Apparently there is a run on Iodine in the US as people panic. I-131 is one of the major fission products of a nuclear reactor and could potential get taken up in the thyroid...but it decays in a few days. If you're really that worried, salt your food a little extra hard.
http://www.youtube.com/watch?v=9QS0q3mGP…
I don't think we can compare Chernobyl here. It's much worse especially for the Pacific Northwest.
The rain basically dumps the whole load on the coast once it wafts across the whole pacific.
Regarding the bottom of the post; did you really need a computer model to know that radioactive particles will spread over Japan and the Pacific?