Numerical simulation of the dispersion of artificial radionuclides in the English Channel and the North Sea

Numerical simulations of the drift and dispersion of the artificial radionuclide technetium-99 (99Tc) are performed with a Lagrangian dispersion model. The dispersion model is driven by currents and winds from a 3-D baroclinic circulation model which operates in daily routine. A point source is assumed at Cap de La Hague at which model particles are released one hour after local high water. Using discharge data from the nuclear reprocessing plant at Cap de La Hague, spatial distributions of 99Tc and their temporal evolution are simulated. Driven by currents and winds, the particles are transported through the southern and eastern North Sea into the Skagerrak and the northern North Sea. The calculations cover the period from March 1991 to December 1992. From particle distributions, transport times and transport velocities are calculated. Model data are compared with observations of 99Tc during overview cruises and from time series at certain locations. Generally, agreement between the simulations and measurements is found in the order and the long term trend of 99Tc concentrations.