Text

ATF Fuel Fragmentation, Relocation, and Dispersal Consequences Workshop - Master Presentation
	ML25210A425
Person / Time
Issue date:	07/29/2025
From:	; Office of Nuclear Reactor Regulation
To:	;
References
	Download: ML25210A425 (1)
	v • d • e

ATF Fuel Fragmentation, Relocation, and Dispersal Consequences Workshop July 30, 2025 July 31, 2025

Meeting visuals and audio are through MS Teams.

Participants are in listen-only mode until the discussion and public feedback period. During which, we will first allow in-person attendees to participate, then allow remote attendees to un-mute.

Remote attendees should utilize the hand raised feature in MS Teams, if possible.

This is an Observation Meeting. Public participation and comments are sought during specific points during the meeting.

NRC will consider the input received but will not prepare written responses.

No regulatory decisions will be made during this meeting.

This meeting is being recorded.

Meeting Logistics

Meeting Purpose

Provide an update on recent research results regarding FFRD consequences.

Provide feedback on industrys proposed licensing pathways for power uprates.

Provide feedback on EPRIs and NEIs proposed white papers on coolability and reporting requirements, respectively.

Provide an opportunity for members of the public to ask questions of the NRC staff.

The NRC is not looking for feedback on the Increased Enrichment (IE)

Rulemaking.

Proposed Workshop Schedule

Workshop 1 (May 20-21)

- Fuel Fragmentation, Relocation, and Dispersal

- Recriticality

Workshop 2 (Today)

- Exemptions

- Coolability

- Reporting

Workshop 3

- Transition Break Size

Workshop 4

- Materials

- Inspections

Agenda - Day 1 Time Topic Speaker 8:00 am Welcome NRC 8:05 am Opening Remarks NRC, NEI 8:10 am Advanced Fuels and Power Uprates: Licensing Pathways NEI, Constellation 8:50 am NRC Studies on Post-FFRD Consequences NRC 9:30 am Rule Exemption Under 10 CFR 50.12 Duke 10:00 am Plant Hatch Potential Pilot Approach for EPU Southern 10:30 am Break 10:40 am Assessing Debris Bed Coolability EPRI 11:00 am Coolability of Dispersed Fuel EPRI 11:30 am LOCA Reporting NEI, Dominion 12:00 pm Adjourn NRC Topic times are estimated based on the participation level and presentation length.

Agenda - Day 2 Time Topic Speaker 9:00 am Welcome NRC 9:05 am Discussion 10:30 am Break 10:40 am Discussion 11:45 am Public Comment Period 11:55 am Closing Remarks NRC, NEI 12:00 pm Adjourn NRC Topic times are estimated based on the participation level and presentation length.

Opening Remarks

POWER UPRATES:

LICENSING PATHWAYS Al Csontos Director, Fuels Baris Sarikaya Principal Engineer, Constellation July 30, 2025

of the Original Licensed Thermal Power Opportunities exist for additional uprates Domestic/international precedent >120%

EO direction for larger uprates sooner OB3 tax credits incentivize uprates Courtesy of the Electric Power Research Institute Courtesy of the Electric Power Research Institute

>70% of sites have a level of interest/planning for one or more power uprates with a combined capacity increase of 3 GWe

Nearly 50% of sites have varying interest/plans for one or more of the enabling changes (ATF/

LEU+, Extended Fuel Cycles, and/or RI LOCA)

NRC/Industry workshops in line with intent of ADVANCE Act and Executive Orders Power Uprates: Current Aspirations https://www.nei.org/resources/reports-briefs/the-future-of-nuclear-power-2024-survey

Funding for Restart, Completion, Uprate, or Construction

Expedite and promote production and operation of nuclear energy

DOE facilitate 5 GWe additional capacity through uprates by 2030

Expanding the Nuclear Energy Workforce Ordering the Reform of the NRC:

Decrease regulatory barriers, fixed licensing deadlines, limits on credible risks, wholesale revision of NRC regulations by 2026, etc.

