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Meeting Materials Science & Technology 2019
Symposium Materials Issues in Nuclear Waste Management
Presentation Title Impact of Redox on Crystallization Behavior of Spinel Crystals in HLW Borosilicate Glasses
Author(s) Josef Matyas
On-Site Speaker (Planned) Josef Matyas
Abstract Scope The spinel crystals that precipitated during high-level waste vitrification may clog the riser of the melter and prevent discharge of molten glass. This may be prevented by controlling redox of molten glass. In this study, high-Fe-Ni borosilicate glass was heat treated at 850°C in 2.7% H<sub>2</sub>/Ar (safe gas) or in air for different times up to three weeks to investigate the effect of redox on crystal accumulation and crystal size, morphology, and composition. Compared to oxidizing conditions more crystals formed under reducing conditions but they were smaller and remained suspended in the glass. Concentration gradients of spinel-forming components were observed in spinel crystals and at the spinel/glass interface. The results suggest that the small adjustment of the iron redox through bubbling of the glass in the riser with a safe gas or even argon may prevent accumulation of spinel.


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