Fabrication And Tritium Release Of Solid Solution Li₄（Si,Ti）O₄ Tritium Breeder Material

Energy depletion is a constant topic,as high as the Sword of Damocles.As an inexhaustible clean and efficient energy,nuclear fusion energy is one of the important ways to solve the energy problem in the future.Deuterium and tritium fusion is a kind of fusion reaction which is easy to be realized under the existing experimental conditions,and is a kind of deep and extensive research in the future fusion energy development.The tritium breeder material plays an important role in the fusion reactor cladding as the source of tritium.Therefore,the research and development of tritium breeder materials with superior comprehensive performance is of key significance for the design of tritium production cladding and the development of fusion energy.In the fusion reactor,the breeder cladding has two main functions:one is to realize tritium self-sustaining of the fusion reactor through tritium production by neutrons,and the other is to realize fusion energy export.Therefore,as an important functional material in the tritium production cladding,the tritium breeder should meet the characteristics of high lithium content,strong thermal conductivity,low tritium retention,excellent mechanical properties,neutron irradiation resistance and good material compatibility.However,the existing solid tritium breeder materials can not meet all the requirements.On the basis of the existing solid tritium breeder materials,it is an urgent need to develop the tritium breeder materials that can fully meet the design and operation requirements of tritium production cladding.In this paper,on the premise of nuclide proliferation dose not change materials,according to the world the most important two candidate solid Li₄SiO₄ tritium value-added agent and Li₄TiO₄ material,through the theoretical design,using the same valence and radius of relatively large Ti replace Si atoms,expansion in the cell,new solid solution materials to improve the mechanical properties of ball,at the same time promote the electrical conductivity,thermal conductivity and to further improve the tritium release sex.In this paper,a new solid solution Li₄（Si,Ti）O₄tritium breeding material was systematically studied by theoretical design,material synthesis,property characterization and tritium release performance verification.The ground state properties of Li₄SiO₄,Li₄TiO₄ and the new tritium breeder Li₄（Si,Ti）O₄ were studied based on the first principles of density functional theory.The properties of the new tritium breeder Li₄（Si,Ti）O₄ were predicted.The results show that the total energy at some points decreases after Ti atoms are doped into Li₄SiO₄crystal,which indicates that the new tritium breeder Li₄（Si,Ti）O₄ system is stable.The optimization data of lattice parameters show that the volume of Li₄SiO₄lattice expands when Ti atoms are added.The calculation of band gap value shows that the interstitial space of Li₄（Si,Ti）O₄ system becomes narrower and the electrical conductivity of the material increases,which is expected to reduce the tritium release temperature of the breeder material after irradiation.The calculation results of thermal properties show that the heat capacity of Li₄TiO₄ is much larger than that of Li₄SiO₄,so the thermal conductivity of the new system Li₄（Si,Ti）O₄ may be stronger than that of Li₄SiO₄.The preparation technology of powder and pellet of multiple solid tritium proliferating material was established.The high temperature solid-state reaction conditions of Li₄（Si,Ti）O₄ powder were studied.The results showed that the best conditions for the synthesis of Li₄SiO₄ powder were as follows:Li OH?H₂O and SiO₂were sintered at 800℃for 12 h with the molar ratio of 4/1;The optimum conditions for the synthesis of Li₄TiO₄ powder are as follows:Li OH?H₂O and TiO₂ are sintered at 800℃for 12 h;The optimum conditions for the synthesis of Li₄Si_1-xTi_xO₄ powder are as follows:Li OH?H₂O is used as lithium source,and TiO₂ and SiO₂are used as raw materials for calcination at 900℃for 12 h.At the same time,the preparation process of Li₄（Si,Ti）O₄ pellets by freeze-drying method was studied.The results show that compared with the melting method,the equipment is expensive,the diameter distribution of the prepared pellets is wider,the freeze-drying process is simple and feasible,the preparation process is stable,and the particle size can be effectively controlled.The crystal structure,microstructure,electrical,thermal,mechanical and tritium release properties of Li₄（Si,Ti）O₄ were characterized by XRD,SEM-EDS,UV spectrophotometer,laser thermal diffusion tester,universal mechanical tester and off-line tritium release system.The results show that the tritium breeder Li₄（Si,Ti）O₄ is better than Li₄SiO₄,which is the preferred tritium breeder for fusion cladding at present,in terms of energy conversion,mechanical properties and the performance of radiation release of tritium.Compared with Li₄SiO₄,the optical band gap of Li₄（Si,Ti）O₄ decreases from 5.11e V to 4.77e V,indicating that the electrical conductivity of the new material is enhanced after Ti atom doping.Because Ti atom enters the crystal lattice and develops into a larger structure,the diffusion of lithium ions is accelerated.The thermal conductivity of Li₄（Si,Ti）O₄ is obviously stronger than that of Li4SiO4 when Ti atoms replace Si atoms into the crystal lattice.The mechanical properties of Li₄（Si,Ti）O₄ are obviously stronger than that of Li₄SiO₄,and the average crushing strength of the proliferating spheres increases from 15 N to 50N as a result of solid solution strengthening.After Ti doping,some desorption points with lower activation energy are formed on the grain surface,which makes the tritium release temperature of Li₄（Si,Ti）O₄ after neutron irradiation significantly lower than that of Li₄SiO₄,which is beneficial to improve the tritium release performance of the material.The tritium release performance of Li₄（Si,Ti）O₄ and Li₄SiO₄-Li₂TiO₃ and Li₄SiO₄-Li₂SiO₃ biphasic ceramics breeder pellets designed and proposed in this paper was compared and studied.The tritium release performance of Ti oxide doped breeder materials was comprehensively evaluated,and the possible factors affecting the tritium release behavior of biphasic ceramics breeder pellets were analyzed.The results show that:（1）The tritium release behavior of Li₄（Si,Ti）O₄ breeder pellets is very complex,and the main tritium release form is tritium water,and the tritium water proportion of the three kinds of pellets is about 86.7%.Compared with Li₄SiO₄ beads,the tritium release performance is better at low temperature.With the increase of Ti doping ratio,the tritium release temperature of the main peak decreases gradually;（2）The tritium release form of Li₄SiO₄-Li₂TiO₃ biphasic ceramics breeder pellets is mainly tritium gas.The main peak tritium release temperature is 550℃.The tritium release behavior of the biphasic ceramics is different from that of Li₄SiO₄ and Li₂TiO₃breeder pellets.The tritium release of the biphasic ceramics is co-controlled by the diffusion process and the surface reaction,and the reaction rate of tritium on the grain surface is slow;（3）The release of tritium gas from Li₄SiO₄-Li₂SiO₃ biphasic ceramics breeder pellets is still the most important form of tritium release.With the increase of neutron injection amount,the tritium release temperature of the sample increases gradually,which may be mainly caused by the existence of Li₂SiO₃ phase and radiation defects.Above all,this thesis starting from fusion tritium production cladding design requirements,without changing the nuclide and can improve the density of lithium and improve the stability of the material premise,the design has developed a new kind of solid solution state tritium breeder Li₄（Si,Ti）O₄ through the system research has shown that the material thermal conductivity,mechanical properties and performance of tritium in aspects and so on all have significantly improved,solid solution state Li₄（Si,Ti）O₄ can be used as the future fusion m1 tritium production material of a kind of important candidate material,the material of the successful development of fusion of our country the development of the production function of tritium cladding material is of great significance.