High-Level waste glass dissolution in simulated internal waste package environments

The rate of radionuclide release as a result of leaching of high-level radioactive waste (HLW) glass is important to the performance of engineered barriers. The modified product consistency test (PCT), with regular leachant exchanges, was used to determine the leaching rate of simulated HLW glasses (West Valley Demonstration Project Reference 6 and Defense Waste Processing Facility Blend 1) in aqueous solutions of FeCl2 and FeCl3 at 90 EC. These conditions were selected to simulate an internal waste package (WP) environment containing steel corrosion products and oxidized by radiolysis. Substantially higher initial B and alkali release rates, approximately a factor of 50 to 70 times greater than those in deionized water, were measured in 0.25 M FeCl3 solutions. The initial leaching rate for B and alkali was found to be pH-dependent and decreased as the leachate pH was increased. While the leach rate for Si did not show any significant change in the pH range studied, the leach rate for Al showed a minimum. The minimum in the leach rate of Al occurred at different pH values. The study indicates that elements in the glass matrix are released incongruently. (authors)