Electron Equivalents Redox Model for High Level Waste Vitrification

Abstract

Control of the REDuction/OXidation (REDOX) equilibrium in high level waste (HLW) glass melters is critical in order to eliminate the formation of metallic species from overly reduced melts while minimizing foaming from overly oxidized melts. To date, formates, nitrates, and manganic species in the melter feeds going to the Savannah River Site (SRS) Defense Waste Processing Facility (DWPF) have been the major parameters influencing melt REDOX. The sludge being processed for inclusion in the next DWPF Sludge Batch contains several organic components that are considered non-typical of DWPF sludge to date, e.g. oxalates and coal. A mechanistic REDOX model was developed to balance any reductants and any oxidants for any HLW melter feed. The model is represented by the number of electrons gained during reduction of an oxidant or lost during oxidation of a reductant. The overall relationship between the REDOX ratio of the final glass and the melter feed is given in terms of the transfer of molar Electron Equivalents.