Source term estimation and atmospheric dispersion simulations of radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant due to accident

Nagai, Haruyasu  ; Chino, Masamichi; Terada, Hiroaki   ; Katata, Genki; Nakayama, Hiromasa   ; Ota, Masakazu  

Japan Atomic Energy Agency (JAEA) has been undertaking the task to reconstruct the atmospheric dispersion of radioactive materials discharged from the Fukushima Daiichi Nuclear Power Plant by using computer simulation. As the first step, the source term of radioactive materials discharged into the atmosphere was estimated by coupling environmental monitoring data with atmospheric dispersion simulations under the assumption of unit release rate (1 Bq/h). By using the estimated source term, detailed analysis on the local dispersion around the plant and regional scale dispersion over the eastern Japan area were carried out by WSPEEDI-II simulations. The formation processes of high dose rate zone around north-west direction from the plant and deposition over the eastern Japan area were well reproduced.