Long-term leaching experiments of full-scale cemented waste forms: Experiments and modeling

Experimental findings of full-scale leach tests performed on simulated cemented waste forms and self-shielded concrete waste containers for periods up to 19 yr in saturated salt brines (NaCl- and Q-brine) are presented. Measurements cover the evolution of leachant composition and the release of radionuclides such as Cs, U, and Np. Performance of the waste forms and the self-shielded concrete waste containers depends on the pore volume of the hardened cement/concrete, which is correlated to the water/cement ratio of the waste forms. Cesium release follows a linear time dependence. Samples, especially those having a high pore volume, show almost complete release of Cs in. the period of investigation. Uranium release is independent of the leach period. Uranium concentrations are controlled by thermodynamic equilibrium Neptunium is released only to a small extent; concentrations are close to the detection limit. Modeling of the cement corrosion progress allows the prediction of the evolution of the brines in terms of pH, calcium concentration, etc. and the identification of solids controlling the solubilities of the main components and of uranium.