Modeling of strontium leaching from carbonated Portland cement pastes using a simplified diffusion-kinetic analytical model

One of the main challenges in nuclear waste management is to predict release of radionuclides during their long-term disposal within an intact matrix in the repository. One way to tackle this challenge is to conduct leaching experiments which emulate radionuclide release under extreme conditions in a relatively short time. In this work we present a simple analytical diffusion-kinetic model for strontium leaching from cylindrical samples of Portland cement paste. The model accounts explicitly for both strontium diffusion and strontium carbonate precipitation. We compare this model with a standard diffusion model, and demonstrate that it better fits experimental strontium leaching data from samples that showed minor carbonation, as well as samples that showed atmospheric carbonation. This diffusion-kinetic model gives rise to narrower prediction bounds and substantially smaller errors. Furthermore, it provides experimentalists conducting leaching tests an easily implementable tool to analyze their data in systems where precipitation is expected to occur. The approach presented here may serve as an alternative to a plain diffusion analysis often found in standardized leaching protocols, and to more intricate thermodynamic numerical software.