ML25240A908
| ML25240A908 | |
| Person / Time | |
|---|---|
| Issue date: | 09/05/2025 |
| From: | Delosreyes J Licensing Processes Branch |
| To: | Jennivine Rankin Licensing Processes Branch |
| Shared Package | |
| ML25240A895 | List: |
| References | |
| Download: ML25240A908 (1) | |
Text
September 5, 2025 MEMORANDUM TO:
Jennivine K. Rankin, Acting Branch Chief Licensing Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation FROM:
James Delosreyes, Project Manager
/RA/
Licensing Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
SUBJECT:
MEETING
SUMMARY
OF THE JULY 30-31, 2025, U.S. NUCLEAR REGULATORY COMMISSIONS ACCIDENT TOLERANT FUEL (ATF) FUEL FRAGMENTATION, RELOCATION, AND DISPERSAL (FFRD) CONSEQUENCES WORKSHOP On July 30-31, 2025, the U.S. Nuclear Regulatory Commission (NRC) staff held a public workshop with representatives of industry to discuss topics related to FFRD including a proposed white paper submittal from the Nuclear Energy Institute (NEI). The meeting was held in a hybrid format (i.e., attendance in-person, virtual, and teleconference) and conducted over two days. The meeting notice is available in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML25210A594. The presentation slides are available in ADAMS under Accession No. ML25210A425. The list of meeting attendees is enclosed.
The NRC staff began the public meeting with an introduction and explanation of logistical information. Scott Krepel, NRCs Branch Chief of the Nuclear Methods and Fuels Branch in the Division of Safety Systems, and Al Csontos, NEIs Director of Fuels, provided opening and closing remarks. The topics discussed during the meeting are summarized below.
Please direct any inquiries to James Delosreyes at James.Delosreyes@nrc.gov.
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Background===
This workshop was the second in a series of workshops to discuss topics related to FFRD to take place over the span of several months with the first held on May 20-21, 2025. Most, if not all, of these workshops will also serve as a venue to discuss draft submittals from industry for white papers related to the topics of discussion.
CONTACT:
James Delosreyes, NRR/DORL 301-415-4141
Advanced Fuels and Power Uprates: Licensing Pathways The industry representatives began with a background on power uprates, moving on to their future goals and highlighting the economic incentivizes of recent legislation and executive orders. Correspondence among industry and NRC such as the annual update survey and power uprate regulatory issue summary were also discussed. Industry representatives advocated that application bundling for both pressurized water reactors and boiling water reactors (BWRs) would enhance regulatory effectiveness. Industry representatives proposed a plant pilot program for potential bundled applications (e.g., a fuel transition combined with a power uprate),
as well as future tabletop exercises. Details on implementing exemptions for the program were elaborated upon in later presentations.
NRC Studies on Post-FFRD Consequences The NRC staff presented preliminary modeling results on the post-accident consequences of FFRD during loss-of-coolant accident (LOCA) scenarios, using TRACE and core models informed by high-burnup fuel data. The analysis compared conservative licensing assumptions with best-estimate conditions, evaluating variables such as power profiles, emergency core cooling systems (ECCS) train availability, and offsite power loss. Fuel dispersal was modeled with a combination of conservative assumptions and informed engineering judgments. A uniform debris bed was assumed to form on the spacer grid immediately below burst locations, with flow resistance simulated via 1-D hydraulic components.
The simulations showed that peak cladding temperatures (PCTs) remained within acceptable safety margins across most scenarios. The study acknowledged modeling limitations, including potential overestimation of global dispersal and exclusion of de-entrainment effects. While TRACE is not validated for licensing and may not contain all physical models necessary to simulate fuel dispersal and downstream impacts, the results may offer valuable insights for integrated risk-informed evaluations and future regulatory considerations.
Rule Exemption Under 10 CFR 50.12 Duke Energy (Duke) outlined its strategy for pursuing regulatory exemptions under Title 10 of the Code of Federal Regulations (10 CFR) 50.12 to support upcoming power uprates and fuel cycle extensions across multiple plants, with implementation targeted for spring 2029, and emphasized the need for regulatory predictability. Duke is actively engaged in NRC workshops and industry whitepaper efforts and is considering exemptions where the application of existing regulations may not be necessary to achieve their intended safety objectives.
