Comparative analysis of nuclear waste solidification performance models: Spent ion exchanger-cement based wasteforms

Abstract

Solidification performance for cement based radioactive wasteforms was investigated and linked to the hydraulic performance using mechanistic and empirical models. Within this context, the short-term developments of the compressive strength, porosity, and permeability of cement based matrices of varying water content were assessed. For matrices of low-water content, diffusion reaction is the dominant solidification mechanism due to super-saturation of CSH phases. As the water content increases, nucleation and growth reaction controls the process. The nature of the immobilization of inorganic ion exchangers and polymer modification in cement based matrices and its effect on the relative change in the compressive strength and permeability were investigated. The reductions in the solidification performance for cement-inorganic exchanger wasteforms were attributed to the excess amount of Ettringite in case of alumina exchangers and to the reduction in the hydrated phases formation for the rest of the inorganic exchangers. The permeability of the alumina-cement wasteform is fairly constant up to 16 % loading, whereas this behavior is noted up to 10 % loading of the rest of the inorganic exchanger and absent for organic exchangers-modified cement wasteforms.