A three dimensional σ-coordinate model to simulate the dispersion of radionuclides in the marine environment: application to the Irish Sea

A three dimensional model to simulate the tide induced dispersion of radionuclides in the sea has been developed. The model uses normalized σ-coordinates in the vertical so that resolution is not reduced in the shallower regions. The hydrodynamic equations are solved and, simultaneously, the three dimensional advection diffusion dispersion equation (also written in normalized coordinates) is solved too. An instantaneous flow and depth dependent eddy viscosity has been used. The model has been applied to study the dispersion of l37Cs in the eastern Irish Sea, where a nuclear fuel reprocessing plant releases radionuclides. The hydrodynamic part of the model has been tested by comparing observed and computed values of tidal elevations, phases and currents. The model gives, in general, a good representation of the water circulation in the sea. Also, it gives results in agreement with observations when measured and computed levels of l37Cs are compared. In order to show how the model can be used to obtain water quality parameters of interest, it has been applied to obtain the turn over time of a region of the sea. It has also been applied to simulate the dispersion of a pollutant after an hypothetical accidental discharge.