To reduce regulatory uncertainty, Duke proposed a tabletop exercise with the NRC later in the year to walk through exemption scenarios, including those related to fuel cladding, spent fuel pool criticality, and updates to the licensing basis should Duke decide to implement Electric Power Research Institutes (EPRIs) Alternative Licensing Strategy (ALS). The company prefers policy clarification over exemption or revision for ALS implementation and is aligning its approach with NRC-approved methodologies. Key milestones include an upcoming pre-submittal meeting and exemption request submission.
Plant Hatch Potential Pilot Approach for EPU Southern Nuclear presented a potential pilot approach for implementing an Extended Power Uprate (EPU) at Plant Hatch, proposing an increase in licensed thermal power from 2804 MWt
to 2960 MWt. The strategy includes operation within the MELLLA+ domain to enhance operational flexibility and proposes a combined License Amendment Request (LAR) to streamline the regulatory process. A key enabler for this approach is the anticipated release of Regulatory Guide (RG) 1.183, Revision 2. This RG provides updated guidance on aerosol scrubbing and source term modeling for BWRs, which is critical for dose consequence evaluations under uprated conditions.
The presentation emphasized the need for exemptions to implement the revised guidance, particularly for control room dose criteria. If RG 1.183, Revision 2 is delayed, the industry may pursue one of two paths: (1) submitting the EPU LAR with exemptions or (2) proceeding using draft guidance, which introduces regulatory risk due to potential timing misalignments. Southern Nuclear highlighted the importance of early engagement with the NRC to address the complexity of combined or linked submittals and to ensure regulatory clarity for future uprate initiatives.
Assessing Debris Bed Coolability EPRI presented its ongoing research into the coolability of debris beds formed as a result of FFRD, focusing on both in-vessel and ex-vessel configurations. The analysis uses the CORQUENCH code, developed by Argonne National Laboratory, which has undergone validation for ex-vessel severe accident scenarios. Minor modifications are being made to adapt the code for FFRD-specific applications, including modeling of top-flooding conditions and conduction-dominated heat transfer in solidified debris beds. The work supports a defense-in-depth approach and contributes to broader industry efforts to characterize FFRD risks within a risk-informed framework.
The study will evaluate key parameters such as particle size distribution, porosity, decay heat, and water subcooling, with sensitivity analyses planned to assess the robustness of coolability conclusions. The planned schedule includes framework and model development through the summer, with analytical results expected by late fall. Findings will be documented in an EPRI white paper and are intended to inform future NRC workshops and regulatory discussions on FFRD significance and mitigation strategies.
Coolability of Dispersed Fuel EPRI presented a framework for analyzing the in-core coolability of dispersed fuel fragments resulting from FFRD during a LOCA using a modified best-estimate LOCA evaluation model.
The planned study will focus on whether fuel fragments accumulating at spacer grid locations can be adequately cooled to maintain core integrity. Drawing from insights in NUREG/CR-7307, the analysis will assume various debris beds porosities and will evaluate their impact on coolant flow and heat removal, particularly in high-burnup fuel regions.
The modified best-estimate LOCA modeling approach will be tailored for high-burnup conditions. Key assumptions include no lateral redistribution of fragments, fuel mass release localized between burst and upper spacer grids, and varying packing fractions to assess sensitivity. The analysis plans to incorporate decay heat contributions and adjust flow resistance and heat loading accordingly. The goal is to determine whether conservative yet realistic FFRD scenarios still support coolable geometries under large-break LOCA conditions.
LOCA Evaluation Model Change and Error Reporting NEI presented an industry perspective that LOCA reporting requirements under 10 CFR 50.46 could be reduced in light of current modeling capabilities and risk-informed practices. The presentation stated that most reported changes in PCT since 2014 have been negligible, often stemming from minor code maintenance rather than issues that NEI deems as safety-significant issues. NEI argued that the original 1988 reporting framework which was developed under limited computational resources no longer reflects the state-of-the-art in evaluation models, which now offer higher fidelity and better uncertainty characterization.
