PNNL

Abstract

The importance of glass and glass-ceramic nuclear waste forms has been reaffirmed in recent years by the growing interest in nuclear power as a reliable energy source to meet the requirements of technologies such as artificial intelligence. Waste processing schemes for the disposal of halide-containing wastes will be essential for the advancement of nuclear technologies such as non-aqueous fuel reprocessing. Phosphate-based dechlorination and subsequent vitrification of radioactive salt waste into an iron phosphate waste form has been identified as a potential processing scheme for electrochemical processing waste. The impact of H3PO4-based dechlorination of complex salt mixtures on the vitrification process and structure of the final iron phosphate waste form has not yet been investigated. In this work, iron phosphate glass-ceramics were made from simulant salt waste (48LiCl-33KCl-19NaCl mol%) dechlorinated with the H3PO4-based method. The glass forming region was compared to that of traditionally prepared Na2O-Fe2O3-P2O5 systems. For a candidate glass-forming composition, the processing scheme presented here was determined to favor Fe3+ species. The O/P molar ratio was consistent for the candidate composition when dechlorinated at 400°C and 600°C in air and argon environments, indicating glass network connectivity was maintained despite variations in processing parameters. The results presented here validate processing schemes requiring iron-phosphate waste form synthesis following H3PO4-based dechlorination.