One of the 'nice' things about these reactors is that they produce both U-232 and U-233. The reason this is nice, is because U-232 is such a prolific alpha particle emitter, that it tends to go ahead and start a fission reaction without any outside intervention. So if you tried to remove and weaponize the Uranium produced from the reactor you'd likely either poison your supply of U-233, or blow yourself up with a bomb that would take out less than a truck full of fertilizer.
Granted, if there was a safe method to extract the U-233 by product from the reactor, this might be an issue. I know China and India have been working on it for a while since they have pretty rich Thorium deposits, but to my knowledge, it's been ruled as impractical when Plutonium is much easier to produce, the same reasons why we use the nuclear reactors we do, because they have the added benefit of producing weapons grade plutonium.