risks appear to be, short-term and long-term. among short-term risks, there are: radiation burns, radiation sickness; among long-term, there is mutation, and cancer. safety is judged in terms of both acute and chronic exposure.
if the probability of increased risk due to exposure is below what we can measure, statistically, then government bureaucrats know that you will never be able to prove your cancer or birth defects were caused by chronic exposure. so they call it safe.
