The nature of the fireball means you can't really use any type of physical structure to shape it... though I guess multiple miles of rock would work too, but it

The nature of the fireball means you can't really use any type of physical structure to shape it... though I guess multiple miles of rock would work too, but it won't be in the desired direction[1] [1]https://en.m.wikipedia.org/wiki/Operation_Plumbbob#Missing_steel_bore_cap https://en.m.wikipedia.org/wiki/Operation_Plumbbob#Missing_s...