海洋环境腐蚀与生物污损重点实验室知识库

  核能目前广泛应用各个领域，给人类带来便利的同时也带来了困扰。核能使用过程中不可避免地会产生核废料，其中高放核废料辐射性强，半衰期长，发热量大，必须进行安全处置。处理高放核废料最现实的方式为深地质处置。核废料储罐作为其深地质处置第一道保护屏障尤为重要。由于地下水的不断渗入，核废料热量的释放及氧气的消耗殆尽，营造了储罐发生腐蚀及氢脆的近域环境。为了阻止高放核废料随地下水进入生物圈，有必要从腐蚀和氢脆的角度对储罐的寿命进行大时间尺度的安全评估。

  首先通过开路电位和动电位极化曲线电化学测试方法研究了Q235钢，钛及其合金在深地质环境中的腐蚀行为。结果发现膨润土作为缓冲回填材料加入能够有效降低金属材料的腐蚀速率。根据本文所得到的储罐金属材料腐蚀速率随地质处置时间变化模型，单从腐蚀速率角度考虑，作为储罐材料, 钛及其合金要比碳钢具有优势，可存放数十万年甚至数百万年。鉴于高放核废料的辐射性，研究还对比了三种金属材料在最大剂量γ射线辐照三个月和一年后在饱和高压实膨润土中的腐蚀行为。结果表明，辐射对储罐金属材料的影响在高温环境比较大，在低温下几乎没有影响，由于整个处置阶段高温环境时段非常短，因此认为辐射在整个深地质处置过程影响不大。在储罐腐蚀速率随地质处置时间变化模型基础上，本文建立了渗氢效率随地质年代变化模型，进一步了解了氢脆对储罐的影响。结果发现，储罐备选材料渗氢效率随充氢电流密度减小而增加。Q235钢渗氢效率随着地质年代最终呈现增加趋势，这也证实了腐蚀的阴极反应将会由氧还原转为氢还原为主。而TA2与TA8-1与其相反，随着年代增加而降低，这主要是因为钛及其合金上氢化物的生成阻碍氢的扩散。由于氢在Q235钢中扩散较快，其基本不受氢脆影响，而均匀的氢化物分布是钛及其合金发生氢脆的主要原因。

  本论文深入研究了核废料储罐发生腐蚀以及氢脆的机理，评估了核废料储罐在大时间尺度的安全性，对未来储罐材料的科学选择和优化奠定了理论基础，对核废料储罐的寿命预测有指导作用。

    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 γ 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.