CEREA, is a French environmental and atmospheric research center. The following two maps represent computer simulations of the deposition of cesium 137 from the Fukushima and Chernobyl accidents. The simulation from the Fukushima accident shows an area of high deposition in eastern Japan, and very little deposition in western Japan and Hokkaido. The United States and Canada appear to have a received a much less concentrated deposition than eastern Japan, however, especially Alaska and the Pacific northwest have been deemed to have received significant fallout, though much lower than that received by almost of Europe after the Chernobyl Accident.
The maps are quite informative, particularly when compared to each other. However it must be stressed that these are merely educated guesses rather than actually measurements of what has happened. Fluid dynamics are notoriously difficult to predict, pointing to the necessity for ongoing testing and research for levels of environmental contamination. Radioactive fallout does not happen evenly. It is highly dependent on precipitation, leading to areas that may be significantly more radioactive than others . Further, once fallout lands, it has a clear tendency to concentrate into hotspots. Low places, such as gullies or puddles are prime candidates.
CEREA’s website also has a flash animation that you can watch the tragedy of the whole cloud unfolding here: http://cerea.enpc.fr/en/fukushima.html
For comparison’s sake, let’s put up a map of Chernobyl. This is somewhat reassuring, in that most of the US has received less contamination than Europe as a whole. CEREA considers the Chernobyl simulation to have more certainty than the Fukushima simulation, due to the data that has been gathered since the Chernobyl accident, however, it is still a simulation.
So, for Japan, the good news is that western Japan and Hokkaido seems relatively unscathed. Unfortunately, the Japanese government seems intent on shipping waste all over the country for incineration, which is not a bright idea.
For North America the bad news is that radioactive fallout from Fukushima appears to be widespread, though the levels are not terribly high. There is reason for concern, as we have added to our overall levels of exposure to ionizing radiation and environmental toxins in general. However, following the guidelines for a radioprotective and anti-cancer diet and lifestyle should far outweigh the risks associated with this level of contamination.