The effect of gamma irradiation of the volatility and redox state of simulated DWPF high-level nuclear waste glasses

Abstract

Gamma-induced volatility of simulated DWPF high-level nuclear waste glasses is highly dependent upon the redox state of the glass. For oxidized glasses with an Fe{sup 2+}/(Fe{sup 2+} + Fe{sup 3+}) ratio < 0.1, no volatility was detected after gamma irradiation. Since the projected DWPF high-level radioactive waste glasses will be oxidized, no significant gamma-induced volatility is expected for these glasses upto the glass transition temperature. For larger pieces of highly-reduced DWPF simulated waste glass, no volatility was observed (using {approximately}100 mg pieces in the TGA) after gamma irradiation. However, for powdered samples of this reduced glass, volatility changes upon gamma radiation were detected at 350 and 475{degree}C. The volatility at 350{degree}C was due to changes at the glass surface whereas the change in volatility at 475{degree}C were due to interactions of gamma irradiation within the bulk of the glass. The glass transition temperatures of both oxidized and reduced glasses were unaffected by gamma irradiation but did increase upon a second heat cycle. Results are also presented which reveal that no significant change in redox level within the glass occurred as a result of gamma irradiation.