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 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 low-enriched uranium fuel (3 to 5% uranium-235). MOX usually consists of two phases, UO2 and PuO2, and/or a single phase solid solution (U,Pu)O2. The content of PuO2 may vary from 1.5 wt.% to 25–30 wt.% depending on the type of nuclear reactor.
One attraction of MOX fuel is that it is a way of utilizing surplus weapons-grade plutonium, an alternative to storage of surplus plutonium, which would need to be secured against the risk of theft for use in nuclear weapons.[1][2] On the other hand, some studies warned that normalizing the global commercial use of MOX fuel and the associated expansion of nuclear reprocessing would increase, rather than reduce, the risk of nuclear proliferation, by encouraging increased separation of plutonium from spent fuel in the civil nuclear fuel cycle.[3][4][5]