(7gt) Influence of Radioactivity-Induced Charging on Global Transport of Radioactive Aerosols Released during the Fukushima Daiichi Nuclear Power Plant Accident

Teaching Interests:  Process Principles, Aerosol microphysics, Contaminant Transport, Physicochemical Treatment Process

A modeling effort, which largely depends on microphysical processes, is in progress to accurately predict global transport of beta-emitting radioactive aerosols released during the Fukushima Daiichi nuclear power plant accident. Microphysical processes of aerosols carrying beta-emitting radionuclides can be significantly affected by electrostatic aerosol interactions because aerosols can be strongly charged due to beta decay of the radionuclides. The influence of radioactivity-induced charging (RiC) on aerosol processes, however, has been neglected in global transport modeling studies of radioactive aerosols. Thus, this study is focused on including RiC effects on global transport of radioactive aerosols released during the Fukushima nuclear plant accident. RiC effects on aerosol coagulation are incorporated into the TwO-Moments Aerosol Sectional (TOMAS) module of the Goddard Earth Observing System chemical (GEOS-CHEM) transport model (hereafter GEOS-CHEM/TOMAS-RC). During the Fukushima accident, aerosols initially carrying ¹³¹I, ¹³²Te, ¹³⁴Cs, and ¹³⁷Cs were released into the atmosphere. ¹³²Te is transformed into ¹³²I by beta decay, which is subsequently transformed into ¹³²Xe by beta decay, indicating that the radioactive aerosols can carry up to 5 types of beta-emitting radionuclides during atmospheric dispersion. The effects of the decay and subsequent transformation of radionuclides on radioactivity-induced charging, as well as the compositional change of radioactive aerosols undergoing coagulation, are taken into account in the GEOS-CHEM/TOMAS-RC model. Simulation results of the GEOS-CHEM/TOMAS-RC are in good agreement with measurements of the Comprehensive Nuclear-Test-Ban Treaty Organization. Simulation results of GEOS-CHEM/TOMAS are obtained for reference. It is found that radioactive aerosols can be highly charged during global transport and are widely distributed in the northern hemisphere within a couple of weeks from the onset of the Fukushima accident. Because of strong electrostatic interactions of the aerosols, the activity distributions obtained using GEOS-CHEM/TOMAS-RC were largely different from those of the reference simulation. The implications and limitations of the GEOS-CHEM/TOMAS-RC simulations are discussed.