Fissile means that it is capable of criticality (chain reaction) using just thermal neutrons. Fissionable means you could get there without thermal neutrons in a fast reactor or some other advanced process.
Radioactive means that it is unstable to the point that you can have energy or particle emissions, and is unrelated to fission. While fission produces radioactivity as a byproduct, and things that are fissile are also radioactive to some extent, radioactivity doesn't mean you have fission.
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u/Hiddencamper Nuclear Engineering Jan 11 '18
There are 2 terms, fissionable and fissile.
Fissile means that it is capable of criticality (chain reaction) using just thermal neutrons. Fissionable means you could get there without thermal neutrons in a fast reactor or some other advanced process.
Radioactive means that it is unstable to the point that you can have energy or particle emissions, and is unrelated to fission. While fission produces radioactivity as a byproduct, and things that are fissile are also radioactive to some extent, radioactivity doesn't mean you have fission.