Widespread use of high-assay low-enriched uranium raises significant nuclear security concerns

In a Policy Forum, R. Scott Kemp and colleagues argue that promoting new nuclear reactor technologies using high-assay low-enriched uranium (HALEU) threatens the international system of controls that has prevented nuclear weapons proliferation for over 30 years. “Governments and others promoting the use of HALEU have not carefully considered the potential proliferation and terrorism risks that the wide adoption of this fuel creates,” write Kemp et al. The authors warn that if HALEU becomes a standard reactor fuel without strict regulations, nations could obtain and process weapons-usable HALEU, driving nuclear proliferation with little deterrence. Commercial reactor fuels typically have 3 to 5% ²³⁵U, which is insufficient for explosive chain reactions, thereby preventing weaponization. While enrichments above 6% can sustain fast chain reactions, the required mass for a weapon is impractical without advanced enrichment capabilities, limiting this to a few countries. HALEU, containing 10 to 20% ²³⁵U, is necessary for many modern reactors, including microsized designs, which use 19.75% HALEU to avoid the security restrictions of highly enriched uranium (HEU). However, HALEU’s high enrichment levels pose significant security risks, as a single HALEU-fueled reactor could contain enough material for a nuclear weapon. Kemp and colleagues highlight that the U.S. and other countries are subsidizing HALEU reactor development and fuel production without adequately considering the risks. They urge U.S. lawmakers to commission a new review of HALEU’s proliferation and security risks through the Department of Energy’s Nuclear Security Administration, emphasizing the need for a new and lower enrichment limit for weapons-usable uranium. “A key outcome of this study should be to set a new, technically justified, and lower enrichment limit for weapons-usable uranium,” write the authors. “An unfettered HALEU policy leaves no margin of safety.”