31 Moderator Temperature at Minimum Temperature ECCS Transient Results ((

                                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-32 Riser Level above Top of Active Fuel at Minimum Temperature DHRS Transient Results ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-33 Containment Level above Top of Active Fuel at Minimum Temperature DHRS Transient Results ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-34 RCS Pressure at Minimum Temperature DHRS Transient Results ((

                                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-35 CNV Pressure at Minimum Temperature DHRS Transient Results ((

                                                                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 5-36 Moderator at Minimum Temperature DHRS Transient Results ((

                                                                                                         }}2(a),(c) 5.5.4         State-point Evaluation to 72 Hours The minimum level transients are modeled over a timeframe of 24 hours at which time the riser level is expected to be increasing or stable. To demonstrate module conditions beyond 24 hours do not result in reductions in riser level, a series of state point calculations are evaluated for the quasi-steady portion of the ECCS cooling as shown in Table 5-9. The state-point evaluations share the same biasing as the minimum level transients and model an IORV event with loss of AC and DC at transient initiation.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 5-9 Minimum Level State Point Results Hour CLL (ft) 24 4.00 48 4.44 72 5.24 The maximum temperature case for ECCS long-term cooling is modeled over a 12-hour timeframe. By 12 hours transient effects have diminished and the module is in a quasi-steady state. Because the low reactor pool level and high temperature are constant in the model, the effects of the pool boil off are applied earlier in the transient than is realistically expected. As a result the peak pressures and temperatures occur early in the transient when decay heat and stored energy are highest. Additional state points between 12 and 72 hours are provided in Table 5-10 for completeness. Table 5-10 Maximum Temperature State Point Results Hour Moderator Temperature (°F) CNV Pressure (psia) 12 309 72 24 299 62 48 291 54 72 286 49 The minimum temperature case for the DHRS transient is modeled over an 8 hour time period. After this time the module transitions to ECCS. The ECCS transient is modeled over a 12-hour time period. By 12 hours the transient effects have diminished and the module is in a quasi-steady state. To demonstrate the response of module temperature and pressure beyond 12 hours, additional state points between 12 and 72 hours are provided in Table 5-11. Table 5-11 Minimum Temperature State Point Results Hour Moderator Temperature (°F) RPV Pressure (psia) 12 181 4.3 24 174 3.3 48 163 2.5 72 157 2.3 © Copyright 2022 by NuScale Power, LLC 248

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 6.0 Reactivity Control Evaluation 6.1 General Approach and Acceptance Criteria There are four main steps in the subcriticality analyses performed to demonstrate that reactivity control is maintained. ((

                                           }}2(a),(c)

The acceptance criterion is that the calculated core-region boron concentration remains higher than the critical boron concentration until at least 72 hours after event initiation. The following sections summarize the methods for determining the critical boron concentration and evaluating boron transport with bias for dilution to minimize the core boron concentration. 6.2 Boron Dilution Transport Methodology 6.2.1 Boron Dilution Method Overview ((

                                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 6.2.2 Module Mixing Volumes The mixing volumes are shown in Figure 6-1. The volumes are: ((

                                      }}2(a),(c)

Figure 6-1 Boron Dilution Methodology Mixing Volumes ((

                                                                                                     }}2(a),(c)

((

                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                         }}2(a),(c) 6.2.3         Boron Transport Mechanisms The following mechanisms transport boron between mixing volumes. ((
                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                      }}2(a),(c) 6.2.4         Boron Loss Mechanisms The following mechanisms remove boron from the analyzed system.

((

                                            }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                            }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                      }}2(a),(c) 6.2.5         ESB Addition Source The ESB feature adds boron to the system. ((
                           }}2(a),(c)

The method for calculating the boron addition rate from the supplemental boron system is summarized: Spatial and Temporal Discretization and Numerical Solution ((

                                                                                     }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Bed Porosity ((

                                                                    }}2(a),(c)

For equilateral cylindrical pellets loaded into a large cylinder, the porosity as a function of pellet diameter from the wall is based on experimental data measured by Zhang et al (Reference 10.2.17) by pouring equilateral cylindrical pellets into the larger cylinder without additional vibration or tapping. Figure 6-2 shows the porosity as a function of pellet diameters from the wall. Equilateral cylinders are appropriate for the NPM geometry (Section 3.2.3). The experimental work in Reference 10.2.17 evaluated packing fractions for equilateral cylinders with diameters approximately 10 percent the diameter of the container. Therefore, wall effects are significant and the work allowed for quantification of porosity as a function of non-dimensional distance from the wall. In all cases, as distance from the wall increases, the range of porosity decreases. ((

