Nuclear Fuel Most nuclear reactors use “enriched” uranium, meaning the fuel has a higher concentration of uranium-235 (U-235) isotopes, which are easier to split to produce energy. When it is mined, uranium ore averages less than 1% U-235.9 Milling and enrichment processes crush the ore, use solvents to extract uranium oxide (U3O8, i.e., yellowcake), and chemically convert it to uranium hexafluoride (UF6), which is enriched to increase the U-235 concentration in the fuel. Finally, a fuel fabricator converts UF6 into UO2 powder that is pressed into pellets with 3%-5% U-235 concentrations.10 Uranium can be enriched by gaseous diffusion or gas centrifuge. Both concentrate the slightly lighter U-235 molecules from a gas containing mostly U-238, the former with membrane filters and the latter by spinning. Other technologies are currently in development, with laser enrichment processes closest to commercial viability.11 In 2019, 79 metric tons (mt) of U3O8 were extracted from 6 mines in the U.S.12 The highest grade ore in the U.S. average less than 1% uranium, some Canadian ore is more than 15% uranium.13,14 1% of uranium available at reasonable cost is found in the U.S. The largest deposits are in Australia (28%), Kazakhstan (15%), Canada (9%), and Russia (8%).14 U.S. nuclear plants purchased 22,135 mt of uranium in 2020. Fuel was imported mostly from Canada (22%), Kazakhstan (22%), Russia (15%) and Australia (11%).15 Globally, nuclear power reactors are forecast to require 68,269 mt of uranium in 2021.4