Domestic Safeguards and Security Challenges for HALEU
Reduce regulatory uncertainty for prospective licensees of advanced reactors (ARs).
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
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REACTIVITY IMPACT OF REPROCESSING IMPURITIES ON HALEU FEED STOCK
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STOVER, TRACY E.↗
ASSESSMENT OF EXISTING TRANSPORTATION PACKAGES FOR USE WITH LEU+ AND HALEU MATERIAL
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Marshall, William (B.J.)↗
Current Overview of Neutron Moderator Thermal Scattering Kernels for HALEU-Fueled Advanced Reactors
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Al-Qasir, Iyad↗
Environmental Assessment for Use of DOE-Owned High-Assay Low-Enriched Uranium Stored at Idaho National Laboratory
The U.S. Department of Energy (DOE) proposes to make available about 10 Metric Tons (MT) of High-Assay Low-Enriched Uranium (HALEU ) feedstock produced through the electrometallurgical treatment (EMT) process, and other small quantities of HALEU stored at Idaho National Laboratory (INL) for research development & demonstration in support of the commercial nuclear industry and government agencies, including use in advanced reactors. HALEU is a term applied to uranium that is enriched in the uranium-235 (U-235) isotope to a value that is 5% to 20% of the total uranium. Private sector advanced nuclear reactor designs and advanced nuclear fuel designs call for use of HALEU, but currently no commercial facility manufactures HALEU. DOE proposes to expand the fuel fabrication capability at INL to produce HALEU fuel at INL from 10 MT of HALEU feedstock to meet near-term needs. The production requires expansion of the fuel fabrication capability, including the purchase of new equipment and use of facilities at INL’s Materials and Fuels Complex (MFC) and the Idaho Nuclear Technology and Engineering Center (INTEC). DOE has made no decision on the specific use of the fuel. The fuel could be used in advanced reactor design or for the purpose of research and development. DOE would work with other Federal agencies and commercial vendors to determine use of HALEU fuel. Use of this HALEU, including its potential use in a future nuclear reactor, will be analyzed in future National Environmental Policy Act (NEPA) documents by the appropriate agency. The EMT process in operation at the INL converts sodium-bonded spent nuclear fuel into waste forms suitable for disposal as high-level waste and a HALEU product that is unsuitable for diversion to nuclear weapons but could be either reused in fuel or disposed of as waste. The Final Environmental Impact Statement for the Treatment and Management of Sodium-Bonded Spent Nuclear Fuel, DOE/EIS-0306, DOE 2000) discussed the EMT process, but did not make a decision on the disposition or use of the HALEU product from the EMT process. This Environmental Assessment (EA) addresses the HALEU product as HALEU feedstock in production of HALEU fuel.
99 GENERAL AND MISCELLANEOUS↗
A High-Assay Low-Enriched Uranium Fuel Transportation Concept
The uranium 235U enrichment commonly used in fuel production for U.S. light water nuclear reactors typically does not exceed 5 wt%. In contrast, many of the currently investigated advanced reactor concepts demand fuel with higher enrichments. This includes high-assay low-enriched uranium (HALEU), characterized by a 235U enrichment of 5 to 20 wt%. The necessity of HALEU transportation in the fuel production cycle leads to new challenges caused by various technical and regulatory hurdles. Current U.S. Nuclear Regulatory Commission–approved transportation package designs for UF6 with enrichments above 5 wt% provide relatively small payloads [=116 kg (250 lb)]. Furthermore, in accordance with 10 CFR 71.55, package design activities for fissile material enriched above 5 wt% need to consider water infiltration in the containment as part of the criticality safety evaluations. This study presents a transportation package concept for HALEU advanced nuclear reactor fuel with a significantly higher payload of up to 376 kg (830 lb) of fissile material per package and up to 1881 kg (4149 lb) of HALEU per legal weight truck. The anticipated chemical form of the transported material is UO2 downblended from available highly enriched uranium. The concept utilizes a combination of existing transportation packaging, 18 inner canisters, and a novel basket design that includes a borated aluminum flux trap. Criticality and shielding evaluations; fundamental structural, confinement, and thermal assessments; and studies on package operations are presented. The results of this study build significant confidence in the technical feasibility of a high-capacity HALEU transportation package concept while demonstrating the concept’s potential to meet U.S. regulatory requirements.
