Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 1029-1070, 2015
https://doi.org/10.5194/acp-15-1029-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
30 Jan 2015
Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model
G. Katata1,*, M. Chino1, T. Kobayashi1, H. Terada1, M. Ota1, H. Nagai1, M. Kajino2, R. Draxler3, M. C. Hort4, A. Malo5, T. Torii6, and Y. Sanada7 1Japan Atomic Energy Agency (JAEA), Tokai, Naka, Ibaraki, 319-1195, Japan
2Meteorological Research Institute, Japan Meteorological Agency (JMA), Tsukuba, Ibaraki, 305-0052, Japan
3Air Resources Laboratory, National Oceanic and Atmospheric Administration (NOAA), University Research Court, College Park, Maryland, 20740, USA
4Met Office, Exeter, Devon, EX1 3PB, UK
5Canadian Meteorological Centre (CMC), Dorval, Quebec, H9P 1J3, Canada
6JAEA, Chiyoda, Tokyo, 100-8577, Japan
7JAEA, Fukushima, Fukushima, 960-1296, Japan
*now at: Atmospheric Environmental Research, Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT-IMK/IFU), Germany
Abstract. Temporal variations in the amount of radionuclides released into the atmosphere during the Fukushima Daiichi Nuclear Power Station (FNPS1) accident and their atmospheric and marine dispersion are essential to evaluate the environmental impacts and resultant radiological doses to the public. In this paper, we estimate the detailed atmospheric releases during the accident using a reverse estimation method which calculates the release rates of radionuclides by comparing measurements of air concentration of a radionuclide or its dose rate in the environment with the ones calculated by atmospheric and oceanic transport, dispersion and deposition models. The atmospheric and oceanic models used are WSPEEDI-II (Worldwide version of System for Prediction of Environmental Emergency Dose Information) and SEA-GEARN-FDM (Finite difference oceanic dispersion model), both developed by the authors. A sophisticated deposition scheme, which deals with dry and fog-water depositions, cloud condensation nuclei (CCN) activation, and subsequent wet scavenging due to mixed-phase cloud microphysics (in-cloud scavenging) for radioactive iodine gas (I2 and CH3I) and other particles (CsI, Cs, and Te), was incorporated into WSPEEDI-II to improve the surface deposition calculations. The results revealed that the major releases of radionuclides due to the FNPS1 accident occurred in the following periods during March 2011: the afternoon of 12 March due to the wet venting and hydrogen explosion at Unit 1, midnight of 14 March when the SRV (safety relief valve) was opened three times at Unit 2, the morning and night of 15 March, and the morning of 16 March. According to the simulation results, the highest radioactive contamination areas around FNPS1 were created from 15 to 16 March by complicated interactions among rainfall, plume movements, and the temporal variation of release rates. The simulation by WSPEEDI-II using the new source term reproduced the local and regional patterns of cumulative surface deposition of total 131I and 137Cs and air dose rate obtained by airborne surveys. The new source term was also tested using three atmospheric dispersion models (Modèle Lagrangien de Dispersion de Particules d'ordre zéro: MLDP0, Hybrid Single Particle Lagrangian Integrated Trajectory Model: HYSPLIT, and Met Office's Numerical Atmospheric-dispersion Modelling Environment: NAME) for regional and global calculations, and the calculated results showed good agreement with observed air concentration and surface deposition of 137Cs in eastern Japan.

Citation: Katata, G., Chino, M., Kobayashi, T., Terada, H., Ota, M., Nagai, H., Kajino, M., Draxler, R., Hort, M. C., Malo, A., Torii, T., and Sanada, Y.: Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model, Atmos. Chem. Phys., 15, 1029-1070, https://doi.org/10.5194/acp-15-1029-2015, 2015.
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Short summary
The detailed atmospheric releases during the Fukushima Daiichi Nuclear Power Station accident were estimated using a reverse estimation method with atmospheric and oceanic dispersion models. The major releases occurred on the afternoon of 12 March, midnight of 14 March, the morning and night of 15 March, and the morning of 16 March in 2011. Several atmospheric dispersion models with our new source term reproduced the local and regional patterns of I-131 and Cs-137 deposition and air dose rate.
The detailed atmospheric releases during the Fukushima Daiichi Nuclear Power Station accident...
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