Thermoanalytical investigations to study the sudden decrease in process pot temperatures during HLW vitrification through barium-boro-silicate glass formation route

Vitrification process is adopted world wide to immobilize the high level radioactive liquid waste(HLW). Barium borosilicate (SiO2-B2O3-BaO) matrix is adopted for immobilization of sulphate bearing historic HLW generated during early stages of Purex process. Vitrification with the SiO2-B2O3-BaO matrix shows a phenomenon of sudden temperature fall in process pot temperatures during initial soaking hours. Studies presented here indicate that Ba(NaO3)2 used in glass slurry decomposes to BaO2 first and then to BaO. The process involves phase change and is endothermic in nature resulting in sudden fall in process pot temperatures. This report describes the results of the thermo analytical investigations of base glass matrix of SiO2-B2O3-BaO composition. (author)