Dr. Tsubokura's Radiation Lecture Vol.104

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

107. Differences between two post-nuclear disaster evacuation plans

Among all the nuclear incidents that have occurred in the past, the Fukushima Daiichi nuclear power plant accident and the 1986 Chernobyl disaster are the only such events classified as level 7 accidents according to the International Nuclear Events Scale. Although these two events received the same rating, their circumstances and subsequent countermeasures differed.

　In both cases, evacuation plans were formulated based on the estimated annual accumulated air dose rate. However, their estimated levels differed.

　Following the Chernobyl accident, the air dose rate criterion for evacuation was a minimum of 100 millisieverts per year for the first year, meaning that it was mandatory for the residents living in areas with annual air dose rates exceeding 100 millisieverts to evacuate. This decreased to 30 millisieverts in the second year, 25 millisieverts in the third and fourth years, 20 millisieverts in the fifth year, and 5 millisieverts in the sixth year and thereafter. On the other hand, after the Fukushima nuclear disaster, this criterion was set at an annual air dose rate of 20 millisieverts from the first year, and it remained at this level in subsequent years.