ML25077A168

University of Illinois at Urbana-Champaign, Final Safety Evaluation of Fuel Qualification Methodology Topical Report (Redacted)

ML25077A168
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Site:	99902094
Issue date:	04/01/2025
From:	Holly Cruz NRC/NRR/DANU/UNPL
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ML25077A165	List: ML25077A166
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EPID L-2024-NFN-0003
Download: ML25077A168 (1)

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OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN - FINAL SAFETY EVALUATION OF RELEASE 2 OF TOPICAL REPORT UNIVERSITY OF ILLINOIS URBANA-CHAMPAIGN HIGH-TEMPERATURE GAS-COOLED RESEARCH REACTOR: FUEL QUALIFICATION METHODOLOGY (EPID: L-2024NFN0003)

APPLICANT INFORMATION Applicant:

University of Illinois at Urbana-Champaign Applicant Address:

104 South Wright St.

Urbana, Illinois 61801 Docket /Project No(s).:

99902094 APPLICATION INFORMATION Submittal Date: March 11, 2024 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML24071A237 (Reference 1)

Supplement ADAMS Accession No: ML24347A211 (Reference 2)

Regulatory Audit Report ADAMS Accession No.: ML25056A213 (Reference 3)

Brief Description of the Topical Report: The topical report (TR) University of Illinois Urbana-Champaign High Temperature Gas-cooled Research Reactor: Fuel Qualification Report, Release 2 (Reference 2), describes the fuel qualification methodology (FQM) for the University of Illinois at Urbana-Champaign (UIUC) Micro Modular Reactor (MMR) research reactor. As discussed in TR sections 1.3 and 2.2.2, the MMR, designed by Ultra Safe Nuclear Corporation1 (USNC), is a high temperature gas-cooled reactor (HTGR) that uses fully ceramic micro-encapsulated (FCM) fuel pellets containing tristructural isotropic (TRISO) coated uranium oxycarbide (UCO) nuclear fuel particles as its primary heat source. The FQM described in the TR leverages previously obtained experimental data, including the Department of Energy (DOE)-initiated Advanced Gas Reactor (AGR) experiments described in the U.S. Nuclear Regulatory Commission (NRC)-approved Electric Power Research Institute (EPRI) TR EPRI-AR-1(NP)-A, Uranium Oxycarbide (UCO) Tristructural Isotropic (TRISO)-Coated Particle Fuel Performance (Reference 5), for qualification of the TRISO fuel particles contained in the USNC FCM fuel design. Additionally, the FQM described in the UIUC TR includes testing, 1 Although the UIUC FQM TR refers to USNC as the developer of the MMR and associated FQM, NANO Nuclear Energy Inc. (NANO Nuclear) announced on January 13, 2025 (Reference 4), that it had acquired the MMR technology from USNC. NANO Nuclear stated that it planned to continue USNCs existing collaboration with UIUC on the UIUC MMR project.

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION characterization, and analysis that will be performed on the specific FCM fuel form itself. The TR details the methodology, including acceptance criteria, that will be used to qualify the FCM fuel form and the TRISO coated fuel particles contained therein for use in a future MMR research reactor that UIUC plans to build and operate on its campus.

Ultimately, as discussed in the TR Executive Summary and in TR section 1.2.1, the FQM described in the UIUC TR is intended to provide reasonable assurance that the TRISO fuel particles and FCM fuel pellets can operate with a low particle failure rate and level of fission product release, consistent with the design basis analyses for the UIUC MMR. TR section 1.2.3 states that the results of the testing, characterization, and analysis described in the TR will be included in future licensing submittal(s); the use of FCM fuel in the UIUC MMR would be contingent upon NRC review(s) and approval(s) associated with these submittal(s), as appropriate. The NRC staff expects that the proposed FQM could be used to support future construction permit (CP) and/or operating license (OL) applications from UIUC for its planned MMR reactor fueled with the FCM fuel described in the TR.

For additional details on the submittal, please refer to the documents located at the ADAMS Accession numbers identified above.

EVALUATION CRITERIA As discussed in TR sections 1.4.1 and 2.3 and in UIUCs Regulatory Engagement Plan (REP) submitted to the NRC by letter dated June 26, 2023 (Reference 6), UIUC plans to apply to license its MMR under the provisions of Title 10 of the Code of Federal Regulations (10 CFR)

Section 50.21, Class 104 licenses; for medical therapy and research and development facilities, paragraph (c), as a class 104(c) research reactor. Specifically, UIUC plans to submit CP and OL applications to the NRC in the future to request authorization for construction and operation, respectively, of the UIUC MMR. The regulations in 10 CFR 50.34, Contents of applications; technical information require that applicants for CPs and operating licenses include a preliminary safety analysis report (PSAR) and a final safety analysis report (FSAR),

respectively, and describe the information that shall be included in these reports. The NRC staff anticipates that eventual license application(s) for the UIUC MMR would rely on the contents of the TR and this safety evaluation (SE). Therefore, the NRC staff considered requirements of 10 CFR 50.34 in its review of the TR, including 10 CFR 50.34(a)(3)(i) which requires, in part, that a PSAR include principal design criteria (PDCs) for the proposed facility.

The NRC-approved UIUC TR IMRDD-MMR-23-06-A, University of Illinois Urbana-Champaign High-Temperature Gas-cooled Research Reactor: Micro Modular Reactor (MMRTM) Principal Design Criteria (Reference 7), describes the PDCs for the proposed UIUC MMR. These PDCs were developed primarily based on the guidance in Appendix C of NRC Regulatory Guide (RG) 1.232, Guidance for Developing Principal Design Criteria for Non-Light-Water Reactors, Revision 0 (Reference 8), with adaptations, as discussed in the PDC TR. To support the review of the FQM TR, the NRC staff considered applicable PDCs, such as PDCs 10, 16, 26, and others, from the PDC TR.

