From March 11 to April 5.
As reported here:
34 millisieverts of radiation had accumulated over that period at one location in Namie Town, about 24 kilometers northwest of the plant. This equates to about 314 millisieverts per year, more than 3 times the permissible level of 100 millisieverts.
The figure of 314 must factor in some estimate of radiation degradation over a year. 34 millisieverts in 25 days is a rate of 1.36 mSv/day, or 496 in a year, not 314.
The 100 mSv level may be permissible under extreme circumstances, perhaps, but the evacuation standard being used is 20 millisieverts or higher.
Normal average radiation exposure from all sources in the US is 6.2 millisieverts annually. A person living to age 78 would get almost 484 millisieverts in an entire lifetime at that rate. In Namie Town one could conceivably get that same whole lifetime's exposure in a single year.
Nuclear power is safe . . . until it isn't. And then it's unsafe it a big, dirty, relentless and inuring kind of way.
