Dissipating Radiation Clouds?

When radiation dissaptes, it's just being spread over a large area.  It doesn't mean it disappears, so where does it go?  Does it eventually gather in our rain clouds, fall directly to the surface, or rise to the upper layers of the atmosphere?  Isn't it extremely dangerous to assume that something catastrophic on a global scale wouldn't happen and poison everything we need to survive?  The risk doesn't seem worth it to me for the energy produced by the dangerous nuclear plants.  Shut them down!!