Dissolution of Accumulated Spinel Crystals in Simulated Nuclear Waste Glass Melts

Abstract

Currently, efforts are being made to increase the waste loading in vitrified waste forms for the Hanford Tank Waste Treatment and Immobilization Plant, which could result in the formation of crystalline phases within the glass. Spinel crystals that form in glass melts during vitrification of nuclear waste have a negligible impact on the performance of the glass product, and thus a melter operating with a nominal concentration of spinel crystals would be advantageous to accessing broader composition spaces and increases in waste loading. However, the total amount of crystallization must be controlled to reduce risks associated with crystal accumulation in the melter (i.e., melt properties and melter throughput/operation), and therefore a strategy to reduce the risk of failure of the melter from spinel accumulation is of interest. This study describes a method to mitigate spinel accumulation without disrupting melter operation while maintaining melt viscosity and glass product chemical durability requirements. It is found that additives can be incorporated into the glass melt that reduce the quantity of trevorite crystallization by up to 65% while maintaining acceptable viscosities for processing and chemical durabilities as measured by the product consistency test responses for disposal.