A regional simulation study on dispersion of nuclear pollution from the damaged Fukushima Nuclear Power Plant

A nuclear accident involving the leaking of radioactive pollutants occurred at the Fukushima Nuclear Power Plant in Japan, following an earthquake and subsequent tsunami on March 11, 2011. Using official Japanese data on pollutant emissions during the accident, this study simulates the dispersion of nuclear pollutants. The source term of the nuclear leakage of radioactive material is designed using PM2.5 as the tracer of radioactive pollutants, and the study considers dry and wet deposition processes. A coupled-model system is constructed from the air-quality model Models-3/CMAQ and the Weather Research and Forecasting atmospheric model. The transport path and distribution of radioactive pollutants over long and short distances are simulated with different model horizontal resolutions of 30 and 4 km respectively. The long-distance simulation shows that, following the Fukushima nuclear accident, under the effect of westerly winds, radioactive pollutants are transported generally towards the eastern Pacific and reach the American continent after 5 days, but their concentration is only about 10(-7) times the concentration near the Fukushima Nuclear Power Plant. The time required for pollutants to reach the United States is basically consistent with measurements made in California on March 18. Because the upper westerly wind is faster than the lower westerly wind, the distribution of pollutants tilts eastward in terms of its vertical structure. The short-distance (local) high-resolution simulation indicates that strong winds and precipitation associated with a cyclone can accelerate the deposition, diffusion and transport of pollutions, and local cyclonic circulation can change the transport path of pollutants, even resulting in repeated effects of pollution in some areas. Pollutants disperse to southeastern Honshu, Japan, on March 14, 2011, agreeing well with the timing of local observations of increases in the absorbed dose rate. Results also show that radioactive pollutants from the Fukushima nuclear accident are mainly transported and diffuse eastward, resulting in a relatively short-term impact on the Japanese mainland even under the influence of the cyclone system. Therefore, in terms of atmospheric conditions, the location of the Fukushima Nuclear Power Plant is appropriate and could serve as a reference to site selection and protection of other nuclear facilities.