What category does uranium and thorium that are not fissile fall under?

Uranium and thorium that are not fissile fall under the category of source material. This classification is based on their properties and regulatory definitions. Source materials are defined as materials that contain significant amounts of uranium or thorium but do not have the capability to sustain a nuclear fission chain reaction on their own. Instead, they can be mined and processed for use in various applications, including fuel preparation and radiation sources.

In the context of nuclear regulation, source materials are controlled differently than special nuclear materials, which include fissile materials like enriched uranium and plutonium capable of sustaining a chain reaction. Understanding these categories is fundamental for anyone involved in radiation safety, as it informs appropriate handling, storage, and regulatory compliance protocols.