Eidelpes, Elmar↗
A Proposed Path Forward for Transportation of High-Assay Low-Enriched Uranium
Many of the advanced reactors that are being designed will use high-assay low-enriched uranium (HALEU) as the reactor fuel. HALEU is fuel that is enriched between 5% – 20% uranium-235. With the change to higher enriched material, the industry will have new challenges with the development and regulatory approval of enrichment and fuel fabrication facilities and suitable transportation packages to support the economic use of HALEU materials. One area of concern relates to ensure sub-criticality of the material during transportation as identified by the Nuclear Energy Institute (NEI). To evaluate the relevant work, experts, and industry perspectives on HALEU, a workshop was organized to share relevant experience and insights into HALEU transportation, handling, and management. At the August 30 and 31, 2018 workshop, NEI and industry provided the following recommendations to DOE and the national lab complex. 1. DOE and the lab complex should communicate and educate the Nuclear Regulatory Commission (NRC) on criticality issues related to HALEU. 2. Idaho National Laboratory (INL) should support work needed to certify package design for the transportation of HALEU. a. Suggest amending the Certificate of Compliance of an existing package used for the shipment of commercial quantities. b. Suggest DOE provide funding to package designer(s) for analysis and engineering work for a package to be submitted to NRC for approval. 3. INL should provide specific, or a range, of the expected impurities that will be present in recycled naval fuel. 4. In the longer term, DOE and the lab complex should increase the availability of criticality benchmark data to further reduce conservatism in package design. In addition, a couple key takeaways were identified, including: 1. Although the labs can provide additional criticality experiments, industry has enough data to license facilities, overpacks, and cylinders. Validation from additional critical experiments to establish less uncertainty in the benchmarks will be helpful. 2. A collective effort from industry is needed to express consistency on how much information exists or is needed related to criticality. Based on interactions with industry, DOE, and national laboratories, it appears that large-volume transportation of fresh HALEU appears feasible from a criticality perspective. Specifically, an initial review of applicable criticality benchmark experiments identified numerous applicable experiments. However, a more thorough review of a realistic transportation package design is suggested. Therefore, the following next steps are proposed: 1. Evaluate a large volume package with uranium dioxide enriched to 20%. Specifically, the GNF-A NPC package was proposed as a potentially viable option. 2. Based on the results of (1), determine if additional package designs and fuel material should be evaluated. 3. Based on the results of (1), determine if additional criticality experiments would be beneficial to improve the margins for criticality due to uncertainties. 4. Determine DOE transportation needs (packages sizes, shielding requirements, handling/operational requirements, and timing of availability) related to HALEU. 5. Continue to interface with NEI and interested industry companies to determine the appropriate time to engage the NRC.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Comparison of Nuclear Thermal Propulsion Reactor Cores Using Different Fuel Forms, Neutron Spectra, and Uranium Enrichments
A comparison of 300 MWt HEU and HALEU NTP cores using different fuel forms is presented to demonstrate trends and potentially inform fuel development. Compared to HEU, HALEU cores require additional in-core moderation. Beryllium was chosen as the reference in-core moderator material; metal hydrides may also be considered. Typical NTP fuel forms such as carbide and carbonitride solid solutions, carbide-graphite composites, CERMETs and CERCERs were considered together with less typical fuel forms such as UC and U metal. Be-moderated HALEU cores are heavier than HEU cores (1.9-2.7 and 0.9-2.0 metric tons, respectively). Furthermore, HALEU loading is very sensitive to the amount of in-core moderation which translates into tight fabrication tolerances. HALEU cores requires more reactivity control mechanisms than HEU cores to compensate for temperature feed-back. Using enrichments only slightly above HALEU (e.g., 25%) may provide a compromise between the administrative preference for using HALEU and the engineering preference for simplifying the reactor systems by, for example, not using in-core moderators.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
