Kyodo News reports here that radiation levels in Namie (B), 20 km north of the Fukushima Nuclear Plant (A), are 161 microsieverts per hour.
It would take just under 26 days of continuous exposure to such levels to accumulate 100 millisieverts of radiation exposure, and in a year over 1,400 mSv.
Devra Davis for Reuters, here, puts that in its health context:
In terms of cumulative exposure, 100 millisieverts a year is the lowest level at which any increase in cancer risk is clearly evident. A cumulative 1,000 mSv over a lifetime would be expected to cause a fatal cancer many years later in five out of every 100 persons with that kind of exposure.
