29 August 2024

High Assay Low-Enriched Uranium a major proliferation threat

Nuclear Monitor #918

Jan van Evert, reporter Nuclear Monitor

An alarming article in the journal Science warns that high assay low-enriched uranium or HALEU produced with U.S. federal subsidies for small nuclear power reactors can be used to make nuclear weapons. “Were HALEU to become a standard reactor fuel without appropriate restrictions determined by an interagency security review, other countries would be able to obtain, produce, and process weapons-usable HALEU with impunity, eliminating the sharp distinction between peaceful and nonpeaceful nuclear programs”, according to five of the world’s leading academic and independent proliferation experts.

HALEU is enriched to between ten and twenty percent uranium-235, which is much higher than the uranium used for commercial reactors which is enriched to less than five percent. For technical reasons, many of the nuclear reactor designs that engineers want to build today would use HALEU. Since HALEU is below the twenty percent enrichment limit that defines highly-enriched uranium (HEU), which is directly usable in nuclear weapons, development of these reactors has not raised significant proliferation concerns. However, after reviewing information in the open literature to analyse the quantities and enrichment levels of HALEU that the new reactors would use, the authors of the Science paper concluded that HALEU above about twelve percent uranium-235 could be used to make practical weapons with yields comparable to the bombs that destroyed Hiroshima and Nagasaki. The researchers suggest that “a reasonable balance of the risks and benefits would be struck if enrichments for power reactor fuels were restricted to less than 10 to 12% uranium-235”, which would allow many reactor designs to move forward with only modest economic consequences. The experts recommend that if higher enrichments continue to be used, the security standards for protecting HALEU from theft be strengthened to the levels that apply for weapon-usable materials.