The industry proposes requiring only annual PCT summaries without reanalysis or a significance determination, unless risk thresholds are exceeded. NEI also advocated that existing regulatory mechanisms ensure safety-significant issues are reported. The industry presentation called for a more risk-informed, performance-based approach consistent with the ADVANCE Act and NEIMA, and reinforced that current probabilistic risk analysis practices and quality standards are robust enough to support such a risk-informed transition without compromising safety.
Discussion The initial discussion period started with dialogue about the reporting requirements. The NRC staff discussed the purpose of the ECCS reporting requirements and how the staff use the annual and 30-day reports. These reports are used to keep NRC staff aware of deficiencies in the LOCA evaluation methodologies in use, which are used to inform staff of issues that may exist for a wider range of plants, and inform NRC requests for additional information on future LOCA evaluation methodologies. The NRC staff brought up the fuel thermal conductivity degradation issue, a deficiency in modelling that was discovered by the NRC that had implications on plant safety as it had large impacts on PCT and affected a significant portion of the fleet. The NRC staff further noted an error associated with one fuel vendors LOCA evaluation model that involved the failure to account for cladding ballooning when calculating cladding oxidation. The NRC staff also cited the annual 50.46c Safety Assessments as a use of the annual and 30-day reports. The annual 50.46c Safety Assessments estimate the margin that each plant would have if the SECY-16-0033 cladding embrittlement research findings were considered, since those research findings show that the current 50.46 PCT and maximum local oxidation criteria do not ensure post quench ductility in the event of a LOCA. The NRC staff stated concerns about the ability to ensure adequate protection of public health and safety during a LOCA if the annual 50.46c Safety Assessments are not performed and note that the NRC staff are obligated by the Commission to perform the safety assessments (per SRM-SECY-12-0034).
Moreover, in the discussion of the ECCS reporting requirements, the NRC staff questioned whether significant PCT changes would indeed be reporting requirements in 50.72 and 50.73, as indicated by industry. The industry participants were unable to provide an example of a change in PCT being reported under those two regulations. The NRC staff and industry participants also discussed whether there were many significant changes that occur in practice.
Both the NRC staff and industry participants agreed that very few 30-day reports of significant changes to PCT currently end up needing to be submitted. Finally, the NRC staff observed that several factors appear relevant to the significance of changes and errors in LOCA evaluation models, including margin to the acceptance criteria, the impact of the change or error, and the total deviation of all changes and errors from the analysis of record.
During the open discussion on topics other than the ECCS reporting requirements, the NRC staff engaged with industry representatives to clarify the technical basis, limitations, and intended use of the various coolability analyses presented earlier in the workshop. A recurring theme was the recognition that both in-vessel and ex-vessel modeling efforts are informative but inherently limited by current code capabilities, lack of validation data, and simplifying assumptions. The NRC staff emphasized the importance of understanding the degree of reliance placed on these calculations, particularly when they are used to support risk-informed strategies like ALS. Both sides agreed that these models are not suitable as licensing basis calculations but can provide valuable insights to inform broader safety evaluations.
The discussion also explored the need to keep the technical scope bounded and focused, avoiding an open-ended research effort. The NRC staff and industry participants acknowledged that the goal is not to resolve all future uncertainties but to develop a practical, near-term framework that supports decision-making under current regulatory conditions. This includes identifying key uncertainties and understanding their implications for risk. The triplet framework was used to structure the conversation, with the consequence analysis still seen as the least developed area. There was also interest in leveraging collaborative mechanisms, such as the EPRI-NRC memorandum of understanding, to accelerate progress and avoid duplicative work.
Finally, the conversation turned to licensing strategies, exemption planning, and the role of upcoming tabletop exercises. The NRC staff sought clarity on how industry plans to bundle exemption requests and align them with project schedules, particularly for power uprates and new fuel types. There was discussion about the importance of timing, regulatory alignment, and the potential impact of pending rulemakings. Participants agreed that tabletop exercises would be a key venue for refining these strategies and ensuring that all stakeholders have a shared understanding of expectations. The session concluded with a shared commitment to continue integrating technical findings into a risk-informed regulatory framework, with a focus on practical outcomes and clear communication.
