re: Any plutonium can be used in a bomb.
"Pure Pu239 is best, but the other isotopes do not make it unusable. They just make manufacture a little trickier, and the bombs larger due to increased quantity of explosive for compression."
I can't comment on this one- but I will say that at some point you may have to posit a third world country spending trillions of dollars to get and refine enough plutonium from Pebble Bed reactors to make bombs. Thats not exactly easy proliferation.
