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There is absolutely no problem with respect to that, the radiation may spread as much as ten to twenty kilometers at the maximum and even there the people of japan are being given iodine to prevent cancer from exposure to nuclear radiations.

No other country other than Japan will be affected, even Japan will be slightly affected as the good people of Japan have made precautions and done everything within their power to reduce the affect of nuclear radiation on anyone.
They have evacuated large areas around the Daichi power plant and as stated above have also given iodine to all the workers and the people around the  nuclear power plant.

But if a nuclear Reactor Melt down occurs in daichi Japan  then the west coast of USA will be affected.

So there is nothing to worry about for the people of USA other than worrying for the Japan citizens welfare.
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