If a nuclear accident occurs, how will the radioactive spots be transported by the ocean?

This work is the second improved version of a previously published Two-Scales model (M. Toscano-Jimenez, R. Garcia-Tenorio, 2004) for the transport of the nuclear contamination in the ocean. The last advances are: the transport of particles in a third spatial scale (hundreds of km), a new erosion-sedimentation submodel, a new diffusion approach related to analytical methods and a final calibration of the diffusion problems. The Baltic Sea has been 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 Soviet Union due to the Chernobyl accident that occurred at the end of April 1986, and the elected radiotracer Cs-137 was the main long-lived radioisotope emitted to the environment. However, an important aim of this model, validated successfully in the Baltic Sea, is its potential usefulness in other oceanic scenarios affected by a nuclear disaster in the future. It could be an interesting tool to predict and minimize the ecological and economical impacts of future accidents. This model can also be extended easily to nonnuclear contamination problems. It must be noted that the model is three-dimensional and that it is characterized 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 and advection processes. The horizontal resolution of the model is 20 km, while for the vertical resolution a total of six layers are considered. A computation time of approximately 5 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 (Monte Carlo, finite differences) and analytical methods have been properly implemented in the model. The approaches adopted allow us to save a lot of computational time (M. Toscano-Jimenez, R. Garcia-Tenorio, 2003). Experimental information on current spectra has been analysed. The model as a whole has been validated by comparing the evolution of the Cs-137 concentrations with experimental data taken from the literature. The Cs-137 model predictions are in an acceptable agreement with the experimental Cs-137 maps, thereby guaranteeing the validity of the model.