Melter Feed Viscosity during Conversion to Glass: Comparison Between Low-Activity and High-Level Nuclear Waste Feeds

During vitrification of nuclear wastes, a glass melter feed (a slurry mixture of nuclear wastes with glass-forming and glass-modifying additives) becomes a continuous glass-forming melt 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 called a cold-cap. We studied the viscosity of two low activity waste (LAW) melter feeds during heating and correlated it with volume fractions of undissolved solids and gas phase. In contrast to the high level waste (HLW) melter feed, it was found that the effect of compositional inhomogeneity on the LAW melter feed viscosity is relatively negligible and the volume fraction of gas phase is required to represent the viscosity of LAW melter feeds.