Would you fire off a nuke even at your enemy a mere 300-500 miles upwind? Japan can't nuke N.K. without killing their own. We can't nuke N.K. without killing likely more in Japan than N.K. The military option is MOAB's or conventionals capable of doing wide spread damage to key N.K. government installations.
all of that stuff about "nuclear clouds" and such, is way overblown.