CATCLAY: “Processes of Cation Migration in Clayrocks”

The overall objective of the Euratom CATCLAY project is to provide a scientifically well-grounded answer to the following question: Can the migration of actinides and other strongly sorbing radionuclides in clayrocks under consideration for hosting radioactive waste disposal facilities (OpalinusClay, Switzerland; Callovo-OxfordianClaystones, France; BoomClay, Belgium) be predicted by coupling models of (1)their sorption equilibria on representative clay minerals, and (2)the diffusion-driven mass transport of radionuclide sorbed and dissolved species in compacted masses of these clay minerals? The scientific approach is of the ‘bottom-up’ type, in which simpler, analogous systems (here a compacted clay, ‘pure’ illite) are experimentally studied and modelled, and then the transferability of these results to more complex clayrocks is verified. The cations of interest are the moderately sorbing Sr, and three strongly sorbing cations, Co(II), Zn(II) and Eu(III). The enhanced-diffusion of the sorbing cations of interest has been confirmed both in illite system for Sr2+, Co(II) and Zn(II), and in the natural clayrocks, except for Eu(III). The first modelling approach including diffusion in the diffuse double layer promisingly succeeded in reproducing the experimental data under the various conditions both in illite and clayrocks, even though some assumptions made have to be verified.