As someone living near one of europes largest uranium deposits, i can tell you that nuclear itself might be clean, but getting the fuel is anything but. Uranium dont come in nice nuggets like gold, its mixed up with other things so that its only fractions of grams per ton of rock you have to mine. When this rock is processed we are left with big holes in the ground that shifts the level of the waterbed, and big piles of toxic rock dust that leaks all kinds of nasty shit into said ground water.