you vastly underestimate the work required to get a working nuke. you don't just grab the first glowing rock, surrounding it with tnt and call it a day. that stuff require purification and shit, and the equipment required for that isn't one that a civilian power plants will have.  the best they could improvise in that short of a time would be regular bombs mixed with radioactive material, which is 100% of the justification for a full (proper) nuclear retaliation with 1% of the destructive effect.
France