NUREG-1537, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors (Reference 9), Part 1, Format and Content, and Part 2, Standard Review Plan and Acceptance Criteria, provide guidance for preparing and reviewing, respectively, applications for non-power reactors, including research reactors. The most relevant guidance with respect to the FQM TR is contained in sections 4.2, Reactor Core, and 4.5, Nuclear

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION Design, of Parts 1 and 2. Section 4.2 contains guidance related to core design information (including dimensions, materials, mechanical properties, and the mechanical effects of reactor operation) related to a reactor designs fuel, control elements, moderator, reflector, and other reactor core features. Section 4.5 contains guidance related to physical, thermal, and nuclear parameters, characteristics, and operating limits of the reactor core, as they relate to normal steady-state, kinetic, and transient operations of reactor core components.

NUREG-2246, Fuel Qualification for Advanced Reactors (Reference 10), provides a framework for use in qualification of nuclear fuels which UIUC references in TR section 1.4 as part of the regulatory basis for qualification of FCM fuel. The framework discusses the identification of key fuel manufacturing parameters, the specification of a fuel performance envelope to inform testing requirements, the use of evaluation models in the fuel qualification process, and the assessment of the experimental data used to develop and validate models and empirical safety criteria. The framework outlines a set of goals that, when met, can be used to justify that a nuclear fuel design is qualified for use. The NRC staff notes that the FQM TR describes how some of these goals will be satisfied as they relate to the MMR FCM fuel design and the planned manufacturing and testing programs, although the approach of the TR (which provides preliminary information regarding plans for experimental testing and analysis of the FCM fuel design) is not to provide a comprehensive description of every goal.

SECY-18-0096, Functional Containment Performance Criteria for Non-Light-Water-Reactors (Reference 11), which the Commission approved in SRM-SECY-18-0096 (Reference 12),

details criteria that describe how advanced reactor designs may justify the use of a functional containment consisting of multiple barriers to limit the release of radioactive materials, in lieu of a traditional light-water reactor (LWR)-style containment design. As discussed in TR section 1.3.2, the MMR design relies on this functional containment approach, and the fuel comprises several layers of the planned functional containment. However, the acceptability of the functional containment approach for the UIUC MMR, including the performance and modeling of the FCM fuel as part of the functional containment, will be subject to future licensing submittal(s) and is not specifically reviewed or approved in this SE.

The regulations in 10 CFR Part 20, Standards for Protection against Radiation, establish standards for protection against ionizing radiation resulting from NRC-licensed activities. Under future licensing submittal(s), the functional containment design, including retention of fission products within the FCM fuel, will be assessed against the to-be-established specified acceptable radionuclide release design limits (SARRDLs) to ensure that applicable regulatory limits regarding radiological consequences will be met2.

2 TR sections 1.4.1.1 and 1.4.2 state that the public dose limits in 10 CFR Part 20 (e.g., the 100 millirem annual limit on the total effective dose equivalent to an individual member of the public from the licensed operation of a nuclear facility) will be used as accident dose limits for the UIUC MMR because it is a research reactor. The NRC staff notes that this is consistent with guidance in NUREG-1537, Part 1 (Reference 9), which states that calculated accident doses for research reactors have generally been compared to 10 CFR Part 20 limits because there were no specific accident-related regulations for research reactors. However, the Non-Power Production or Utilization Facility License Renewal final rule (NPUF rule) that was published in the Federal Register on December 30, 2024 (Reference 13),

amended the NRCs regulations, in part, by establishing in 10 CFR 50.34 a specific research reactor accident dose criterion of 1 rem (less restrictive than the 10 CFR Part 20 limits). The NRC staff will evaluate future UIUC licensing submittal(s) against applicable regulatory limits that are effective at the time of the future submittal(s). Because the UIUC MMR is a research reactor, the siting requirements specified in 10 CFR Part 100 do not apply to the UIUC MMR; this is unchanged by the NPUF rule.

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION TECHNICAL EVALUATION Scope of Review The TR describes the FQM that will be implemented to support licensing the UIUC MMR research reactor. The FQM, as described in TR section 6, includes the following aspects:

1. Development of fuel product specifications for FCM pellets and TRISO particles.

2. Demonstration of pilot manufacturing and quality control processes capable of consistently meeting fuel product specifications.

3. Performance of testing and characterization of unirradiated fuel and materials (TR section 6.1).

4. Performance of fuel pellet irradiation tests in materials test reactors. (TR section 6.2).

5. Performance of post-irradiation high temperature testing to simulate accident scenario conditions. (TR section 6.3).

6. Performance of post-irradiation examination (PIE) and characterization of tested specimens to determine irradiated fuel performance. (TR section 6.4).

7. Performance of fuel performance modeling calculations in support of fuel qualification (TR section 6.5).

The TR, in sections 1.2 and 7.2, specifically requests NRC review and approval of the aspects of the FQM described in TR sections 6.1, 6.2, 6.3, 6.4, and 6.5, as well as the acceptance criteria detailed in TR section 6.7. TR sections 6.1, 6.2, 6.3, 6.4, and 6.5 effectively correspond to aspects 3 through 7, respectively, from the list above. Therefore, the NRC staffs review of the TR in this SE focuses on the evaluation of the acceptability of the specific aspects of the FQM described in TR sections 6.1 through 6.5 and the acceptance criteria in TR section 6.7.

