Analysis Of Hydrogen Absorption And Hydrogen Embrittlement Of High-level Radioactive Waste Canisters During Corrosion Processes

At present,nuclear energy is widely used in various fields,which not only brings convenience to human beings,but also brings troubles.High level nuclear waste with strong radiation,long half-life and large heat release is an unwanted product produced in the use of nuclear energy.The most realistic way to deal with high level nuclear waste is deep geological disposal.As the first protective barrier of deep geological disposal,nuclear waste container is particularly important.Due to the continuous infiltration of groundwater,the release of nuclear waste heat and the depletion of oxygen,a field environment where container corrosion and hydrogen embrittlement could happen is created.In order to prevent the high-level nuclear waste from entering the biosphere,it is necessary to carry out a large-scale safety assessment of the container life from the perspective of corrosion and hydrogen embrittlement.Firstly,the corrosion behavior of Q235 steel,titanium and its alloy in deep geological environment was studied by open circuit potential and potentiodynamic polarization curves.The corrosion rate in highly compacted bentonite environment proves to be smaller than that of underground water environment.According to the model that the corrosion rate of metal materials varies with the time of geological disposal,only considering the corrosion rate,titanium and its alloys are safer and more reliable than carbon steel for hundreds of thousands of years or even millions of years disposal.In view of the radioactivity of high-level nuclear waste,the corrosion behavior of three metal materials after three months and one year of maximum dose ? irradiation in saturated high compacted bentonite after three months and one year of maximum dose gamma-ray irradiation was also compared.Since the high temperature environment is very short in the whole disposal stage,it is considered that the radiation has little effect on the whole deep geological disposal process.Based on the model of the corrosion rate of the container with the geological disposal time,we established a model of the hydrogen permeation efficiency with the geological disposal time.The results show that the hydrogen permeation efficiency of the candidate materials increases with the decrease of hydrogen charging current density.And the impact of hydrogen embrittlement of container was further understood.The hydrogen permeation efficiency of Q235 steel eventually increased with the geological time,which also confirms that the cathodic reaction of corrosion will change from oxygen reduction to hydrogen reduction,however,TA2 and TA8-1 were opposite and decreased with the time.This was mainly because the formation of hydride on titanium and its alloy hindered the diffusion of hydrogen.Due to the fast diffusion of hydrogen in Q235 steel,it is not affected by hydrogen embrittlement,however,tensile test results show that uniform hydride distribution is the main reason for hydrogen embrittlement of titanium and its alloys.The research evaluated the safety of nuclear waste container on a large time scale and deeply studied the mechanism of corrosion and hydrogen embrittlement of nuclear waste container.Theoretical knowledge was founded for the scientific selection and optimization of future container materials,providing important guidance for the design of container.