Nuclear energy’s future hinges on advanced nuclear reactor fuel sources. This has led to a surge of interest from governments, energy companies, and nuclear engineers in securing HALEU: high-assay low-enriched uranium.
Previously, HALEU was a specialized material, primarily utilized in nuclear reactors for scientific research. However, several companies in the United States are now proposing innovative nuclear reactors designed to generate electricity more efficiently and safely. These advanced reactors, many of which will operate on HALEU, are crucial to the United States government’s strategy for meeting future clean energy needs.
Recently, TerraPower, a company founded by Bill Gates, initiated the construction of one of the first of these new HALEU-fueled reactors. Despite this progress, the United States currently lacks the production capacity to supply the necessary amounts of HALEU for these advanced nuclear reactors. To address this, the U.S. Department of Energy is not only funding the development of these cutting-edge reactors but is also working to ensure a sufficient supply of HALEU fuel.
However, some scientists have expressed concerns about the increased use of HALEU. They argue that HALEU could potentially be used to create a nuclear weapon, a risk not associated with existing reactor-grade fuel. The promise of HALEU in enhancing power generation, coupled with the potential security risks, raises important questions. Here are four key points to consider about HALEU.
What is HALEU?
HALEU stands out from standard nuclear reactor fuel due to its higher concentration of uranium-235, a crucial isotope. Uranium-235 is fissile, meaning its nucleus can split upon absorbing a low-energy neutron, releasing significant energy.
In its natural state, uranium is composed of only about 0.7 percent uranium-235, with the majority being uranium-238. For uranium to be suitable for use in a nuclear reactor, it must undergo enrichment to increase the uranium-235 content. Standard reactor-grade uranium typically contains about 3 to 5 percent uranium-235. When uranium is enriched to 20 percent or higher, it is classified as highly enriched uranium, which has the capability to be used in nuclear weapons, unlike reactor-grade uranium.
HALEU is enriched to levels between 5 to 20 percent uranium-235. This intermediate enrichment level allows HALEU to be utilized in ways that standard reactor-grade uranium cannot. However, despite its enhanced capabilities, the use of HALEU is not as stringently regulated as highly enriched uranium in the United States and other countries.
Growing Popularity of HALEU
The excitement surrounding HALEU is driven by the growing interest in advanced nuclear reactors. These advanced nuclear reactors encompass a diverse array of designs that deviate from the conventional reactor models in the United States.
They are often smaller and may use alternative cooling substances like liquid sodium instead of water. Importantly, many of these advanced reactors require HALEU, typically enriched to just under 20 percent.
Using HALEU allows for the design of more compact and energy-efficient reactor cores, which helps reduce construction costs.
Additionally, HALEU can be utilized in various forms that differ from the traditional uranium dioxide fuel used in current nuclear reactors. Some designs employ metallic fuel or TRISO, poppy seed-sized coated pellets of uranium.
These alternative fuel forms, combined with innovative reactor designs, can enhance safety by eliminating the need for human intervention to shut down the reactor safely.
While most advanced nuclear reactors in the United States are still in the conceptual stage, the Department of Energy is supporting two advanced reactor demonstration projects: TerraPower’s Natrium Nuclear Reactor in Kemmerer, Wyoming, and X-energy’s Xe-100 Nuclear Reactor in Seadrift, Texas. Both of these projects rely on HALEU.
Origin of HALEU
The United States currently lacks an established, large-scale commercial supplier of HALEU. Regardless of the advancements in nuclear reactors, they are ineffective without the necessary fuel. While Russia produces HALEU, a U.S. law enacted in May restricts most imports of uranium from Russia.
To secure fuel for advanced nuclear reactor projects, the U.S. government has been backing initiatives to produce HALEU domestically. Centrus Energy Corp., a company based in Maryland, has started producing HALEU through a demonstration project in collaboration with the Department of Energy (DOE) at an enrichment facility in Piketon, Ohio.
(Credit: Centrus Energy Corporation)
While commercial enrichment operations ramp up, an interim method involves blending preexisting highly enriched uranium with other uranium to reduce its enrichment level. Idaho National Laboratory is currently employing this technique using spent fuel from a decommissioned nuclear reactor, aiming to produce 10 metric tons of HALEU. This effort is intended to ensure a sufficient supply of HALEU to support the initial demonstration of advanced nuclear reactors. The DOE estimates that more than 40 metric tons of HALEU will be required by 2030, with increasing amounts needed annually thereafter. Other nations, such as the United Kingdom, are also making plans to produce HALEU.
The worries around HALEU
HALEU has not traditionally been viewed as a viable material for weapons. However, as HALEU becomes more likely to see widespread use, scientists are re-evaluating its potential. A nuclear weapon made from HALEU with 19.75 percent enrichment could produce a yield comparable to the bomb dropped on Hiroshima in 1945, according to physicist Edwin Lyman and his colleagues.
Although HALEU is more challenging to work with than highly enriched uranium, significantly larger amounts would be required to create a weapon. Nonetheless, the quantity found in a single nuclear reactor could suffice. Lyman, from the Union of Concerned Scientists, points out that a reactor needing 300 or 400 kilograms of HALEU could potentially provide enough material for a crude nuclear weapon with a substantial yield.
The increasing use of HALEU raises concerns about its potential misuse. Countries without nuclear weapons might conceal HALEU to develop them, or terrorist groups could steal the material for malicious purposes. To mitigate this risk, Lyman and his colleagues advocate for stricter security standards for HALEU.
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