Mixed-oxide fuel (or MOX fuel) is nuclear fuel that contains an oxide of more than one element. Most nuclear fuel that is not of the MOX type only contains uranium dioxide. In most cases, the additional oxide will be plutonium dioxide, sometimes thorium dioxide. Any reactor that uses uranium-based fuel will produce plutonium dioxide. Mox fuel consists of about 93% uranium, and about 7% of thorium or plutonium dioxide.