Glass Structure and Chemical Durability of Phosphate Glass Wasteforms Containing High Level Radioactive Nuclear Waste

The chemical durability of iron phosphate (IP) glass containing different contents of high level radioactive nuclear waste (HLW) loading was measured by dissolution rate (DR) method, product consistency test (PCT) and vapor hydration test (VHT). The measurement shows that the IP glass wasteforms containing 65-75 mass% HLW waste loading have excellent chemical durability. The total elemental mass release determined by PCT for all these wasteforms was less than 2.0 g·m-2, and the corrosion rate determined by VHT was less than 0.2 and 3.5 g·m-2·d-1, for the glass containing 70 or 75 mass % HLW waste loading respectively. The glass structure of wasteform was analyzed by Fourier transform infrared (FTIR) and the structure unit of crystallized wasteform was revealed by X-ray diffraction (XRD). The results indicate that the structure unit changed from (PO3)1- groups to isolated (P2O7)4- or (PO4)3- groups with the increase of HLW waste loading in IP glass. When the atomic ratio of O/(Si+P) in the composition of these wasteforms containing high waste loading was between 3.7 and 4.1, the ions such as Al3+, Fe3+, Cr3+ and Zr4+ in the intermediate metal oxide can connect with the isolated (P2O7)4- or (PO4)3- groups by forming the O-Me-O-P bonds, which improved the resistance to be crystallized and enhanced the chemical durability