Any sources for this estimation? I've read nothing even remotely close to that prediction. At its peak, people in Fukushima city were only receiving ~0.06 mSv/day of radiation. This only lasted a couple of days. The vast majority of people didn't even face that since they were evacuated.

In contrast, a transatlantic flight results in about 0.1 mSv of radiation. Someone getting a single abdomen x-ray would get over 0.2 mSv.