The TR includes additional informational sections including sections related to the FCM fuel design, MMR core design, FCM fuel manufacturing processes, quality control, FCM fuel safety, and FCM fuel performance modeling that support the NRC staff review described in the paragraph above. However, this SE does not specifically review or approve these other informational sections of the TR, and therefore makes no findings on these sections.

Additionally, as stated in TR sections 1.2.3 and 7.2, the results generated following implementation of the described FQM will be submitted for NRC review as part of future licensing submittal(s) for the UIUC MMR. Therefore, approval of the FCM fuel design, its ability to meet appropriate acceptance criteria, and its qualification for operation in an MMR at UIUC is subject to appropriate future licensing submittal(s), and is not granted by this SE.

The TR Executive Summary states that the TR describes the FQM for the MMR to be deployed at UIUC which, as discussed above, UIUC plans to license as a class 104(c) research reactor.

Furthermore, in TR section 1.2.3, UIUC states that meeting the acceptance criteria in the TR supports qualification of the FCM fuel for use specifically in the UIUC MMR. To clearly delineate the applicability of the NRC staffs approval of the TR to the MMR research reactor planned to be constructed at UIUC (with a design and class 104(c) licensing approach as described in the TR), the NRC staff imposed TR limitation/condition 1 in this SE.

Design Summary The FCM fuel design is described in TR section 2 and summarized in this SE section for informational purposes. The fuel-containing portion of the design consists of TRISO particles

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION

((

)). The fuel kernel contains UCO fissile material. These TRISO particles are embedded into annular cylindrical FCM fuel pellets that consist of a fueled matrix containing TRISO particles, a fuel-free zone that isolates the particles, and an outer dense surface layer (ODSL) made up of SiC. The FCM pellets ODSLs and TRISO particles coating layers ((

)) will be credited as portions of the UIUC MMRs functional containment approach to fission product retention.

The MMR design is described in TR section 1.3.2 and is also summarized in this SE section for informational purposes. The proposed UIUC MMR would be a 10 megawatt-thermal HTGR. The reactor core consists of FCM pellets stacked within solid graphite blocks to make up the fueled reactor core sections. Helium gas will normally be pumped through the core to transfer the heat generated to a secondary heat transfer system that consists of an intermediate heat exchanger with a molten salt loop. The reactor and core structures, systems, and components (SSCs) will be designed such that safety-related core cooling can be adequately achieved through passive means that do not require helium coolant, electrical power, or operator action. The NRC staff expects that, based on the UIUC MMR PDCs, the design would ensure that SARRDLs will be met through reliance on inherent reactivity feedback, functional containment provided by the FCM fuel form, and passive transfer of heat from the reactor core through the vessel, surrounding below-grade building (i.e., the citadel building), and other associated passive SSCs to the surrounding environment.

Unirradiated Fuel and Materials Testing and Characterization TR section 6.1 includes a list of unirradiated fuel material properties planned to be obtained through testing to confirm future fuel performance models (the NRC staff notes that TR section 6.5 provides additional context related to planned fuel performance modeling; the NRC staff considered this context in its review of the list of properties). TR section 6.1 also discusses mechanical testing that will be performed to demonstrate the adequacy of important features of the FCM fuel. Specifically, ((

)) testing will be performed on surrogate test specimens with ODSLs as well as on as-manufactured FCM pellets. ((

))

The NRC staff notes that the experimental techniques to be used to obtain the unirradiated material properties listed in TR section 6.1 are not specified in the TR. However, during audit discussions and in information provided for audit, as documented in the audit report (Reference 3), UIUC clarified that these material properties are reasonably obtainable using typical material testing techniques previously used in the nuclear industry, and confirmed that

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION generally accepted techniques, such as those specified by the American Society for Testing and Measurement, would be used for obtaining the material properties. The NRC staff considers the approach of using such standards for testing reasonable, although the NRC staff notes that the specific tests and results will be subject to review in future licensing application submittal(s).

The NRC staff considered whether the range of test conditions specified in TR section 6.1 could be reasonably expected to adequately represent the operating conditions predicted for the UIUC MMR design. TR section 6.1 specifies that material property measurements will be made

((

)). The NRC staff finds the approach of determining material properties ((

))

appropriate, as it ensures that the measured properties will be reasonably representative of those expected during UIUC MMR operation. Furthermore, the NRC staff notes that high-temperature safety testing will be performed as discussed in TR section 6.3 to demonstrate fuel integrity during postulated accident conditions; this testing is discussed and evaluated in the subsequent SE section on post-irradiation testing.

The NRC staff considered the differences between the surrogate pellets being tested and the final FCM fuel form, and whether any of the differences would need to be accounted for during data acquisition or subsequent modeling. Based on the information in TR section 6.2.2, supported by audit discussions and information provided for audit as documented in the audit report (Reference 3), the NRC staff expects that the likeness between the surrogate pellets and the final fuel form is sufficient for the testing to be performed on the surrogate pellets to support the qualification of the FCM fuel. Specifically, the NRC staff notes that the manufacturing specifications and physical properties of the pellets to be used in surrogate testing, as well as techniques for the testing, are such that the planned test conditions and expected results obtained can be expected to reasonably represent or, in many cases, bound the conditions that the FCM fuel is expected to be subjected to in the UIUC MMR. For example, TR section 6.2.2 states that ((

]. Additionally, based on information in TR section 6.2.2, the NRC staff expects that manufacturing and resultant material properties of the surrogate pellets will be effectively identical to the as-designed FCM pellets, with any differences being inconsequential to the intended outcomes of the testing.

