Mainly Plutonium fuel. They are usually started on highly enriched uranium (i.e., weapons grade) fuel, with a breeding blanket of depleted uranium surrounding the core. Over time the breeding blanket...
The advantage is mainly that more active fuel can be created than is used, so getting 'something for nothing'. However experimental reactors such as the sodium cooled fast reactor at Dounreay in...
They may become important in the future but are not at the moment. This type of reactor has been built as prototypes, but is not in commercial use. The importance is that the present type of reactors...
Liquid sodium (Na) or sodium-potassium alloy (NaK) are preferred in fast reactors because they do not act as moderators (slow down neutrons). This leaves the neutron flux fast, improving breeding...