The first reactor to produce electricity (in 1951) was EBR-1, an American fast neutron reactor (Idaho).
The most attractive feature of fast-neutron reactors, from the point of view of prospective energy resources, is their ability to regenerate, or even overgenerate, fissile material, and thus utilize all the uranium extracted from the mine (via conversion of uranium 238 into plutonium).
The neutron energy spectrum in the core of such reactors must be "fast", which means that light bodies containing hydrogen or carbon cannot be used. Current reactors are cooled by liquid metals, generally sodium. This results in functional and technological constraints on the fuel, which have an impact on its design and manufacture.
The industrial maturity of fast breeder reactors (FBRs) is still some way off, and their characteristics and fuels are set to evolve. In addition, objectives linked to the reduction of actinide inventories may lead to the definition of very new products.