Mixed oxide fuel, commonly referred to as
MOX fuel, is
nuclear fuel that contains more than one
oxide of
fissile material, usually consisting of
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 power generation. For example, a mixture of 7% plutonium and 93% natural uranium reacts similarly, although not identically, to LEU fuel. MOX usually consists of two phases, UO
2 and PuO
2, and/or a single phase solid solution (U,Pu)O
2. The content of PuO
2 may vary from 1.5 wt.% to 25–30 wt.% depending on the type of nuclear reactor. Although MOX fuel can be used in
thermal reactors to provide energy, efficient fission of plutonium in MOX can only be achieved in
fast reactors.