On the sensitivity of a marine dispersion model to parameters describing the transfers of radionuclides between the liquid and solid phases

Abstract

The sensitivity of a marine dispersion model for non-conservative radionuclides, pre viously developed and validated for the English Channel, to parameters describing the exchanges between the liquid and solid phases (suspended matter and bottom sediments) has been studied using a Monte Carlo method. A probability distribution is assigned to each parameter. They are sampled to obtain a set of model parameters and a model run is carried out. This process is repeated to obtain a distribution of model outputs. Partial correlation coefficients are calculated to assess the relative influence of each parameter on model output. Errors are also assigned to model results. Three situations are studied: an instantaneous release of radionuclides, a continuous release and the case of a contaminated sediment behaving as a long-term source of radionuclides. Calculations have also been carried out for two radionuclides with different geochemical behaviour: 137Cs and 239,240Pu. The results indi cate that all parameters are relevant, depending on the phase we are interested in obtaining the result and on the source term (instantaneous, continuous or due to sediments). However, parameters that are, in general, more influential are kinetic rates, mixing depth in the sedi ment and mean radius of suspended and sediment particles. This suggests that including sev eral particle sizes in future radionuclide dispersion models could lead to an improvement in model results. Differences have also been found with respect to the relevance of some para meters depending on the geochemical behaviour of the radionuclide.