Phase Field Study On Void Dynamics In Uranium Dioxide Under Irradiation And Temperature Effect

The purpose of this subject is to establish a unified two-dimensional phase field model,and a corresponding program to simulate nuclear material under the condition of irradiation behavior of void evolution.The void evolution rule of uranium oxide is analyzed in the system of grain boundary and temperature gradient.Reference to some research achievements of other researchers,here I rebuild the system free energy,free energy,including matrix void free energy and free energy of grain boundary,the expression for the vacancy concentration,interstitial atoms concentration of order parameter of the functional and grain boundary.Then,based on the Cahn-Hilliard equation and TDGL equation,the void atoms,interstitial atoms and grain boundary in the study area were changed over time,so the evolution of void in the region was obtained.At present,although there have been some phase field model can describe the evolution of the void on the literature,more for single factor,it is lack of consideration of grain boundary,and the evolution of temperature gradient satisfying the two factors of void uniform phase field model.Based on the development of phase field program,this paper simulates the evolution behavior of the nuclear material in the irradiated conditions to verify the feasibility of the program and reveal the new rules of the void evolution.The simulation process is divided into two parts,which are under the irradiation of uranium dioxide material in the void of the dynamic evolution,as well as the temperature gradient of uranium dioxide material in the void of the dynamic evolution.The void in the state of nature can absorb the void atoms and grow up,it can be reduced with the surrounding interstitial atoms.Under the irradiation conditions,more void atoms and interstitial atoms can be excited,and the cascade collision effect can be promoted to form a void.This effect is limited in the polycrystalline material with void atoms,interstitial atomic annihilation,and the property of the grain boundary.The vacancy atoms are formed in the periphery of the grain boundary because of their concentration gradient,At the same time,the peak area of the void is formed at a certain distance from the grain boundary.Due to the higher surface diffusion coefficient of the atoms in the uranium dioxide material,it is known that the surface diffusion mechanism plays a dominant role during the thermal migration of voids in uranium dioxide,accompanied by a certain amount of steam transport flow.Results show that for small void(its area smaller than ? ?m~2),in accordance with analysis model of case,you can find the migration characteristics consistent with the analysis model of void,migration rate is a constant,nearly changes of void in shape.In contrast,the circular shape of the large void(its area larger than 12 ?m~2)was observed,and the shape of the cashews was observed.After a long period of evolution,the deformed void splits into smaller voids.Depend on the size of the void migration behavior is due to the interfacial energy(keep the round shape of void)and the surface of the anisotropic diffusion flow(due to the spread of the uneven surface of the void)combination effect.In addition,due to the void shape relaxation effect,the void initial shape changes the migration speed and migration time(for large voids).However,it has only a slight effect on the long time of void migration.