Retention Properties of Carbide-Corundum Ceramics Containing Carbon-14, Caesium-137, and Strontium-90

The system C–Al–TiO₂ is of considerable interest for the processing of irradiated reactor graphite waste with the retention of biologic hazardous carbon-14. Investigations of this system were conducted both theoretically and experimentally. Previously, the thermodynamic calculations of the phase composition of resulting end product were performed for a wide variety of components content in the system being investigated. These simulation results have been supported by XRD-analysis of produced specimens. The experimental processing of reactor graphite was conducted by the use of self-sustaining reactions in C–Al–TiO₂ mixtures. A search of modifier additives was performed to perfect end product properties. Test specimens were produced by mass ranging from 0.2 to 3 kg in the argon atmosphere. Various techniques were applied to characterize the produced specimens. The compressive strength of specimens of doped carbide-corundum matrices synthesized ranged from 7 to 18 MPa. The carry over of Cs-137 and Sr-90 during synthesis reaction was about 3% wt. The leachability attained of Cs-137 and Sr-90 from specimens was around 10⁻⁵ g/(cm².day). The carbon-14 is combined in the end product in chemically and thermic stable titanium carbide. The carry-over of the carbon combined in carbon monoxide from the reacting mixtures during exothermic process was less than 1% wt. This corresponds roughly to up 0.01% wt. of the carbon-14 inventory, which can be present in the irradiated reactor graphite.