Vitrification and testing of a Hanford high-level waste sample. Part 2: Phase identification and waste form leachability

Abstract

A sample of Hanford high-level radioactive waste from Tank AZ-101 was vitrified into borosilicate glass and tested to demonstrate its compliance with regulatory requirements. Compositional aspects of this study were reported in Part 1 of this paper. This second and last part presents results of crystallinity and leachability testing. Crystallinity was quantified in a glass sample heat treated according to the calculated cooling curve of glass at the centerline of a Hanford Waste Treatment Plant canister. By quantitative X-ray diffraction analysis and image analysis applied to scanning electron microscopy micrographs, the sample contained 7 mass% of spinel, a solid solution of franklinite, trevorite, and other minor spinels. Glass leachability was measured with the product consistency test and the toxicity characteristic leaching procedure. Measured data and model estimates were in reasonable agreement. Leachability results were close to those obtained for the non-radioactive simulant. Models were used to elucidate the effects of glass composition of spinel formation and to estimate effects of spinel formation on glass leachability.