A three-scales model for the dispersion of radioactive spots from nuclear emergencies. Application to the Baltic Sea after the accident of Chernobyl

This model is a improved version of a previously published Two-Scales model 1111 and includes the transport of particles in three spatial scales: small (kilometres), medium (decades of km), and large (hundreds of km). A 3-D dispersion model has been developed to analyse and simulate the dispersion of nuclear contaminants in marine ecosystems. This model is characterized by presenting high spatial resolution, by taking into account the possible binding of a fraction of the Contaminants to the suspended matter as well as its consequent sedimentation, and especially by formulating the diffusion processes using an original approach. The horizontal resolution of the model is 20 km, while for the vertical resolution a total of six layers are considered. The Baltic Sea has heen elected as the validation scenario of the model and the radionuclide Cs-137 as the radiotracer to be analysed. This scenario was the most contaminated ecosystem out of the Sonet Union due to the Chernohyl accident occurred at the end of April 1986, and the elected radiotracer Cs-137 was the main long-lived radioisotope emitted to the environment. A computation time of approximately 9 hours by using a Matlab code in a personal computer (AMD-1.4 GHz) was necessary. Different classical tools in Oceanography as well as different numerical methods (Monte Carlo, Finite differences) have been properly implemented in the model. The approaches adopted allow to save a lot of computational time [lo]