A Th reactor can cook above delayed critical (obviously, otherwise how does it power up?
A LFTR starts with a core of U (I believe it is U235) in the Berylium Fluoride - That is what powers it. The Thorium (in the blanket layer) is only there to breed more U (U232), slow neutrons, carry away heat. LFTR's are still reactors powered by U, the cool thing is 1. breeding more U, 2. operates at atmospheric pressures, 3. uses Berylium Fluoride for cooling & heat transfer and therefore does not need water, 4. They don't need massive containment vessels for steam so they are also much smaller. No water means no pressure build up (steam) and no hydrogen being split from H2O (big boom & fire).
Somewhere in the decay chain, Pu can/is created but in very minute quantities, not enough for weaponization and I believe it gets consumed as well in the long run. I haven't read up on LFTR for a while so I forget where the Pu goes. I read/saw somewhere the amount that was generated and my feeble memory wants to believe it was a few milligrams per year in an ocean of molten Beryllium Fluoride.