TR section 1.2.2 states that potential phenomena related to vibration-induced mechanical wear and its potential to impact FCM fuel pellet performance over the planned period of operation of the UIUC MMR are not within the scope of the FQM TR. During audit discussions and in information provided for audit, as documented in the audit report (Reference 3), UIUC confirmed that vibration and wear will be assessed through testing and will be addressed in future licensing submission(s) planned to support qualification of the FCM fuel for use in the UIUC MMR. The NRC staff imposed TR limitation/condition 2 to ensure that these phenomena will be appropriately addressed to support the final qualification of the FCM fuel for use in the UIUC MMR.

The NRC staff considered whether TRISO particle failures could result if an FCM pellet were to fracture. ((

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))

Based on the above, the NRC staff finds that the material properties that will be obtained through testing can be reasonably expected to support the planned fuel performance modeling.

Specifically, based on the information on testing and characterization of unirradiated fuel and materials in TR section 6.1, in combination with information on irradiation testing in TR section 6.2 and other information referenced from the TR and discussed in subsequent sections of this SE, the NRC staff expects that the appropriate properties will be obtained to support stress evaluation of FCM fuel such that its integrity can be assessed over the range of operating conditions expected in the UIUC MMR. Furthermore, the NRC staff finds the specifications of the surrogate test specimens and the testing conditions to be reasonably representative of the described as-manufactured FCM fuel and the expected UIUC MMC operating conditions.

Therefore, the NRC staff finds the unirradiated fuel and materials testing and characterization plan described in TR section 6.1 reasonable for use to support qualification of FCM fuel for use in the UIUC MMR.

The NRC staff notes that TR section 6.1 references information regarding the irradiation behavior of chemical vapor infiltration (CVI) SiC and use of material properties in fuel performance modeling. These topics are addressed in the subsequent SE section on fuel performance modeling.

Irradiation Testing TR section 6.2 describes irradiation tests of FCM fuel and materials that will be performed in materials test reactors as part of the FQM. The objectives of the irradiation tests are described in TR section 6.2 and summarized below.

1. ((

))

2. ((

]

3. ((

))

The NRC staff understands from the TR that the objectives aim to demonstrate the effectiveness of the radionuclide retaining features of the FCM fuel design both independently and integrally, and to demonstrate this performance over bounding operating conditions. The NRC staff notes that demonstration of FCM fuel performance will rely on the objectives listed in the TR and will be further supported by testing performed under the DOE AGR program.

Specifically, the NRC staff understands from the TR that the planned irradiation testing aims to bolster and confirm the radionuclide retention performance of TRISO particles demonstrated under the AGR program and to demonstrate that differences in pellet/compact manufacturing

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION between the AGR fuel and the planned FCM fuel will not negatively impact radionuclide retention performance. The NRC staff finds that testing based on these objectives can reasonably be expected to support demonstration of adequate irradiation performance of the FCM design, which would be assessed in future licensing submission(s) following the performance of testing and modeling.

In describing the irradiation tests that will be conducted, TR section 6.2 describes the types of specimens to be tested, and provides general descriptions of the testing to be performed.

Specifically, ((

)) will be irradiated during testing in two different test facilities under different conditions. Steady-state long-term tests at the High Flux Reactor (HFR) in Petten, Netherlands will be used to represent normal operations, and short-duration failure tests at the Massachusetts Institute of Technology Nuclear Research Reactor (MITR) in Cambridge, Massachusetts will be performed to represent transient (i.e.,

postulated accident) irradiation conditions. As discussed in TR section 6.2.4, the testing in the HFR will be performed ((

))

The NRC staff acknowledges the approach of performing testing to multiple burnup levels such that initial UIUC MMR operation can be justified based on ((

)) and finds the approach reasonable. However, the NRC staff notes that licensing of the UIUC MMR for operation to any specific burnup level would require appropriate testing and supporting analyses to be completed to support UIUC MMR operation to that burnup level prior to any operation beyond a previous burnup limit in a UIUC MMR license.

TR section 6.2.2 states that the test specimens will consist of ((

)) The NRC staff notes that the scaling discussed in TR section 6.2.2 appears reasonably small and therefore expects that dimensional differences can reasonably be accounted for during modeling, consistent with NUREG-2246 goal Experimental Data (ED) G4.

The NRC staff considered the manufacturing processes used to create the test specimens and whether any meaningful manufacturing or material differences, compared to the standard FCM design, would be introduced that may impact the testing or applicability of the obtained data. In information provided for audit and during audit discussions, as documented in the audit report (Reference 3), UIUC confirmed that the test specimens will be manufactured in largely the same fashion as the as-designed FCM fuel (FCM pellet manufacturing is described in TR section 3.2).

Most differences will be minor and primarily related to ((

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)). The NRC staff therefore notes that the planned manufacturing of test specimens reasonably aligns with NUREG-2246 goal ED G4.

TR section 6.2 also describes specific testing parameters including differences in cooling between the testing and the planned UIUC MMR operation, which the NRC staff finds reasonable because internal material stresses during testing will bound those expected during UIUC MMR operation.

