Used nuclear fuel has long been reprocessed to extract fissile materials for recycling and to reduce the volume of high-level wastes. New reprocessing technologies are being developed to be deployed in conjunction with fast neutron reactors which will burn all long-lived actinides.
Mixed oxide (MOX) fuel provides about 2% of the new nuclear fuel used today. MOX fuel is manufactured from plutonium recovered from used reactor fuel. MOX fuel also provides a means of burning weapons-grade plutonium (from military sources) to produce electricity.
Over one-third of the energy produced in most nuclear power plants comes from plutonium. It is created there as a by-product. Plutonium has occurred naturally, but except for trace quantities it is not now found in the Earth's crust.