Molecular Dynamics Simulation Of Radiation Damage Of Reactor Structural Materials

The structural materials in the nuclear reactor are constantly exposed to large flux neutrons,causing variations in component size,shape and yield strength,which can lead to accidents and limit reactor life.Therefore,understanding the formation and evolution of irradiation defects is of great significance,and grain boundary defects(GBs)have long been considered to affect the evolution of radiation damage in metals.However,the mechanism of action of the grain boundary and the defective atom produced by irradiation has not been unified and clearly understood.To this end,this paper use molecular dynamics method to carry out a large number of cascade collision simulation studies on body-centered cubic(bcc)Fe-10Cr grain boundary and hexagonal close-packed(hcp)Zr grain boundary.This paper studied the microstructure changes and the Structural features of cluster defects of iron-chromium alloys produced by PKA(Primary Knock-on Atom)at different distances from the grain boundaries.It is found that when the PKA atom is located at the grain boundary,a large gap and vacancy defect cluster(size from 11 to 409)and many small clusters(number from 5 to 50)are generated at the grain boundary.The size and number of the cluster depend heavily on PKA energy,while depend weakly on temperature.The PKA atom at distance of 1nm from the GB,sometimes produces large size defect clusters both inside and outside the GB region.When the PKA atom is at 1nm,2nm and even 3nm,4nm from the GB,the GB will effectively absorb the interstitial atoms.It is found that the atomic ratio of Cr-interstitial to total interstitial produced at the GB region is much less than one at outside of GB region.In the analysis of cluster structure,it is found that the grain boundary system and the iron-chromium single crystal system will form a large number of iron-vacancy-chromium,iron-vacancy-iron self-gap dumbbell structures in the<110>and<111>directions,the Cr interstitial atoms tend to be distributed in the outer region of the grain boundary during the cascade stabilization phase and form a large amount of iron-vacancy-chromium self-gap dumbbell structure.In addition,the microscopic defects of radiation and the structural changes of clusters caused by the different distances of PKA atoms with different energies from ?-zirconium grain boundaries are also studied,as well as the vacancy and gap formation energy and the variation of atomic eccentricity threshold energy with grain boundary distance.The result we found the vacancy formation energy,interstitial formation energy and atomic displacement threshold energy near the GB decrease with decreases distance from the GB.Their value at the GB is significantly less than the corresponding energy in the intact crystal.The effect of GB on interstitial formation energy is greater in distance and size than in vacancy formation energy,and the magnitude of the effect on the displacement threshold energy depends on the incident direction of PKA atoms.The degree of coincidence of the displacement peak and GB increases as the PKA atom distance from the GB plane increases first and then decreases,and it is significantly affected by the PKA energy.The smaller of PKA energy,the greater of maximum overlap between the displacement peak and GB regions.And the PKA atom position corresponding to the maximum degree of coincidence is closer to the GB center plane.The PKA atom position is less than the critical distance the number of vacancy is greater than the number of interstitial outside the GB.however,when it is larger than the critical position,the number of interstitial is greater than the number of vacancy outside the GB.This shows that the PKA atom is within the critical position.and the number of GB absorbs more vacancies.Conversely,PKA atoms are outside the critical position and the number of interstitial absorbed by the GB is greater.When the coincidence degree between the displacement peak and the GB is low,the number of defects occurring outside the grain boundary is larger,whereas the number of defects occurring outside the grain boundary is smaller.Finally,it was found that the defect configuration resulting from the cascade collision is closely related to the degree of coincidence between the displacement peak and GB.