                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-2 Porosity as a Function of Pellet Diameters from Wall ((

                                                                                                          }}2(a),(c)

Boric Acid Solubility Limits and Fluid Properties ((

                                           }}2(a),(c) Boric acid solubility limits as a function of temperature are used. A fourth order polynomial fit to the data is used for the calculation. The temperature range used extends from 15 degrees C to 170 degrees C (288K to 443K, or 59 degrees F to 338 degrees F). The higher temperature data are from Reference 10.2.16. Figure 6-3 represents the data and demonstrates appropriateness of the polynomial fit. ((
                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                }}2(a),(c) These approaches are reasonable considering available experimental data from literature.

Figure 6-3 Boric Acid Solubility Limit as a Function of Temperature ((

                                                                                                           }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Packed Bed Maximum Fluid Velocity Fluid flow through a packed bed requires a driving pressure gradient to overcome frictional and other pressure losses. ((

                                                                                       }}2(a),(c) The model is as follows:
                                                                                  *         *2 Re            Re P  L- =  = A ---------l- + B -----------

l l g l *

Ga Ga l l

                                                                               -3/2 A = 150 s
                                                                                -4/3 B = 1.75 s

2 1/3 36 V s = --------------- 3 p S p 6V p d e = --------- Sp

l ul de Re = ------------------------

l l ( 1 - B ) 2 3

l d e B Ga = ---- g --------------

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Reference 10.2.18 identifies that the Ergun formulation is well suited for flow through packed beds with average porosity 0.35 -0.55, particles are of similar size, and flow

l ul de rates are moderate, with modified Reynolds number Re = ------------------------ - between l l ( 1 - B )

1 and1000 (where d e is particle diameter is porosity). ((

                                                                                  }}2(a),(c)

Pellet Surface Wetting Fraction As fluid flows through a packed bed, it is possible that not all surface area of particles is in contact with liquid. This scenario is accounted for using a wetting fraction to determine the effective surface area of the solid in contact with liquid. Julcour-Lebigue et. al. (Reference 10.2.19) developed a correlation for the wetted fraction considering effects of fluid velocity, particle shape and bed porosity, and compared the calculated results to extensive experimental data. The wetting fraction is correlated as a function of the Froude number, Morton number, and bed porosity, which accounts for flow behavior at the pellet scale, physical properties of fluid, and bed topology effects. This allows for separation of the effects of viscosity and particle diameter. The model is as follows: 0.139 0.0195 -1.55 C 4 f = 1 - exp -1.986Fr Mo N l l B 4 2 u Fr l = -------l-gd v 4 g Mo l = ----------- l 3 l l C4 1 ( 1 + 5Fr l Fr c ) N = cos ( ) 4 © Copyright 2022 by NuScale Power, LLC 260

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 65

                                                               =  ---------

180 2 u c Fr c = ------- - gd v

                                                                                 -3 m u c = 2.0  10 ----

s u f ( u < u l,bound ) = ------------------ ( u < u l,bound ) u l,bound The correlation has a mean standard deviation of 5 percent to the data used in its derivation. The wetting fraction is derived from data covering a range of:

1. Volumetric equivalent particle diameter d v [1.8-7.0 mm] or [0.04 - 0.28 in]

1/3 6V p d v = ------------ 3 1/3 For equilateral cylinders of diameter and height D, d v = --- D~1.14D 2 For example, 0.25 in. diameter equilateral cylinders, d v ~ 0.29 in

2. Bed porosity [0.37-0.41]

3. Water, heptane, ethanol, gasoil fluids give a range of viscosity

4. Superficial liquid velocity [0.0015- 0.008 m/s] or [0.005 - 0.026 ft/s]

Representative NPM conditions are considered. ((

                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0

3. ((

                                        }}2(a),(c)

Therefore, it is concluded that correlation provides a reasonable method to calculate the wettability fraction in the NPM, provide the volumetric equivalent particle diameter are within or close to the range of data used to develop the correlation. Boron Oxide Dissolution Rate Finally, the boron oxide dissolution rate is calculated. As summarized above, boron oxide hydrates, preferentially converting to boric acid, and then the boric acid solution must diffuse away from the boron oxide solid surface. ((

