Nuclear bombs are strongly disinclined to "go boom" unlike say TNT. Turning the energy from splitting atoms into a large explosion, which is what you want from a weapon, will require precise timing. If you get it wrong either nothing happens, or you maybe create a small detonation, and cover a modestly sized area with dangerous debris from the failed attempt. Just throw a box of grenades into a waste water treatment plant or something instead for a fraction of the cost.