When a reactor goes foom or a nuke is detonated, I'd like to see a radioactive coating applied to everything in the area (and for surface blasts, applied to a much larger radius than the actual crater). I'm thinking something like the snow layer you get in Taiga biome. Like Tesla coils, you'd take some damage when you got with a certain range of the fallout blocks. Perhaps instead you could trigger a long lasting radiation sickness using the Hunger or Poison code. With a tip-of-the-hat to the Fallout game, Rad-X (rad resist potion) and Rad-Away (cures radiation poisoning) could be crafted. Using a Canning Machine to make them (instead of the Brewing Stand) would be more in theme with IC2 and give another reason to build a canning machine.
The fallout blocks would not evapourate nor be subject to destruction via explosion. In fact if it's possible, fallout in the area of effect of TNT would be doubled if there's room to place the extra blocks. The fallout blocks need to be shoveled up. You'd get "irradiated muck" which, like snowballs, you could combine to form "irradiated dirt" blocks. Into the Canning Machine and you get Radioactive Waste that looks like a 44 gal drum with a nuke sign on the side. Then throw the waste into a furnace and you'd get normal dirt block.
I appreciate that there are much higher priorities in the IC2 world but there y'go. My suggestion for the day