                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                     }}2(a),(c)

Dissolver Source Term Solution Process ((

                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                 }}2(a),(c) 6.3      Critical Boron Concentration The change in core reactivity during XPC is primarily dependent on the moderator temperature coefficient (MTC), along with the temperature change of the moderator, and the buildup and decay of the xenon concentration after shutdown. These factors are contingent upon the core burnup, power level, CRA configuration, axial offset, and core thermal-hydraulic conditions. Reactivity calculations are performed for beginning of cycle (BOC), middle of cycle (MOC), and end of cycle (EOC) conditions. Calculations at EOC are limiting compared to BOC and MOC due to the large negative MTC present at EOC.

Core reactivity is evaluated over a range of moderator temperatures that are sufficiently low to bound the lowest possible temperatures expected during the cooldown, considering the minimum pool temperature operating range. As summarized in Section 4.1, the reactivity calculations are performed using the CMS5 software code suite. CASMO5 is used to generate explicit cross-section libraries for the core design. The cross-section libraries are applicable for temperatures below the minimum core moderator temperature during extended passive cooling (e.g., libraries are generated that are applicable for temperatures as low as 68 degrees F). SIMULATE5 calculations are performed to evaluate core reactivity for core configurations and conditions present after reactor shutdown and moderator cooldown from extended DHRS or ECCS cooling. Although SIMULATE5 is a static code, it has the capability to evaluate reactivity changes due to transitory xenon. ((

                                                                                                     }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                               }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                                                  }}2(a),(c) 6.4      Assess Margin to Criticality The boron concentration results in the module determined from the boron transport calculations are compared to the appropriate SIMULATE5 calculated critical boron concentration results to demonstrate that the core boron concentration remains above the critical boron concentration for at least 72 hours after event initiation.

6.5 Simplified Method to Demonstrate Adequate Reactivity Control during Extended DHRS Operation ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                                    }}2(a),(c)

Table 6-1 Example Results of Vapor and Liquid Flow during Extended DHRS Operation ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Table 6-1 Example Results of Vapor and Liquid Flow during Extended DHRS Operation (Continued) ((

                                                                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-4 Two-Volume Boron Transport ((

                                                                                                     }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-5 Ratio of Cold and Hot Region Concentrations for 2-Volume Transport, as a Function of Vapor, Liquid Mass Flow Rate ((

                                                                                                        }}2(a),(c) 6.6      Representative Results Results from a spectrum of representative critical boron calculations in Figure 6-6, Figure 6-7, and Figure 6-8 show the EOC results to be limiting. The representative calculations show the effect of xenon reactivity response after trip, for constant boron concentration at the initial concentration, and constant core temperature conditions. The boron transport calculations account for the effect of temperature change and core concentration change over time after transient initiation.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-6 Boron to Critical BOC (all cases) ((

                                                                                                        }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-7 Boron to Critical MOC (all cases) ((

                                                                                                         }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-8 Boron to Critical EOC (all cases) ((

                                                                                                              }}2(a),(c)

Representative results of an injection line LOCA using the boron dilution methodology are provided in Figure 6-9 and Figure 6-10. Figure 6-9 shows the transient boron concentration in each mixing volume plotted along with the critical boron concentration in the core. Figure 6-10 shows the boron mass in each mixing volume plotted along with mass that is removed from the system as a loss term. As shown in Figure 6-9 ((

                            }}2(a),(c) In this case the acceptance criteria are met because the core and riser boron concentration remains above the critical boron concentration, ensuring subcriticality.