To meet the 5 GWe by 2030 goal, licensing efficiencies needed Executive Orders (EO) Impacting Uprates

Tax credits for nuclear generation similar with additional bonus:

Zero-Emission Nuclear Production Credit - 45U Clean Electricity Production Credit - 45Y Clean Electricity Investment Credit - 48E

Added path to qualify for the 10% energy community bonus (45Y)

Full tax credits only if BOC before 2034 (45Y/48E)

Incentivize additional capacity through nuclear generation:

Power uprates, plant restarts, and new builds Nuclear Provisions in the OB3 Act

©2025 Nuclear Energy Institute 6 Treasury regulations provide only limited methods to determine capacity for purposes of calculating tax credit value for uprates OB3 expands flexibility, allowing capacity increases to be measured in any reasonable manner, including:

Interconnection agreements or other filings with FERC, NRC, or similar entities Reports by an independent professional engineer RTO/ISO reports showing capacity increase Any other method provided by the Treasury Secretary Flexibility for Power Uprates - 45Y/48E

Planned Power Uprate Licensing Submittals

Determining and planning for NRC resource and budget needs to power uprate submittals RIS intent to promote early communication on power uprate-related licensing activities Utility voluntary responses complete:

Proprietary responses included along with publicly available information (next slide)

NEI generic response submitted as well NRC Regulatory Issue Summary

of Reactors Name of Plant Descritption of LAR Projected Submittal date*

Projected Completion date Power Ascension Date with PUR/Fuel Cycle Changes Additional details and comments 1

Dominion - Millstone U3 24-Month Cycles Q2-4 2026 Q4 2027 Q2 2028 (1) Address SFP storage requirements; (2) 50.68 Exemption; (3) Update dose analyses for LEU+/HBU with potential 50.67 exemption; (4) Address COLR method changes (internal and fuel vendor methods) to support LEU+/HBU 1

Wolf Creek MUR using LEFM's Q4 2026 Q3 2028 2

Duke - Brunswick U1 & U2 MUR Q1 2027 Q4 2027 U1 Q1 2028 U2 Q1 2029 2

Southern Co. - Hatch U1 & U2 Extended Power Uprate Q2 2027 U2 Q1 2029 U1 Q1 2030 MELLLA+ in Q2 2027 2

PSEG - Salem U1 & U2 Stretch Power Uprate with MUR Q2 2027 Q4 2028 U1 Q4 2029 U2 Q2 2029 (1) Implement FSLOCA Methodology; (2) RG 1.236 Ejected Rod Analysis; (3)

Adopt Gap Release Fractions from RG 1.183 R1; (4) Use ADOPT Fuel Pellet Type; (5) Non-LOCA PAD5 Fuel Rod Code; (6) DVR Based MUR 2

Duke-McGuire U1 & U2 Extended Power Uprate Q2 2027 Q4 2028 U1 Q4 2029 U2 Q4 2030 (1) Address updates to Duke Energy in-house methodologies and (2) transition to increased enrichment, high burnup fuel 1

Energy Northwest-Columbia Generating Station Extended Power Uprate Q2 2028 Q4 2030 Q2 2031 Combined LAR application for EPU and MELLLA+

1 Duke - Catawba U1 Extended Power Uprate Q2 2028 Q4 2029 U1 Q2 2031 (1) Address updates to Duke Energy in-house methodologies and (2) transition to increased enrichment, high burnup fuel.

2 Southern Co. - Farley U1 & U2 Extended Power Uprate Q3 2028 U2 Q2 2031 U1 Q4 2031 (1) AST RG 1.183 Rev 1 in Q3 2026; (2) SFP Criticality Analysis in Q2 2027; (3)

Other Fuel/Methodology Updates in Q4 2029; (4) 24-mo fuel cycle in Q1 2032 2

Southern Co. - Vogtle U1 & U2 Extended Power Uprate Q4 2028 U1 Q4 2030 U2 Q2 2031 (1) AST RG 1.183 Rev 1 in Q2 2025; (2) SFP Criticality Analysis in Q2 2026; (3)

Other Fuel/Methodology Updates in Q2 2027; (4) 4 RCCAs and 24-month fuel cycle in Q2 2030

Submittal dates/strategy subject to change

>20 Planned Power Uprates

>5 Extended Fuel Cycles

(>30 Additional TBD)

Uprates and Advanced Fuels Synergy

Begin construction by the end of 2033 Additional Uprates with Advanced Fuels Innovation (RI-LOCA, T@T, Coatings, 19x19, etc.)

EO: 5GW by 2030

MUR: 9 6 m, SPU: 12 9 m, and EPU: 18 12 m NRC/NEI Uprate Review Efficiency Workshops:

Flexibility for sequential, combined concurrent reviews PWR: Uprates with 24M cycles (LEU+/HBU)

BWR: EPU + MELLLA+ + MUR

NRC graded approach guidance:

Binning of technical issues (L/M/H)

NEI/EPRI AI Power Uprate Licensing Round Robin Power Uprate Regulatory Improvements

PWR Bundling Example

ATF/LEU+/HBU to achieve uprates and/or 24-month fuel cycles (PWR)

Analytical synergy for combined review efficiencies:

Uprates and Advanced Fuels Transition

Chapter 15 Analysis:

