This Nature article throws some cold water on the claims that thorium isn't very useful for making weapons.

http://www.nature.com/nature/journal/v492/n7427/full/492031a...

Unfortunately the article is paywalled.

U233 more readily fizzes than booms, since it fissions faster it tends to pre-explode before getting into a really good super critcal state (probably something to do with the .6 instead of 1.6 delayed neutrons per 100 fissions mentioned above, it also has a slightly better neutron production factor than u-235).

U233 will have U232, which decays through some very high energy gamma emitters, making U233 impossible to smuggle through shipping ports etc... These gamma emissions also kill humans in minutes, so would-be bomb makers would need to use robots or other remote handling techniques to fabricate a bomb. This is something a rouge state would have a hard time pulling off, and is practically out of reach of basic terrorists.

It's not impossible but it would be easier/cheaper to just mine/steal some natural uranium and build centrifuges. It's easy to make U233 from thorium and thorium is abundant, so, really, how would reactors make thorium/U233 more available to rouge states when they could basically make it themselves, and why would they choose the U233 route?

That Nature article was also linked in the original article. See point 3 towards the end.

Scorecard

Uranium derived bombs extant ~20,000

Thorium derived bombs extant =ZERO.

The US & USSR would have been making Thorium derived weapons if it were practical. We DIDN'T. That should tell you something.