Properties and solubility of chrome in iron alumina phosphate glasses containing high level nuclear waste

Abstract

Chemical durability, glass formation tendency, and other properties of iron alumina phosphate glasses containing 70 wt% of a simulated high level nuclear waste (HLW), doped with different amounts of Cr2O3, have been investigated. All of the iron alumina phosphate glasses had an outstanding chemical durability as measured by their small dissolution rate (1 ∙ 10^-9 g/(cm2 ∙ min)) in deionized water at 90 °C for 128 d, their low normalized mass release as determined by the Product Consistency Test (PCT) and a barely measurable corrosion rate of < 0.1 g/(m2 ∙ d) after 7 d at 200 °C by the Vapor Hydration Test (VHT). The solubility limit for Cr2O3 in the iron phosphate melts was estimated at 4.1 wt%, but all of the as-annealed melts contained a few percent of crystalline Cr2O3 that had no apparent effect on the chemical durability. The chemical durability was unchanged after deliberate crystallization, 48 h at 650 °C. These iron phosphate waste forms, with a waste loading of at least 70 wt%, can be readily melted in commercial refractory crucibles at 1250°C for 2 to 4 h, are resistant to crystallization, meet all current US Department of Energy requirements for chemical durability, and have a solubility limit for Cr2O3 which is at least three times larger than that for borosilicate glasses.