Interaction of cementitious materials with high-level waste matrices

The paper discusses the expected evolution of the interface between the waste form and the near field in the case of disposal following the Supercontainer Design, and the main mechanisms of radionuclide release by the waste forms and how they are expected to be influenced by the concrete of the Supercontainer. The related experimental programme and its first results are presented. The Supercontainer conditions probably increase the radionuclide release rate from vitrified waste, compared to bentonite based engineered barrier system, because of pump effect by secondary phase formation at high pH. A decrease of dissolution rate possible only if pH at the glass surface decreases with time. This is likely but difficult to quantify. The high pH of Supercontainer conditions seems to have relatively little effect on the long term fuel stability, but some potential problems (alpha threshold, colloid formation, difference between UO2 and spent fuel, impact of sorption on concrete) must be investigated more in detail.