Effects of UO3 on the structure, thermal and chemical stability of borosilicate glass matrix

•Synthesis of multicomponent borosilicate glasses containing up to 40 wt% UO3.•U transforms IVSi-O-IVB to IVSi-O-IIIB and enhances glass transition temperature.•EXAFS fit shows that U is present as UVI/UV, with similar ratios within the series.•The dissolution rate of the 30 wt% sample is the lowest among the U-loaded samples.•Nanoindentation reveals 30 wt% U O3 sample is ∼ 11 % weaker than matrix glass. The glass matrix of composition: 55SiO2–10B2O3–25Na2O-5BaO-5ZrO2 was incorporated with 10 to 40 wt% of UO3 by melt quenching technique. Neutron diffraction and Reverse Monte Carlo simulations revealed that the borosilicate network consists of SiO4, BO3 and BO4 units; upon adding 10 % UO3 the B-O coordination increases from 3.08 to 3.86 and subsequently decreases with a further in increase in UO3 content. X-ray absorption near edge and Extended X-ray absorption studies revealed that U exist in 5+ and 6+ oxidation states with U-O coordination numbers of 8 and 6 respectively. The thermal stability decreases and weight losses increases with the addition of UO3 in the glass matrix, the sample with 30 wt% UO3 has thermal stability comparable to that of matrix glass and exhibits lowest dissolution rate in water. Nanoindentation measurements showed that the microstructure of sample with 30 wt% UO3 is 11 % weaker than that of the matrix glass.