Property/Composition Model for Phosphate Glasses Containing Hanford AZ102 LAW

Nuclear power is a key component in the strategy to meet the countrys energy goals and technologies are needed to improve the reliability of current reactors and disposing safely of nuclear wastes. Vitrification is considered the preferred process for nuclear waste disposal and the U.S. Department of Energy (DOE) currently approves only borosilicate glasses (BS) for that purpose. However, many nuclear wastes have complex compositions that are poorly soluble in BS glasses while Fe-phosphate (FeP) glasses can dissolve larger amounts of problematic components (i.e., S, Al, Na, halides, and heavy metals). This work will provide a property/composition model for FeP glasses containing simulated AZ102 LAW (low activity waste), a defense waste stream that is difficult to vitrify in BS glass due to its high combined sulfate (17 wt. %) and alkali (80 wt. %) content. Similar statistical modeling work can then be applied to wastes from domestic fuel cycles. Phase I will focus on the system P2O5Fe2O3Al2O3Na2OSO3 (which corresponds to 91 6 wt. % of the final vitrified waste, based on previous work) to identify a potential compositional region for further study in Phase II and vitrifying the Hanford AZ102 LAW. The properties for the modeling include, melting temperature and glass formability of the compositions, and chemical durability of the FeP glass waste forms. Phase II task will be extended to include a statistically experimental design with a larger number of components to produce a qualified composition region with melt processing parameters and glass form properties that meet DOE requirements. The deliverables are intended to include (1) highest attainable waste loading, (2) good glass formation tendency, and low melting temperatures, (3) high retention of sulfate, SO3, and other volatile/ hazardous species, and (4) a chemical durability that meets DOE requirements. Prior work with the AZ102 waste has demonstrated that this waste can be vitrified in FeP glasses with an sulfate content exceeding in 40% the DOE recommended sulfur retention limit. FeP glasses can vitrify wastes that are poorly suited for BS glasses. In particular, FeP glasses can dissolve and retain a much high sulfate content than is possible in BS glass. This work will provide additional data confirming the potential of FeP glasses to vitrify problem wastes at Hanford and a method for analyzing other similar wastes.