Chemical Activities of Components in Simulated High-Level Radioactive Waste Glasses and Their Vaporization Behavior

High-level radioactive wastes are solidified by incorporating into borosilicate glasses。To establish the safety in the vitrification processes，it is very important to suppress the vaporization of fission products from the glasses。In this research project，vapor species and their partial pressures over various borosilicate glasses with simulated high-level radioactive wastes were studied.From these data，the degree of the suppression of the vaporization for alkalis，tellurium and strontium was studied quantitatively by comparing the chemical activities of the corresponding components in the glasses.1。The oxide component of R_2O-B_2O_3-SiO_2(R=Li，Na，K，Rb and Cs)for borosilicate glasses is rewritten to be RBO_2-SiO_2 by the use of the pseudo component.In these glasses，the chemical activity of CsBO_2component is the smallest among RBO_2ones。This indicates that the vaporization of Cs is most suppressed thermochemically among alkalis.2。The vaporization of alkali borosilicate glasses in the R_2O-Cs_2O-B_2O_3-SiO_2system，where R=Li，Na，K and Rb，was studied。Partial pressures of CsBO_2(G)over the glasses with Li and Na are lower than those with K and Rb，indicating that chemical activities of the CsBO_2components in the glasses with Li and Na are small.3。Chemical activity of TeO_2component in the alkali borosilicate glass is extremely small in comparison with that for the CsBO_2 one，that is，the vaporization of TeO_2(G)is suppressed much more than that of CsBO_2(G).4.From the glass with the oxide composition of SrO·B_2O_3·SiO_2，strontium vaporizes as Sr(G)，SrBO_2(G)and SrsiO(G).5.The chemical activity of Sr(BO_2)2component in the borosilicate glass is smaller than that of RbBO_2one。From this comparison，the suppression of the vaporization of Sr is more difficult thermochemically than that of Rb。

High-level radioactive wastes are solidified by incorporating into borosilicate glasses. To establish the safety in the vitrification processes, it is very important to suppress the vaporization of fission products from the glasses. In this research project, vapor species and their partial pressures over various borosilicate glasses with simulated high-level radioactive wastes were studied. From these data, the degree of the suppression of the vaporization for alkalis, tellurium and strontium was studied quantitatively by comparing the chemical activities of the corresponding components in the glasses.1. The oxide component of R_2O-B_2O_3-SiO_2(R = Li, Na, K, Rb and Cs) for borosilicate glasses is rewritten to be RBO_2-SiO_2 by the use of the pseudo component. In these glasses, the chemical activity of CsBO_2 component is the smallest among RBO_2 ones. This indicates that the vaporization of Cs is most suppressed thermochemically among alkalis.2. The vaporization of alkali borosilicate glasses in the R_2O-Cs_2O-B_2O_3-SiO_2 system, where R = Li, Na, K and Rb, was studied. Partial pressures of CsBO_2(g) over the glasses with Li and Na are lower than those with K and Rb, indicating that chemical activities of the CsBO_2 components in the glasses with Li and Na are small.3. Chemical activity of TeO_2 component in the alkali borosilicate glass is extremely small in comparison with that for the CsBO_2 one, that is, the vaporization of TeO_2(g) is suppressed much more than that of CsBO_2(g).4. From the glass with the oxide composition of SrO・B_2O_3・SiO_2, strontium vaporizes as Sr(g), SrBO_2(g) and SrsiO(g).5. The chemical activity of Sr(BO_2)2 component in the borosilicate glass is smaller than that of RbBO_2 one. From this comparison, the suppression of the vaporization of Sr is more difficult thermochemically than that of Rb.