"Natural uranium" refers to uranium that is found in nature without any additional processing or enrichment. It is the uranium as it exists in its raw state. Full definition
The colorless, odorless, radioactive gas, which forms as a by - product of natural uranium decay in rocks, builds up in homes, causing lung cancer. (discovermagazine.com)
To produce this fuel, companies enrich the concentration of U235 in natural uranium hexafluoride (UF6) to the appropriate level and sell the fuel to utility customers. (centrusenergy.com)
Reactors not using natural uranium fuel require uranium enrichment,... (aaas.org)