No they can't, for the simple reason, that you need a huge amount of uranium to get a certain amount of enrished one, not to mention the Nuclear reactor fulls has many other components additive, that makes it really hard to get weapon grade uranium
Some 50 kg to 55 kg of U
235 is needed to create a nuclear bomb. That is, if the enrichment ratio is 5%, you need more than a tonne of Uranium to build a nuclear bomb. Extremely difficult, if not impossible to obtain that much material.