Radioactive materials that are capable of undergoing or sustaining nuclear fission and thus require controls to assure nuclear criticality [see criticality definition] safety during transport Fissile materials [see fissile materials definition] include plutonium-238, plutonium-239, plutonium-241, uranium-233, and uranium-235 (DOE TRADE Glossary and Acronyms of Emergency Management Terms ORAU 91/K-37 November 1991 ) Back to Top