Modelling of ⁶⁰Co concentrations in the dissolved and particulate phases in the Loire estuary

EDF, Laboratoire National d'Hydraulique et Environnement, 6 quai Watier, 78401 Chatou cedex, France

Abstract

EDF has initiated a program assessing the fate of radionuclides released by nuclear power plants located along the river basin. In order to estimate the behaviour of radionuclides associated with suspended sediment in the Loire estuary, a multivariate transport model has been developed. Several dissolved and particulate constituents can be simultaneously computed, the later being followed in the superficial sediment according to the deposition events. Modelling of salinity and suspended matter was included as having an influence on sorption kinetics, and on radionuclide transport. Indeed, the association of radionuclides with particle can affect their residence time in sedimentation zones of water systems. Partitioning of radionuclides between water and suspended matter is usually expressed as Kd, concentration ratio between particulate and dissolved phases. In the simulations presented, particulate and dissolved ⁶⁰Co behaviour were considered to interact with suspended solids and salinity trough sorption and desorption kinetics, distribution coefficients being considered as representing equilibrium conditions seldom reached in nature. Simulation was carried out for two river discharges (high river input and low river input). The computed results are compared with observed values for surface levels, salinity and suspended matter as well as ⁶⁰Co concentrations.