Coupled processes in the near-field

Underground radioactive waste disposal sites constitute systems of extreme complexity because they are the scene of a great number of physical and chemical phenomena, that have to be included in the safety assessment, and have numerous effects both on the solid confining media (natural and engineered barriers) and on the fluid phase as well as being mutually interactive. They are difficult to quantify because of the lack of field and laboratory data. Although in recent years the tendency in model development has been to treat the phenomena conceptually rather than using the black box' approach, this has oriented the research more toward complicating the basic transport equations (advective-dispersive equation, Darcy's equation) than toward a comprehensive study which would lead to a complete, original and rigorous treatment of the problem as a whole. We are therefore, at present, very far from a unification of the tremendous amount of existing studies which, at the moment, is limited to simply collecting and combining them, more or less successfully (but, at any rate, very empirically). In view of this situation, there is no way of avoiding a review listing the main research fields currently under investigation and the various models to which these investigations have given rise. However, and in the spirit of this workshop, whose aim is to collate these studies, which although they have a common objective are widely scattered, we will present the method which we think is best suited to a rational and exhaustive study of systems with multiple field, potentials and flows, in particular the near field. In doing so, we are encouraged by the increasing number of studies in the same spirit and although this approach seems, at the moment, to belong to a more distant future in model development, we will give a specific example of a case where it can be used with success. (au) (24 refs., 4 figs.)