11. Marine Dispersion Modelling and Expertise Tools for Accidental Radiological Contamination of French Coasts

IRSN develop tools to manage any marine contamination of French coastal areas. In case of radioactive accidental marine contamination, we should be able to evaluate and anticipate the post-accidental situation: contaminated areas localisation and contamination levels, and possible consequences. Many sites should be considered for potential source terms into the sea: Coastal Nuclear Facilities, Military Harbours as homeports of nuclear powered vessels, and different river mouths that could be contaminated by any accidental release from a nuclear power plants situated upstream.

The modelling tool, STERNE (Simulation du Transport et du transfert d’Eléments Radioactifs dans l’environNEment marin), simulates radionuclide dispersion and contamination of water and marine species, incorporating spatial and temporal processes. To operate it, 3D hydrodynamic data should be provided routinely to IRSN crisis center. Different possible radiological source terms can be taken into account: direct liquid releases, atmospheric depositions or river inputs of radionuclides. STERNE calculates radionuclides transport using advection and diffusion equations offline from hydrodynamic calculation. Radioecological model based on dynamic transfer equation to evaluate concentrations in marine organisms is also implemented. Needed radioecological parameters (concentration factors and single or multicomponent biological half-lives) have been compiled for some important radionuclides and for generic marine species (fishes, molluscs, crustaceans). Dispersion and transfer calculations are carried out simultaneously on a 3D grid. Results, available as netcdf files can be represented on maps, with possibility to follows temporal and spatial evolution. Post-treatment and representation are then possible.

In parallel, marine environment stakes and characteristics are compiled for the different sites, identifying potential stakes for human protection like aquaculture areas, beaches, or industrial water intakes, and ecological richness. This information will be used to facilitate decision-making during an emergency and could serve as a basis for post-accident sampling strategies leading to realistic environmental impact assessment.