Property modification of a high level nuclear waste borosilicate glass through the addition of Fe2O3

The pro rata addition of 0-20 wt% Fe2O3 to a UK high level waste (HLW) borosilicate glass containing 25 wt% model UK HLW has been studied in terms of the effects of Fe2O3 addition on glass chemical durability, thermal properties, density and redox. Mixtures have been successfully melted in Pt crucibles at 1050 and 1150°C, and resulting glasses are x-ray amorphous. Addition of Fe2O3 increases glass density and HLW loading per unit volume increases by 3·5% for 10 wt% Fe2O3 addition. Chemical durability has been measured using the methodology of product consistency test B (ASTM C1285) for 7, 14 and 28 days. Leach rate and solution pH is reduced by the addition of Fe2O3. Overall test results suggest that 5-10% Fe2O3 addition provides optimum improvement in chemical durability. Thermal stability and Tg are unaffected by 0-15 wt% Fe2O3 addition. 57Fe Mossbauer spectroscopy reveals that Fe is present in these glasses as Fe3+ ions in tetrahedral coordination, strengthening the glass network through increased network polymerisation. The results also suggest that increasing the Fe2O3 content of the glass changes the character and makeup of the interfacial layers formed during corrosion.