| The two main objectives of this research were dictated by the chemical composition of the Idaho National Engineering and Environmental Laboratory (INEEL) calcined high-level nuclear waste. The first objective is to develop waste forms specifically to address the immobilization of INEEL sodium-containing calcined waste in order to identify a source material that would be compatible with the established processing requirements for the waste form. These selection criteria include no excessive water demand, proper mineralogical composition of the waste form, low leachability, waste loadings greater than 20 wt% calcine and also readily available to the Idaho National Engineering and Environmental Laboratory (INEEL) in large quantities once the pozzolan(s) selection is made. The primary objective aims at studying hydrothermal transformation and kinetics of dissolution of the waste forms.; The chemical durability (dissolution) of the waste forms was established by subjecting the samples to modified Product Consistency Test (PCT) for 24 hours at 90°C. The conductivity, pH and species concentrations of the PCT solutions plotted as a function of time decreased nonlinearly with increasing processing time. This trend was observed in all hydroceramic host samples processed from 75 to 200°C. The host mixed with waste samples heat-treated from 75 to 150°C showed decreasing conductivity and pH trend and before reaching a steady state. The increasing trend observed in the 175 and 200°C samples is due to reverse chemical reactions that occur in those samples.; From the data collected, it is recommended that a processing regimen be developed that utilizes the addition of calcined Troy clay with a waste loading of 30 wt% and processed between 175 to 200°C for 8 to 10 hours and 100% relative humidity.; Based on the analytical concentrations of species measured in the PCT test solutions, hydroceramic waste forms are recommended to be stored/buried in Teflon-lined stainless steel canisters. Combination parameters, such as anions coupled with high pH and high temperature generated from radioactive wastes in addition to the presence of sulfate, chloride, and fluoride, can have deleterious corrosion effects on the stainless steel. (Abstract shortened by UMI.)... |
