Immobilization of Technetium-99 in a Lead Borosilicate Glass

Abstract

The volatility of Technetium-99 (99Tc) makes vitrification of Tc-containing nuclear waste at high temperatures a challenge. In this paper, we report the development of a lead borosilicate glass with a nominal composition of 73.1PbO–10.1B2O3–13.1SiO2–3.7Al2O3 (wt%) and a depressed melting temperature (750 °C) to decrease Tc volatilization during vitrification. The lead borosilicate glass was able to incorporate up to ∼1.8 wt% Re (as a surrogate for 99Tc), and the results of a product consistency test showed that it was chemical durable. Raman and Fourier transform infrared spectra showed that Re was incorporated into the lead borosilicate network as ReO4− and the small addition of Re did not induce any detectable changes to the B and Si network. At the same time, nuclear magnetic resonance measurements suggested that some of the ionic Pb in the glass turned to covalent Pb with the addition of KReO4. No loss of Re was detected when vitrification of the Re-containing lead borosilicate glass was conducted at 750 °C, and only ∼12% of the Re volatilized when the temperature was ramped up to 1100 °C. Our findings confirm suggestions that lead borosilicate glass would be an attractive candidate waste form for immobilizing Tc concentrate.