As DeWitte also noted, when Oklo submits the license application submission to the NRC, it will be for the nation’s first civilian effort geared to a micro-reactor and non-water reactor. Getting the first site use permit from INL and having the opportunity to work with the HALEU is already “a pretty big step to lining up all the key pieces to be able to demonstrate something in the very early 2020s,” he said. //

High-assay, low-enriched uranium (HALEU) is nuclear fuel that is enriched to a higher degree (of between 5% and 20%) in the fissile isotope U-235. In comparison, the world’s current fleet of light water reactors (LWRs) typically uses fuel enriched to less than 5% U-235. As experts note, HALEU promises to provide more power per volume than conventional reactors, and its efficiency allows for smaller plant sizes. It also promises longer core life and a higher burn-up rate of nuclear waste.

According to the Nuclear Energy Institute (NEI), many advanced reactor concepts—including some micro-reactors (many smaller than 10 MW), high temperature gas reactors in the 100-MW to 200-MW range, and salt reactors—may require this type of fuel. HALEU could also be used in existing light water reactors. Though NEI suggests annual commercial requirements for HALEU could soar to a cumulative 185.5 metric tons annually, there is no current supply of HALEU. But because establishing a commercial supply of HALEU would require sufficient demand and a minimum of 7 years to develop fuel cycle infrastructure, the industry trade group has urged the DOE for years to tap into its access of high-enriched uranium and downblend it in the interim to supply HALEU for demonstration purposes. The DOE has heeded these calls and recently ramped up efforts to establish HALEU fuel production capability, noting that in the near future, it will be critical to U.S. leadership, as global competition heats up to design and build small modular reactors as well as larger non-LWR reactors. //

Until a commercial HALEU market is established—which will require that more advanced nuclear reactors clear demonstration and ultimately come online—INL will lead efforts to provide the fuel for research and demonstration. For now, it plans to provide HALEU for Oklo through the recovery and treatment of HEU from used fuel from the 19-MWe EBRII (a demonstration reactor, that operated from 1963 to 1994) that was previously being treated and processed for disposal.

The process to down-blend the HEU to HALEU involves a three-step electrometallurgical treatment. First, the irradiated fuel is prepared and place into a molten salt electrorefiner, which facilitates recovery of uranium metal from fission products and transuranics. Then, the recovered uranium undergoes vacuum distillation to remove electrorefiner salt and is down blended to an enrichment of less than 20% U-235. Finally, the recovered uranium metal is configured to support fuel fabrication by reheating and casting it into low-dose, reduced-size HALEU “regulus.” //

Another interesting aspect about this announcement “is that it shows you can actually reuse [spent nuclear fuel (SNF)],” DeWitte noted. That aspect is important because nuclear waste management in the U.S. has stalled for nearly three decades, owing largely to a political impasse on the disposal of SNF. Today, according to the NEI, more than 84,000 metric tons of SNF is temporarily being stored in pools and casks in 35 states.