Modelling the tidal dispersion of 137Cs and 239,240Pu in the English Channel

A numerical model to simulate the tidal dispersion of non-conservative radionuclides in the English Channel has been developed. The model solves the shallow water hydrodynamic equations and, simultaneously, the suspended matter equation which includes deposition and resuspension terms. The model considers that radionuclides can be present in three phases: water, suspended matter and bottom sediments. Thus the equations whose solutions give the temporal evolution of activities in the three phases must be solved too. The transfer of radionuclides between the liquid and solid phases has been described in terms of kinetic transfer coefficients. The model has been applied to simulate the dispersion of 137Cs and 239,240Pu released from a nuclear fuel reprocessing plant at La Hague (France). The model gives a realistic estimation of the activity levels detected in the Channel. The transit time of radionuclides from La Hague to the Dover Strait has also been calculated, using the cross-correlation function method, under different weather conditions.