- AOOs/LOCA/ATWS/SBO/Dose

- Stability (BWR)

- SG tube rupture (PWR)

- Locked rotor (PWR), etc

Chapter 4 / 6

Fuel Pool Storage Power Uprates Advanced Fuel Transition

Chapter 15 Analysis:

- AOOs/LOCA/ATWS/SBO/Dose

- Stability (BWR)

- SG tube rupture (PWR)

- Locked rotor (PWR), etc

Chapter 4 / 6

Fuel Pool Storage Improved licensing efficiencies with reduced iterative & duplicative reviews Similar

BWR Bundling Example

EPU & MELLLA+ Case Study Implementation Example Combined License Applications Nine Mile Unit 2 Peach Bottom EPU 31 23 MELLLA+

22 18 MUR 9

Review Time (months) 53 50 Implementation Time (months) 76 62

Core Flow (%)

120 EPU ICF BWR Operating Domain - MELLLA+

BWR Operating Domain - MUR 122 uncertainty EPU Analytical Limit uncertainty MUR

Combined Applications Previous example: > 72 months with 3 submittals in series Combined Application: < 18 months with 3 submittals combined.

Review Time (months)

Nine Mile-2 Peach Bottom EPU 31 23 MELLLA+

22 18 MUR 9

Review Time (m) 53 50 Implementation Time (m) 76 62 Review time (months)

Combined Application Review EPU MELLLA+

MUR Total (m) 12 - 18 Combined License Applications

©2025 Nuclear Energy Institute 20 BWRs do not need high burnup / increased enrichment for Power Uprates Stay within the current 62 GWd/MTU limit FFRD is not a concern for BWR Power Uprates (burnup 62 GWd/MTU)

Currently, risk-informed LOCA implementation is very difficult for BWRs TBS determination

TBS determination is very difficult for BWRs TBS applicability

About half of the BWR fleet is Small Break Limited

Power Uprates will increase the number of SB Limited BWRs

Risk-informed LOCA is not applicable to SB Limited BWRs FFRD

RI-TBS enables BWRs (and PWRs) a path for RI-LOCA adoption:

RI-TBS also helps address FFRD for burnup beyond 62 GWd/MTU 2.

For uprates, expectations for addressing FFRD burnup limits?

3.

FFRD could be an unresolved issue non-ALS PWRs 4.

RG 1.183 R2:

Need to address FFRD?

Need for Risk Informed-TBS RI TBS helps address all these issues

Flexible language for RI-TBS implementation enables BWRs (and PWRs) a path for addressing FFRD:

NRC adoption of Industrys RI-TBS white paper RI-TBS topical report submission at a later date 2.

However, if FFRD Burnup limits change or RG 1.183 R2 requires addressing FFRD:

RI-TBS solution will be needed Risk Informed-TBS Implementation

©2025 Nuclear Energy Institute 24 Industry plans for >3GWe power uprates EO: Facilitate 5GWe with uprates by 2030 Regulatory predictability and stability key to meet bundled LAR review timeliness Due diligence for exemption path for early adopters and potential schedule delays Table-top exercises for a lead BWR and PWR to test bundled LAR licensing path Increased market confidence:

Meeting costs and schedules Meeting NRC review timeliness goals Path Forward

Questions

NRC Studies on Post-FFRD Consequences Fuel Fragmentation, Relocation, and Dispersal (FFRD) Workshop July 30, 2025 Scott Krepel Branch Chief, Nuclear Methods & Fuel Analysis (NRR/DSS/SFNB)

Credit where credit is due This presentation is based on analytical work done by the Office of Nuclear Regulatory Research:

- James Corson, RES/DSA/FSCB

- Joseph Staudenmeier, RES/DSA/CRAB-I 2

Post-FFRD Consequences Overview

Thermal hydraulics (T-H) model & core model

Typical licensing assumptions vs best estimate

Recap - fuel dispersal estimates

Fuel dispersal modeling

Post-FFRD core coolability results

Summary 3

TRACE model 4

Core Design Model 5

From ORNL/TM-2020/1700, Full Core LOCA Safety Analysis for a PWR Containing High Burnup Fuel, Oak Ridge National Laboratory, 2020.