A Review of Candidates for a Validation Data Set for High-Assay Low-Enrichment Uranium Fuels
Many advanced reactor concept designs rely on high-assay low-enriched uranium (HALEU) fuel, enriched up to approximately 19.75% 235 U by weight. Efforts are underway by the US government to increase HALEU production in the United States to meet anticipated needs. However, very few data exist for validation of computational models that include HALEU, beyond a few fresh fuel benchmark specifications in the International Reactor Physics Experiment Evaluation Project. Nevertheless, there are other data with potential value available for developing into quality benchmarks for use in data- and software-validation efforts. This paper reviews the available evaluated HALEU fuel benchmarks and some of the potentially relevant benchmarks for fresh highly enriched uranium. It then introduces experimental data for HALEU fuel irradiated at Idaho National Laboratory, from relatively recent irradiation programs at the Advanced Test Reactor. Such data should be evaluated and, if valuable, collected into detailed benchmark specifications to meet the needs of HALEU-based reactor designers.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
High Assay Low Enriched Uranium - A material in demand and the supply efforts underway
The presentation briefly describes the HALEU demand, sources of supply, & work underway @ INL to meet some of the demand. It highlights HALEU recovery from EBR-II, process enhancements including recasting via multi tier drip cast crucible method to produce reduced dose and reduced physical size uranium ingots referred to as regulus. Includes additional polishing, to improve applicability to meeting HALEU needs and briefly touches on innovative recycling concepts under development (i.e. Zircex). HALEU enables reactors of reduced size, provides for increased fuel efficiency and longer core life, all of which contribute to less waste generation. Supplying HALEU from recycled material has the potential for further reductions in waste generation through via reductions in SNF disposition.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
The HTR-Proteus Benchmark: Analysis and Use as a Verification and Validation Case
This presentation outlines the evaluation and application of the HTR-Proteus benchmark as a verification and validation (V&V) case for advanced reactor modeling tools. The work supports the U.S. Department of Energy’s HALEU Availability Program (HAP) and the joint DOE/NRC DNCSH project, which aims to reduce criticality safety uncertainties in commercial-scale HALEU fuel cycle and transportation systems. The HTR-Proteus experiments, conducted at the Paul Scherrer Institute, provide high-fidelity data for TRISO-fueled, graphite-moderated pebble bed reactors with high neutron leakage—conditions relevant to HALEU transport scenarios. This study focuses on Cores 4.2 and 4.3 of the HTR-Proteus benchmark, analyzing key sources of uncertainty including pebble packing, TRISO particle positioning, and core height. Using Project Chrono for realistic pebble geometries and Serpent, SHIFT, and MCNP for neutronics simulations, the study quantifies the impact of these uncertainties on the effective multiplication factor (keff). Results show that a sample size of 110 pebble configurations is sufficient to converge keff, with ±30 pcm uncertainty due to packing randomness. TRISO positioning and core height variations also significantly influence keff, highlighting the importance of detailed modeling in V&V efforts. The benchmark serves as a valuable test case for validating the Griffin reactor physics code and improving confidence in HALEU system simulations.
