Research on immobilization of radioactive waste by method of SYNROC synthesis

The titanate-based ceramics (SYNROC) are considered as the most advanced synthetic materials for long-term immobilization of radioactive waste. The formation of SYNROC formulation is presented in this work. Phase equilibrium are established in the CaO-TiO₂-ZrO₂ system at 1250^oC, using X-ray diffraction. The existence of two ternary phases, zirconolite (CaZrTi₂O₇) and perovskite (CaTiO₃), was confirmed in the CaO-TiO₂-ZrO₂ system. The SYNROC formulation (zirconolite, perovskite, hollandite) are obtained by using BaO, Al₂O₃ addition to CaO-TiO₂-ZrO₂ system and annealed at 1250^oC. Strontium titanate SYNROC samples were synthesized in loading simulated radioactive waste. Sr took part directly in the synthesis process. As a result, loading content issue is basically resolved. The products were characterized by shrinkage, water absorption, microhardness X-ray diffraction. The leaching rate was measured by ANSI standard. The results indicate that the Sr²⁺ in SrTiO₃ compound with high density, low leach rate and high property stability and the synthesis process is feasible in technology and economy. It can be concluded that the titanate SYNROC is a promising material to immobilize radioactive waste. (author)