With the world on the cusp of a revolutionary transition to new high-efficiency, low-carbon technologies for power and propulsion, the attraction of nuclear energy as a source of such fuels is irresistible. But a pioneering study of fuel enrichment reveals the true proliferation risk around the High-assay Low-enriched Uranium (HALEU) fuel touted as the next-generation nuclear power and space-powering fuel.


The Awakening of a Dormant Risk

HALEU was sold as an ideal nuclear fuel for next-generation nuclear reactors such as the sodium-cooled TerraPower or the space-based system DRACO, short for Demonstration Rocket for Agile Cislunar Operations. The higher rates of efficiency and the supposedly weapons-grade-sub-threshold level of enrichment cemented it a starring role in massive public funding by the US and the UK, and a long era of relaxed security at facilities that used HALEU.

Still, it is a new piece of evidence that undermines the narrative about legal safety profiles normally told about HALEU by its proponents. In an article for Science, researchers have now argued that the 300 kg of HALEU planned to be fed into applications such as DRACO is ‘well-suited to make a nuclear weapon’, as Edwin Lyman, director of Nuclear Power Safety at the Union of Concerned Scientists and one of the paper’s lead authors, told The Guardian. The exact judgement depends somewhat on assumptions about the engineering capabilities of nation-states, including jihadi factions. But it pushes to the forefront a whole new set of international security questions.

Recalling Forgotten Dangers

At the heart of the problem is the isotopic composition of uranium itself. Mined uranium is made up of two major isotopes, uranium-238 and uranium-235, and the latter is the key ingredient in both reactors and weapons. Enrichment increases the concentration of uranium-235. Low-enriched uranium (LEU), with uranium-235 concentrations below 10 per cent, is widely used in reactors today. The higher concentrations are of greater concern. The growth industry of the moment is in a fuel component known as HALEU, enriched between 10 and 20 per cent.

The 20 per cent is effectively a boundary that separates low-enriched uranium from highly enriched uranium, which is clearly viable for weapons use. However, it is now becoming clear that this distinction is unlikely to be a meaningful one for proliferation risk with HALEU. ‘The reality is that threshold is not really a limit of weapons usability,’ Lyman explains, pointing to a 1954 Los Alamos National Laboratory study that classified HALEU as ‘weapons significant’ if ‘sufficient quantity is present’, a finding that casts the old sense of assurance over HALEU quality and quantity in a different light.


The Tipping Point of Nuclear Safety

While this discussion about HALEU’s risk may be technical, it highlights the urgent need to revise security protocols and international agreements on nuclear material. That is because the discovery that seemingly innocuous quantities of HALEU could be converted to a weapons-grade uranium fuel spurs substantial proliferation risks. That revision of policy and perception about nuclear fuel use is especially important as countries move faster to develop new, more efficient nuclear technologies for the energy sector and for exploration missions in space.

Striking a Balance: Progress versus Proliferation

At this moment in the history of the nuclear age, as the risk of innovation and proliferation become increasingly intertwined with one another, the path to the future must be balanced. Nuclear power’s new promise for clean energy and iconic feats of human ingenuity such as space exploration must be balanced against the imperatives of global security and the accompanying commitments to non-proliferation. Safeguards must improve, international partnerships must increase in transparency, and risk calculations must remain an integral part of every step along the way.

An Ongoing Dialogue for a Secure Future

These concerns are troubling in their own right but they also represent an opportunity for countries and people, scientists and policymakers to talk more openly and proactively about nuclear material security. They provide a reason to re-examine the standards and expectations for nuclear material security and consider how they might evolve alongside the evolution of nuclear technology. Just as nuclear technology is evolving, and nuclear fuels are becoming hotter and moving faster, so too must our vigilance and nuclear security efforts.


This theme of ‘sense’, our ability to access and account for the full range of nuclear proliferation challenges, has been pervasive in our exchanges about HALEU and its attendant risks. In embracing a comprehensive ‘sense’ about nuclear issues, encompassing technical, political and normative dimensions alike, humans propel the establishment of wise choices and robust security architectures that will contain the risks of nuclear proliferation. Through a collective ‘sense’ of responsibility and caution, humanity can fulfil its dual goals of nuclear progress and peaceful use on the one hand, and nuclear non-proliferation and security on the other.

Jun 11, 2024
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