Nuclear fuel recycling. Storage cylinders at a uranium tails yard of a nuclear fuel production facility in Ohio, USA. The uranium tails are the U-238 isotope removed during the enrichment process of nuclear fuel production. This uranium will later be used in a fast breeder reactor. The non-fissile U-238 is mixed with small amounts of plutonium before being fed into the reactor. There the fission of the plutonium liberates sufficient neutrons to sustain the chain reaction and to convert U-238 into Pu-239. Each of these 14-ton cylinders has the same energy potential as 60 million barrels (9.5 billion litres) of oil.