fissile material; fissionable material
Technical term in nuclear physics and engineering; refers to substances capable of sustaining a nuclear fission chain reaction.
Uranium-235 is a typical fissile material.
核分裂 (nuclear fission) is the process; 核分裂性物質 is the material that undergoes fission.
Compound of 核分裂 (nuclear fission) + 性 (-ity, property) + 物質 (material).