Zirconium and Rubidium Solubility in Aluminoborosilicate Glasses for Radioactive Waste Immobilization

In search of novel waste form materials for vitrifying high-level radioactive waste with various compositions and improving the way in which they are used, we have prepared and investigated waste form materials in the Na₂O–Rb₂O–SrO(Ba,Ca)–B₂O₃–SiO₂–Al₂O₃–ZrO₂ system. Using electron microscopy, X-ray diffraction, and infrared spectroscopy characterization of samples prepared by rapid cooling of melts containing 3.6–4.5 mol % rubidium, we have demonstrated the formation of a homogeneous glassy material, determined the solubility limit of zirconium in the glass, and identified uniformly distributed baddeleyite crystals, which indicate that the starting melt contained excess zirconium. In samples containing 6.7–8.5 mol % rubidium, we observed the formation of a less homogeneous material with considerable amounts of crystalline zirconium- and rubidium-containing phases. Analysis of the data obtained has made it possible to optimize the percentages of zirconium and rubidium in the composition of radioactive waste in the case of its immobilization via vitrification with the use of waste form materials of the system studied here.