Hi ER

The main advantage as far as waste is concerned is that both the thorium and integral fast reactors 'burn' less fuel and so make less waste.

Enriched uranium reactors fission U235 (enriched from its usual 0.7% to 3-5%) and a bit of plutonium made from U238 while the reactor operates. Once the U235 drops to about 0.3% the fuel is considered to be depleted and is set aside as 'waste' - yet most of the uranium (97-95% U238, a bit less in the end) is still there, it has just been made highly radioactive by long-lived plutonium and other transuranics. About 95% of potential fuel is thrown away in this fuel cycle, and the waste is deadly for +10,000 years.

Thorium and integral fast reactors burn up virtually all the fissiles, leaving short-lived isotopes (all those split atoms) that decay to safe levels in just 300-500 years. Those are real wastes as they can't be fissioned or made into fuel with a net energy release. A neutron or proton beam could decay them away quicker by spallation (which you rightly perceived to be another word for 'splitting' - 'fission' is usually reserved as a term for net energy- releasing splitting), but stored in artificial rock and thoroughly mixed it's basically useless as a radiological dispersal weapon.

What's more the total waste is about 50-100 times less - one ton per year versus 100 tons/year for a 1000 MW reactor. Whats more there's no 'depleted uranium' (U238 minus the U235) left sitting around, and the mine tailings are reduced immensely - lower grade, easier to reach ores become viable to mine.

That's one 'hidden' down-side of nuke power - the mildly radioactive sludge left after mining & extracting the uranium, because of the actinides that get exposed and concentrated during the processing. Hundreds of tons for every ton of uranium ore. With thorium and integral fast reactors that problem almost vanishes. Japanese studies have suggested uranium could even be extractable, with a net energy gain, from sea water if reactor heat was used to evaporate it and concentrate the solutes. It would then be a true renewable because uranium is continually leached from the continents into the oceans, making dirt-mining the stuff un-necessary.

Adam