Sulfate Retention and Segregation in Simulated Radioactive Waste Borosilicate Glasses

Sulfate segregation from processing radioactive waste glasses causes an acceleration of the melter refractory corrosion and partitioning of radionuclides in the segregated layer. A sulfate retention (SR)-composition relationship has been established for various simulated high-level and low-activity waste glass compositions in terms of the relative non-bridging oxygen (NBO) concentration in the melt. Phosphate was found to significantly increase sulfate retention. However, the correlation between SR and NBO could not explain the sulfate segregation tendency. For instance, glasses with a higher ratio of boron to sodium suppress sulfate segregation in the melt in which SR is expected to be lower. As sulfate segregation is a kinetic process, occurring in the batch to glass conversion process, initial reactions of the batch materials are considered to have stronger effects on the sulfate segregation tendency, pointing out the need to study the impact of batch materials on sulfate segregation