2012 年 46 巻 2 号 p. 99-111
Massive radioactive materials were released into the atmosphere after the accident of the Fukushima Daiichi Nuclear Power Plant (FD1NPP) caused by the Tohoku Earthquake and Tsunami on 11 March 2011, and transported and deposited to the land surface in a regional scale. A large amount of dataset has been opened such as the routine monitoring of radiation dose, fallout, and the regional map of radionuclides deposited to the surface soils by an intensive field measurement and aircraft monitoring by MEXT. In contrast, continual field measurements for atmospheric radioactivity were made only at seven stations in the Kanto area, while they are necessary to evaluate the initial radiation exposure, to validate results of atmospheric transport models, and to estimate the emission inventory of radionuclides. In this review, the following five points are introduced. (1) Summary of release rate estimation from the FD1NPP by the combination of WSPEEDI-II with atmospheric radioactivity of 131I and 137Cs and radiation dose. (2) The possible mechanisms of many peaks of radiation dose during 11-16 March 2011 which were measured at the monitoring posts near the FD1NPP. (3) Possible mechanism of regional transport and the surface deposition of radionuclides. (4) Summary of atmospheric 131I in aerosols and gases, and 131I/137Cs in the atmospheric radioactivity. (5) An intensive one-year field measurement of atmospheric radioactivity of 137Cs at Fukushima and Koriyama since May 2011.