Sorption results obtained with Boom clay for Am, Pu, Eu, Tc and Np under near in-situ conditions are presented, and the significance of K d values in Boom clay is discussed. Clay humic acids are shown to be a controlling factor in the sorption of Am, Eu, Np.
Results with Tc and Pu are different and need further examination. Experiments to determine the mobility of light molecular weight organic material in compacted Boom clay is discussed.
INTRODUCT~N
The Belgian programme of basic research in the migration of radionuclides in Boom clay (B.C.) has been operating along two ways. The first approach, carried out on the CEN/SCK site of Mol, has attempted to obtain data for i~ ready use in migration modelling mainly from diffusion experiments on clay plugs with and without reconsolidation, with a great concern for preserving or reproducing the real conditions of the clay in the formation. The second aspect, more academic, aims at identifying the nature of the interactions between the mdionuclides and the clay and to elucidate the various mechanisms of the retention. It has mainly been the task of A. Cremers and others in the Catholic University of Leuven (K.U.L.) in close collaboration with the CEN/ SCK (Bayens, 1984b, c, d).
However, the direct approach to the study of migration appeared unsatisfactory if considered alone. The rate of obtaining useful data is indeed far too slow. Other routes, such as sorption studies and the measurement of low D's in clay gels were therefore followed to attempt the evaluation of migration parameters (Cremers and Thomas, 1966;Cremers, 1968Cremers, , 1984)). The interactions during migration of the various active waste elements between themselves and with the much more abundant inactive ones can be estimated from the knowledge of the sorption mechanisms that have been identified for the waste elements. *Work performed under contract with the European Atomic Energy Community in the performance of its R & D-programme on Management and Storage of Radioactive Waste.