Modeling the long-term leaching behavior of 137Cs, 60Co, and 152,154Eu radionuclides from cement–clay matrices

This study investigates the leaching characteristics of radionuclides commonly found in radioactive waste streams, specifically 137Cs, 60Co, and 152,154Eu, from immobilized waste matrices in various cement–clay grouts to understand the effect of clay additives on the leaching behavior. The objective was to assess how different clay components influence the leaching patterns of these solid waste matrices. The methodology involved employing the International Atomic Energy Agency (IAEA) standard leaching method to analyze the leach patterns of radionuclides immobilized in ordinary Portland cement (OPC), OPC–bentonite, and OPC–red clay grouts. Results indicated that the inclusion of clays effectively reduced leach rates in the order of OPC–bentonite < OPC–red clay < OPC for all studied radionuclides, with the dominant leaching mechanism identified as diffusion. Mean apparent diffusion coefficients and leachability indices were calculated for the waste matrices. Additionally, simplified analytical models were developed to predict the cumulative leach fraction (CLF) over time, presenting a valuable screening tool for assessing the performance of waste matrices under repository conditions.