I was flattered by all the advice I got to eschew a return through Narita, Tokyo's airport, and avoid any radiation risk. I spent about an hour in transit, and got about 50x the radiation from flying at 37000 feet than I would have standing for an similar time near the troubled reactors. I was more worried over the food. Normally they stock local Japanese provisions in transit. You can tell because the meals taste better than the standard fare. Well, on the final leg we were served sub-standard fare. Bad food in this case is safer food.
The risk of this hour in transit was trivial. You can tell by comparing it with a normal activity - eating a banana.
Bananas are radioactive and there is a Banana Equivalent Dose (BED) standard. For those of you who like equivalence, consider this:
A radiation dose equivalent of 100 μSv (10 mrem, or 1,000 BED) increases an average adult human's risk of death by about one micromort—the same risk as driving 40 miles in a car, eating 40 tablespoons of peanut butter, or of smoking 1.4 cigarettes.
News today is 10x the amount of radioactive cesium and iodine fell in the Tokyo rainfall - but still at minuscule levels. A banana produces about 14 Bq (becquerels). The normal fall is about 100 bananas per meter, and thus spiked 10x to a kilo-banana. Good thing I stayed indoors and didn't drink tap water. Bad for the Japanese if this continues, although still at very low levels. (And I bet you didn't know that low levels of radiation were all around, all the time?)
There is a chart below showing all the equivalence, which I sourced from The Big Picture. Click on it to make it readable. A day near the plant is 3.5 μSv, or 35 bananas. A six hour flight from NY to LA is 12 times more radiation, or 400 bananas. My 18 hour flight is 36 times more than a day in the Fukushima area, or a little over a 1200 bananas (1.2 kiloBED) - thus worth about one micromort, as noted in the comment above.
Y'all were at more risk commuting every day than I was.