Until now, the central pillar of the Japanese government’s energy policy has been the nuclear fuel cycle. This fuel cycle entails the extraction of plutonium from reprocessed spent nuclear fuel, and using it to fuel Fast-Breeder Reactors (FBR).
The superior neutron economy of a fast neutron reactor makes it possible to build a reactor that, after its initial fuel charge of plutonium, requires only natural (or even depleted) uranium feedstock as input to its fuel cycle. This fuel cycle has been termed the plutonium economy.
As for the FBR, active development has been pushed forward in United States, France, Russia, U.K., Germany, and Japan until approximately 20 years ago.