The fast-evolving energy landscape worldwide and the ever-increasing energy demands has made it necessary even for the nuclear world to explore newer, better alternatives that offer improved fuel efficiency, longer core lives and significantly decreased waste production relative to the current operating nuclear reactor fleets deployed. This is not just applicable to reactor technologies, but also to the choice of nuclear fuel. The traditional nuclear reactor uses enriched uranium as fuel, which is defined as “uranium having a higher abundance of the fissile isotope U-235 than natural uranium.” Natural uranium comprises 0.7% of the U-235 isotope by mass, with the remaining 99.3% composed of U-238. The enriched Uranium fuel used by traditional reactors contains between 3-5% of U-235. A new category of fuel is currently under development, named High-Assay Low-Enriched Uranium (HALEU), which  is defined as uranium enriched to greater than 5% and less than 20% of the U-235 isotope.

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The higher fissile isotope content gives HALEU several advantages over the conventional nuclear fuel, such as increased energy density, improved safety margins for operation, higher operational power flexibility of reactors and reduced nuclear waste. These factors make HALEU the perfect fuel candidate for the current emerging Small Modular Reactor (SMR) concepts. These innovative SMR concepts are capable of operating under conditions that are different than those of LWR fuels, including variations in neutron energy spectra, fuel temperatures, cladding and coolant, and potentially interacting with other adjacent materials. They can deliver elevated temperatures and are primarily based on advanced Generation IV reactor technologies, many of which are specifically designed to use HALEU fuels. HALEU can enable higher burn-up, which leads to more efficient fuel utilization. This allows for longer cycle lengths (the time intervals at which the reactor is shut down for fuel shuffling, fresh fuel loading and maintenance). This has a direct positive impact economically, as one can generate more energy with the same amount of fuel. HALEU fuel also enables reactors to be operated with greater safety margins, due to better heat management and lower reactivity in transient situations. This reduces the risk of nuclear accidents. They can significantly reduce the volume of nuclear waste produced, due to more efficient use of uranium. This reduction in nuclear waste makes it easier to store and manage over the long term. Furthermore, HALEU can play an important role to transition from open fuel cycle to fully closed cycles that implement recycling and reusing of spent fuel. However, the characterization of the associated waste streams needs to be properly studied for a meaningful comparison to be possible.

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Current High-Assay Low-Enriched Uranium (HALEU) projects in the world

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According to the International Atomic Energy Agency (IAEA), several nuclear reactor projects using HALEU technology are currently under development worldwide. The overall investment in HALEU technology has significantly increased, thus reflecting growing interest in this technology. Some of the most advanced projects include :

• The Molten Salt Reactor (MSR) developed by Terrestrial Energy in Canada (to be operational by end of 2020s).

• PRISM sodium-cooled fast reactor (NFR) developed by GE-Hitachi in the USA (construction to begin in 2020s).

• EDF’s high-temperature reactor (HTR) project in France (scheduled for commissioning in 2030).

• China’s supercritical water reactor (SCWR) using HALEU fuel which is currently under development (commissioning date planned in the 2030s).

 

Challenges

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Guaranteed that HALEU fuel provides for a great alternative to the conventional nuclear fuels that have been used these many years, especially considering the Gen IV reactor technologies and SMR concepts, which have been developed and proposed, keeping in mind the capabilities of HALEU fuel. However, everything has a price. The use of HALEU comes with significant implications and challenges in various aspects. To begin with, there are challenges on the nuclear fuel cycle’s front end, where there is need for thorough studies and development of specific measures to account for the criticality considerations that concern the production, handling and storage of an enriched uranium product above 5%. Furthermore, there is need for development of adequate transportation solutions for HALEU fuels as the industry canisters commonly used for UF6 transport need to be adapted and requalified for such higher enrichment level.

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Furthermore, there exist challenges even at the back-end fuel cycle. Irrespective of their operating capacity and size, the innovative features of the HALEU-fuelled advanced reactors directly impact the waste streams and spent fuel characteristics of these systems. While these features offer many benefits in terms of fuel economy, economics and safety behaviors, their effect on the volume and type of radioactive waste produced cannot be disregarded. There is little to no information in this regard and also on how the waste interacts with the reactor containment and structural material that is being used. Thus, characterization of spent fuel chemical properties will also be necessary to identify possible materials issues regarding the stability and durability of waste. While in some cases advanced technologies may exhibit improvements in these areas (example: better containment of radionuclides within the multiple barrier layers in a TRISO fuel pebble), these benefits need to be confirmed experimentally before being incorporated into a waste management strategy.

The spent fuel handling and processing facilities currently in place were designed to handle fuel with an initial enrichment level below 5%. Despite existing safety and design margins, managing spent fuel with an initial enrichment exceeding 5% requires additional measures to support the safety assessments for the spent fuel. Moreover, it is compulsory that these assessments and the spent fuel handling process is in compliance with the authoritative IAEA Safety Standards, irrespective of the uranium enrichment levels. This implies that there is an immediate and international need for sound experimental data in the field of nuclear criticality safety, fuel performance and reactor system analysis that can accurately represent the HALEU-based systems in all their diversity. These data will serve as building blocks for the new simulation codes and methods that are needed to validate the HALEU-based systems to support their future design and licensing.

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In conclusion, HALEU presents a promising alternative to conventional nuclear fuels, offering enhanced efficiency, safety, and reduced waste—particularly suited for next-generation reactors like SMRs and Generation IV designs. However, its successful deployment hinges on overcoming significant technical and regulatory challenges related to fuel handling, transport, waste characterization, and safety compliance. Addressing these issues through focused research, updated infrastructure, and robust international standards is essential to fully realize HALEU’s potential in the future nuclear energy landscape.

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