Ming Tang1
Clemson University1
Glass waste forms are currently used to stabilize legacy high-level waste (HLW) materials, and glass is the baseline technology for treatment of HLW that would result from reprocessing commercial used nuclear fuel (UNF). Due to the low solubilities (< 1.5 mass% for silicate-based glass) of the chloride/fluoride ions and evolution of Cl<sub>2</sub>/F<sub>2</sub> gas from the melt under operation temperature, it is not suitable to employ the borosilicate glasses as the host for the full-salt waste streams. Phosphate glass, for example iron phosphate glass, exhibited promising properties as waste form candidates including good chemical durability; high solubility for many heavy metals (e.g., uranium, cesium, molybdenum), noble metals, and rare earths. In the first part of this study, we intend to develop and optimize highly durable and easily processable iron phosphate glass waste form to immobilize the salt streams from advanced nuclear fuel cycle by tailoring the composition of the glasses at intermediate melting temperatures (950 – 1,200 C). For the compositional variation study, different Fe:P ratio vs waste loading in iron phosphate glass waste forms are fabricated; various glass modifiers are added into iron phosphate glass compositions to improve chemical durability and reduce melting temperature. The preliminary result shows promising for iron phosphate glass waste form being an improvement over other candidate waste forms. In the second part of this study, our focus is to fabricate SnF2-P2O5 glasses with low melting temperature (400 C) and high waste loading up to 50 wt% salt waste streams. Chlorophosphate glasses in the systems Sn–Fe–P–O–Cl and Sn–O–P–Cl have been developed via replacing fluorine by chlorine. The range of melting temperature in these glasses system is between 400-500 C or even lower which could avoid the volatilization of chloride and fluoride and improve salt retention or solubility. Low glass transformation temperatures, acceptable chemical durability, and good water resistance suggest that these glasses may be suitable for immobilizing chloride-based and/or fluoride-based salt streams through vitrification.