... half life of minutes means it halves radiation level measured every so many minutes, doesn't mean it disappears in minutes. Revise your math based on that.
Generally the most dangerous nuclear material is that with a half life comparable to the lifespan of a human, ie decades. Yes there are spikes of radiation, but they dissipate quickly. 23 times the normal levels? I receive a day's worth of background radiation in an hour... as long as that doesn't happen for a month it's not likely to affect my health.
The real problem is if the nuclear fuel escapes into the atmosphere - that's where you end up with clouds that are dangerous. It hasn't happened in Japan yet, despite the physical assault the earth has thrown at it. Radioactive gases have been vented, and are short lived, and low risk because it's total exposure to radiation that causes the real health issues.
So far I still only see reports of one worker exposed to levels of radiation that are equivalent to a few years worth of radiation in an hour. That person may get cancer, and has every right to be worried, but you can get cancer from inhaling coal dust too. Or smoking, or, depending on what the media wants to pick up and run with, eating potatoes, or breathing. The point is, don't believe the hype that the media is using to sell stories. They don't seem to know what they're talking about. As soon as someone admits "radiation leak" the media broadcasts "Chernobyl" and the average Joe starts overreacting. These stories are alarmist, pure and simple, and it's selling newspapers and online advertising, while at the same time putting enough fear into people to affect the rescue and recovery efforts from the natural disaster.
I were in Tokyo I'd keep an eye out for any official reports about a genuine containment failure, while continuing to live my life.
Oh yes, those who use this as a tool to fear nuclear power need also to remember that this is a 40 year old plant, and there is new technology in such things which prevents the chance of even a partial meltdown, period. Very clever stuff where the fuel is embedded in material that expands as it gets too hot, which effectively moderates the fission reaction and prevents it going past a certain point.