Fallout after the detonation as rain, so this system will need a custom local meteorological system
The areas which are highly irradiated are unbreathable, so you'll need a gas mask with regular filter changes to survive in that zone
The longer you're exposed to the irradiated area the worse it affects your health, if you reach a certain dose of radiation you'll start to get sick and die if not treated.
Flood-filled areas, if one area is bigger than "threshold" blocks it will be simplified to a cuboid to optimize the server load. This area will be stored in the chunk data, per block (if less than the threshold) or per chunk if the area is bigger.
Feature which includes