Many different solvent extraction processes have been devised to produce particular product and waste streams. For example, it may be attractive to avoid separation of a pure plutonium stream in order to limit proliferation risks, or it may be useful to separate long-lived isotopes from high level liquid waste for separate treatment, so that the radiotoxicity of the remaining high level waste decreases more rapidly through decay. In some cases, separations are designed to fit with specific national regulatory requirements and many of these processes could be used in combinations to give particular, desired out­comes. Some examples are given in Table 4.

4 Waste Management Options

The critical decision in the ‘‘back end’’ of the nuclear fuel cycle is whether or not to reprocess (in other words, whether the cycle is closed or open). If an open fuel cycle is chosen (e. g. as in Sweden), then waste management is essentially confined to the management of spent fuel and reactor decommissioning wastes,

with the former dominating the radioactive content of the wastes. Inter­nationally, deep geological disposal, usually preceded by some decades of cooling to limit heat and radiation load on the host rock, is always assumed to be the management route for spent fuel. There is currently no operational disposal facility for spent fuel.

In a closed fuel cycle, as described above, there are many more options for the management of different streams. As a country which has operated a closed nuclear fuel cycle for over 50 years, the UK’s approach to managing these different waste streams is fairly typical. Conventional Purex processes will produce uranium and plutonium product streams, and a liquid high level waste stream, which in current thinking will be vitrified for deep geological disposal. Concepts for disposal of vitrified high level waste are generally quite similar to those for spent fuel, because the heat and radiation loads are similar. However, as outlined above, removal of most of the actinide inventory would allow the hazard from vitrified high level waste to decrease faster than that from spent fuel.

Operations at all stages of either a closed or open fuel cycle will generate lower activity wastes associated with uranium mining, fuel fabrication, energy generation and spent fuel management. These are generally classified on the basis of their radioactive content (in the UK, classification is in decreasing order of radioactivity: intermediate level, low level and very low level wastes; see Chapter 6). In a closed fuel cycle, a wide variety of process wastes, for example 14C — or 85Kr-containing gases from fuel shearing and dissolution, or water from storage ponds, is also created. These are decontaminated where necessary (for example stripping of 14CO2 from gases by precipitation as BaCO3, or removal of 90Sr and 137Cs from aqueous effluents by ion exchange) prior to discharge to the environment under regulatory authorisa­tion. The radioactive wastes from an open fuel cycle tend to be smaller in volume and less diverse than from a closed one. Obviously, the total activity is not changed.