Effect of Concrete Waste Form Properties on Radionuclide Migration

Assessing the long-term performance of Category 3 waste cement grouts for radionuclide encasement requires a thorough understanding of radionuclide-cement interactions and retention mechanisms such as sorption and precipitation. This study aims to enable accurate predictions of radionuclide fate upon contact with groundwater. In fiscal year 2008, numerous concrete-soil half-cell tests were initiated to quantify the diffusion of iodine (I) and technetium (Tc) from concrete into uncontaminated soil over 1 and 2 years. The experiments also included the evaluation of the moisture distribution profile within the sediment half-cell. Various experimental setups were established using fractured concrete with and without metallic iron. Results indicated that the concentrations of I and rhenium (Re) were significantly lower in non-carbonated monoliths compared to the interfacial levels. Notably, the maximum concentrations were observed within the first 5 mm of the monolith, and an asymptotic concentration decrease was observed at varying moisture contents. Specifically, carbonated concrete monoliths demonstrated greater overall diffusion rates for I and Re compared to non-carbonated ones. These findings provide insights into the factors affecting radionuclide migration behavior in concrete waste forms.