As discussed in TR sections 1.3.2 and 6.2.2, one notable difference between the test specimens and the MMR FCM as-fabricated design is that the test specimens will be enriched to ((

)), while the nominal as-fabricated FCM fuel is intended to contain low-enriched uranium (LEU)+, i.e., uranium enriched to ~9.9 percent uranium-235. However, TR section 6.2.4 explains that internal stresses during testing will bound those expected in the UIUC MMR. Additionally, the NRC staff notes that, as summarized in TR table 2.2, the enrichment used in AGR testing of TRISO particles encompasses LEU+ (and higher) enrichment, supporting TRISO particle performance over a range of enrichments. Based on this AGR experience and the bounding nature of the pellet stresses expected during testing, the NRC staff finds the enrichment difference between the test specimens and the as-designed FCM fuel reasonable. However, the staff notes that any enrichment differences should be adequately accounted for, as necessary, in fuel performance and/or radionuclide release calculations used to justify adherence to regulatory dose limits in future licensing submission(s),

consistent with NUREG-2246 goal ED G4.

Based on the above, the NRC staff finds that the planned irradiation testing can be reasonably expected to achieve the objectives of the testing. Specifically, the NRC staff finds that the irradiation tests in the HFR and MITR will provide irradiation data reasonably representative of expected steady-state operations and postulated accident conditions to support the demonstration of the FCM fuels operational reliability and radionuclide retention capabilities over the full range of UIUC MMR operating conditions. Furthermore, the NRC staff finds that the types of test specimens can reasonably be expected to provide testing data that can be used to support the three objectives of the irradiation testing in a manner that demonstrates each objective independently.

Post-Irradiation Testing TR section 6.3 describes the planned post-irradiation testing that will be performed as part of the FQM. Specifically, high-temperature furnace testing of specimens, to occur following the planned irradiation testing, is described. The goal of the testing is to determine the effectiveness of FCM pellets in retaining fission products ((

))

The NRC staff considered that, depending on the timing between completion of irradiation testing and performance of high-temperature safety testing, short-lived isotopes may decay away between the tests. However, in information provided for audit and during audit

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION discussions, as documented in the audit report (Reference 3), UIUC indicated that short-lived isotopes important to dose consequence analysis for postulated accidents will be accounted for by measuring longer-lived isotopes that are known to exhibit similar release characteristics.

The NRC staff finds the post-irradiation testing described in the TR acceptable because it can be reasonably expected to provide appropriate insight regarding radionuclide release behavior of FCM fuel under accident conditions to inform accident scenario modeling and dose consequence estimations to support future licensing of the UIUC MMR. Specifically, representative test specimens will be subjected to testing that will challenge the radionuclide retention capabilities of important retention features to demonstrate their effectiveness and to provide important release characteristics for use in modeling. Additionally, the NRC staff notes that PIE techniques, discussed in the next section of this SE, will be used to confirm the results of the irradiation testing and high temperature testing.

Post-Irradiation Examination TR section 6.4 describes the PIE techniques that will be used as part of the FQM to support the results obtained during irradiation testing and post-irradiation testing. PIE will include ((

)) The NRC staff finds the incorporation of the described PIE techniques in the FQM appropriate for use to help confirm the applicable data obtained during testing. Specifically, the NRC staff finds that the PIE described will serve to support the use of the obtained data for modeling, and that the PIE provides for physical examination of the tested specimens to further ensure that unacceptable amounts or types of degradation or failure will not occur in FCM fuel.

Fuel Performance Modeling TR section 6.5 states that fuel performance modeling will be used to assess the performance of the MMR FCM fuel based on the experimental results from testing. [

)) The stress calculations will be performed using Abaqus (described in TR section 5.2) ((

)). The NRC staff notes that TR section 5.2 regarding Abaqus is informational in nature, and therefore the NRC staff makes no determination regarding the acceptability of the described Abaqus method(s). However, the NRC staff notes that it considers the conceptual approach described in TR section 6.5.1 of using a stress analysis method (which the NRC staff expects would be reviewed for approval in future licensing submission(s)) ((

)) to estimate pellet failure thresholds and/or probabilities, as appropriate, to support future licensing and qualification of FCM fuel for use in the UIUC MMR to be reasonable. As discussed in TR section 6.5.2, the fission product release calculations will

((

)), relying on TP3-DIFFUSION calculations, as described in TR section 5.1. The NRC staff notes that TR section 5.1 regarding TP3-DIFFUSION is also informational in nature, and therefore the NRC

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION staff makes no determination regarding the acceptability of the described TP3-DIFFUSION method(s). However, the NRC staff notes that it considers the conceptual approach, described in TR section 6.5.2, of ((

)) to be reasonable.

The NRC staff also considered whether the referenced testing data and planned testing activities described in the TR could reasonably be expected to provide the material properties needed to support the planned fuel modeling and analysis necessary for qualification of the fuel.

This included consideration of ((

)). The NRC staff expects the described testing plans and other referenced information to be consistent with the collection of a reasonable set of applicable data that may be used to support effective modeling of the FCM fuel in the UIUC MMR core. Therefore, based on the collection of adequate data for modeling and also based on the reasonableness of the conceptual approaches for the fuel performance modeling as discussed above, the NRC staff finds the general testing and modeling plans discussed in TR section 6.5 and other portions of TR section 6 to be reasonable and acceptable.

