Comparative study of HTO diffusion on individual and coupled systems of compacted bentonite and fresh ordinary Portland cement paste

The radionuclide transport on the interface of compacted bentonite and cementitious materials has been rarely investigated. The goal of our project is to understand how processes at the interface of bentonite and cementitious materials affect the transport properties of bentonite. The paper describes methodology and evaluation procedure applied on HTO through-diffusion experiments on compacted bentonite/fresh hardened cement paste interface (coupled system). Under the same experimental conditions, HTO through-diffusion experiments were performed on individual materials and compared to experiments in the coupled system. To compare these two types of experiments, samples were saturated separately and coupled before the start of the through-diffusion experiments. An original method of modelling and evaluation of through-diffusion experiments performed in coupled system was applied. The effective diffusion coefficients of HTO in the compacted bentonite in both experimental arrangements, individual and coupled, were found to be in a very good agreement. Based on these finding, the prepared procedure of evaluation of through-diffusion experiments on the coupled system of two porous materials can be considered applicable on further planned studies of bentonite interfaces. A less good agreement, but still satisfactory, was obtained for the fresh hardened cement paste.