The fundamental principles of transmutation, outlined above, have been applied in the analysis and performance assessment of different types of reactors: thermal neutron reactors, fast reactors and sub-critical, i. e. source-driven, reactors. The analysis has been mostly applied to TRU transmutation and has been described e. g. in Ref. 5. Here we shall summarize the most significant results related to TRU transmutation and to long-lived fission product transmutation. Finally the potential impact of transmutation on the fuel cycle will be discussed.

The transmutation performances of different thermal neutron reactors have been widely investigated in the last decade. Focus has been on PWRs, high temperature reactors (HTRs) and on the use of inert matrix fuels (IMF) in PWRs. (IMF are fuels without uranium, which do not, therefore, form new plutonium).

The drawbacks indicated in the previous section, i. e. the build-up of higher mass TRU elements and shortage of neutrons when the core is loaded with MA, have been confirmed by detailed studies (see, e. g., Refs 6 and 7). At present, even if some studies are still ongoing on thermal reactors (in particular there are recent studies related to CANDU reactors), most of the leading laboratories in the world have now focused their studies, both theoretical and experimental, on TRU transmutation in fast neutron spectrum reactors, FRs.