Modeling and sensitivity analysis of transport and deposition of radionuclides from the Fukushima Dai-ichi accident

X Hu,E Bou-Zeid,D Li,S Shen,H Huang

doi:10.5194/acp-14-11065-2014

Abstract

Abstract. The atmospheric transport and ground deposition of radioactive isotopes 131I and 137Cs during and after the Fukushima Dai-ichi 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 of emission characteristics (including the emission rate, the gas partitioning of 131I and the size distribution of 137Cs) on the simulated transport and deposition is examined. The results show that the model can predict the wind fields and rainfall realistically and that the ground deposition of the radionuclides can also be captured reasonably well. The modeled precipitation is largely influenced by the microphysics schemes, while the influence of the horizontal diffusion schemes on the wind fields is subtle. However, the ground deposition of radionuclides is sensitive to both horizontal diffusion schemes and microphysical schemes. Wet deposition dominated over dry deposition at most of the observation stations, but not at all locations in the simulated domain. To assess the sensitivity of the total daily deposition to all of the model physics and inputs, the averaged absolute value of the difference (AAD) is proposed. Based on AAD, the total deposition is mainly influenced by the emission rate for both 131I and 137Cs; while it is not sensitive to the dry deposition parameterizations since the dry deposition is just a minor fraction of the total deposition. Moreover, for 131I, the deposition is moderately sensitive (AAD between 10 and 40% between different runs) to the microphysics schemes, the horizontal diffusion schemes, gas-partitioning and wet deposition parameterizations. For 137Cs, the deposition is very sensitive (AAD exceeding 40% between different runs) to the microphysics schemes and wet deposition parameterizations, but moderately sensitive to the horizontal diffusion schemes and the size distribution.

Highlights

Large amounts of radionuclides were released into the atmosphere after the nuclear accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) on 11 March 2011
Hu et al.: Modeling and sensitivity analysis of transport and deposition of radionuclides deposition of radionuclides (Andronopoulos and Bartzis, 2010; de Sampaio et al, 2008; Lauritzen et al, 2007; Lutman et al, 2004; Terada and Chino, 2008; Leelossy et al, 2011). For this particular accident at Fukushima, the Community Multi-scale Air Quality (CMAQ) model (Morino et al, 2011), the Lagrangian transport models HYSPLIT and FLEXPART with meteorological conditions provided by the Weather Research and Forecasting (WRF) model (Srinivas et al, 2012), and the WRF-Chem tracer model which directly couples the simulation of the chemistry and meteorology (Huh et al, 2012, 2013) have been used
Tokyo Electric Power Company (TEPCO) (2012) estimated the amount of 131I and 137Cs released to the atmosphere using their company’s atmospheric dispersion calculation program Dose Information Analysis for Nuclear Accident (DIANA) and the air dose rate measured from a monitoring car that moved around the FDNPP

Summary

Introduction

Large amounts of radionuclides were released into the atmosphere after the nuclear accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) on 11 March 2011. Hu et al.: Modeling and sensitivity analysis of transport and deposition of radionuclides deposition of radionuclides (Andronopoulos and Bartzis, 2010; de Sampaio et al, 2008; Lauritzen et al, 2007; Lutman et al, 2004; Terada and Chino, 2008; Leelossy et al, 2011) For this particular accident at Fukushima, the Community Multi-scale Air Quality (CMAQ) model (Morino et al, 2011), the Lagrangian transport models HYSPLIT and FLEXPART with meteorological conditions provided by the Weather Research and Forecasting (WRF) model (Srinivas et al, 2012), and the WRF-Chem tracer model which directly couples the simulation of the chemistry and meteorology (Huh et al, 2012, 2013) have been used. It is clear that an accurate simulation of meteorological fields is a necessary condition for the accurate simulation of the transport and deposition of the radionuclides

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Conclusion