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-9 Transient Boron Concentrations for Dilution Sensitivity ((

                                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 6-10 Transient Boron Mass for Dilution Sensitivity ((

                                                                                                    }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 7.0 Boron Precipitation Evaluation and Analysis Results The NPM uses boron for core reactivity control during normal operation. During the long-term cooling phase of ECCS operation, boiling in the core region is expected to concentrate boron in the liquid in the core and riser region relative to the downcomer region; the lower riser holes provide a flow path for liquid and boron transport to mitigate redistribution inside the RPV. After ECCS valves open, dissolved boron from the ESB recirculates from containment into the RPV. Therefore, the concentration of the boron in the reactor vessel core and riser region is analyzed to demonstrate that boron precipitation does not occur and coolable geometry is maintained. 7.1 General Approach and Acceptance Criteria The boron transport methodology is similar to the boron dilution methodology described in Section 6.2 with appropriate assumptions to neglect loss terms and maximize boron transport from the CNV into the RPV. The saturation temperature of the CNV vapor space is compared to the solubility limit, or precipitation temperature for boric acid as a function of concentration in the core/riser mixing volume. The maximum allowable boron concentration during operation is conservatively assumed. Additional boron from ESB is assumed as described in Section 7.2.5. The solubility limit is shown in Figure 7-2. 7.2 Methodology 7.2.1 Boron Precipitation Method Overview Boron transfer between regions is calculated based on thermal-hydraulic analysis input. ((

                                      }}2(a),(c) 7.2.2         Module Mixing Volumes

((

                                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                         }}2(a),(c)

Figure 7-1 Boron Precipitation Methodology Mixing Volumes ((

                                                                                                     }}2(a),(c)

((

                                }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 7.2.3 Boron Transport Mechanisms The following mechanisms transport boron between mixing volumes. ((

                                                          }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                              }}2(a),(c) 7.2.4         Boron Loss Mechanisms

((

                                                                        }}2(a),(c) 7.2.5         ESB Addition Source

((

                                            }}2(a),(c) 7.3      Boric Acid Solubility Limit The boric acid solubility limit used in the boron precipitation methodology based on tabulated data from Reference 10.2.15 and Reference 10.2.16, as shown in Figure 7-2 in convenient units (for temperatures up to 212 degrees F; the full dataset is shown in Section 6.2.5).

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 7-2 Boric Acid, Boron Solubility Limit as a Function of Temperature ((

                                                                                                       }}2(a),(c) 7.4      Assess Margin to Boron Precipitation The boron concentration results in the module determined from the boron transport calculations are compared to the appropriate boron solubility limits to demonstrate that the core boron concentration remains below the solubility limit for at least 72 hours after event initiation.

7.5 Representative Results Representative results of a high point vent line break outside containment using the boron precipitation methodology are provided in Figure 7-3 and Figure 7-4. Figure 7-3 shows the transient boron concentration in each mixing volume plotted along with the boron precipitation limit. Figure 7-4 shows the boron mass in each mixing volume. ((

                                                                                                      }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 ((

                                                         }}2(a),(c) There is significant margin between the maximum concentration and the solubility limit.

Figure 7-3 Transient Boron Concentrations for Example Precipitation Evaluation ((

                                                                                                  }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 Figure 7-4 Transient Boron Mass for Example Precipitation Evaluation ((

                                                                                                   }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 8.0 Quality Assurance The NuScale Power, LLC Quality Assurance Program Description, MN-122626 (Reference 10.1.3), complies with the requirements of 10 CFR 50 Appendix B (Reference 10.1.2) and Quality Assurance Requirements for Nuclear Facility Applications, ASME NQA-1 2008 and NQA-1a-2009 Addenda (Reference 10.1.1). As described in Reference 10.2.1, the NRELAP5 code was developed following the requirements of NuScales QAP. The XPC and reactivity control analysis is performed and documented in accordance with NuScales QAP. © Copyright 2022 by NuScale Power, LLC 286

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 9.0 Summary and Conclusions This report documents the XPC EM developed for analysis of an NPM design basis extended passive cooling event progression with the DHRS or ECCS. The EM was developed applying a graded approach to the requirements of Reg Guide 1.203, and using applicability evaluations previously performed for the LOCA EM (Reference 10.2.1) and non-LOCA EM (Reference 10.2.5) as appropriate. Analysis calculations are performed with this EM to demonstrate the collapsed liquid level remains above the top of core, the core remains subcritical, and boron concentration remains below the precipitation limit. The NRELAP5 code is used to evaluate the thermal-hydraulic response of the module to demonstrate adequate core cooling is maintained and collapsed liquid level remains above the top of the core. The module thermal-hydraulic response is evaluated with NRELAP5 for a range of sensitivity calculations needed to evaluate boron transport. The critical boron concentration for a range of conditions is calculated with the CMS5 code suite. Boron transport analyses implemented in MATLAB, or another computational device to facilitate the calculation process, evaluate the boron concentrations in regions of the module to demonstrate that core boron concentrations remain above the critical concentration and below with solubility limits for boron precipitation. The PIRT developed for the XPC EM focused on the module thermal-hydraulic response and on phenomena associated with boron transport. Bottom-up evaluation of the models used to simulate the important phenomena identified in the PIRT was performed. Top-down assessments of the EM were performed for simulation of extended DHRS and extended ECCS conditions, considering available integral effects testing, results of code validation against test data, conservatisms in the EM, and sensitivity calculations. With respect to extended ECCS cooling, ((

