Solubility of uranium oxide in aluminosilicate glass melts
Abstract
The immobilization of highly radioactive waste using vitrification process has been in application since many decades (1). This process is now under investigation for conditioning Intermediate Level and Long Life Waste (ILW-LL) using aluminosilicate glasses as host matrices. The vitrification must be able to maintain, within a certain range of compositions and redox potential, the actinides solubility. It is known that uranium chemistry is complex in glass-forming systems due to the presence of many oxidation states (VI, V, IV) (2).
This paper presents the uranium solubility study in aluminosilicate glass melts as a function of melt composition and oxido-reduction potential (oxygen fugacity) (Figure 1). Ternary SiO2-Al2O3-CaO (CAS) and SiO2-Al2O3-MgO (MAS) systems are considered. In those glasses, Al content is increased while keeping the Si/Ca and Si/Mg ratio constant. Further XANES analyses on selected samples have allowed the precise quantification of uranium oxidation states. The specific experimental methodology is detailed and solubility results combined with uranium valencies data are discussed on a thermodynamic point of view.