73 - NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Analysis of the 30B UF 6 Container for Use with Increased Enrichment
Commercial light-water reactor (LWR) operators and fuel vendors are pursuing advancements in fuel and reactor design that include increasing 235 U enrichment from low enrichment (<5 wt.% 235 U) to low-enriched uranium+ (LEU+) (10 wt.% > 235 U > 5 wt.%) and high-assay low-enriched uranium (HALEU) (20 wt.% > 235 U > 10 wt.%). These advancements will necessitate the ability to transport LEU+ and HALEU fuel materials. Assessment of Existing Transportation Packages for Use with HALEU(ORNL/TM-2020/1725) assesses the potential to use currently licensed transportation packages for the transportation of HALEU by evaluating a representative package for each uranium fuel form category (for example, oxide and/or metal in fuel assemblies, fuel pins, powder, pellets, and uranium hexafluoride [UF 6 ].) This report expands on the UF 6 analysis.
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Hypothetical Sodium-Cooled Fast Reactor Fuel Transport Using the Existing ES-3100
Increased industry interest in increased enrichment fuels is associated with a heightened interest in high-assay low-enriched uranium (HALEU)-based systems, as novel designs look to take root as alternatives to traditional LWRs. Increased enrichment with novel reactors can produce designs that, in theory and in some historical experience, are capable of operation at increased burnups, higher energy density, and other unique features compared to conventional LWRs. As part of a Department of Energy (DOE) initiative to increase the availability of HALEU fuel, initial funding sourced from the Inflation Reduction Act of 2022 (H.R. 5376) [1] resulted in the DOE/NRC Criticality Safety for Commercial-Scale HALEU Fuel Cycle and Transportation (DNCSH) project, part of the HALEU Availability Program. The project aims to support the Nuclear Regulatory Commission (NRC) in providing data for criticality safety validation of reactor designs that, while perhaps demonstrated in limited capacity, represent more exotic systems than those that regulators are accustomed to reviewing.
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Technology Development of a High-Capacity High-Assay Low Enriched Uranium Transportation Concept
This paper discusses the technology development (TD) efforts that led to the development of a High-Capacity High-Assay Low Enriched Uranium Transportation (HALEU) transportation concept. In 2018, the Department of Energy (DOE) Office of Nuclear Technology and Research Development tasked Idaho National Laboratory (INL) to investigate strategies to transport large quantities of HALEU. To complete this task, INL collaborated with Pacific Northwest National Laboratory and Oak Ridge National Laboratory. The project was completed in 2020, and one of the project outcomes was a transportation concept that consisting of five individual Type B packages transported on a single legal-weight truck (LWT). The total payload capacity of this concept is 1,881 kg (4,149 lb) of HALEU in the form of uranium dioxide (UO2) powder. The concept utilizes an existing Type B packaging design carrying a novel fuel basket design with an incorporated flux trap. The basket can be loaded with 18 individual fuel canisters. The research collaboration investigated the U.S. certification potential of this concept. This part of the project included evaluations of criticality safety, radiological safety, thermal safety, structural integrity, and confinement under hypothetical accident scenarios of transport. The results of these evaluations demonstrated a promising potential for U.S. certification of this concept. Eventually, the described efforts led to the pursuance and issuance of a U.S. patent, thus, protecting the associated intellectual property (IP). Current short-term goals include making this IP available to private industry partners for licensing, directly supporting DOE’s objectives of accelerating commercialization of national laboratory-generated IP. If additional funding becomes available, long-term research goals could include exploring the feasibility of transporting other uranium chemical forms (e.g., UF4) with this concept, or refining operational procedures to load or unload the packagings.
