Preparation And Properties Of High-entropy Pyrochlore Type High Level Radioactive Waste Solidification Matrices

The safe disposal of high-level radioactive waste is related to the sustainable development of nuclear energy.At present,the commonly used disposal method internationally is to use solidification matrix to solidify high-level radioactive waste,followed by deep geological burial.However,radioactive nuclide decay and geological disasters can cause serious damage to the solidification body,causing radioactive nuclides to leak back into the biosphere,posing a huge threat to human health.Therefore,the solidification matrices need to have excellent radiation resistance and mechanical property.High-entropy pyrochlore,as a new type of high-level radioactive waste solidification matrices,have received widespread attention,but there is relatively little research on its radiation resistance and mechanical property.The main work of this article is the study of the preparation,crystal structure,radiation resistance and mechanical property of titanate pyrochlore type high-entropy ceramics,and to explore the influence of entropy value on their radiation resistance and mechanical property.The possibility of synthesizing high-entropy pyrochlore (Eu_0.25Gd_0.25Y_0.25Lu_0.25)₂Ti₂O₇（HTP-1）is analyzed by VASP software.The calculation result shows that the sintering temperature of titanate pyrochlore type high-entropy ceramics prepared by high-temperature solid state method should be greater than 1225 K.Using X-ray diffraction technology,it is found that HTP-1 and(Sm_0.2Eu_0.2Gd_0.2Y_0.2Lu_0.2)₂Ti₂O₇（HTP-2）form a single-phase pyrochlore structure at a preparation temperature of 1673 K.In order to further investigate the crystal structure of HTP-1 and HTP-2,Raman spectroscopy is used to characterize them.The result shows that HTP-1 and HTP-2 exhibit lattice distortion,and all A-site elements have entered the A-site sublattice.Combined with the characterization results of energy dispersive X-ray spectrometer,showing that the single-phase pyrochlore HTP-1 and HTP-2 are successfully prepared.In order to explore the radiation resistance of titanate pyrochlore type high-entropy ceramics,the in-situ ion beam irradiation technology is used,and the SRIM software calculation results show that the radiation resistance of HTP-2 is better than that of HTP-1.At the same time,both HTP-1 and HTP-2 exhibit excellent mechanical property,and their experimental values are greater than the predicted values calculated by Vegas’s law.By comparing the hardness of HTP-2 with that of HTP-1,it is found that the mechanical properties of titanate pyrochlore type high-entropy ceramics also increase with the increase of material entropy.High-entropy pyrochlore not only can solidify multiple radioactive nuclides at the same time,but also have excellent radiation resistance and mechanical property,demonstrating great potential in the engineering application of high-level radioactive waste solidification.