Radiation Distribution Measurements in Fukushima Prefecture


IEICE TRANSACTIONS on Communications   Vol.E97-B   No.9   pp.1752-1758
Publication Date: 2014/09/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E97.B.1752
Type of Manuscript: INVITED PAPER (Special Section on Ambient Intelligence and Sensor Networks)
wireless,  sensor,  radiation,  network,  

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On March 11, 2011, a huge tsunami caused by the Great East Japan Earthquake destroyed all the electrical power facilities in the Fukushima Daiichi nuclear power plant. As a result, the reactors were badly damaged, and radioactive particles were widely scattered in the surrounding areas. In order to study the behavior of the radioactive particles emitted from the Fukushima Daiichi nuclear power plant, different measurement tools were developed. This paper describes two types of wireless radiation sensor networks and a two-dimensional radiation-level mapping system using a radio-controlled multi-copter. The measurements were analyzed, and the following conclusions were made regarding the radioactive particle distribution and its variation with time.
(1) Radiation level has gradually decreased with time.
(2) The rate of decrease in radiation is faster than that calculated from the half-life.
(3) The radiation-level distribution is not uniform and sharply varies even within short distances such as tens of meters.
(4) The locations of the hot spots have not changed, and the peak radiation levels are constantly decreasing.
By using two-dimensional maps, the radiation levels can be lowered more effectively by selectively removing the highly radioactive materials. The residents can also use the map to reduce their exposure to radiation by avoiding hot spots.