Well... first off you must not have noticed my tagline.
Secondly, How many nuclear weapons have we detonated UNDERGROUND, and how many have melted their way to the core of the Earth? Why hasn't the radioactivity from all those detonations poisoned all the water supplies?
Since there is a giant layer of MOLTEN MAGMA under the crust, wouldn't the radioactive material dissolve into the magma and have about as much effect as pissing in the ocean?