Oxide fuel technology is of course pretty mature, as that's what current generation LWR's all use. However, it has severe disadvantages in a LMFBR. US thinking was apparently that they would jump straight to metal fuel (EBR-II and the canceled IFR), other who have used it see it as a stopgap until nitride fuels become available (e.g. Russia is experimenting with nitrides in their fast reactors).
As for economics, technically breeding is extremely cool (catnip for physicists!), but with current uranium prices there's no particular economic driver to develop and commercialize the technology. I think it's very hard to compare prices for mature LWR technology and various one-off fast breeder prototypes, let alone paper reactors. It's useful as a backstop for rising uranium prices, however.
> There is a precedent for commercial licensing of the LMFBR in the US. Terrestrial Energy (Bill Gates's company) is making noises about building one but they are holding their cards so close to their chest that it's hard to believe they have a realistic plan to do it.
The Bill Gates backed company is Terrapower. They have some agreement with GE Hitachi to develop and commercialize the technology, called "Natrium". AFAIU the Natrium reactor is heavily inspired by the canceled IFR, using metal fuel. We'll see what happens, interesting tech though.
(Terrestrial Energy is the company behind the "IMSR" molten salt reactor. It's a thermal spectrum uranium burning, non-breeding reactor design, though)
