Algodoo

first of all, see my earlyer scene "realistic nuke and a mortar for the basic idea and general insructions.

extra instructions: if you put the nuke on the ground and press d it will detonate on the ground as if it was a "normal" stationary bomb (rather than a missile)

on the top of the nuke you will see an irregular "bump", if you delete this or if it comes into contact with a killer that has a collideset of 8, it will put the nuke into "pressure detonate mode", now, if it comes into contact (with reasonable pressure) with an object that has a collideset of 3 it will light its 3 second fuse

good luck, and have fun