An Atomic Bomb made only of BRCK, COAL, GOO, IGNC, PLUT, and DEUT. The idea is very little plutonium and no unstable or imaginary materials like gasses or walls. The bomb is about 85% reliable.
Technically speaking this is a nuclear reation not an atomic reaction. The nucleus breaks apart releasing energy. an "atomic" bomb would be TNT becase the reactions occur between atoms.