Reverse estimation of amounts of I and Cs discharged into the atmosphere

Terada, Hiroaki   ; Chino, Masamichi

Japan Atomic Energy Agency has been trying to estimate the source term of iodine and cesium discharged from the Fukushima Daiichi Nuclear Power Station into the atmosphere for the assessment of the radiological dose to the public. The method applied in this estimation is a reverse estimation of source term by coupling environmental monitoring data with atmospheric dispersion simulations under the assumption of unit release rate (1 Bq h). For the source term estimation, environmental monitoring data on air concentrations of iodine and cesium and air dose rates were used. These data were observed over East Japan, almost in Fukushima Prefecture. The SPEEDI (System for Prediction of Environmental Emergency Dose Information) network system and the Worldwide version of SPEEDI (WSPEEDI-II) were used for calculating air concentrations and dose rates. We estimated the release rates and total amounts of I and Cs from March 12 to April 5, 2011.