In 2013, two years after the disaster, Japan’s permanent radiation-exclusion zones were unveiled in the Japanese media.
The Japanese government identified areas measuring between 20 and 50 millisieverts a year as suitable for restricted living (visitation but not yet permanent inhabitations).
Areas measuring fewer than 20 millisieverts a year of annual exposure were designated as habitable zones and preparations were made for lifting evacuation orders in these areas (“About 60 Percent,” 2013.)
In effect, Japan increased its national exposure level from one, to up to 20 millisieverts a year, while allowing partial habitation in areas with up to 50 millisieverts.
In comparison, the Soviets set the Chernobyl exclusion zone at five millisieverts a year “Japan Groups Alarmed,” 2011.
This elevated level applied for children as well as adults.
In November 2013, Japan announced it was changing its method of atmospheric monitoring to an individualized badge system. According to a November 9, 2013 report from The Asahi Shimbun, the badges underestimated exposure levels by seven times when compared to the atmospheric monitoring technique that had previously been deployed by aircraft “Lower Radiation Readings,” 2013.
This change essentially increases permissible exposure levels.
Source : Majia’s Blog