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Preliminary conceptual design of fast neutron spectrum nuclear thermal rocket cores using monolithic uranium nitride fuel
This paper presents a few nuclear thermal rocket (NTR) reactor core preliminary conceptual designs based on the use of monolithic uranium nitride (UN) fuel plates or pins clad with tungsten (W), alloyed or unalloyed as needed. High-assay low-enriched uranium (HALEU) as well as high-enriched uranium (HEU) are considered. Nominal core thermal powers are between 300 and 1100 MW corresponding to thrusts between 66 kN and 240 kN. The estimated thrust-to-reactor-weight ratios (T/WRx) achievable with the HEU plate and pin configurations are between 3.8 and 10.9. The T/WRx achievable with the HALEU plate and pin configurations are lower, 1.9–4.0, than those achievable with HEU. It is noteworthy that even a relatively modest increase in fuel enrichment above the HALEU limit enables a significant increase in T/WRx. It must be emphasized that these results do not yet account for uncertainties and that the appropriateness of the assumed fuel thermal design limits for normal operation (i.e., peak centerline temperature of 3100 K) will need to be confirmed. Finally, just like for the other UN-based fuels currently considered for NTR applications (i.e., CERMET and CERCER), the proposed UN fuel systems need significant testing in prototypic conditions to confirm the appropriate performance for safe NTR applications. However, the monolithic fuel systems may have, overall, a higher technology readiness level (TRL), and, consequently, shorter fuel development and validation time may result.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Depletion benchmark for a high-assay low-enriched uranium fuel experiment in the advanced test reactor
Reactor physics depletion benchmarks for high-assay low-enriched uranium (HALEU) fuel are limited in number. In particular, there is limited data for HALEU benchmarks for U-10Mo (uranium-10% molybdenum) plate fuel that is being developed for use in the United States’ high performance research reactors including the Advanced Test Reactor (ATR), Advanced Test Reactor Critical Facility (ATR-C), High Flux Isotope Reactor (HFIR), Massachusetts Institute of Technology Reactor (MITR), University of Missouri Research Reactor (MURR), National Bureau of Standards Reactor (NBSR). These six reactors currently operate with highly enriched uranium dispersed fuel in an aluminum matrix. In support of conversion to a HALEU fuel, qualification of U-10Mo formed into a monolithic foil is being performed. Fuel qualification involves irradiating fuel specimens in the ATR. The irradiation tests provide an opportunity to benchmark depletion capabilities of reactor physics codes in support of the ATR operation, as well as develop benchmarks that can be used by other institutions to benchmark other reactor physics codes. This paper documents the development of a benchmark model of the irradiation of the ATR Full-size plate In center flux trap Position 7 (AFIP-7) experiment using the depletion codes MC21 and Advanced Dimensional Depletion for Engineering of Reactors (ADDER).
Nielsen, Joseph W. [Idaho National Laboratory (INL↗
Design of a High-Assay Low-Enriched Uranium Tri-Structural Isotropic Critical Experiment for Advanced Reactor Validation
High-assay low-enriched uranium (HALEU) fuel is a key component of many small modular reactor designs. Critical experiments are an important way to understand the neutronic performance of systems by obtaining nuclear data validations through measurements. Data reduce uncertainty and risk by showing that systems respond as predicted to changes such as temperature, subsequently advancing the overall technology readiness level of the materials within. Numerous critical experiments have been performed at the National Criticality Experiments Research Center (NCERC) operated by Los Alamos National Laboratory at the Nevada National Security Site since it became operational in 2011. However, the first experiment with HALEU fuel did not occur until 2024. Through extensive engineering, the experiment described in this paper was successfully designed and executed for the Comet vertical lift assembly at NCERC to perform measurements with HALEU tri-structural isotropic fuel that will assist in validation of nuclear data and computational modeling of small modular reactors for years to come.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
An Assessment of Applying Pyroprocessing Technology to Advanced Pebble-Type Fuels
With an expected increased demand for high-assay low enriched uranium (HALEU) to supply advanced reactors, the possibility of recovering actinides from various used nuclear fuels (UNF) is being reassessed. Pebble-type fuels such as tristructural isotropic (TRISO) fuel are intended to be directly disposed after use, but the HALEU remaining in each pebble is a resource with increasing value. An economically feasible recovery strategy would maximize the amount of HALEU recovered for reuse in new fuel without increasing the waste volume relative to the direct disposal of used TRISO fuel. We are evaluating the technical feasibility of recycling TRISO or pebble fuels to recover actinides for reuse as new fuel for advanced reactors by using pyrochemical methods.
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