A numerical model that simulates the dispersion of radionuclides in the English Channel has been applied to study the dispersion of conservative and non-conservative radionuclides released from La Hague nuclear fuel reprocessing plant. The model is based upon previous work and now is able to simulate dispersion over long time scales (decades), explicitly including transport by instantaneous tidal currents and variable wind conditions. Wind conditions are obtained from meteorological statistics using a stochastic method. Outputs from the model are treated using time-series analysis techniques. These techniques allow the determination of characteristic times of the system, transport velocities and dispersion factors. This information may be very useful to support the decision-making process after an emergency situation. Thus, we are proposing that time-series analysis can be integrated with numerical modelling for helping decision-making in response to an accident. The model is first validated through its application to actual releases of 99-Tc and 125-Sb, and characteristic times for several radionuclides (a conservative one, 137-Cs and 239,240-Pu) are given next. Characteristic transport velocities and dispersion factors have been calculated as well.