Modelling the global atmospheric transport and deposition of radionuclides from the Fukushima Dai-ichi nuclear accident

Abstract. We modeled the global atmospheric dispersion and deposition of radionuclides released from the Fukushima Dai-ichi nuclear power plant accident. The EMAC atmospheric chemistry – general circulation model was used, with circulation dynamics nudged towards ERA-Interim reanalysis data. We applied a resolution of approximately 0.5 degrees in latitude and longitude (T255). The model accounts for emissions and transport of the radioactive isotopes ¹³¹I and ¹³⁷Cs, and removal processes through precipitation, particle sedimentation and dry deposition. In addition, we simulated the release of ¹³³Xe, a noble gas that can be regarded as a passive transport tracer of contaminated air. The source terms are based on Chino et al. (2011) and Stohl et al. (2012); especially the emission estimates of ¹³¹I are associated with a high degree of uncertainty. The calculated concentrations have been compared to station observations by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO). We calculated that about 80% of the radioactivity from Fukushima which was released to the atmosphere deposited into the Pacific Ocean. In Japan a large inhabited land area was contaminated by more than 40 kBq m^-2. We also estimated the inhalation and 50-year dose by ¹³⁷Cs, ¹³⁴Cs and ¹³¹I to which the people in Japan are exposed.