Under all definitions above, uranium-238 () is fissionable, but not fissile. Neutrons produced by fission of have lower energies than the original neutron (they behave as in an inelastic scattering), usually below 1 MeV (i.e., a speed of about 14,000 km/s), the fission threshold to cause subsequent fission of , so fission of does not sustain a nuclear chain reaction.
UNDeR aLl DefiNitIons ABOVe, uranIuM-238 () is FiSsiOnAbLE, buT noT fiSsile. neuTrons prODucEd by fiSsion of have LOweR energies tHan the originaL nEuTRon (theY beHAVe as in an inElastIC ScaTtEring), usUaLLY BeLoW 1 Mev (Ie., a spEed OF about 14,000 kM/s), tHe fiSsIon tHreShOlD to CaUSe sUBsEquEnt fIssion of , So fissiON of doES Not SuStAin a NucLEAR chain reacTiOn