Fast Reactors

The development of fast reactors for electricity generation is largely in abeyance except in Japan and Russia. Work is, however, progressing on the use of fast reactors for consumption of excess plutonium and the destruction of minor actinides (MAs) and long — lived fission products (LLFPs). However, a number of fuel cycle options are being investigated, e. g. in the CAPRA-CADRA programme (Hesketh, 2003).

5.6.4.1 Plutonium Burning Fuel Cycles. Fuel cycles based on a fast reactor plutonium breeding cycle are being investigated for possible adaptation to plutonium consumption. In the CAPRA-CADRA project the European fast reactor (EFR) concept is being considered whereby the plutonium content of a MOX fuel assembly is increased at the expense of U-238; this, therefore, results in net plutonium destruction. Inert matrix assemblies have also been considered based on a plutonium nitride cycle.

5.6.4.2 Minor Actinide Target Fuels. Fuel cycles that produce and burn equal amounts of plutonium and which can destroy MAs and LLFPs are the subject of advanced fuel research. To do this, conventional fast reactors are possible but accelerator driven systems (ADS) may have some advantages. The latter are considered later in the book. From the view point of target fuel assemblies both designs are similar. There are essentially two approaches to fuel design:

homogeneous — where the MA or LLFP is mixed with the fuel, and

heterogeneous — where there is a separate target assembly.

The target materials being considered include oxide, nitride and cermet (ceramic/metal) fuels; of these, nitride fuels are the most promising. There are many options that are being researched, see for example (Hesketh, 2003).

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