TR section 6.5.3 discusses long-term FCM TRISO fuel degradation. Specifically, the fuel degradation mechanisms discussed in TR sections 4.2 and 4.4 are further considered with regard to their potential to challenge the fuel over long periods of time. Most notably, TR section 6.5.3 indicates that chemical attack of SiC was identified as the primary cause of TRISO particle failure during the AGR experiments. TR section 6.5.3 states that chemical attack of SiC is a time-dependent phenomenon, and palladium is regarded as a major contributor to SiC attack as noted in TR section 4.2.6. However, as discussed in TR section 6.5.3, a conservative prediction of palladium penetration shows reasonable margin to FCM failure under conservative UIUC MMR operating conditions and residence time. Additionally, the NRC staff expects that maintenance of helium coolant purity as discussed in TR sections 4.4.4 and 6.5.3 will help ensure that external chemical attack of the FCM ODSL is minimized. Based on the discussion in TR section 6.5.3, the NRC staff finds that the approach for fuel performance modeling described in the TR appears to reasonably account for slowly-occurring time-dependent fuel degradation phenomena.

The NRC staff notes that the results of fuel testing and modeling and associated adequacy justification(s) will be subject to future licensing review(s) following the completion of the planned testing, model development, and fuel performance analysis.

Fuel Acceptance Criteria TR section 6.7 includes TR table 6.3, which outlines four fuel acceptance criteria. The first two criteria are related to the manufacturing of TRISO particles and FCM pellets. The third criterion is related to the analysis of FCM fuel operation over the MMR operating envelope and ensuring that qualification limits (presented in TR tables 2.5 and 2.6) are met. The fourth criterion is related to the fission product release fraction of FCM fuel and ensuring the fraction remains below limits that will be established based on source term analysis and site boundary dose limit requirements. These criteria are discussed further below.

The first criterion specifies that as-fabricated FCM TRISO fuel meets the limits presented in TR table 2.2, and further provides a list of the specific relevant parameters. The NRC staff reviewed

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION TR table 2.2 and noted that the table provides a direct comparison between the limits specified for FCM TRISO particles and actual values from the DOE AGR experiments. The NRC staff notes that the FCM TRISO fractions specified align reasonably well with those observed during the AGR experiments. Therefore, the NRC staff determined that the fuel limits specified in TR table 2.2, in conjunction with the fourth criterion in TR table 6.3 related to fission product release limits, can be reasonably expected to provide assurance that the manufacturing of FCM TRISO particles will not result in unacceptable and/or non-conservative levels of defects and/or resultant fission product release. Accordingly, the NRC staff finds the first criterion and the specified FCM TRISO fuel limits acceptable.

The second criterion specifies that the thickness of the as-fabricated FCM ODSL meets the limit in TR table 2.3, and that the FCM pellets include zero pellets with a defective ODSL (i.e., 100 percent of pellets pass the hermeticity test). TR sections 3.4 and 6.1 include details describing the [

)) that will ensure that the criteria are met. The NRC staff expects the planned approach will help ensure that FCM fuel pellets will be manufactured with effective ODSLs, such that the ODSLs can reasonably be relied upon as integral parts of the UIUC MMR functional containment. Therefore, the NRC staff finds that the second acceptance criterion, and the planned approach to demonstrate that FCM fuel meets it, are acceptable.

The third criterion pertains to analysis of MMR operations under normal, anticipated operational occurrence (AOO), and design basis accident (DBA) conditions and states that the analysis shall confirm that FCM fuel will operate within the qualification limits presented in TR tables 2.5 and 2.6. The NRC staff reviewed TR tables 2.5 and 2.6 and notes that the limits specified are intended to create a normal operating envelope for FCM fuel in the MMR. The limits specified include: maximum best estimate burnup, maximum burnup with uncertainty, maximum best estimate fast neutron fluence, maximum fast neutron fluence with uncertainty, peak fuel temperature, peak fuel temperature with uncertainty, and time-average peak fuel temperature.

The NRC staff notes that the tables provide a direct comparison to values for these parameters during the AGR experiments and that ((

)). Given the similarities between the FCM and AGR TRISO particle designs, the positive performance of TRISO during the AGR experiments, the additional level of fission product retention promoted by the presence of the ODSL in FCM pellets, and [

)), the NRC staff finds the third acceptance criterion, including the limits established in TR tables 2.5 and 2.6 as referenced in the criterion, reasonable and acceptable.

The NRC staff considered whether any additional fuel qualification limits beyond those specified in TR tables 2.5 and 2.6 could be appropriate to ensure establishment of a comprehensive fuel qualification envelope for FCM fuel in the UIUC MMR. Specifically, during the audit, as documented in the audit report (Reference 3), the NRC staff inquired regarding differences between the MMR and AGR acceptance criteria, particularly the exclusion of power density and particle packing fraction. In information provided for audit, as also documented in the audit report, UIUC indicated that ((

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION

)). The NRC staff considers the information UIUC provided during the audit to provide additional confirmation that the proposed third acceptance criterion is reasonably comprehensive.

The fourth criterion specifies that the fission product release fraction from FCM fuel pellets during MMR normal operation, AOOs, and DBAs must be lower than the maximum allowed value based on source term analysis showing that site boundary dose limits are not exceeded.

The NRC staff notes that, while the testing results and maximum allowable value(s) of release fraction(s) are not known at this time, the nature of the comparison described by the criterion is consistent with UIUC MMR PDC 10 and UIUCs intent to adhere to regulatory dose limits as discussed in TR section 1.4. Therefore, the NRC staff finds the fourth criterion acceptable.

The NRC staff notes that the acceptance criteria described in TR section 6.7 and discussed in this SE section are preliminary in nature as of the date of Release 2 of the UIUC FQM TR, and therefore, may not be all-encompassing or final with respect to the set of criteria that will ultimately be required to fully qualify FCM fuel for use in the UIUC MMR. Specifically, the NRC staff notes that experimental testing, data collection, and analyses described in this FQM have not yet been completed and, therefore, the NRC staff acknowledges that the final set of fuel qualification acceptance criteria that will be used to qualify and license (under future licensing submittal(s)) FCM fuel for use in the UIUC MMR may differ from those postulated and proposed in this FQM TR. Accordingly, the NRC staff imposed TR limitation/condition 3 in this SE.

