Modeling and sensitivity analysis of transport and deposition of radionuclides from the Fukushima Daiichi accident

Abstract

Abstract. The atmospheric transport and ground deposition of radioactive isotopes 131I and 137Cs during and after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident (March 2011) are investigated using the Weather Research and Forecasting/Chemistry (WRF/Chem) model. The aim is to assess the skill of WRF in simulating these processes and the sensitivity of the model's performance to various parameterizations of unresolved physics. The WRF/Chem model is first upgraded by implementing a radioactive decay term into the advection-diffusion solver and adding three parameterizations for dry deposition and two parameterizations for wet deposition. Different microphysics and horizontal turbulent diffusion schemes are then tested for their ability to reproduce observed meteorological conditions. Subsequently, the influence on the simulated transport and deposition of the characteristics of the emission source, including the emission rate, the gas partitioning of 131I and the size distribution of 137Cs, is examined. The results show that the model can predict the wind fields and rainfall realistically. The ground deposition of the radionuclides can also potentially be captured well but it is very sensitive to the emission characterization. It is found that the total deposition is most influenced by the emission rate for both 131I and 137Cs; while it is less sensitive to the dry deposition parameterizations. Moreover, for 131I, the deposition is also sensitive to the microphysics schemes, the horizontal diffusion schemes, gas partitioning and wet deposition parameterizations; while for 137Cs, the deposition is very sensitive to the microphysics schemes and wet deposition parameterizations, and it is also sensitive to the horizontal diffusion schemes and the size distribution.

Horizontal Resolution Dependence of Atmospheric Simulations of the Fukushima Nuclear Accident Using 15-km, 3-km, and 500-m Grid Models

“…This was most likely because these two models had completely different aerosol physics (cf. sensitivity studies conducted by Draxler et al 2015;Morino et al 2013;Hu et al 2014) and vertical advection handling at the lowermost model layer.…”

“…The accident became the largest nuclear disaster since Chernobyl, and resulted in the dispersion and deposition of a large amount of radionuclides in the environment of eastern Japan. Since then many numerical simulations have been performed to predict or assess the effects of the nuclear accident using atmospheric chemistry transport models (e.g., Chino et al 2011;Morino et al 2011Morino et al , 2013Yasunari et al 2011;Takemura et al 2011;Schöp-pner et al 2011;Sugiyama et al 2012;Mathieu et al 2012;Stohl et al 2012;Katata et al 2012a, b;Terada et al 2012;Christoudias and Lelieveld 2013;Adachi et al 2013;Saito et al 2015;Hu et al 2014;Arnold et al 2015). Some models were used to estimate the amount of radionuclides released from the FDNPP, coupled with a reverse analysis.…”