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Oxide nuclear fuel containing more than one metal oxide; in the usual power-reactor context it refers to uranium–plutonium oxide fuel. Its initial averaged composition does not preclude local variations or actinide redistribution in oxide fuel during service.

A plutonium oxide, $\mathrm{Pu}{\mathrm{O}}_2$, used as a component of mixed oxide nuclear fuel. Its use requires attention to decay heat, chemical compatibility and the distribution of fissile material; no fabrication recipe is specified.