Predicting the Spinel–Nepheline Liquidus for Application to Nuclear Waste Glass Processing. Part I: Primary Phase Analysis, Liquidus Measurment, and Quasicrystalline Approach

Abstract

The crystal-melt equilibria in complex 15 component simulated high-level waste (HLW) glass melts are modeled on the basis of quasicrystalline concepts. A pseudobinary phase diagram between a transition metal ferrite spinel (an incongruent melt product of transition metal iron-rich acmite) and nepheline is defined in Part II on the basis of these concepts. The pseudobinary lies within the Al 2 O 3 -Fe 2 O 3 -Na 2 O-SiO 2 quaternary system that defines the crystallization of basalt glass melts. Part I defines the complex transition metal species that crystallize in waste glasses, the role of the octahedral site preference energies, the evidence for quasicrystalline clustering in waste glasses, and the potential quasicrystalline exchange reactions at the liquidus. The liquidus model developed on the basis of these concepts has been used to prevent unwanted crystallization in the world's largest HLW melter for the past 4 years while allowing 410 wt% higher waste loadings to be processed. J ournal

High Level Waste (HLW) Vitrification Experience in the US: Application of Glass Product/Process Control to Other HLW and Hazardous Wastes

“…The liquidus model developed based on these concepts has been used to prevent unwanted crystallization in the DWPF HLW melter for the past six years while allowing >10 wt% higher waste loadings to be processed. The liquidus model and the pseudobinary are shown [17,18] to be consistent with all of the thermal stability data generated on DWPF HLW glasses. The model ranges developed on 105 different glass compositions and validation ranges (161 glasses) are given in Table IV.…”

“…The crystal-melt equilibria was modeled based on quasicrystalline concepts [17,18]. A pseudobinary phase diagram between a ferrite spinel (an incongruent melt product of transition metal iron rich acmite) and nepheline was defined.…”

Impacts of Small Column Ion Exchange Streams on DWPF Glass Formulation: Kt01, Kt02, Kt03, and Kt04-Series Glass Compositions

“…11,13,14 This semi-empirical model is currently incorporated in PCCS to predict the spinel liquidus temperature from glass composition. 3 Spinels are expected to be the primary crystalline phase in DWPF glasses.…”

Durability and Nepheline Crystallization Study for High Level Waste (Hlw) Sludge Batch 4 (Sb4) Glasses Formulated With Frit 503

“…16 The combination of high Al 2 O 3 and Na 2 O concentrations, coupled with lower SiO 2 concentrations as waste loadings are increased (given the primary source of SiO 2 is from the frit), shifts the overall glass compositions toward the nepheline phase field, raising the potential for nepheline crystallization. Therefore, strategic frit development efforts 17 have been made to suppress the development of nepheline formation by lowering the Na 2 O content while increasing B 2 O 3 , Fe 2 O 3 , and/or Li 2 O concentration in the frit.…”

“…In terms of processing, the Defense Waste Processing Facility (DWPF) uses a liquidus temperature (T L ) model [1][2][3] and an imposed T L limit for feed acceptability to avoid bulk devitrification within the melter. In terms of performance of the glass waste form, the impact of devitrification on durability depends on the type and extent of crystallization.…”