Abstract
In order to assess the radiological dose to the public resulting from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan, especially for the early phase of the accident when no measured data are available for that purpose, the spatial and temporal distribution of radioactive materials in the environment are reconstructed by computer simulations. In this study, by refining the source term of radioactive materials discharged into the atmosphere and modifying the atmospheric transport, dispersion and deposition model (ATDM), the atmospheric dispersion simulation of radioactive materials is improved. Then, a database of spatiotemporal distribution of radioactive materials in the air and on the ground surface is developed from the output of the simulation. This database is used in other studies for the dose assessment by coupling with the behavioral pattern of evacuees from the FDNPS accident. By the improvement of the ATDM simulation to use a new meteorological model and sophisticated deposition scheme, the ATDM simulations reproduced well the 137 Cs and 131 I deposition patterns. For the better reproducibility of dispersion processes, further refinement of the source term was carried out by optimizing it to the improved ATDM simulation by using new monitoring data.
Highlights
The Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan, which was triggered by the magnitude 9.0 earthquake and resulting tsunami on March 11, 2011, caused a month-long discharge of significant amount of radioactive materials into the atmosphere
Deposition pattern was increased by using the new source term and new GEARN, especially around southwestern and northern areas from FDNPS, where the original WSPEEDI (Fig. 5(a)) under- and over-estimated, respectively, compared with the 137Cs deposition of airborne monitoring (Fig. 6(a))
The reproducibility of 137Cs deposition pattern in the vicinity of FDNPS was decreased by using WRF
Summary
The Fukushima Daiichi Nuclear Power Station (FDNPS) accident in Japan, which was triggered by the magnitude 9.0 earthquake and resulting tsunami on March 11, 2011, caused a month-long discharge of significant amount of radioactive materials into the atmosphere. One is for the internal dose due to short lived radionuclides such as radioiodine during the early phase of the accident, which cannot be assessed by using measured data Another is for the external dose due to the direct radiation from radioactive plume and the ground shine at the point without measurement, which were considered to have large temporal variation caused by several plume passages. To solve these problems, the atmospheric transport, dispersion and deposition model (ATDM) simulation that can reproduce the spatial and temporal distribution of radioactive materials is useful. By simulating atmospheric dispersion conditions to be consistent with measurements, calculation results can complement spatiotemporally discrete measurements for dose assessment
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