Samples of real irradiated (i-)graphite from bushings of RBMK reactor after several types of decontamination treatments were put in contact with aqueous solutions modelling underground water of Nizhnekansky massif (Russia) equilibrated with bentonite for periods up to 1.5 years. Leach rates of radionuclides and evolution of graphite surface morphology and oxidation state were monitored using nuclear spectroscopy, SEM and XPS. After the experiment, less than one third of surface carbons remains unoxidised. Extensive precipitation of secondary phases (alumosilicates, carbonates) was observed on some samples and is possibly correlated with surface oxidation extent. The leach rates of dose-forming 14C and 36Cl are comparable with the leach rates of radionuclides in glassy waste forms. According to the current study i-graphite could be regarded as a waste form, which is suitable for near-surface disposal.

Slow cooling of phosphate melt at liquid nuclear waste solidification yields glass-crystalline material. Partial crystallization during melt solidification results in elemental partitioning among crystalline phase and glass: Al, Cr, Fe are concentrated in the crystalline phosphate phase while Ca, Ni, La, U enter predominantly in the residual glass. Glass dissolution rate and leach rate of La and U as rare earth and actinide surrogates depends strongly on the glass composition, for example reduction of Al2O3 content in the glass to ∼10-12 wt.% increases leachability by three orders of magnitude as compared to the glass with specified composition (∼18-22 wt.% Al2O3).