When nukes go off, they should release a ton of Dark Grey Particles that after about a minute settle on the ground and become Little Piles of Radioactive Fallout. If you go near it you get Radiation Poisoning, unless of course you are wearing your Hazmat Suit complete with Compressed Air tanks
After a few Minecraft days the Piles should turn into Piles of dust which dont harm you. Radioactive Fallout should be able to be Picked up with a Shovel, giving you Radioactive Dust, which you can Centrafuge (If you have GT Installed) into little bits of Uranium/Plutonium. Dust Piles should be able to be picked up and they can be used in place of Scrap in the Fertiliser Recipe.
Also, talking of Fertiliser, IC2 Fertiliser should be able to be used in Forestry Multifarms (but for less as its a little cheaper), providing an actually possible fully automated Farm.