Its Stable Isotope Solidified Titanium-based Ceramic Crystal Structure

The development of nuclear energy and nuclear technology is one of the greatest achievements in20th century. However, a large number of radioactive wastes are generated by human exploitation and utilization with the development of nuclear energy and nuclear technology. The management of radioactive waste is of far-reaching significance for strategic development. It is not only related to environment protection and human security, but also involves the future energy problem. Solidification is the key link for the management of radioactive waste, and titanate ceramic has a very important research value as a potential ceramic curing base material for high level radioactive waste.Simulating high level radioactive nuclide U⁴⁺ with Ce⁴⁺, the perovskite, sphene and zirconolite doped with cerium have been synthesized through a high temperature solid-state method. The crystal structure and stability of each solidified body have been systematiclly investigated by Rietveld whole pattern fitting, XRD, SEM, EDS, TG/DSC, ICP and ICP-MS.Results show that perovskite, sphene and zirconolite solidified body can be synthesized by a high temperature solid-state method under a certain temperature and soaking time. The incorporation of Ce nuclide promotes the sintering of three titanate ceramics solidified body, and the close packing of crystalline grain made solidified body a higher density and lower porosity.Three titanate ceramics all can achieve the lattice solidification of nuclide cerium. Perovskite can load cerium less than23.21wt%, about0.2⁰.25calcium structural units. Zirconolite can load cerium less than26.28wt%, about0.6⁰.7zirconium structural units. Sphene has a relatively low capacity of cerium, only2.38wt%. However, EDS analysis indicates that nuclide without entering sphene lattice mainly hosted between the grains of sphene for filling the gap of grain boundary, which is also conducive to the stability of solidified body.Three titanate ceramics solidified body have good lattice stability. Although the incorporation of cerium can result a certain distortion of its crystal structure, the solidified body still maintain a stable structure. The crystal structure of perovskite belongs to the orthorhombic system, space group is Pbnm sphene solidified body belongs to the monoclinic system, space group is P121/A1zirconolite solidified body belongs to the monoclinic system, space group is C12/c1. Cerium nuclide can completely be holden in three titanate ceramics lattice becoming solid solution when its dosage below the maximum capacity. While the cerium nuclide dosage exceeds the maximum capacity, it becomes independent mineral coexisting with main phase mineral.Perovskite, sphene and zirconolite solidified body have good high temperature stability and leaching performance benefit from the stable ceramic phase and lattice solidification of nuclide. Decomposition or phase transition do not occur after heat treatment at200,400,600,800and1000℃, and the phase of solidified body also remains unchanged. The leaching rates of three titanate ceramics solidified body are much lower than that of HLW glass form. And the leaching rate of perovskite and zirconolite solidified body is roughly equal, which is better than that of sphene.