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.