THERMOCHEMICAL STUDY OF VAPORIZATION OF SODIUM BOROSILICATE GLASS MELT CONTAINING TELLURIUM

High-level radioactive wastes which are separated by fuel reprocessing will be solidified by incorporation into borosilicate glass matrixes and stored to minimize the release of fission products to the biosphere. The vaporizaton behavior of sodium borosilicate glass melt with a composition of 1Na//2O-1B//2O//3-3SiO//2-0. 15TeO//2 has been studied by a mass spectrometric Knudsen effusion method in the temperature range 991-1151 K. Vapor species of NaBO//2(g), Na//2(BO//2)//2(g), Te(g), Te//2(g), TeO(g) and TeO//2(g) have been identified. On the basis of the measured partial pressures of tellurium containing vapors, the enthalpy of formation and the dissociation energy for Te//2(g) and the reaction enthalpy for 2TeO(g) reversible reaction 0. 5Te//2(g) plus TeO//2(g) have been determined. Chemical activities and activity coefficients of the TeO//2 and NaBO//2 components have also been derived. From these results it can be concluded that the vaporization of the components is suppressed thermochemically.