Snowflakes, like other precipitation, form around some sort of condensation nucleus -- in other words, dust. Pure snow and fresh rain is actually pretty dirty.

Snowflakes, like other precipitation, form around some sort of condensation nucleus -- in other words, dust. Pure snow and fresh rain is actually pretty dirty. You might have noticed how clean windows won't be clean after they get rained on and it dries. It seems plausible to me that some of the radioactive particles would be a form that could be incorporated into snowflakes, but I'm not an expert. http://en.wikipedia.org/wiki/Cloud_seeding http://en.wikipedia.org/wiki/Cloud_seeding