Characterization of clay (bentonite)/crushed granite mixtures to build barriers against the migration of radionuclides: diffusion studies and physical properties.

Abstract

Granitic rocks are considered as one of the probable sites for the storage of high level radioactive wastes in Spain. The engineered barriers play, in this type of rocks, an essential role becauso the must guarantee the protection of the canister against the agressiveness of the environment, the longest possible delay of the transfer of radionuclides to the hydrogeologic environment and the isolation of the storage itself. The materials used as barriers must meet a series of characteristics, such as: low hydraulic conductivity, high thermal conductivity , high swelling capacity, hicgh radionuclide retention capacity and a mineralogical stability preserved for the site conditions and for a long period of time. These properties ar met, in general, by smectitic clays compacted at high densities. The study of these properties in Spanish clays is the principal objective of this contract (CEC Nº FI 1W-0191-ECTT), wich also considers the possibility of usaing illitic clays and crushed granites, in order to decrease the mineralogical disequilibrium between the barrier an the storage rock. Once a detailed haracteristaiopn of thirty commercial Spanish clays was carried out, two of them were selected, one illitic and the other smectitic to carry on further studies on: mechanical, hydraulic and thermal properties of the compacted blocks, radionuclide retention capacity, solution diffusivity and mineralogical stability.