Influence of emission rate on atmospheric dispersion modeling of the Fukushima Daiichi Nuclear Power Plant accident

The role of emission rate in atmospheric dispersion modeling was investigated in this study. Six different emission rates that were estimated by the Japan Atomic Energy Agency and Norwegian Institute for Air Research after the Fukushima Daiichi Nuclear Power Plant accident were used as inputs to FLEXPART-WRF, a Lagrangian particle dispersion model. High-resolution (1 km) meteorological data in a local scale region (100 km) were downscaled dynamically by the Weather Research and Forecasting model from a reanalysis of ERA-Interim during 11-31 March, 2011, and were used to drive the model. The accumulated deposition of 137Cs was used to assess the simulations. Deposition occurred mainly during four periods dominated by wet deposition due to precipitation, which were 15, 20-22, 25, and 30-31 March. The basic deposition pattern was established on 15 March, shortly after the highest emission rates of 14 March, and the largest variation in deposition with the different emission rates was also observed in this period. Emission rates estimated are usually not independent from the models and meteorological input data. The model-meteorology combination used for emergency response activities had better be the one used to determine the source term.