Current Licensing vs Best Estimate

LOOP vs non-LOOP 6

Current Licensing vs Best Estimate

Chopped cosine vs double-peak from PARCS 7

Current Licensing vs Best Estimate

ECCS availability (1 train vs 2 trains) 8

Fuel Dispersal Estimates 9

Chopped Cosine, Offsite Power Unavailable Chopped Cosine, Offsite Power Available PARCS Power, Offsite Power Unavailable PARCS Power, Offsite Power Available PARCS Power, Offsite Power Available, 2 ECCS Trains 863 852 834 816 774 FAST Peak Cladding Temperature (oC) 49 44 55 49 25 Burst Rods (% of total) 41 38 58 50 24 Second Cycle Burst Rods (% of total) 3700 3400 2100 2000 1300 Dispersed Mass (RIL Model C) (kg UO2) 2500 2300 980 940 700 Dispersed Mass (RIL Model A) (kg UO2) 1500 1400 540 530 380 Dispersed Mass (RIL Model A, single grid span)

(kg UO2)

Fuel Dispersal Estimates

Axial locations of bursts 10

Fuel Dispersal Estimates

IFBA vs non-IFBA rods 11 Burst rods Intact rods

Fuel Dispersal Modeling Conservatively assumed all dispersed fuel forms a uniform bed on the spacer grid immediately below the axial span where most bursts occur 12 Studsvik data from NUREG-2160, Post-test Examination Results From Integral, High-Burnup, Fueled Tests at Studsvik Nuclear Laboratory, August 2013 ORNL data from Integral LOCA Fragmentation test on high-Burnup fuel, Nuclear Engineering & Design 367, (2020),

110811, ISSN 0029-5493

Fuel Dispersal Modeling Dispersed fuel grouped into 4 simplified dispersed-fuel beds at different axial locations 13 1

2 3

4 5

6 7

8 9

10 11 12 13 14 15 15 13 14 15 16 17 18 19 14 25 26 27 28 29 30 31 32 33 34 35 13 39 40 41 42 43 44 45 46 47 48 49 50 51 14.61 kg @ 10 ft 12 55 56 57 58 59 60 61 62 63 64 65 66 67 5.9 kg @ 10 ft 11 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

.85 kg @ 6 ft 10 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 33.18 kg @ 4 ft 9

105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 8

122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 7

139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 6

156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 5

173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 4

191 192 193 194 195 196 197 198 199 200 201 202 203 3

207 208 209 210 211 212 213 214 215 216 217 218 219 2

223 224 225 226 227 228 229 230 231 232 233 1

239 240 241 242 243 244 245

Fuel Dispersal Modeling Dispersed fuel beds modeled as 1-D hydraulic components (VALVEs) that partially close at times of bursts, as follows:

Lower core bursts occur at ~30 sec Upper core bursts occur at ~100 sec Partially closed valve flow area scaled to achieve loss coefficient consistent with particle sizes of 4 mm and a porosity of 0.4 (Ergun equation)

Does not explicitly account for de-entrainment of water droplets in flow hitting debris bed Earlier sensitivity studies showed heat deposition from debris bed into fluid most likely has little impact on PCT Local dispersal estimates bounded; global dispersal overestimated by 100+ kg 14

Core Design Model 5

From ORNL/TM-2020/1700, Full Core LOCA Safety Analysis for a PWR Containing High Burnup Fuel, Oak Ridge National Laboratory, 2020.

Current Licensing vs Best Estimate

LOOP vs non-LOOP 6

Fuel Dispersal Estimates

IFBA vs non-IFBA rods 11 Burst rods Intact rods

Fuel Dispersal Modeling Conservatively assumed all dispersed fuel forms a uniform bed on the spacer grid immediately below the axial span where most bursts occur 12 Studsvik data from NUREG-2160, Post-test Examination Results From Integral, High-Burnup, Fueled Tests at Studsvik Nuclear Laboratory, August 2013 ORNL data from Integral LOCA Fragmentation test on high-Burnup fuel, Nuclear Engineering & Design 367, (2020),

110811, ISSN 0029-5493

Fuel Dispersal Modeling Dispersed fuel grouped into 4 simplified dispersed-fuel beds at different axial locations 13 1

2 3

4 5

6 7

8 9

10 11 12 13 14 15 15 13 14 15 16 17 18 19 14 25 26 27 28 29 30 31 32 33 34 35 13 39 40 41 42 43 44 45 46 47 48 49 50 51 14.61 kg @ 10 ft 12 55 56 57 58 59 60 61 62 63 64 65 66 67 5.9 kg @ 10 ft 11 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

.85 kg @ 6 ft 10 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 33.18 kg @ 4 ft 9

105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 8

122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 7

139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 6

156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 5

173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 4

191 192 193 194 195 196 197 198 199 200 201 202 203 3

207 208 209 210 211 212 213 214 215 216 217 218 219 2

223 224 225 226 227 228 229 230 231 232 233 1

239 240 241 242 243 244 245

Fuel Dispersal Modeling Dispersed fuel beds modeled as 1-D hydraulic components (VALVEs) that partially close at times of bursts, as follows:

Lower core bursts occur at ~30 sec Upper core bursts occur at ~100 sec Partially closed valve flow area scaled to achieve loss coefficient consistent with particle sizes of 4 mm and a porosity of 0.4 (Ergun equation)

Does not explicitly account for de-entrainment of water droplets in flow hitting debris bed Earlier sensitivity studies showed heat deposition from debris bed into fluid most likely has little impact on PCT Local dispersal estimates bounded; global dispersal overestimated by 100+ kg 14

Top Line PCT Results 15

Detailed Inspection of Results Lower elevation blockages dont impact top line PCT 16

Detailed Inspection of Results Blockages in adjacent fuel assemblies do not have a significant effect on PCT for highest power fuel 17

Detailed Inspection of Results Extended PCT trend (200-500 sec) driven by cladding node immediately above blockage 18 Location 04-12 Location 06-13

Detailed Inspection of Results PCT results relatively insensitive to assembly/rod power level 19 Location 04-12 Location 06-11

Detailed Inspection of Results PCT trend similar for 14.61 kg simulated blockage vs 5.9 kg simulated blockage 20 Location 06-03 Location 06-13

Detailed Inspection of Results Axial flow suggests significant reduction in flow leading to stagnant region immediately above blockage 21

Detailed Inspection of Results Somewhat unusual axial void fraction distribution surrounding blockage 22 No blockage Blockage

Summary Some modeling conservatisms:

All debris assumed to form a uniform debris bed on grid immediately below cladding failure Dispersed fuel modeled slightly higher than estimates Some caveats:

Effects of de-entrainment of water droplets in debris bed not accounted for Two-sided heating of cladding due to fuel inside and outside not addressed Uncertainty exists with respect to some of the relevant phenomenology Some speculation:

1-D junction with flow area adjusted to achieve a target loss coefficient may not be the best representation The assumption of a uniform debris bed may be extremely conservative relative to reality 23

Summary TRACE has been benchmarked extensively, but it is not validated for licensing purposes The calculations performed represent best estimate conditions with some modeling conservatisms Report on results is draft and subject to change However, this information could be used by NRC staff with other information as part of an integrated risk evaluation 24

Rule Exemption Under 10 CFR 50.12 July 30, 2025 Tara Matheny - Duke Energy Stan Hayes - Duke Energy Dennis Earp - Duke Energy

=

Background===

Duke Energy is pursuing power uprates and fuel cycle extensions for multiple plants with implementations starting in spring of 2029 Regulatory predictability and certainty is needed to ensure these projects can be executed efficiently and predictably.

Duke Energy would like to see the rulemaking approved and issued by 1st Quarter of 2027 The company continues to actively participate in industry whitepaper preparation and NRC workshops Duke Energy is exploring an option for exemption under 10 CFR 50.12 10 CFR 50.12(a)(2)(ii) Application of the regulation in the particular circumstances would not serve the underlying purpose of the rule or is not necessary to achieve the underlying purpose of the rule 2

Opportunities to Reduce Regulatory Uncertainty Continued workshop discussions Pre-submittal Meetings Licensee specific discussion to ensure understanding and expectations Tabletop Exercise Discuss the proposed licensing process First of a kind application Licensing efficiency Alignment early in the process 3

Tabletop Exercise Proposed tabletop exercise with NRC in September after the completion of the FFRD workshops Explore connections between vendor topicals and Duke Energy submittals Efficiency improvements Using NRC-approved methodologies Step through all associated aspects of the proposed exemption(s)

Transportation Package Receipt Process at Utility Site Spent Fuel Pool and New Fuel Storage Pool Licensing Updates to the Licensing Basis

- Alternate Licensing Strategy (ALS)

- Reg Guide 1.183 Rev 2 and 10 CFR 50.67 Accident Source Term 4

Exemptions and Timeline Expected timeline for exemption submittal Detailed submittal information provided in future tabletop exercise Fuel cladding exemption request for 10 CFR 50.46 August 15, 2025 SFP Criticality LAR submittal June 2026 Could include 10 CFR 50.68 exemption for greater than 5 wt% U-235 Pre-submittal meeting August 11, 2025 Pending approval of the Studsvik Supplement 5

Implementation of Alternative Licensing Strategy (ALS)

Regulatory clarity and predictability on implementation of ALS ALS is not part of the current rule considerations and a policy determination is needed to include ALS Option 1-Policy Clarification Option 2-Policy Exemption Option 3-Policy Revision Policy clarification is the preferred path for implementation ECCS design is not changing and cannot change without NRC approval Additional discussion proposed in future tabletop exercise 6

7

T. Kindred, P.E.

Consulting Engineer Nuclear Fuels and Safety Analysis Plant Hatch Potential Pilot Approach for EPU

The picture can't be displayed.

