MOX = plutonium plus uranium (natural, reprocessed or depleted) = weapon grade plutonium (therefore it is explosive) -Wkipedia

Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material. MOX fuel contains plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium (LEU) fuel used in the light water reactors that predominate nuclear powergeneration. For example, a mixture of 7% plutonium and 93% uranium reacts similarly, although not identically, to LEU fuel.

One attraction of MOX fuel is that it is a way of utilizing surplus weapons-grade plutonium,