Study Of Corrosion Mechanism Of Copper Material In High-level Radioactive Waste Packaging Containers Under The Coupling Effect Of Groundwater And Irradiation

The treatment and disposal of high-level radioactive waste generated by nuclear weapons development and operation of nuclear power plants has become a major safety and environmental protection issue.Deep geological disposal is one of the most feasible methods for the disposal of high-level radioactive waste,and the high-level radioactive waste packaging container is the first important barrier to contact with the external environment,and its integrity is related to the leakage of high-level radioactive waste.The packaging container is continuously exposed to various radiations released by the waste body and erosion from the water in the gap of the buffer layer.Both radiation and water chemistry may affect the integrity of the packaging container material.Among them,Cl~-has a significant corrosion behavior on the packaging container material.influences.Therefore,studying the corrosion behavior of container materials in groundwater and irradiation environment has practical engineering value.This paper takes copper as the candidate material for the cladding of geological disposal containers for high-level radioactive waste.It uses a combination of experiment and numerical simulation to explain it from the perspective of microscopic electrons and atoms through a first-principles calculation method based on density functional theory.Experimental phenomena.In the experiment,the coupling effect of groundwater and irradiation was studied by using high energy linear electron accelerator and groundwater simulation solution.The surface morphology of the materials before and after irradiation corrosion was characterized by atomic force microscope(AFM)and scanning electron microscope(SEM).The results show that defect clusters appear on the surface of pure copper samples after irradiation,and obvious corrosion pits appear on the surface of pure copper samples after groundwater alone.Compared with electron irradiation and groundwater alone,groundwater irradiation coupling effect can enhance the corrosion of pure copper samples.In the aspect of numerical simulation,based on the first-principles calculation method,the structural stability,electronic properties and mechanical properties of intrinsic point defects and he defects caused by copper irradiation damage were studied;the adsorption configuration,adsorption energy and electronic properties of chlorine atoms adsorbed on Cu(110)surface and Cu(110)surface with vacancy were studied.The results are as follows:1)For point defects caused by Cu radiation damage,the introduction of defects causes lattice distortion,which reduces the stability of the system.The magnitude of lattice distortion caused by defects introduced by the same atom is proportional to the formation energy of the corresponding defects.The sequence of eigenpoint defects and He defects in the crystal lattice is as follows:vacancy or alternate position,octahedral space,tetrahedral space;At the same location,the eigenpoint defects occupied space prior to the HE defects.The sequence of capture by vacancy to interstitial atoms and defects at different positions is as follows:Cu interstitial atoms>He interstitial atoms;Tetrahedral interstitial atom>octahedral interstitial atom;2)After the introduction of octahedral interstitial atoms,some electrons transfer to higher energy levels,so that the covalent interaction between them and the nearest Cu atom is weakened and the stability of the system is reduced.In addition,compared with the octahedral He interstitial system,the gain and loss of electrons in the octahedral self-interstitial system is more obvious,the interaction between atoms is stronger,and the system stability is stronger;3)The He substitution site atoms increase the bulk modulus and Young’s modulus of the system,increase the volumetric deformation resistance and hardness of the system,and other defects make the volumetric deformation resistance of the system weaker.He substitution site atoms and vacancies enhance the shear resistance and brittleness of the system,while other defects all weaken the shear resistance and brittleness of the system.4)The adsorption of Cl atom on Cu(110)surface and Cu(110)surface with vacancy is the most stable;the interaction of d orbital electrons of Cu ion with s orbital and p orbital states of Cl atom leads to the adsorption of Cl atom on Cu surface.After adsorption,Cu atoms in the surface layer lose electrons,while Cl atoms gain electrons.5)The Cl atom adsorbs on the Cu(110)surface and the Cu(110)surface containing vacancies,which increases the surface activity of the adsorption surface,makes the Cu surface unstable,and causes the corrosion electrochemical reaction on the Cu surface;Cu(110)surface vacancies The generation of defects reduces the surface stability,and the adsorption energy is lower than the perfect Cu(110)surface.After adsorption,the charge transfer number of Cl ions increases,and the activation effect of Cl ions on the Cu(110)surface containing vacancies is enhanced,which makes the system stable Lower,the surface is more unstable,and eventually the surface is more prone to corrosion.