The Pyongyang wind rose indicates that a lot of the fallout will be carried N, NW, and W -- i.e. to the Chinese territory. I doubt they would welcome nuking so close to their borders.
http://www.weatheronline.co.uk/weather/maps/city?FMM=1&FYY=2...
This leaves aside the question of how real these sanctions are, and how much China will keep helping NK behind the scenes.