NUREG-2246 Considerations The NRC staff considered the goals associated with the fuel qualification assessment framework (FQAF) described in NUREG-2246 and how they relate to the FQM described in the TR. The NRC staff notes that the goals described in NUREG-2246 encompass the entirety of a fuel qualification framework and reflect a completed state of design, testing, and analysis that can be used to justify that a fuel design is qualified. The FQM TR subject to this SE provides preliminary information regarding plans for experimental testing and analysis of the FCM fuel design and therefore does not demonstrate comprehensive satisfaction of the NUREG-2246 FQAF goals. Therefore, the NRC staff does not make any specific findings in this SE regarding the FQMs ability to satisfy NUREG 2246. However, the NRC staff provides the following insights regarding the details in the TR as they relate to the goals in NUREG-2246 because the TR references NUREG-2246 and presents initial plans toward FCM fuel qualification in accordance with these goals.

NUREG-2246 goal G1 relates to fuel specifications, which are described, informationally, in TR sections 2 and 3. While the NRC staff did not specifically review these sections in detail, the NRC staff expects based on the information in the TR that the FCM fuel design can reasonably be specified in accordance with goal G1.

NUREG-2246 goal G2 relates to the fuels margin to safety limits, which relies heavily on the determination of a fuel performance envelope based on analysis of postulated accident conditions. As of the date of this SE, postulated accident conditions and a methodology for accident analysis have not been submitted to the NRC, and therefore, no fuel performance

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION envelope or safety limits have been specifically defined. As such, the NRC staff cannot make any determination regarding NUREG-2246 goal G2 in this SE. However, the NRC staff notes that preliminarily predicted UIUC MMR operating and accident conditions are discussed in TR section 2.4, and the NRC staff notes that the testing planned as part of the FQM, in combination with AGR experience, appears to bound the predicted conditions. Therefore, the NRC staff expects that the planned testing envelope will provide data useful to establish a fuel qualification envelope that has a reasonable likelihood of bounding the to-be-determined fuel performance envelope and associated safety limits.

NUREG-2246 goal Evaluation Model (EM) G1 relates to evaluation model capability of modeling the geometry, materials, and physics of the fuel. A summary of planned modeling to evaluate FCM fuel performance is provided in TR sections 4 and 5 for informational purposes, but was not specifically subject to review in this SE. Therefore, the NRC staff makes no specific findings regarding specific fuel performance modeling methods in this SE. However, TR section 6.5 provides the overall fuel performance modeling approach planned to support fuel qualification.

As discussed in the corresponding SE section above, the NRC staff finds the approach reasonable, based on the preliminary information provided. Furthermore, the NRC staff expects that a detailed description of completed testing, modeling, and analysis in future licensing submission(s) could reasonably be used to justify satisfaction of NUREG-2246 goal EM G1.

NUREG-2246 goal EM G2 relates to the evaluation models incorporation of experimental data, quantification of error, and adherence to the test envelope. The TR does not provide specific details regarding how the planned models will incorporate the data that has been, or is planned to be, obtained through testing or from existing references. Therefore, the NRC staff makes no specific determination regarding fulfillment of NUREG-2246 goal EM G2. However, the NRC staff notes that the planned experimental testing and referenced data appears to support the eventual satisfaction of this goal and its subgoals.

NUREG-2246 goal ED G1 pertains to independence of data used to develop and assess the evaluation model. While specific plans regarding which data will be used for each purpose, and how data will be used for each purpose, are not delineated in the TR, the NRC staff notes that the planned testing activities, in combination with previously performed testing, appear to provide for reasonably diverse sets of data that can be expected to support the satisfaction of NUREG-2246 goal ED G1.

NUREG-2246 goal ED G2 pertains to coverage of the fuel performance envelope by the test envelope. The NRC staff notes that the fuel performance envelope will be determined based on safety analyses that have not yet been reviewed by the NRC staff, and that the TR specifies a fuel qualification envelope based on preliminarily predicted UIUC MMR operating and accident conditions. While the NRC staff notes that the planned testing and referenced data appear to reasonably reflect the expected operating and accident conditions, the NRC staff cannot specifically determine whether NUREG-2246 goal ED G2 is met until testing is completed and the fuel performance envelope is specifically defined.

NUREG-2246 goal ED G3 pertains to experimental data quality assurance, use of established experimental techniques, and experimental uncertainty quantification. The NRC staff considered the testing descriptions in the TR and the information UIUC provided during audit discussions and in information provided for audit, as documented in the audit report (Reference 3), related to quality assurance. The NRC staff expects that the planned testing conducted as part of the FQM will be performed under appropriate quality assurance program(s) using established

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION measurement techniques and that experimental uncertainty will be appropriately quantified as necessary. Therefore, the NRC staff expects NUREG-2246 goal ED G3 to reasonably be met during and following completion of the planned experimental testing.

NUREG-2246 goal ED G4 pertains to test specimen fabrication consistency with the planned fuel design, and justification of how any distortions are accounted for. The TR specifies that the test specimens will be fabricated in the same fashion as the as-designed FCM fuel. Additionally, the FCM TRISO particles ((

)). Therefore, the NRC staff expects reasonable consistency between the test specimens and prior data/experience, as well as the fuel manufacturing specifications. The NRC staff notes that distortions are described in the TR, but the distortions appear to be reasonable and will be justified and accounted for through modeling. Therefore, the NRC staff expects NUREG-2246 goal ED G4 to reasonably be met during and following completion of the planned experimental testing and modeling.

