Immobilization of high- level waste using fly ash glass frits

High level liquid waste (HLLW) is a waste generated from reprocessing of spent nuclear fuel. This waste contains many fission products and a few actinides. The waste is immobilized with borosilicate glass. The important factors influencing the characteristics of the waste-glass among others are waste content and glass frits composition. Fly ash is the ash generated from coal firing. The ash composed of SiO₂, Al₂O₃, CaO and Fe₂O₃, which is similar to that of glass frits. It was assumed that fly ash is possible to be used as substitute for glass frits. The aims of this research was to study the utilization of fly ash for HLLW immobilization. Some waste-glass were studied, namely waste-glasses A, B, C that contain waste loading of 23.21; 36.75 and 50.133 wt% respectively, and waste-glass D that was immobilized with fly ash without addition of SiO₂ oxide. A standard glass from JAEA was used as reference. The characteristics to be observed were density. leaching rate and devitrification. The higher the density and waste loading of the waste-glass, made the the leaching rate higher. The waste-glass with the highest density was the waste-glass C, while the highest leaching rate was the waste-glass D. Devitrification occurred on the waste glass A under 700 °C 5 hours heating. The devitrification was identified by the formation of crystal dominated by SiO₂. It was concluded that the fly ash can be used as glass frits on immobilization of HLLW with addition of SiO₂ for improvement of waste-glass characteristics, in order to meet the requirement. (author)