Fuel elements that have been used in the nuclear fuel cycle and removed from the reactor because they contain too little fissile material and too high a concentration of radioactive fission products. They are highly radioactive.
Fuel elements that have been removed from a reactor after use because they contain too little fissile and fertile material and too high a concentration of unwanted radioactive by-products to sustain reactor operation. Spent fuel is both thermally and radioactively hot.
Irradiated fuel that is permanently discharged from a nuclear reactor. Except for possible reprocessing, this fuel must eventually be removed from its temporary storage location at the reactor site and placed in a permanent repository.