Have always been intrigued by these things but only ever found confusion of strong opinions, for and against. Finally happened across rational explanation of the technology along with irrational cancellation by politicians. Sounds like they could have been a magic silver bullet but our favourite planet likely to be in socio-political collapse before this technology could ever be revived – Extract from James Hansen ” Storms for my grandchildren”, Atoms for Peace:

Richard Nixon in his June 4, 1970 presidential energy message to Congress said “Our best hope today for meeting the nation’s growing demand for economical, clean energy lies with the fast breeder reactor.” USA had top nuclear experts in the world and the top .. was Argonne National Laboratory. A low level of support allowed steady progress to continue until, in 1994, the Argonne scientists had tested all necessary  components and were ready to build a demonstration  fast reactor power plant. At that point, the Clinton-Gore administration cancelled the program. In his 1994 State of the Union address, Bill Clinton announced “we will terminate unnecessary programs in advanced reactor development”. Argonne scientists  were told not only to stop the research but also to dismantle the project, with all involved instructed by DOE to not publicise it.

Like em or hate em, no sense holding your breath expecting them to rise from landfill site any time soon.