The radiation plume of 400 milliseiverts is from a small area of certainly no more than 100 square meters. If we assume that the Fukushima Daiichi reactors collectively manage a plume the size of a square kilometer, then to get comparable numbers we need to multiply the 400/hour by (24 x 365) to get a year's worth. Assume uniform distribution and divide by 500 million (global distribution). That comes out to .007 milliseiverts / year. I know of no scenario in which the Japanese reactors could sustain an emission rate of 400 milliseiverts per hour for a week, much less for a year, nor how there could they generate radioactive fallout uniformly over a square kilometer.
I am told that I am off in my calculations above, but off in the correct direction, which is to say the levels are too large. That's unfortunate in that I don't like to be wrong, but it also emphasizes my point, which is that the absolute worst case has no more global effect than did an event that many weren't even aware of, and which didn't have any great global effect.
The important lesson from Japan is that we took obsolete reactors with old designs and safety features, and subjected them to a 9.0 quake and a very large tsunami, and the damage to the planet is an unfortunate but hardly decisive event.
It is now time to stop worrying about this mess until things settle and we can see precisely what we have learned, and factor that into the next generation designs. Note that almost everywhere in the world we are building reactors with much better design and far better safety features than those being destroyed now. Concentration on how awful is the nuclear mess takes our attention off the economic and human disasters from the earthquake and tsunami.
If you liked this article, please give it a quick review on ycombinator or StumbleUpon. Thanks