LIMITATIONS AND CONDITIONS The NRC staff applies the following limitations and conditions on the NRC staffs acceptance of this TR:

1. Approval of this TR for incorporation by reference to support licensing application(s) for construction and/or operation is limited to the MMR design located at UIUC, as the design is generally described in the subject TR, licensed under the provisions of 10 CFR 50.21(c), as a class 104(c) research reactor. Any departure from the UIUC design or licensing approach described in the TR would require justification in the referencing licensing submission and would be subject to NRC review for acceptability.

2. Applicants referencing this TR to support qualification of FCM fuel for use in an MMR shall ensure that all appropriate degradation phenomena, including vibration and resultant wear or degradation of FCM pellets, are adequately identified and dispositioned as part of the referencing submittal or another applicable licensing submission.

3. The acceptance criteria described in TR section 6.7 are preliminary in nature as of the date of Release 2 of the UIUC FQM TR. The set of acceptance criteria that will ultimately be appropriate to qualify FCM fuel for use in the UIUC MMR may change depending on the outcomes of planned testing activities and safety analyses. Therefore, licensing submittals referencing this TR and seeking qualification of FCM fuel shall ensure that the acceptance criteria relied upon to demonstrate adequate fuel qualification are appropriate and justified in the context of the specific licensing submittal.

CONCLUSION On the bases discussed above, the NRC staff has determined that sections 6.1, 6.2, 6.3, 6.4, 6.5, and 6.7 of the UIUC TR University of Illinois Urbana-Champaign High-Temperature Gas-Cooled Research Reactor: Fuel Qualification Methodology, Release 2, provide an acceptable methodology to support qualification of the described FCM fuel product for use in the UIUC MMR. Specifically, the TR describes planned testing, modeling, and acceptance criteria that will ultimately be relied upon to justify qualification of the fuel form in future licensing submittals(s).

The NRC staff concludes that the described FQM appears reasonable in the context of the applicable regulations and guidance outlined in the Evaluation Criteria section of this SE and

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION can therefore be used to support future FCM fuel qualification licensing submittals for the UIUC MMR research reactor design, subject to the limitations and conditions discussed above.

OFFICIAL USE ONLY PROPRIETARY AND EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY AND EXPORT-CONTROLLED INFORMATION REFERENCES

1. Letter from UIUC to NRC, Submission of the University of Illinois Topical Report, University of Illinois Urbana-Champaign High-Temperature Gas-Cooled Research Reactor: Fuel Qualification Methodology, Release 01, dated February 29, 2024, Document No. IMRDD-MMR-24-01, dated March 11, 2024 (ML24071A237).

2. Letter from UIUC to NRC, Submittal of the University of Illinois Topical Report, University of Illinois Urbana-Champaign High-Temperature Gas-Cooled Research Reactor: Fuel Qualification Methodology, Release 02, dated December 4, 2024, Document No. IMRDD-MMR-24-01, dated December 12, 2024 (ML24347A211).

3. Email from NRC to UIUC, Issuance of Final Audit Report for UIUC Fuel Qualification Topical Report, dated February 25, 2025 (ML25056A213).

4. NANO Nuclear Energy Inc. Press Release, NANO Nuclear Energy Closes Acquisition of Patented Micro Modular Reactor (MMR) and Pylon Transportable Reactor Technologies, dated January 13, 2025. Available at https://ir.nanonuclearenergy.com/news-releases/news-release-details/nano-nuclear-energy-closes-acquisition-patented-micro-modular (accessed January 14, 2025).

5. Letter from EPRI to NRC, Transmittal of Published Topical Report, Uranium Oxycarbide (UCO) Tristructural Isotropic (TRISO) Coated Particle Fuel Performance:

Topical Report EPRI-AR-1(NP)-A, dated November 23, 2020 (ML20336A052).

6. Letter from UIUC to NRC, USNRC Project No. 999902094: UIUC Regulatory Engagement Plan Revision Submission, dated June 26, 2023 (ML23178A259).

7. Letter from UIUC to NRC, Written Communication as Specified by 10 CFR 50.4 Regarding the University of Illinois at Urbana-Champaign - Safety Evaluation for Topical Report Related to Principal Design Criteria (EPID: L-2023-NFN-0013), dated July 25, 2024, dated July 26, 2024 (ML24208A066).

8. NRC Regulatory Guide 1.232, Guidance for Developing Principal Design Criteria for Non-Light-Water Reactors, Revision 0, dated April 2018 (ML17325A611).

9. NUREG-1537, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Part 1, Format and Content, and Part 2, Standard Review Plan and Acceptance Criteria, dated February 1996 (ML042430055 and ML042430048).

10. NUREG-2246, Fuel Qualification for Advanced Reactors, dated March 2022 (ML22063A131).

11. SECY-18-0096, Functional Containment Performance Criteria for Non-Light-Water Reactors, dated September 28, 2018 (ML18114A546).

12. SRM-SECY-18-0096, Staff Requirements - SECY-18-0096 - Functional Containment Performance Criteria for Non-Light-Water-Reactors, dated December 4, 2018 (ML18338A502).

13. NRC Final Rule, Non-Power Production or Utilization Facility License Renewal, dated December 19, 2024 (published in Federal Register December 30, 2024, 89 FR 106234).

Principal Contributor: D. Beacon, NRR Date: April 1, 2025