Molecular Dynamics Study On The Influence Of Stress On Irradiation Defects And Evolution Of Zirconium Materials

As a material widely used in PWR,zirconium is affected by high heat flux and pressure.Neutrons and heavy ions produced by nuclear reactions can also cause radiation damage to the material.As the cladding material of the fuel element,the uranium dioxide nuclear fuel is wrapped inside.The heat is transferred to the external coolant,which causes the cladding material to be subjected to strong thermal stress.In addition,during the operation of the reactor,due to local stresses caused by expansion defects,impurities and fission gas generated by nuclear fuel,coupled with radiation creep,external mechanical loads,and stresses from all directions will act on the materials.They are important factors that ultimately leads to tensile deformation of zirconium materials.In this paper,a single crystal stacking model of α-Zr was established by using molecular dynamics simulation method.The cascaded radiation damage of zirconium caused by 1-4 ke V PKA,the change of mechanical properties after irradiation and the analysis of material defects under stress were studied.The diffusion behavior of self-interstitial atoms and 4-SIA defect clusters composed of four BS type self-interstitial atoms in the material is simulated.The formation energy and diffusion coefficient of defects under various strain conditions are calculated,and the diffusion activation energy is fitted.The influence of tensile strain and direction on the diffusion behavior of defects under several temperature conditions is studied.The main conclusions are as follows:1.The single crystal α-Zr material will have Frenkel defects,that is,interstitial atom-vacancy pairs,in the case of PKA bombardment with 1-4ke V energy.The number of defects quickly reached a peak after PKA incident.Although most of the defects gradually recovered under the action of annealing,there were still a few point defects in the final model.Cascade radiation damage reduces the tensile properties ofα-Zr,the yield limit of the material decreases with the increase of PKA energy,the dislocations appear in the material earlier,when the material is irradiated with higher energy PKA.2.Under unstrained conditions,1-SIA diffuses three-dimensionally in α-Zr.Although uniaxial tensile strain does not significantly change the diffusion behavior of 1-SIA,as the strain degree increases,the proportion of the unidirectional diffusion coefficient of defects along the strain direction in the total diffusion coefficient has an upward trend,and the the phenomenon is more obvious in low temperature conditions.In addition,the tensile strains in the directions of [11(?)0],[1(?)00] and [0001]decrease the diffusion activation energy of 1-SIA.3.The diffusion phenomenon of 4-SIA defect clusters under no strain is three-dimensional,and the diffusion range is small;the tensile strain in the [11(?)0]crystal direction has the most obvious influence on the diffusion and is one-dimensional diffusion,and when the tensile strain in the [1(?)00] and [0001]crystal directions,the impact on diffusion is not obvious.The tensile strain in the[11(?)0] and [1(?)00] crystal directions promotes the diffusion of defect clusters,while the tensile strain in the [0001] crystal direction inhibits the diffusion of defect clusters.