Volatilization of sodium and boron from nuclear waste glass and associated effects on glass structure and thermal stability

•Na volatilizes predominantly through the diffusion-controlled process.•B volatilizes through both diffusion-controlled and chemical reaction processes.•The loss of Na and B results in the higher fraction of BO3 units and the more polymerized Si-O network.•The loss of Na and B causes the deterioration of the glass thermal stability.