That picture right there was the amount of radiation leaking and going out into the atmosphere from a nuclear power-plant. All this radiation that is going around could not only cause cancer if your exposed to too much of it but also it contributes to children being born with autism, hows that for clean and safe.
Finally there is always the possibility that a nuclear plant could experience a meltdown or worst an explosion letting out both a ton of radiation polluting the area for years to come or a large explosion destroying the are and all around it.