>I don't know who in the thorium boosters' club started the "light water reactors were meant for weapons plutonium" meme but it's nonsense.

Maybe the misunderstanding started from the fact that the first British power-generation reactors were intended to produce weapons-grade plutonium. Those reactors were quite different from light-water reactors: graphite-moderated, gas-cooled, and using unenriched fuel.