A review of the cast stone formulation for nuclear waste immobilization

This review aims to collate the properties of the Cast Stone cementitious waste form, a specific ternary blend of blast furnace slag (BFS, 47 wt%), fly ash (FA, 45 wt%) and ordinary Portland cement (OPC, 8 wt%). This mixture has been studied as a candidate for use in nuclear waste immobilization at the U.S. Department of Energy Hanford Site over the last 20 years. The blend has been tested for immobilizing liquid waste (including pre-treated waste, low-activity waste and mixed low-level wastes), immobilizing secondary wastes generated from vitrification, and encapsulating solid waste. As new formulations are developed at Hanford and around the world, this review provides the current state of knowledge on one of the most studied formulations for waste immobilization in the U.S. This review focuses solely on the 47/45/8 BFS/FA/OPC Cast Stone formulation and does not include the relatively close saltstone formulation nor construction "cast stone". This report summarizes the fresh and cured properties of Cast Stone, the impact of varying water-binder ratio and waste chemistries, spectroscopic material characterizations, and field testing and modeling efforts specific to Cast Stone's long-term performance. Relationships between the existing datasets and waste form properties are identified and discussed. From the data available, Cast Stone can provide consistent material properties that meet the disposal requirements or waste acceptance criteria of generic disposal sites, but is not yet employed for waste immobilization in practice.