Nuclear reprocessing is a process where the spent fuel is treated to recover the unused fuel. It is not necessary to reprocess the spent nuclear fuel, however it is better for the environment because it reduces the waste volume. The principal reason for reprocessing used fuel is to recover unused uranium and plutonium in the used fuel elements and thereby closing the fuel cycle. The level of radioactivity in such 'light' waste after about 100 years is much lower than in spent fuel not reprocessed. Reprocessing has been the policy in Europe, Russia and Japan.

In the last decade interest has grown in separating ('partitioning') individual radio nuclides both to reduce long-term radioactivity in residual wastes and to be able to transmute separated long-lived radio nuclides into shorter-lived ones, mostly by fission. In 2005 this interest in more fully closing the fuel cycle grew, driven by concerns about long-term resource utilisation and proliferation resistance.

Reprocessing to recover uranium (U) and plutonium (Pu) avoids the wastage of a valuable resource. Most of the used fuel is U-238 with less than 1% U-235 and up to 1% is plutonium. The U-235 and plutonium can be recycled as fresh fuel, saving some 30% of the natural uranium otherwise required. It also avoids leaving the plutonium in the used fuel.

The history of reprocessing at Sellafield has been marked by many management and technical difficulties. It is not proposed that reprocessing of spent fuel will be part of the next phase of nuclear power production in the UK.

For more information see paper on reprocessing.