Leaching Studies of Synroc Crystalline Ceramic Waste Forms

Abstract

ABSTRACTThe leaching performance of pressureless sintered SYNROC crystalline ceramic waste forms containing simulated high-level radioactive waste has been evaluated under different leach conditions, i.e. in deionized water and in a simulated brine (Q-brine) at different leach temperatures. The leach solutions were analyzed using inductively coupled plasma and atomic absorption spectrometry (ICPS and AAS) to determine the concentrations of the simulated waste elements and the matrix components released into the leachants. The leach rates of Ba and Ca were in the range of 0.1 to 0.02 g/(m2.d) after one week of leaching in deionized water at 150 °C. No significant difference in the leach behaviour of SYNROC was observed in distilled water and in simulated brine. The leached surfaces of SYNROC were characterized using Rutherford backscattering spectrometry (RBS), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and elastic recoil detection analysis (ERDA). RBS and SIMS analyses revealed the existence of near-surface layers enriched in Ti and depleted in Ba and Ca. Elastic recoil detection analysis showed the existance of hydrated surface layers on the leached SYNROC which were much thinner than those observed in parallel work with borosilicate waste glasses. Radiation damage produced by ion implantation increased the otherwise very-small leach rates of SYNROC. At high damage levels, SYNROC was shown to become amorphous (metamict).