The primary objective of present day fuel cycles is to optimise energy production, while at the same time minimising costs and maximising safety. This has given rise to a number of fuel cycle variants to be considered in which fuel is recycled between different reactor systems, see for example, Ion and Bonser (1997). This is discussed more fully in Chapter 5. There are particular operational safety issues relating to the management of spent fuel, etc., as mentioned in the previous section. These are concerned with safe storage practices, maintenance of sub-criticality in fuel storage ponds and flask transport safety and security.

Spent fuel represents the most highly radioactive waste arising from the fuel cycle, due to the presence of particular fission products. It, therefore, represents the significant waste radiological hazard associated with nuclear plant operations. It may also include fissile and fertile uranium or plutonium and possible breeding products, which might be re-utilised by recycling or reprocessing. The fission product radiological hazard will remain, however, whether or not these materials are recovered.

Policy issues are likely to play a continuing role in the development of advanced fuel cycles. Reprocessing and recycling, together with improved uranium resource manage­ment can lead to a reduction in waste volumes and toxicity, thus improving the sustainability of nuclear power plant operation but this may not be a preferred option due to economic reasons or proliferation concerns. Recycling of plutonium in LWR MOX cores reduces the spent fuel radiotoxicity by a factor of 3 if the MOX fuel itself is not recycled (Bertel and Wilmer, 2003). Multiple reprocessing and recycling can reduce radiotoxicity further.

Reprocessing practices also reduce the volumes of radioactive waste significantly. Each tonne of spent fuel contains about 1.5 m3 of high level waste. After reprocessing, less than 0.5 m3 of waste remains, including 0.115 m3 of vitrified high level waste and 0.35 m3 of intermediate waste. Additionally further compacting can be carried out after disposal.