When someone speaks of a Thorium 232 reactor, they often fail to mention that it is the breeding of Uranium 233 from the Thorium, which provides a fissionable fuel.
As said by many, our stockpile of used fuel rods retain about 95% of their initial energy content. Processed to fuel a salt coolant based reactor, this fuel reserve could power the grid for the better part of a century.
The U233 rings a bell. I kind of remember reading that a while back now that you mention it. Not a nuclide I know much about either though.
I'm skeptical that salt coolants will ever be practical due to their absurdly high freezing point. We had one salt cooled reactor in a submarine, the S2G... it was eventually replaced with an S2W PWR because of coolant solidification. Maintenance was next to impossible.
The prototype for the S2G was upstate NY. (It was called S1G) Unlike the naval PWRs, it had a massive containment sphere built around it. We called it the "Death Star" or "Dig Ball" back over twenty years ago. Death Star name is obvious, but the Dig Ball name came from having the S1G replaced with a D1G PWR years later.
I'm not sure if this is true or not, but the size of the Dig Ball was supposedly the volume of that would contain the coolant at atmospheric pressure should the coolant piping rupture. But the S1G had molten salt coolant that would supposedly explode on contact with air, unlike the PWRs that would instantly flash to steam. Still, the Dig Ball is big, so perhaps it did use size instead of strength to contain whatever it was containing.