Special Nuclear Material (SNM) is defined in 10 CFR 20.1003 as "(1) Plutonium, uranium-233, uranium enriched in the isotope 233 or in isotope 235, and any other material that the NRC, pursuant to the provisions of section 51 of the AEA, determines to be SNM, but does not include source material; (2) or any material artificially enriched by any of the foregoing but does not include source material."

SNM is important in the fabrication of weapons grade materials and as such has strict licensing and handling controls.