                     }}2(a)(c) Overall, it is concluded that with the different calculational devices and conservatisms applied, the EM is applicable to simulate the module extended ECCS cooling response.

With respect to extended DHRS cooling, bottom-up and top-down assessment of NRELAP5 concluded that the code was adequate to simulate the extended DHRS cooling thermal-hydraulic response, with ((

                                          }}2(a)(c)

The XPC EM analyses are performed with a biased set of assumptions and initial conditions based on sensitivity results. For selected events, representative results are provided to demonstrate application of the evaluation model for the NPM. The © Copyright 2022 by NuScale Power, LLC 287

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 representative results demonstrate that the collapsed liquid level remains above the TAF, showing the DHRS and ECCS provide adequate core cooling for an extended period. In addition, boron precipitation is evaluated and representative results show boron precipitation does not occur for the conditions evaluated for extended passive cooling, thereby demonstrating the core remains in a coolable geometry. Potential criticality during cooldown was evaluated and representative results indicate acceptable reactivity margin is available for design basis cooldown scenarios. The XPC EM is applicable to NPM plant designs if the following criteria are met:

1. The plant design is as described generally in Section 3.2.

2. The plant design has the specific features or requirements identified in Table 3-3.

3. The conclusions of supporting evaluations identified in Section 3.2.3 are met.

4. The range of conditions for extended ECCS cooling are within the range identified in Table 4-11.

5. The range of conditions for extended DHRS cooling are within the ranges identified in Table 4-8 and Table 4-9.

6. Any changes to the LOCA EM or non-LOCA EM applicability ranges identified in Table 4-11, Table 4-8, or Table 4-9 are identified for impact on the XPC EM.

7. Boron oxide pellet diameter is less than 0.25 in, or applicability of the slow-biased boron dissolution method is specifically justified and approved.

After application of the methodology is approved for a plant design, cycle-specific evaluations are required to confirm the analysis of record remains applicable. Comprehensive identification of required cycle-specific evaluations is outside scope of this report. © Copyright 2022 by NuScale Power, LLC 288

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 10.0 References 10.1 Source Documents 10.1.1 American Society of Mechanical Engineers, Quality Assurance Requirements for Nuclear Facility Applications (QA), ASME NQA-1-2008 and NQA-1a-2009 Addenda, New York, NY. 10.1.2 U.S. Code of Federal Regulations, "Domestic Licensing of Production and Utilization Facilities," Appendix B, Part 50, Chapter I, Title 10, "Energy," (10 CFR 50 Appendix B). 10.1.3 NuScale Power, LLC, NuScale Power, LLC Quality Assurance Program Description, MN-122626, Revision 0. 10.2 Referenced Documents 10.2.1 NuScale Power, LLC, Loss-of-Coolant Accident Evaluation Model, TR-0516-49422-P, Revision 3. 10.2.2 U.S. Code of Federal Regulations, "Domestic Licensing of Production and Utilization Facilities," Section 50.46, Part 50, Chapter I, Title 10, "Energy," (10 CFR 50.46). 10.2.3 U.S. Nuclear Regulatory Commission, "Design-Specific Review Standard for NuScale SMR Design," Section 6.3, Emergency Core Cooling System, Revision 0, June 2016. 10.2.4 U.S. Nuclear Regulatory Commission, "Design-Specific Review Standard for NuScale SMR Design," Section 15.6.5, Loss of Coolant Accidents Resulting from Spectrum of Postulated Piping Breaks within the Reactor Coolant Pressure Boundary, Revision 0, June 2016. 10.2.5 NuScale Power, LLC, Non-LOCA Methodologies, TR-0516-49416, Revision 4. 10.2.6 U.S. Nuclear Regulatory Commission, Transient and Accident Analysis Methods, Regulatory Guide 1.203, Revision 0, December 2005. 10.2.7 American National Standards Institute/International Society of Automation, "Flow Equations for Sizing Control Valves," ANSI/ISA-75.01.01-2007, Research Triangle Park, NC. 10.2.8 U.S. Nuclear Regulatory Commission, "Design-Specific Review Standard for NuScale SMR Design," Section 5.4.7, Decay Heat Removal (DHR) System, Revision 0, June 2016. 10.2.9 NuScale Power, LLC, Nuclear Analysis Codes and Methods Qualification, TR-0616-48793-P-A, Revision 1. © Copyright 2022 by NuScale Power, LLC 289

