A MSR breeder can potentially burn 98% of the available energy; ThorCon is a converter, but not a breeder. From what I can glean from their website and documentation, it looks like they get about 20% burnup.
> I'm not familiar with Thorium reactors at all, so forgive me for asking: how much long-lived nuclear waste do they produce?
Almost none of the 250,000 year stuff. Almost entirely the 300 year stuff. Also, about 1/4 the total mass of all waste product.
Additionally, according to their documentation, the 250,000 year stuff is ultimately cycled back into the reactor to be destroyed. Most long-lived nuclear waste is fissionable, so you can just use it as more fuel, given that you can remove the fission products from the fuel easily.
Molten salt corrodes stainless at a rate of 0.025 mm / year. The solution: make the walls thicker, change out and inspect the primary vessel and plumbing every 4 years; you get 40 years per millimeter.
Never been a fan of HTGRs; the problem with LWRs is pressure, and what happens if you get to much of it or have a material failure. HTGRs have the same issue (though, not the potential for thermocatalytic degredation of the fuel elements).