Sodium-aluminum-iron phosphate glasses as legacy high level waste forms

Legacy liquid high level wastes (HLW) generated at former defense programs, which are under storage in stainless steel tanks at PA Mayak have high Fe/Al contents. They will be vitrified in a new EP-500 J-heated ceramic melter, which is planned to be commissioned in 2016. Like previous melters of the same type, the new melter will produce aluminophosphate based glass. Due to high content of iron oxides in the HLW the glass obtained will have base sodium-aluminum-iron phosphate composition. Complex sodium-aluminum-iron phosphate glassy materials with various Al2O3 to Fe2O3 ratio containing high level waste (HLW) surrogate were designed, produced, and characterized by X-ray diffraction and scanning electron microscopy. The samples were annealed by a canister centerline cooling regime at the EP-500 plant. Addition of B2O3 and partial Fe2O3 substitution for Al2O3 in the materials increases resistance to devitrification whereas further substitution and NiO incorporation increase significantly tendency to devitrification. All the glasses had low leachability satisfying to Russian standard R 52126-2003 (similar to MCC-1 at 25 °C) but the glasses at Al2O3:Fe2O3 ratio close to 1 were found to be the highest chemically durable.