What is MOX fuel ?
Fuel consisting of a mixture of uranium and plutonium oxides is referred to as a MOX (mixed oxide) fuel. Uranium fuel consists of enriched uranium in which the concentration of uranium 235 — the combustible element in natural uranium — is artificially increased. In MOX fuel, by contrast, anything from 4 to 9 percent plutonium is used in place of enriched uranium to mix with natural uranium or with the uranium that is left after enrichment (i.e., depleted uranium).