Hmmm, very low yield for a first time Nuke,mebbee they just turfed a few hundred tons of HE down the mine shaft and lit the blue touch paper,cheap way of getting everybodies knickers in a twist.
I am Kim Jong-Il... Dear Leader... you must pay attention to me, and my Mao suit, and my teased-out hair, and my... well, large standing Army... and starving people, and b*llocked economic system... O.K., it was TNT and PETN... you got me...