Alert

The NRC is shutdown due to the lapse in appropriations. Exempted activities to maintain critical health and safety activities and progress on critical activities, including activities outlined in Executive Order 14300, as described in the OMB Approved NRC Lapse Plan will continue.

Fissile material

A nuclide that is capable of undergoing fission after capturing low-energy thermal (slow) neutrons. Although sometimes used as a synonym for fissionable material, this term has acquired its more-restrictive interpretation with the limitation that the nuclide must be fissionable by thermal neutrons. With that interpretation, the three primary fissile materials are uranium-233, uranium-235, and plutonium-239. This definition excludes natural uranium and depleted uranium that have not been irradiated, or have only been irradiated in thermal reactors.

Page Last Reviewed/Updated Tuesday, March 09, 2021