First-principles Study On The Defect Structure Of Zirconium Alloy Cladding

The development of nuclear power is an important means to alleviate energy problems.As an important safety barrier for nuclear power plants,cladding tubes are not only used to install nuclear fuel pellets and transfer heat,but also an important cladding structure to prevent leakage of fission products in nuclear reactions.As a fuel cladding,zirconium alloy is facing the problem of irradiation damage of materials in the reactor,so it needs to have good comprehensive mechanical properties,its composition components are Sn,Fe,Ni and Cr,and the alloy elements Sn,Fe,Ni,Cr can improve the mechanical properties,corrosion resistance and thermal conductivity of the material,and reduce the sensitivity of the surface state to corrosion.Among them,Sn and Fe dominate.In this paper,the most important Zr-Sn and Zr-Sn-Fe alloys are the research objects,and then Then,the simulation study on the irradiation damage of zirconium alloy by fission fragments was carried out.Based on the first-principles calculation method of density functional theory,the formation energy of Sn elements with different amounts in pure zirconium supercells was calculated,the stability of Sn doped into pure Zr supercell structure was studied,and Sn was determined in pure The most stable position in the zirconium supercell,and then doped with Fe element to study the role of Fe as an important component of the zirconium alloy;then doped the zirconium alloy model again to establish the fission fragments Xe and Kr to irradiate the zirconium cladding Defect model after injury.For the Zr-Sn alloy and Zr-Sn-Fe alloy models,the properties of lattice parameters,elastic modulus,shear modulus,Poisson's ratio,state density DOS and differential charge density were calculated,and the Zr-Sn supercell structure was analyzed.Calculate the mechanical and thermal properties of the defect model,analyze the influence law and mechanism of Xe and Kr on the Zr-Sn cladding,and provide a basis for the design and research of the zirconium alloy cladding material.The study mainly reached the following conclusions:(1)For Zr-Sn alloy,the B / G values of pure Zr supercell structure,VS defect structure,SS defect structure,TIS defect structure and TIS defect structure are all greater than 1.75,Poisson's ratio is greater than 0.3,Zr-Sn The alloy is ductile;the formation energy of the SS defect structure is negative,which is easier to form;the G value and E value of the SS defect structure are the largest,and the SS defect structure material has the strongest hardness;the defect structure has different degrees of charge transfer,Indicating that the interaction between atoms is stronger after Sn doping,and the unit cell stability is enhanced.(2)For Zr-Sn-Fe alloy,the values of B / G and poisson's ratio become larger after doping with Fe atoms,indicating that the material of Zr14 Sn Fe system has better ductility,that is,the doping of Fe atoms can reduce the possibility of embrittlement to a certain extent Charge transfer data shows that the charge transfer number of Zr15 Sn system and Zr14 Sn Fe system doped with Fe atoms increases,Sn atoms and Fe atoms gain electrons,Zr loses electrons,the gain and loss of electrons is more obvious,indicating that when doped with Fe atoms,Zr-The stability of Sn-Fe system is strengthened.(3)For the zirconium alloy doped with fission gas,the fission fragments Xe and Kr will reduce the resistance to deformation of the zirconium alloy;doping Xe and Kr will reduce the hardness of the zirconium alloy;from the results of Debye temperature calculation,Xe doping After Kr,the covalent bond strength decreases.