Multiscale and multiphase Lagrangian modelling of the radioactivity dispersion in the sea after accident at the Fukushima NPP.

Abstract

The Lagrangian multiphase model of the radionuclide transport in the sea is applied to simulate dispersion of radioactivity released from Fukushima dai ichi NPP due to the accident. The particle-tracking model describes transport and transfers of radioactivity between water, suspended and bottom sediments. The sediment transport model simulates deposition and resuspension of non-cohesive, cohesive sediments and mixture of fractions of different size of cohesive/non-cohesive sediments. The Pacific Ocean currents are simulated using MOM3 model with resolution whereas coastal transport processes are described by coastal circulation model with high resolution. A number of scenarios of radioactivity release were simulated and results were compared with available observations of radionuclide concentrations. It was concluded that main problems in predicting radioactivity dispersion in the Fukushima NPP case are (i) correct estimation of source including air deposition and coastal run-off and (ii) accurate prediction of local currents because they are driven here by highly variable currents governed by Kuroshio/Oyashio system. The Fukushima NPP accident clearly demonstrated need in integrated regional system of forecasts of radioactivity dispersion in air, ground and marine environments to be used in comprehensive decision-support systems.ansfers of radioactivity between water, suspended and bottom sediments. The sediment transport model simulates deposition and resuspension of non-cohesive, cohesive sediments and mixture of fractions of different size of cohesive/non-cohesive sediments. The Pacific Ocean currents are simulated using MOM3 model with resolution whereas coastal transport processes are described by coastal circulation model with high resolution. A number of scenarios of radioactivity release were simulated and results were compared with available observations of radionuclide concentrations. It was concluded that