PNNL

Abstract

A 51-sample composition variation study was performed on glass-ceramic waste forms for a raffinate waste stream from aqueous reprocessing of used nuclear fuel containing high fractions of Mo, alkalis, alkaline earths, and rare earths. The study was designed with a single-component-at-a-time variation approach off a centroid composition. The components that were varied included Al, B, Ca, Li, Mo, Na, rare earths, Si, Zr, and others (containing minor components). Data analysis included crystallization curves, microstructure, and phase compositions. A number of components (Li2O, B2O3, rare earth oxides, MoO3, Na2O, and ZrO2) significantly impacted the concentration and chemistry of phases, especially the primary phases of oxyapatite [i.e., Ca2RE8(SiO4)6O2; RE = rare earth] and powellite (i.e., AEMoO4; AE = alkaline earth), precipitated in the slow-cool heat-treated waste form; minor phases included cerianite [i.e., CexZr(1-x)O2], Ba-molybdate [i.e., Ba(Gd0.67Mo0.33O3], LiTe, and pollucite [i.e., CsAlSiO4].