Fabrication Of The Solid Tritium Breeder Ceramic Pebbles And The Study Of Its Tritium Release Properties

At present,Deuterium(D)-Tritium(T)fusion energy has been considered as the most potential green energy,which can solve the energy problems for human beings in the future.However,as T is rare in nature,it is necessary to solve the tritium fuel problem,so the tritium breeder blanket is designed in nuclear fusion reactors,Li2TiO3 and Li4SiO4 ceramic pebbles are considered as the most potential solid tritium breeder due to their excellent mechanical properties and good tritium release behavior.However,so far,the production of tritium ceramic pebbles can only reach the laboratory level or tens of kilograms level,which can not meet requirement of hundreds of tons for tritium breeding blanket in practical application.Therefore,it is a key challenge that how to mass fabricate tritium breeder ceramic breeder at a low cost in the future.In addition,tritium release data of Li2TiO3 and Li4SiO4 tritium breeder ceramic pebbles are scattered,and most of the tritium data are focused on ceramic powders.Thus,the tritium release behavior of tritium breeder ceramic pebbles needs to be further studied under specific processes,especially in the potential bi-phase Li2TiO3-Li4SiO4 ceramic pebbles.Firstly,the study was conducted from the synthesis of ceramic powder,the Li2TiO3 ceramic powder with good dispersion was successfully fabricated via nonhydrolytic sol-gel method and water controlled-release solvothermal process,and the ceramic pebbles with excellent properties were prepared by indirect wet process.The nano-structure Li2TiO3 powder with average grain size of 24 nm were synthesized at 650℃,and the phase transition temperature for β-Li2TiO3 fabricated by this method was only 600℃.The results shows that the Li2TiO3 ceramic pebbles with excellent comprehensive properties,such as the diameter of 1.3mm-1.5 mm,crush load of 67 N3 sphericity of 0.97,the relative density of 84.9%,the grain size of 2.85 μm and porosity of 19.84%can be obtained for samples sintered at 1050℃.Moreover,the Li2TiO3 ceramic powder with the average grain size of 35 nm was successfully fabricated at 550℃ via water controlled-release solvothermal process,and the phase transition temperature for fabrication of β-Li2TiO3 was 450℃.The results also show that the Li2TiO3 ceramic pebbles have excellent comprehensive properties,such as the average diameter of 1.2mm,the average grain size of 1.4 μm,the sphericity of 0.98,the crushing load of 53 N and the porosity of 29.8%when the sintering temperature was 950℃Secondly,from the view of the improvement of the mechanical properties of ceramic pebbles,the effects of doped SiC powder on the properties of Li4SiO4 ceramic pebbles were systematically studied.It is found that the content of SiC powder has a certain effect on the phase and the morphology of Li4SiO4 ceramic pebbles.The optimal additive amount of SiC powder is 0.1 wt%,which can effectively reduce the sintering temperature by 250℃ to fabricate Li4SiO4 ceramic pebbles.The densification activation energy of SiC doped Li4SiO4 ceramic pebbles is 481.13 KJ mol-1 via calculating the shrinkage and activation energy,which is lower than that of Li4SiO4 ceramic pebbles.When the sintering temperature is 800℃,the Li4SiO4 ceramic pebbles give excellent performance,such as the ceramic grain size of 5.42 μm,internal pore distribution uniform,thermal conductivity of 1.97 W/(m·K),relative density of 90.3%,crushing strength of 65.3 N.Thirdly,considering the preparation efficiency of ceramic pebbles,high quality Li2TiO3 ceramic pebbles were prepared by centrifugal granulation method.The fluidity and packing density of ceramic powders were improved by spraying drying process.It is found that the binder has a certain influence on the sphericity of ceramic pebbles,and compared with other binder of PVA and PVP,the binder solution of sesbania gum can improve the plastic of ceramic powder,which can obtain the ceramic pebbles with high strength,dense internal structure and high sphericity.But,when the concentration of sesbania binder exceeds 0.3%,the Li2TiO3 ceramic pebbles appear stratified on the cross section.The experiment result shows that the Li2TiO3 ceramic pebbles sintered at 1000℃ have optimal mechanical properties such as a crushing load of 108 N and relative density of 92.4%TD.Therefore,the centrifugal granulation method proposed in this paper can not only prepare Li2TiO3 ceramic pebbles in a large scale,but also provides theoretical guidance for the study of other tritium breeding materials.Afterwards,a new bi-phase Li2TiO3-Li4SiO4 ceramic pebbles was designed and prepared,in which the core part is Li2TiO3 and the shell part is Li2TiO3-Li4SiO4.According to EDEM simulation and experimental results,the optimal rotation speed of preparing ceramic pebbles fabricated by centrifugal granulation is 50 r/min.The ceramic pebbles with dense internal structure can be obtained by spraying ethylene glycol solution on the surface of Li2TiO3 core in that it can increase the adhesion strength between the core and shell.The experimental results display that the Li2TiO3-Li4SiO4 ceramic pebbles sintered at 1100℃ have a uniform diameter of 1 mm,a good sphericity of 0.97 and an excellent crushing load of 82.4 N,and the porosity of core and shell are 3.21%and 10.73%,respectively.The Li2TiO3Li4SiO4 ceramic microspheres can be mass produced by centrifugal granulation,which provides an important guidance for the large-scale preparation of lithium tritium breeder pebbles in the future.Finally,the tritium release behavior of LiTiO3,Li4SiO4 and Li2TiO3-Li4SiO4 ceramic pebbles was estimated by using the tritium thermal desorption spectroscopy(tritium-TDS)system.It was found that the tritium release types of the three breeder ceramic pebbles were mainly in the form of tritium water(HTO),and the tritium release temperature sequence was as follows:Li4SiO4<bi-phase Li2TiO3-Li4SiO4<Li2TiO3,and the tritium release content of Li4SiO4 ceramics was the highest.With the decrease of the heating rate,the tritium release peak of all ceramic pebbles moved to low temperature side.Moreover,the experiment shows that the tritium release behavior of the breeding ceramic pebbles was affected by the diffusion process and surface desorption.The annihilation process of defects of three ceramic breeder pebbles was further studied by means of ESR test.It was found that the ceramic pebbles would produce O’-center and E’-center defects after neutron irradiation.It is found by isothermal heating experiments that irradiation defects will be annihilated with the increase of temperature,which corresponds to tritium release process.