Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

Abstract

A simulated (inactive) borosilicate high-level waste (HLW) glass was produced on a full-scale vitrification line with composition simulating vitrified oxide fuel (UO 2 ) reprocessing waste. As-cast samples were compositionally homogeneous (Type I microstructure) and/or compositionally inhomogeneous displaying compositional 'banding' and frequently containing 'reprecipitated calcine' (Type II microstructure).Crystal phases identified in as-cast samples were: tetragonal RuO 2 , cubic Pd-Te alloy, cubic (Cr,Fe,Ni,Ru) Sn and U). Cracking in samples was attributed to thermal expansion mismatch between the borosilicate HLW glass matrix and RuO 2 , cristobalite (both α and β), (Na,Sr,Nd,La)MoO 4 and zektzerite on cooling. There was also a contribution from the cristobalite α-β phase transition.

A Thermodynamic Approach to Predict the Metallic and Oxide Phases Precipitations in Nuclear Waste Glass Melts

“…This contribution is synonymous with vaporisation phenomena due to the formation of Se, Te and Ru oxide gaseous species: SeO 2(g) , TeO 2(g) , Te 2 O 2(g) , TeO (g) , SeO (g) and RuO 3(g) . These calculations are in good accordance with the experimental results from the studies performed on platinoid insoluble fines in nuclear waste glasses [32][33][34]. …”

“…The phase separation of calcium and sodium molybdates in simplified complex glass waste forms were studied thoroughly [34][35][36][37]. Nevertheless, the thermodynamic approach was rarely retained to explain this phenomenon.…”

Phase separation and crystallization effects on the structure and durability of molybdenum borosilicate glass

“…Molybdenum is a fission product coming from spent fuel reprocessing solutions, and is weakly soluble in glass [12][13][14][15]. When the content is higher than its solubility limit, processes of phase separation and of crystallization lead to the formation of heterogeneous glasses [16].…”

Single phase melt processed powellite (Ba,Ca)MoO4 for the immobilization of Mo-rich nuclear waste

“…High level waste has been incorporated into borosilicate glass waste forms at the industrial scale for several decades and is an established technology [3][4][5][6].…”

“…GCM waste forms are advantageous for the immobilization of these species since they form a stable phase within a glassy matrix [11]. A primary Mo containing crystalline phase that forms during GCM processing has been found to be a (Ba,Ca)MoO 4 powellite phase [5,11]. These phases have been observed and studied as a component of a multiphase waste form system.…”