...I guess the next step would be thorium...since there is plenty of it on our planet.No thorium reactor works
up to now, despite India investing much research in it.
All proposals, including Rubbia's one, need to mix some plutonium with the thorium, and the 233
U they breed doesn't replace Pu to start the reactor. Which, if you put proper figures, means 10 uranium reactors for 1 thorium reactor. In other words, they'd make insignificant use of the thorium deposits.
Details there http://saposjoint.net/Forum/viewtopic.php?f=66&t=2026
As an alternative, existing PWR can burn Pu+Th instead of U. It's done in Russia and planned elsewhere. Same result for cheaper.