Public Comments No public comments were received during this meeting.
No regulatory decisions were made during this meeting.
Enclosure:
List of Attendees
Package: ML25240A895 Meeting Summary: ML25240A908 Meeting Notice: ML25210A594 Meeting Slides: ML25210A425
- via eConcurrence NRC-001 OFFICE DORL/LLPB/PM DORL/LLPB/LA DORL/LLPB/BC DORL/LLPB/PM NAME JDelosreyes DHarrison JRankin JDelosreyes DATE 9/3/2025 9/4/2025 9/5/2025 9/5/2025
Enclosure LIST OF ATTENDEES U.S. Nuclear Regulatory Commission Accident Tolerant Fuel Fuel Fragmentation, Relocation, And Dispersal Consequences Workshop July 30-31, 2025 9:00 am - 12:00 pm U.S. Nuclear Regulatory Commission (NRC)
First Name Last Name Steve Bajorek Michelle Bales Ronald Ballinger Philip Benavides Andrew Bielen Mike Call Alice Chung Alex Collier James Corson James Delosreyes Elijah Dickson Denise Edwards Richard Fu David Garmon Craig Harrington Kevin Heller Todd Hilsmeier Kevin Hsueh Joshua Kaizer Michelle Kichline Daniel King Scott Krepel Lucas Kyriazidis John Lehning Michael Mahoney Don Marksberry Sean Meighan Joseph Messina Seung Min Jack Minzer Bryant Christopher Nellis Jennie Rankin Aida Rivera-Varona River Rohrman Joseph Staudenmeier Robert Tregoning Chris Van Wert Shilp Vasavada Weidong Wang Sunil Weerakkody Jen Whitman Josh Whitman Non-NRC First Name Last Name Organization (if provided)
Birol Aktas Lightbridge Victoria Anderson Nuclear Energy Institute (NEI)
Duane Avery II Constellation Jennifer Baker Xcel Energy Kevin Barber Westinghouse Electric Company (Westinghouse)
Mark Bensi Vistra Corp Jana Bergman Curtiss-Wright Ruxandra Bobolea Dominion Sofia Bouhrizi EDF France Daniel Bowers Stars Alliance Andrew Bowman Westinghouse Dave Breeding Framatome Greg Broadbent Entergy Justin Byard Dominion YJ Choi Electric Power Research Institute (EPRI)
James Cirilli EPRI Aladar Csontos NEI Cecile Dame MPR Associates Steven Dolley S&P Global Joshua Duc Duke Energy (Duke)
Dennis Earp Duke Virgilio Esquillo Dominion Jerrod Ewing Westinghouse William Freebairn S&P Global Richard Garcia Energy Northwest Lisa Gerken Framatome Mark Conrad Handrick Duke Stan Hayes Duke Zachary Hollcraft Alva Energy Jerald Holm Framatome Christopher Holst Energy Northwest Jeanne Johnston Southern Zeses Karoutas Westinghouse Storm Kauffman MPR Associates Thomas Kindred Southern Jeffrey Kobelak Westinghouse David Kortge Constellation Samuel Lafountain Southern Matthew Leonard Westinghouse Guangjun Li General Electric (GE)
Scott Luchau Dominion Edwin Lyman Union of Concerned Scientists Alex Markivich Dominion Oskar Mrtensson SSM Sweden Tara Matheny Duke Bruce Montgomery NEI Brian Mount Dominion Shirley Movalo Eskom Kurshad Muftuoglu EPRI Matthew Nudi EPRI Stephen OHearn Dominion Geoff Pihl Duke Ian Porter GE Richard Rogalski Energy Northwest Baris Sarikaya Constellation Jim Schott Enercon Richard Skowron Duke James Smith Westinghouse Christopher Smith Duke Fred Smith EPRI Scott Stanchfield Entergy William Steelman Entergy Charles Stroupe Duke Heather Davis Szews Duke Yoshinori Takechi NRA Japan Milan Tesinsky Westinghouse Ryan I Treadway Duke Donald Vanover Jensen Hughes Wayne Wasser Enercon Lewis Wells Constellation Gordo Wissinger Framatome