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Revision 0 10.2.10 Tuunanen, J., H. Tuomisto and P. Raussi, "Experimental and Analytical Studies of Boric Acid Concentrations in a VVER- Reactor During the Long-Term Cooling Period of Loss-of-Coolant Accidents," Nuclear Engineering and Design, (1994): 148:217-231. 10.2.11 Clark et al., Drift-flux correlation for rod bundle geometries, International Journal of Heat and Fluid Flow, (2014): 48:1-14. 10.2.12 Kukuljan, J., J. Alvarez, and R. Fernandez-Prini, "Distribution of B(OH)3 between water and steam at high temperatures, Journal of Chemical Thermodynamics, (1999): 31: 1511-1521. 10.2.13 Kataoka, I. and M. Ishii, Prediction of Pool Void Fraction by New Drift Flux Correlation, NUREG/CR-4657, June 1986. 10.2.14 NuScale Power, LLC, "Nuclear Analysis Codes and Methods Qualification," TR-0616-48793-P-A, Revision 1. 10.2.15 Crapse, K.P., and E.A. Kyser, III, Literature Review of Boric Acid Solubility Data, SRNL-STI-2011-00578, Revision 0, August 2011. 10.2.16 Kracek, F.C., G.W. Morey, and H.E. Merwin, The System, Water-Boron Oxide, American Journal of Science, (1938): 35-A:143-171. 10.2.17 Zhang, W., et al., "Relationship between packing structure and porosity in fixed beds of equilateral cylindrical particles," Chemical Engineering Science, (2006): 61:8060-8074. 10.2.18 Nemac, D., and J. Levec, "Flow through packed bed reactors: 1. Single-phase flow, Chemical Engineering Science, (2005): 60:6947-6957. 10.2.19 Julcour-Lebigue, C., et al., "Measurements and Modeling of Wetting Efficiency in Trickle-Bed Reactors: Liquid Viscosity and Bed Packing Effects, Industrial and Engineering Chemistry Research, (2009): 48: 6811-6819. 10.2.20 Park, J.K., and K.J. Lee, "Diffusion Coefficients for Aqueous Boric Acid, Journal of Chemical and Engineering Data, (1994): 39:891-894. 10.2.21 Okawa, T., et al., New Interfacial Drag Force Model Including Effect of Bubble Wake, Journal of Nuclear Science and Technology, (1999): 36:1030-1040. © Copyright 2022 by NuScale Power, LLC 290

LO-133393 : Affidavit of Mark W. Shaver, AF-133396 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com

NuScale Power, LLC AFFIDAVIT of Mark W. Shaver I, Mark W. Shaver, state as follows: (1) I am the Licensing Manager 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 method by which NuScale develops its Extended Passive Cooling and Reactivity Control Methodology. NuScale has performed significant research and evaluation to develop a basis for this method 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 Extended Passive Cooling and Reactivity Control Methodology. 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. (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 AF-133396 Page 1 of 2

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 01/05/23. Mark W. Shaver AF-133396 Page 2 of 2}}

v t e Letter Sequence Request
EPID:L-2022-TOP-0017, LLC, Submittal of the NuScale Standard Design Approval Application (Open)
Initiation Request, Request, Request, Request, Request, Request Acceptance... Administration Questions 27 June 2024 Answers Results Approval... Other: ML22365A002, ML23067A298, ML23068A094, ML23068A095, ML23068A301, ML23068A302, ML23206A106, ML23206A107, ML23265A154, ML23265A159, ML24178A423
MONTHYEAR2023-03-16 [Table View]

ML23005A308

Text

SUBJECT:

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