Preliminary Numerical Experiments on Oceanic Dispersion

It was reported that after the magnitude 9.0 earthquake and resulting tsunami that occurred on March 11, 2011, some radioactive material, including iodine and cesium, was discharged into the Pacific Ocean because of the Fukushima Daiichi nuclear power plant (NPP) disaster. High concentrations of I and Cs were found in the seawater and seabed sediment along the coastline of Fukushima Prefecture. In addition, radionuclides were detected in marine products caught near Fukushima Prefecture. In response to this situation, assessment of the distribution of concentrations of radioactive materials by means of computer simulation, as well as oceanic survey, is urgently required. The Japan Atomic Energy Agency (JAEA), in cooperation with the Japan Marine Science Foundation and Kyoto University, has been working on numerical experiments to predict the spread of I and Cs in the marine environment and to estimate how much of these materials were released. The numerical experiments were carried out using the oceanic dispersion model SEA-GEARN and the ocean general circulation model (OGCM) developed by Kyoto University and the Japan Marine Science Foundation. The numerical experiments took into account depositions calculated using the atmospheric dispersion model GEARN in WSPEEDI-II of I and Cs released into the atmosphere. The numerical experiments were performed from March 12 to April 30, 2011. This paper focuses on the amounts of I and Cs that were released during the above-mentioned period, as well as the concentrations of these materials in the seawater. II. Description of Numerical Experiments