©2025 Nuclear Energy Institute 2 EPU To Meet Increasing Power Demands in Georgia with Reliable Clean Energy Proposed increase to licensed power level from 2804 MWth to 2960 MWt, which is an increase of 5.6% from CLTP or 121.5% of the OLTP.

MELLLA+

To Improve Operating Flexibility at Extended Power Uprate Levels Allow operations in the MELLLA+ domain to provide maximum operations flexibility. At 121.5% OLTP, MELLLA+

will allow a core flow window range similar to the currently licensed MELLLA domain.

Combined LAR to Support Efficient Licensing Strategy To Gain Efficiency in the Development, Review, and Implementation of the LAR Plant Hatch Potential Pilot Approach for EPU

The picture can't be displayed.

©2025 Nuclear Energy Institute 3 Regulatory Guide 1.183 Rev. 2 The second revision of the Alternative Source Term Regulatory Guide is essential to facilitate uprate initiatives for Boiling Water Reactors (BWRs).

It addresses a long-standing industry need for modeling aerosol scrubbing within the suppression pool, a need recognized as far back as 30 years ago in NUREG-1465 (pg.

19).

This guide offers crucial direction on pathway-specific source terms for BWRs.

Enables modeling of existing BWR safety systems Assuming no rule change, necessary exemptions for the implementation of RG-1.183 Rev. 2 include:

§50.67 associated with control room dose criteria.

No increase in licensed burnup or enrichment would be requested to support EPU Additional uprates (beyond currently planned) will require NRC provided significant effort and needed advances in dose consequence analysis guidance (ML24005A102, ML24066A177, ML24304A864) planned for Rev. 2.

Utilities seeking uprates for BWRs would benefit from the improved realism of the dose methods communicated in Rev. 2 Plant Hatch Potential Pilot Approach for EPU

The picture can't be displayed.

(ML24243A161)

Workshop on EQ and Deposition (3Q25)

HNP Submits HNP AST Rev. 2

(??)

HNP EPU Submittal (2Q27)

NRC Approves HNP AST Rev. 2 LAR (??)

NRC Approval of HNP EPU (2Q28)

Discussion Topics

During HBU workshop (September 2024, ML24243A161) it was communicated RG-1.183 Rev. 2 was expected in 2025.

Requires rule change to §50.67 for GDC 19

If RG-1.183 Rev. 2 is not released in 2025 industry sees two options:

Option 1: Submit for Rev. 2 approval w/exemptions as part of the EPU LAR

Option 2: Submit coincident with EPU using available draft guidance, but runs the risk of linked submittals (RG-1.183 Rev. 2 LAR may not be finished before EPU LAR is submitted)

Industry would like to discuss these options with considerations for

Potential for increased complexity of combined (EPU, AST Rev. 2) submittals

Potential for increased complexity of linked submittals (LIC-109 implications)

Potential for increased regulatory uncertainty associated with utilizing draft guidance Plant Hatch Potential Pilot Approach for EPU

The picture can't be displayed.

Break

w w w. e p r i. c o m Matt Nudi, Risk & Safety Management EPRI NRC Public Workshop July 30, 2025 Application of CORQUENCH - Defense-in-depth analysis Assessing Debris Bed Coolability

2 Background

Work is being developed to assess the ability to cool postulated debris beds resulting from FFRD phenomena

- This is one element of several EPRI/industry efforts intending to demonstrate that FFRD is prevented (i.e., ALS), or can be risk-informed to more appropriately characterized its likelihood, consequence (i.e., RI-TBS)

Coolability research intends to provide defense-in-depth analysis, while also fitting into the characterization of the importance of FFRD

- It will leverage decades of lessons learned from severe accident analysis and state-of-the-art modeling tools Key question:

- What is the significance of FFRD for severe accident progression with respect to maintaining a coolable condition for in-vessel & ex-vessel debris beds?

