Fissile Material

Material capable of undergoing fission by interaction with slow neutrons (uranium-233, uranium-235, plutonium-239, and plutonium-241).

Uranium-233, uranium-235, plutonium-239, and plutonium-241, or any combination of these radionuclides. Fissile material means the fissile nuclides themselves, not material containing fissile nuclides. Unirradiated natural uranium and depleted uranium and natural uranium or depleted uranium that has been irradiated in thermal reactors only, are not included in this definition. Certain exclusions from fissile material controls are provided in 10 CFR 71.15.

Material of plutonium239, plutonium241, uranium233, uranium235, or any combination of these radionuclides. This term does not apply to material containing
fissile nuclides, un-irradiated natural uranium and un-irradiated depleted uranium, or to natural uranium or depleted uranium that has been irradiated in thermal reactor only.