Cs-containing Synrock: Its Synthesis And The Influence Of Cs/Ba Ratio On Its Structural Stability

Synrock,because of its low leach rate for single phases and negligible thermal expansion,is a hopeful candidate for disposal of HLW.At present,a lot of scientific research strength have been spent in immobilizing radwaste in synroc.The most of investigations mainly emphasized the ability of the host phase to accommodate actinides nuclides immobilized,chemical stability of solidified and anti radiation stability,etc.Few works were performed to reveal the influence of fission nuclides and daughter on the structure and stability of solidified body.Generally,the oxidation state and radius are different between the radioisotope parent and daughters,which may change the structure and chemical stability of solidified body.To evaluate the long-term stability of radwaste forms,it not only regard long-lived nuclide effects on stability of solidified body,but also need to focus on the influence of fission nuclides and its decay daughter effects on stability of synrock.The experiment seize the favorable conditions that fission nuclides 137 Cs have stable isotope in nature,the synrock preparation of different ratios of Cs/Ba with hollandite phase as the host.Simulation study on the evolution of the synrock structure of Ba_xCs_yTi₈O₁₆ series effects by 137 Cs and its decay daughter 137 Ba.Using XRD,SEM and other methods analyse the effects of phase,structure and morphology.By using density functional theory study of Cs substitution of Ba ceramic phase change,structure transformation and stability change,etc.（1）CsNO₃,Ba（NO₃）₂,Ti₂O₃,TiO₂ as raw materials,through the discussion of the formula design,finally using high temperature solid-state method at 1250℃,3h sintered in 5%H₂/Ar atmosphere,successfully prepared Ba_xCs_yTi₈O₁₆ series ceramic.（2）The crystallinity of Bax CsyTi₈O₁₆ is about 80%,and the grain size is about600nm;The refinement results show the ceramic phase belongs to tetragonal phase,and the lattice parameters with the increase of Cs doping concentration is increased,the cell volume of V by the influence of the lattice parameter is bigger;the grain growth is good,clear boundaries,with the increase of Cs concentration,grain shape by gradually transformed into columnar hexagonal structure;the relative density is larger than 80%.（3）In Hollandite Ba_1.05-xCs_xTi₈O₁₆ ceramic,with the substitute Cs for Ba the Fermi level into the conduction band,the density of States has decreased.With the increase of Cs concentration,system can increase,cell volume increase,but the system remained the tetragonal structure,so the ceramic has better structure stability.