Could it be that the radiation standards are too strict? I saw an article about the Chernobyl exclusion zone a few years back that showed basically a nature preserve, full of plants and animals apparently thriving, with no obvious deformities.
I saw a documentary of Nuclear Power that covered Chrnoby. basically people have been living there since a year after the explosion. whole villages of peasants, with no ill effects. Growing crops, raising livestock. They interviewed a priest from a church withing in viewing distance of the pant who says he never evacuated.
I saw that too. The place was chock full for deer with beavers busily creating dams. Trees and plants were going thick. If the few building disappeared the place would look primeval.