Effects of electron irradiation in nuclear waste glasses

Abstract

This article summarizes recent studies of electron irradiation damage in sodium borosilicate, iron phosphate and aluminophosphate glass waste forms using a modern analytical electron microscope. Three different borosilicate (wt%) (17.72% B₂O₃–16.67% Na₂O–64.61% SiO₂, 17.78% B₂O₃–15.83% Na₂O–61.39% SiO₂–4.99% Fe₂O₃ and 17.86% B₂O₃–15.90% Na₂O–61.63% SiO₂–4.61% FeO) and iron phosphate (mol%) (45% Fe₂O₃–55% P₂O₅, 20% Fe₂O₃–80% P₂O₅, and 20% Fe₂O₃–20% Na₂O–60% P₂O₅) glasses, and an aluminophosphate (mol%) (44.5% P₂O₅–31.5% Al₂O₃–20.2% Na₂O–3.8% K₂O) glass were studied. Results indicate that all these glasses decomposed under the 200 kV electron irradiation (at doses higher than 1.0 × 10²⁶ e m⁻²). Migration of alkali elements from the irradiated centres to the peripheries under irradiation occurred in the alkali element-containing glasses, which results in the formation of alkali element-depleted and -enriched phases. Formation of bubbles was only observed in the alkali element-containing iron phosphate and aluminophosphate glasses, not in sodium borosilicate glasses when irradiated over a broad of dose rates (1.6 × 10²² e m⁻² s to 8 × 10²⁶ e m⁻² s). Separation of boron-rich phase from silicon-rich phase, iron-rich/aluminium-rich phase from phosphorous-rich domains were observed in the three types of glasses, respectively. Further irradiation resulted in formation of small particles. In Fe-containing borosilicate glasses, the Fe is associated with the boron-rich phases after phase separation.

Acknowledgements

This work has been supported by the Environmental Management Science Program of the U.S. Department of Energy under Grant No. DE-FG07-01ER63152 and Contract No. DE-AC06-76RLO 1830. The JEOL-2010F STEM/TEM used for this study was funded by NSF through the Grant DMR-9871177 and is operated by the EMAL at the University of Michigan. We also acknowledge Professor D.E. Day of the University of Missouri, Rolla, for supplying the FeP glass forms.