Study On Electrochemical Corrosion Of Containment Steel Liner Based On Microscopic Model

The containment steel liner is the last line of defense to prevent the diffusion of radioactive materials,and the steel liner plays a crucial sealing role.Corrosion of the steel liner is the most important factor affecting the sealing performance of the steel liner.Once the steel liner undergoes electrochemical corrosion,it will lead to a reduction in the thickness of the steel liner and a reduction in its mechanical properties,which can easily lead to steel liner tear accidents in serious accidents,bringing significant safety hazards to the safe operation of nuclear power plants.The main causes of corrosion of the containment steel liner are chloride ion erosion and the presence of foreign matter.Both chloride ions from the containment structure to the surface of the steel liner and the presence of foreign matter can change the alkaline environment,causing corrosion of the steel liner.Based on this theory,numerical simulation of the containment steel liner was conducted.The research work and conclusions are as follows:(1)A two-dimensional mesoscopic model of the containment vessel is generated based on the Fuller grading curve,and a chloride ion diffusion model in concrete is established based on Fick’s second law.The reliability of the model is verified.The numerical results agree well with the reference test data,demonstrating the reliability of the model.Using this model,the effects of coarse aggregate and interfacial transition layer on chloride ion diffusion in concrete were analyzed.The results show that the volume ratio of coarse aggregate affects the diffusion of chloride ions in concrete: the shape of coarse aggregate has no effect on the diffusion of chloride ions;The interfacial transition layer effect and cracks can accelerate the diffusion rate of chloride ions in concrete.(2)Based on Butler-Volmer’s law,a two-dimensional electrochemical corrosion model was established,and the reliability of the numerical simulation of electrochemical corrosion was verified by simulating experimental data in the literature.The results show that the area ratio of cathode and anode has a significant impact on the corrosion rate in electrochemical corrosion;As the resistivity increases,the corrosion potential of the cathode and anode moves in both positive and negative directions,respectively;The corrosion current density gradually decreases as the resistivity increases.(3)Based on Fick’s second law and Butler Volmer’s law,a two-dimensional mesoscopic model of chloride ion electrochemical corrosion was established.By modifying the definition of corrosion zone and the Tafel slope of the anode,chloride ion and electrochemical corrosion were coupled in the COMSOL p Hysical field.The following conclusions were obtained:During the three stages of electrochemical corrosion on the surface of steel liner,the corrosion potential gradually decreased as the corrosion zone expanded;At the beginning of corrosion,macrocell corrosion dominates,and after overall corrosion,microcell corrosion dominates.Macrocell corrosion current density shows a decreasing trend,while microcell corrosion gradually increases,and eventually exceeds the value of macrocell corrosion current density after 30.2 years;The corrosion potential and current density are mainly affected by the concentration difference of chloride ions,independent of the number of segments divided by the concentration gradient;Based on the numerical model of electrochemical corrosion,the corrosion rate was calculated and the erosion age was estimated.