Development and issues of air dose rate monitoring systems in Fukushima prefecture with emphasis on portable monitoring posts

As a countermeasure against the nuclear disaster that took place in Fukushima, Japan in mid-March, 2011, a number of monitoring posts, including portable ones, have been introduced particularly to Fukushima prefecture among others. First, in this paper the damages and countermeasures concerning principally the air dose-rate monitoring systems that were prepared prior to the Great East Japan Earthquake, which triggered the giant tidal waves, and then caused the nuclear accident are reviewed. The tidal waves also damaged the radiation monitoring systems in Fukushima prefecture so severely that for nearly half a month following the nuclear accident there were hardly any organized monitoring activities within the 20 km range of the nuclear power plant. Nevertheless, outside the 20 km range the promptly constructed air dose-rate monitoring system could largely track main flows of radioactive plumes emitted from the nuclear plant. Starting from this situation, in this report, how a large-scale monitoring system with over 600 portable monitoring posts among others has been developed in Fukushima prefecture is reviewed. Furthermore, the operation records of the newly constructed monitoring system are analyzed. Consequently, it is revealed that more missing data tend to emerge at considerably high rates in every winter, and the trend is still maintained. (author)