An ordinary large nuclear power reactor (1000 MWe LWR) gives rise to about 20-25 tonnes of spent fuel a year, containing 200-250 kilograms of plutonium. Plutonium, like uranium, is an immense energy source. In the plutonium extracted from used reactor fuel, the Pu-239 can be used as a direct substitute for U-235 in the usual fuel. If the spent fuel is reprocessed, the recovered plutonium oxide is mixed with uranium oxide to produce mixed-oxide (MOX) fuel, with about 5% Pu-239. Plutonium can be used on its own in fast neutron reactors, where the Pu-240 also fissions, and so functions as a fuel (along with U-238). It is thus said to be "fissionable", as distinct from fissile. ... Recovered plutonium can only be recycled through a light water reactor once or twice, as the isotopic quality deteriorates. However, fast neutron reactors can then use this material and complete its consumption.