3 Scope of Analysis Will evaluate one in-vessel and one ex-vessel debris bed configuration In-Vessel Configuration in Lower Head Ex-Vessel Configuration in Containment Sump

4 CORQUENCH Overview Under development by Argonne National Laboratories since 1990s

- Originally supporting MACE and OECD/MCCI programs

- More recently - expanded validation through ROSAU program Traditionally focused on ex-vessel scenarios including MCCI

- Mechanistically calculates water ingress and ultimate ability to cool severe accident debris beds Code contains fundamental elements needed to assess coolability of potential debris beds resulting from FFRD phenomena CORQUENCH well qualified to assess FFRD debris bed coolability Ref: Figure 1-1a from https://publications.anl.gov/anlpubs/2018/10/146345.pdf

5 Minor modifications to CORQUENCH for FFRD application Water level (top flooding)

Modification of conduction heat-transfer model Ability to start calculations with fuel debris in a fully solidified state Current modeling assumes only conduction heat transfer in lower debris bed region

- Where water not yet present from top flooding Potential enhancement may consider addition of convective cooling due to steam flow

6 Boundary Conditions Key assumptions

- Fragment particle size distribution

- Porosity and packing within debris bed

- Fuel mass released

- Decay heat input

- Injection water subcooling Inputs will be aligned with in-core coolability assumptions Will require some judgment regarding in-vessel and ex-vessel debris bed conditions

- Sensitivity analysis will be used to assess impact of key assumptions on ability to demonstrate coolability

7 Schedule & Conclusions EPRI coolability research will evaluate both in-core & debris bed conditions Schedule

- Framework development - July/August 2025

- Model development - August/September 2025

- Analytical results - October/November 2025 Results to be discussed in subsequent NRC workshops

- White paper - Early 2026 Technical work will be published in EPRI White Paper - Early 2026

8

w w w. e p r i. c o m TOGETHERSHAPING THE FUTURE OF ENERGY

w w w. e p r i. c o m Kurshad Muftuoglu Fuel Reliability Program, EPRI NRC Public Workshop July 30-31, 2025 Framework for Analytical Approach Coolability of Dispersed Fuel

2 Outline Core coolability

- Scope Impact of FFRD on PCT and Oxidation Coolability of accumulated fuel fragments at spacer location

- Background NUREG/CR-7307 observations

- Analysis Framework Assumptions and other considerations

3 Core Coolability For core coolability, the analysis examines the potential for dispersed fuel fragments to accumulate at spacer grid locations, where they may obstruct coolant flow and act as localized heat sources.

The study aims to assess whether the combination of both the dispersed fuel fragments and those retained within the rod can be adequately cooled during a LOCA, thereby maintaining core integrity and ensuring continued safety margins.

4 Discussion Points from NUREG/CR-7307 (Dispersal PIRT)

Initially porous fuel debris beds allow for cooling.

Fuel rods above a blockage caused by fuel debris would be expected to be cooled.

With respect to coolable geometry during an FFRD LOCA, the impact of debris beds around spacer grids needs to be evaluated.

5 Core Coolability Analysis Framework Starting with an approved BELOCA EM modified for high burnup modeling

- Code modification is necessary to model the accumulation of fuel fragments at the spacer location.

- Simplifying assumptions and boundary conditions as input will be utilized.

Evaluations to be performed for a prototypical Large-Break LOCA scenario, which is already conservative, with realistic/reasonable assumptions for FFRD phenomena.

6 Key Assumptions and Modeling Approach Fuel mass release

- Burnup and temperature threshold is to be considered along with the radial temperature distribution of the high-burnup fuel.

- For high burnup assembly, the fuel prone to dispersal is mainly in the ballooned region and between the burst location and the upper spacer grid.

- After burst, it is assumed to be collected at the lower spacer grid.

- No lateral redistribution of fragments is assumed.

7 Key Assumptions and Modeling Approach Porosity and packing of accumulated fuel can be treated as a sensitivity.

Proposed packing fractions 50%, 70%, 90%, covering a range that extends from reasonably realistic to conservative.

Resistance to flow and heat loading would be adjusted accordingly.

Heat load of the accumulated fuel fragments will consider the additional decay heat contribution at the nodal location.

8

w w w. e p r i. c o m TOGETHERSHAPING THE FUTURE OF ENERGY

©2025 Nuclear Energy Institute 2 Industry appreciates the opportunity to hold open and transparent dialogue with staff at these public workshops Applications for uprates, extended cycle lengths and/or advanced fuels incoming Aligning requirements to minimize administrative burden while improving overall efficiency for both industry and regulator without a reduction in safety Workshops align with the intent of the ADVANCE Act for the development of modern, risk-informed, and efficient processes to ensure safety while minimizing burden Background/Objectives of the Workshops

Requires use of risk-informed and performance-based techniques within the existing regulatory framework ADVANCED Act (Accelerating Deployment of Versatile, Advanced Nuclear Clean Energy Act)

Promotes streamlined licensing and regulatory modernization Emphasizes the need for efficient communication and data sharing between the NRC and stakeholders Executive Orders Emphasizes need for efficient regulatory processes Promote regulatory process improvements Drivers for Modernization

Significant changes, defined as those having an absolute magnitude of 50ºF, must be reported in 30 days. reanalysis The NRC considers a major error or change in any direction a cause for concern because it raises potential questions about the adequacy of the evaluation model as a whole.

