We use a Lagrangian particles dispersal method to track where free floating material (fish larvae, algae, phytoplankton, zooplankton…) present in the sea water near the damaged Fukushima Daiichi nuclear power station plant could have gone since the earthquake on March 11th. THIS IS NOT A REPRESENTATION OF THE RADIOACTIVE PLUME CONCENTRATION. Since we do not know how much contaminated water and at what concentration was released into the ocean, it is impossible to estimate the extent and dilution of the plume. However, field monitoring by TEPCO and modelling by the Sirrocco group in University of Toulouse, France both show high concentration in the surrounding water (highest rate at 80 Bq/L and 24 Bq/L for respectively I-131 and C-137) . Assuming that a part of the passive biomass could have been contaminated in the area, we are trying to track where the radionuclides are spreading as it will eventually climb up the food chain.
The dispersal model is ASR’s Pol3DD. The model is forced by hydrodynamic data from the HYCOM/NCODA system which provides on a weekly basis, daily oceanic current in the world ocean. The resolution in this part of the Pacific Ocean is around 8km x 8km cells. We are treating only the sea surface currents. Particles in the model are continuously released near the Fukushima Daiichi power plant since March 11th. The dispersal model keeps a trace of their visits in the model cells. The results here are expressed in number of visit per surface area of material which has been in contact at least once with the highly concentrated radioactive water.
ASR ltd – Fukushima Radioactive Seawater Plume dispersal simulation