| The disposal of nuclear wastes have always been a topic that people discuss widely.Especially,the high-level radioactive wastes?HLWs?are extremely harmful to the human living environment due to their high radiotoxicity and long half-life.Therefore,how to safely and effectively dispose HLW is a huge problem for humans.Pyrochlore is considered as an ideal solidified substrate for high-level radioactive wastes due to its superior radiation resistance,stable structural properties,good mechanical properties and low leaching rate of incorporated species.In this study,low-cost raw materials were used to prepare solidified Gd2Ti2O7 pyrochlore body by self-propagating high-temperature synthesis plus quick pressure technology?SHS/QP?.Simultaneously curing doped simulated actinides in Gd2Ti2O7 pyrochlore A,B,and A/B positions to explore Performance.Using X-ray diffraction?XRD?,Raman spectroscopy,electron backscattered diffraction?BSE?,scanning electron microscopy?SEM?and inductively coupled plasma mass spectrometer?ICP-MS?and other testing methods investigate the phase structure,micromorphology,chemical stability and radiation resistance of Gd2Ti2O7 pyrochlore solidified body.The main results show as follows:?1?In the study of the preparation of Gd2-xEuxTi2O7 by A-site solidified Eu simulation of actinide nuclides in Gd2Ti2O7 pyrochlore,the maximum value of x is 0.4.The pressure time under the optimal density is 27s,the maximum density and Vickers hardness is 4.97 g.cm-33 and 9.55 G Pa.The normalized leaching rates of Cu,Gd and Eu after 42d are LRCu=2.25×10-5g.m-2.d-1and LRGd=2.82×10-6g.m-2.d-1and LREu=8.89×10-6g.m-2.d-1.?2?To improve the radiation resistance of titanate–pyrochlore,Zr was incorporated to substitute the Ti site of Gd2Ti2O7 pyrochlore.Gd2(Ti1-xZrx)2O7?x=0,0.05,0.15,0.25,and 0.35?pyrochlores were prepared by SHS,and 5MeV Xe20+was used to perform alpha-ray irradiation simulation experiments.Gd2Ti2O7 pyrochlore was tested at irradiation doses of 5×1014ions/cm2,1×1015ions/cm2,2×1015ions/cm2,and 4×1015ions/cm2.The surface was amorphized after irradiation,and the pyrochlore phase transit to the phase of the fluorite phase.Under the irradiation dose of 4×1015ions/cm2,Gd2(Ti1-xZrx)2O7 pyrochlores with different Zr content was irradiated.The result of grazing incidence angle?=5°shows that at this detection depth the pyrochlore have fluorite structure and are partially amorphous.The test results of?=0.5°showed that the surface of the samples were completely amorphized.?3?Simultaneous excess doping simulation of the A/B sites in Gd2Ti2O7pyrochlore with Sm2O3/ZrO2,and recording the reaction system temperature of different doping amounts with a paperless recorder.The results show that as the the amount gradually increases the reaction temperature of the system decreases significantly.When the excess is 20%,the reaction system cannot sustain itself.The maximum solid solution of Gd2Ti2O7 pyrochlore to Sm2O3/ZrO2 is 10%?SZ-10?.The rapid compaction process of pyrochlore-based at the maximum solid solution is used to investigate the maximum density to obtain the solidified body.The solidified body of SZ-10 sample exhibits good bulk density of 5.56 g·cm-3,high Vickers hardness of11.20±0.2 GPa,as well as excellent chemical aqueous durability.The results of EDX spectrum analysis showed that the distribution of each element was uniform.The final chemical formulation of SZ-10 sample is calculated as Gd1.81Sm0.23Ti1.75Zr0.22O7.The normalized leaching rates of element 42 days obtained by the MCC-1 immersion method on solidified body were LRGd=1.92×10-4g·m-2·d-1,LRSm=1.51×10-4g·m-2·d-1and LRCu=3.90×10-3g·m-2·d-1... |
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