A nuclear reactor which can produces more fissile nuclear fuel than it consumes, because the neutrons breed fissile fuels from 238U and 232Th. Breeder reactors were popular until increasing reserves of uranium where found.
For instance, it was claimed that the release of one ton of plutonium into the atmosphere could give every person on earth lung cancer, and operating breeder reactors on a large scale would double the amount of plutonium on earth every ten years ("AEC Asks Billions for the Breeder" 1971).
Reportedly, the increase to 20 GWe would be achieved through a mix of pressurized heavy water reactors (PHWRs), light water reactors and fast breeder reactors, including construction of five fast breeder reactors of 500 MWe each and the import of eight light water reactors of 1000 MWe each.
The three stage nuclear power programme, which is to be implemented sequentially, aims to multiply the domestically available fissile resources through the use of natural Uranium in Pressurised Heavy Water Reactors (first stage), followed by use of Plutonium obtained from the spent fuel of Pressurised Heavy Water Reactors in Fast Breeder Reactors, in the second stage.
But energy demand tapered off with slower economic growth in Japan, and the development of fast-breeder reactors stopped when the Monju Fast Breeder reactor in Fukui Prefecture had to be shut down after a serious accident in December 1995.