Well I doubt the fallout would be substantial in the US. However I was watching the news and they said the immediate area would be un-inhabitable for decades. Then theirs the fact that the wind would carry the particals across a large amount of the country.
Radiation could be blown over Tokyo if the wind blows right. Which would mean Tokyo would be contaminated as well for quite some time. Today their are still reports of radition illnesses in Hiroshima and Nagasaki. I've heard like last year of birth defects supposedly caused by the radiation left from WWII.
Now I don't know how bad the contamination would be in Tokyo if the radiation was spread over their. I also don't know how much of the country would be covered if the radiation leak contaminated that much. In the end it could mean birth defects, other abnormal effects to the peoples bodies. Increase in deseases caused by Radiation.
It could contaminate crops damaging Japan's ability to grow its own food. According to the images shown on CTV the contamination could cover the majority of the country if the winds are right. If that occured it would be catastropic for Japan.
Also last I heard their were two plants near melt down. If they both went who knows how much more damage could be done. In the end if either plant goes Japan will be devestated for decades to come!