The Defense Waste Processing Facility (DWPF) at the Savannah River Site (SRS) has been vitrifying high-level radioactive waste (HLW) through a Joule heated melter since 1996. As part of waste quality acceptance, phase stability of the borosilicate glass waste forms must be determined. From the commencement of waste processing into the present-day, waste form compositions have varied and phase stability has continued to be determined by creating Time-Temperature-Transformation (TTT) diagrams. Crystallization behavior and TTT diagrams have been examined for varying glass waste compositions using isothermal heat treatments and X-ray diffraction (XRD) phase analysis. Typically, transition metal ferrite based spinel, nepheline, acmite, and lithium silicate crystalline phases are precipitated. Glass composition-crystalline phase stability relationships will be discussed for a recently processed composition and historical compositions.
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