All PCT changes must be reported annually While errors or changes which result in changes in calculated peak clad temperatures of less than 50ºF are not considered to be of immediate concern, the NRC requires cognizance of such changes or corrections since they constitute a deviation from what previously has been reviewed and accepted.

At the time (1988), available computer resources limited the robustness of LOCA EMs contributing to uncertainty in the ability of the EMs to be able to estimate the impact of changes Historical Perspective

©2025 Nuclear Energy Institute 5 Inferred Purpose Maintain confidence in evaluation models Licensing basis must reflect current state of the plant and account for known phenomena and uncertainty (for realistic evaluation models)

Simplify communication and create consistency NRC feedback Current use is highly subject to interpretation Inconsistent application of reporting requirements Overly burdensome

Majority of reporting are <10ºF for changes such as code maintenance

Not risk-informed Purpose vs. Current Practices

Since 2014 x < 0°F 11%

6%

x = 0°F 59%

82%

x > 0°F 30%

12%

In 2014, Industry presented the results of a survey of 50.46 reports and demonstrated that for more than a 950 estimates the majority of errors results in an estimated PCT of zero degree Fahrenheit New survey performed to evaluate reporting trend since 2014 Since 2014, more than 1200 estimates were reviewed and found that the majority of estimates continue to be a PCT of zero degree Fahrenheit

©2025 Nuclear Energy Institute 7 Improvements in Estimation Considerable improvement in LOCA state-of-knowledge Considerable improvement in modeling capability Considerable improvement in computing resources How does staff use reporting letters currently?

Does magnitude or plant licensing basis affect usage?

Please provide examples [i.e., Annual ECCS Safety Assessment (ML25043A133)]

Assessment Annual Report Trends LOCA analysis capability has increased significantly, as well as the knowledge and capability to evaluate changes or errors commensurate with their potential significance, such that high fidelity of the EMs is maintained.

©2025 Nuclear Energy Institute 8 Industry recognizes NRC desire to maintain knowledge of evaluation model, but requirements should Align with NRC usage Avoid redundancy or conflicting regulatory requirements

10 CFR 50.72 and 10 CFR 50.73 requires reporting of unanalyzed conditions that degrade plant safety (e.g., Event Notification 50639, 50640, and 50641)

10 CFR Part 21 requires reporting of errors in analyses that result in substantial safety hazard Should be commensurate with risk significance LOCA EM errors are typically recorded corrective action programs Resident inspectors have access to a plant Corrective Action systems Improved telecommunications increase accessibility of licensee corrective action programs Modernization of Reporting Requirements

Significance - Redundant; Alternatively, should be risk based

Reanalysis - Estimates are better informed Adequacy of current tools eliminates need for reanalysis schedule

Modern evaluation techniques often capture current plant state and account for uncertainty of non-trivial errors/changes Satisfies NRC cognizance of changes or corrections from year to year.

Does everyone need to report on an annual basis, or could it be required once a licensee reached a specific PCT value (i.e., 2000F)?

Modernization of Reporting Requirements

Robust use and implementation of PRA insights and risk-informed decision-making for over 20+ years through verified and approved programs/submittals in multiple applications with increased degree of quality expectation and level of detail (e.g., Risk Informed Completion Times, 50.69 Risk Informed Categorization of SSCs, Surveillance Frequency Control Program, Reactor Oversight, Plan Licensing Basis Changes, Maintenance Rule)

Specific Requirements:

RG-1.200 Rev. 3 Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities

Application specific requirements (e.g. RG-1.174)

PRA Change program requirements covered in ASME/ANS PRA Standard (ASME/ANS RA-S-1.1)

- approved standard per regulatory review

RG-1.200 Rev. 3 communicates PRA upgrade frequencies (4 years)

Each application has its own application on quality and configuration control

NEI 17-07 for quality standards pertaining to PRA Peer Reviews

Utility specific procedures, guides, job aids for quality and configuration control Robustness on the Use of Risk Insights, Technical Quality, Configuration Control The current guidance, metrics, and expectations regarding PRA Technical Adequacy, meeting the principles of risk-informed decision making is more than sufficient for the use of such tools, to the extent that significant additional guidance and over-conservatisms are not warranted nor should they prevent the realistic use of risk information to inform changes in regulation (as expected from the Commission PRA Policy Statement)

Discussion Period

Break

Discussion Period

Public Comment Period

Closing Remarks

Adjourn

ML25210A425

Text

=

2 Background

Navigation menu

Search