Crystallization and rheological study of a Nd-oxyapatite-bearing melt

Current French nuclear waste glasses have been designed to avoid the precipitation of crystals during the vitrification process. Removing this constraint would reduce the volume of glass produced, and therefore the cost of storage. However, the impact of crystallization on both glass melt properties and cooled glass durability needs to be investigated. This paper focuses on the impact of crystals on glass melt rheology. A simplified Nd-rich nuclear glass was used to study the rheological behavior of an apatite-bearing melt. We followed the evolution of viscosity during crystallization for different conditions of shear and performed steady-state and transient studies on the crystallized glass melt. An obvious acceleration of crystallization kinetics was observed as the shear was increased, and the melt showed a very shear thinning behavior for an apatite fraction above 3%vol. The effective maximum packing fraction was determined for different conditions of shear.