Radionuclide dispersion simulations for the Fukushima case are conducted using a high-resolution nested ocean prediction model, called as Japan Coastal Ocean Predictability Experiment (JCOPE). The JCOPE model has been developed, based on the Princeton Ocean Model, to provide information about upper-ocean conditions near Japan both for research and application purposes. Both a particle tracking method and an advection-diffusion code are utilized for dispersion simulations of radionuclide that is discharged directly into the ocean. Results indicate reasonable distribution of Cesium 137 and Iodine 131 after the incident.

The results demonstrate complex current fields and their variability associated with local wind forcing, tides, and meso-scale eddies in the area off Fukushima. The radionuclides are significantly dispersed due to strong mixing effects of the surface current variability. In the near-shore region, the wind forcing is a dominant factor that controls the flow field, while large-scale currents and eddies advect the radionuclides in the off-shore region. A part of the radionuclides are transported rapidly to the east along the northern flank of Kuroshio.

An additional case including atmospheric fallout is under calculation and comparisons of the results from the two cases will also be discussed in the presentation.