No abstract

Nuclear waste can be vitrified by mixing it with glass‐forming and ‐modifying additives. The resulting feed is charged into an electric glass melter. To comprehend melting behavior of a high‐alumina melter feed, we monitored the volume expansion of pellets in response to heating at different heating rates. The feeds were prepared with different particle sizes of quartz (the major additive component) and with varied silica‐to‐fluxes ratio to investigate the glass melt viscosity effects. Also, we used additional melter feeds with additives premelted into glass frit. The volume of pellets was nearly constant at temperatures <600°C. After a short period of volume shrinkage at ~600°C‐700°C, foam generation produced massive volume expansion. The low heat conductivity of foam hinders the transfer of heat from molten glass to the reacting feed. The extent of foaming increased with faster heating and higher melt viscosity, and decreased with increasing size of quartz particles and fritting of the additives. Volume expansion data are needed for the mathematical modeling of the cold cap.

During nuclear waste vitrification, a melter feed (a slurry mixture of a nuclear waste and various glass forming and modifying additives) is charged into the melter where undissolved refractory constituents are suspended together with evolved gas bubbles from complex reactions. Knowledge of flow properties of various reacting melter feeds is necessary to understand their unique feed-to-glass conversion processes occurring within a floating layer of melter feed called a cold cap.The viscosity of two low-activity waste (LAW) melter feeds were studied during heating and correlated with volume fractions of undissolved solid phase and gas phase. In contrast to the high-level waste (HLW) melter feed, the effects of undissolved solid and gas phases play comparable roles and are required to represent the viscosity of LAW melter feeds. This study can help bring physical insights to feed viscosity of reacting melter feeds with different compositions and foaming behavior in nuclear waste vitrification. K E Y W O R D Sfoaming, nuclear waste feed, undissolved solids, viscosity

Types of melter feed materials affect glass production rates. This study focuses on the effects of alumina sources on melting behavior of high-alumina high-level-waste melter feeds containing different alumina sources, namely, gibbsite, boehmite, and corundum. The heat flow from the glass melt to the cold cap, a floating layer of the reacting feed, is partially hindered by a foam layer at the bottom of the cold cap. Volume expansion tests and thermoanalytical methods revealed that a slow-melting feed with corundum foamed extensively, whereas a fast-melting feed with boehmite had a low reaction heat and produced less stable foam. The foam thickness, a critical factor for the rate of melting, estimated using the relationship between the heat conductivity and foam porosity was in reasonable agreement with experimental observation.