Fissile material - Definition and Overview

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Fissile material is composed of atoms that can undergo nuclear fission and sustain a fission chain reaction. The term "fissile material" is used more in a regulatory context than in a scientific context. The International Atomic Energy Agency defines "fissile material" as:[1] (http://www.iaea.or.at/ns/CoordiNet/safetypubs/iaeaglossary/glossarypages/f.htm#fissilematerial)

• uranium-233
• uranium-235
• plutonium-238[2] (http://cted.inel.gov/cted/eh_mat/212595lp.pdf)
• plutonium-239
• plutonium-241
• neptunium-237[3] (http://packages.llnl.gov/doe_ord/o54803.html)
• curium-244[4] (http://packages.llnl.gov/doe_ord/o54803.html)

"Fissile" is distinguished from "fissionable". "Fissionable" are any materials with atoms that can undergo nuclear fission. "Fissile" is defined to be materials that are fissionable by slow neutrons. "Fissile" is more restrictive than "fissionable".

Fissile materials may be further categorized[5] (http://cted.inel.gov/cted/eh_mat/212595lp.pdf):

• Fissile Class I: no controls
• Fissile Class II: limits on amount of materials shipped
• Fissile Class III: special shipping arrangements are needed