| With the continuous development of nuclear energy,a large amount of nuclear waste is produced each year,which contains a large number of highly radioactive nuclear waste.After deep solidification of high-level nuclear waste,deep geological burial is the main method for handling nuclear waste.Therefore,choosing a good solidified material is a problem that must be solved in the development of nuclear energy.In the process of selecting solidified materials,we must first consider the radiation resistance of the materials and study the macro and microscopic changes of the materials in the irradiation environment.Due to its low leaching rate,good physicochemical properties and its resistance to radiation,pyrochlore-structured Lu2Ti2O7 can be widely studied as a candidate for curing radioactive waste materials.There are mainly two research methods on the irradiation damage of materials:experimental methods(high-energy electron irradiation,ion irradiation,neutron irradiation,plasma irradiation)and computer simulation methods(dynamic Monte Carlo,first principles,molecules Dynamic simulation).In this paper,the experimental method used ion irradiation.The simulation method used molecular dynamics simulation and SRIM simulation based on Monte Carlo.For ion irradiation experiments,we used different ions to irradiate the pyrochlore structure of Lu2 Ti2O7 at different doses at room temperature and then characterize it with GIXRD.In the process of establishing a simulation box in a molecular dynamics simulation experiment,the potential energy that we use first is the short-range potential-the Buckingham potential and the long-range potential-the Coulomb potential.Since Buckingham is attracting potential near the nuclear position,it is not consistent with the actual situation.Therefore,near the nucleus,the Coulomb repulsion potential was used to correct the potential energy function model suitable for studying the dynamic process of irradiation.Secondly,in the selection of ensemble,we found that the two ensembles are little different from each other in the generation and annihilation of defects.Due to the need to monitorchanges in ensemble volume,we use the NPT ensemble.Finally,there are mainly two kinds of point defects generated during the process of irradiating Lu2T2O7.One is the Frenkel pair.We use the Voronoi method and the comparison method to determine;the other is the antisite defect,and we use the order parameter method and comparison method to determine.From the ionic experiments that pyrochlore pellets of Lu2Ti2O7 were irradiated with 200 keV light He+ and 800 keV heavy Kr2+ ions at room temperature.The microstructural evolution induced by different ions irradiation was observed by grazing incidence X-ray diffraction(GIXRD).Ordered pyrochlore to partial amorphous phase transition was achieved under 800 keV Kr2+ ions irradiation to fluence of 2×1015 ions/cm2.However,a pyrochlore to a defect fluorite phase transformation was observed in the pyrochlore Lu2Ti2O7 irradiated by 200 keV He+.No amorphization was observed even to a higher fluence of 2.×1017 He+/cm2.Molecular Dynamics Simulation and SRIM were performed to interpret the above observation on the basis of point defect concentration and defect recombination rate.Finally,we also studied the influence of different kinds of initial PKA on the pyrochlore irradiation performance,the irradiation damage caused by different incident energy irradiation pyrochlore,and the defect changes in pyrochlore caused by the initial PKA with different incident directions.The number of defects generated by the initial PKA of the same energy and different kinds of ions increases with the increase of the atomic mass of the initial PKA.In the initial PKA of the same kind of different energy,the higher the energy is,the more defects are generated;the initial PKA with the same energy in different incident angle will induce different number of defects. |
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