As far as I know even a high dosis isn't lethal per say. But the higher the energy the radiation is transmitting, the more likely you'll die.
I don't think there is any radiation that you can call "safe". No, the sun isn't "safe". But maybe there's a level at which you can say it's "no more than usual".
Either way I'll be happy without Nuclear power.
~"I never let school interfere with my education"~ -Mark Twain