【作者】 刘辉；

【导师】 邱玮；

【作者基本信息】 长沙理工大学 ， 动力工程及工程热物理， 2018， 硕士

【摘要】 熔盐堆是具有第四代核能技术特点的六大核反应堆型之一,而且是一种利用低熔点、高沸点和热转化效率高的氟化盐作为冷却剂以及燃料载体的液态燃料堆,而熔融氟化盐对熔盐堆中的材料具有极强的腐蚀性。不锈钢作为未来熔盐堆关键部件的候选材料之一,目前广泛的应用于大部分商用核反应堆。因此,本论文通过静态腐蚀浸泡实验研究了几种不同的不锈钢在初始杂质离子的LiF-NaF-KF盐中的腐蚀行为,研究对比了 304、316、316L、316LN和316H不锈钢的抗高温熔盐腐蚀性,并分析了影响304和316H不锈钢在熔盐中腐蚀行为的因素;研究分析了熔盐中SO42-离子的含量对316L不锈钢的腐蚀行为影响;研究分析了熔盐中添加杂质Zr2+对耐高温不锈钢316H的腐蚀行为影响。其主要结果和结论如下:在700°C的熔融氟化盐中,几种不锈钢的抗高温熔盐腐蚀性从低到高次序为:304(最差)、316、316L、316LN、316H(最好)。由于Mo元素能够在晶界上形成含Mo化合物,从而降低了 Cr元素在晶界上的扩散流失速度,增强了含Mo不锈钢的抗高温熔盐腐蚀性。因此,304不锈钢的抗高温熔盐腐蚀性最差。腐蚀后不锈钢的近表面存在Cr、A1的氮化物析出相层,析出物的形成对合金中Cr元素的扩散流失起到一定的阻碍作用,因此能够降低合金在熔盐中的腐蚀速率。316L不锈钢在熔盐中的腐蚀速率与盐中SO42-离子的含量呈线性增加关系。分析表明合金中的Cr元素与SO42-离子反应生成Cr2O3和S元素,然后S元素与合金中的Mn元素反应形成MnS,而后Cr2O3和MnS将熔于熔盐中来加速合金的腐蚀。在LiF-NaF-KF 盐中增加 Zr2+离子能减缓 316H 不锈钢的腐蚀速率,由于 Zr2+在高温熔盐中不稳定,极易形成稳定态Zr4+,并且Zr比合金中的Cr更加活泼,所以Zr2+在熔盐中将被优先腐蚀为Zr4+,从而消耗熔盐中的杂质离子来减缓316H不锈钢的腐蚀速率。通过本研究总结了几种不锈钢的抗高温熔盐腐蚀性的优劣次序,阐述了不锈钢在熔盐中的腐蚀机理,揭示了不锈钢在熔盐环境中Cr、Al氮化物和晶界处含Mo化合物的析出对腐蚀的影响,阐明了盐中SO42-以及Zr2+的添加对不锈钢在熔盐中的腐蚀影响。本研究对316不锈钢能够应用于熔盐堆具有重要的意义。更多还原

【Abstract】 The Molten Salt Reactor(MSR)is the one of the six nuclear reactor types of the IV nuclear power technical features,which uses fluoride salts of low melting point,high boiling point and high termal conversion efficiency as coolant and fuel carrier.However,molten fluoride salts are strong corrosive to the molten salt reactor structural materials.The stainless steel is one of the candidate materials for the major parts of the molten salt reactor in the future and was widely used in the most commercial nuclear reactor.Corrosion behavior of several different stainless steel in initial impurity ions LiF-NaF-KF salt by static corrosion immersion experiments have been studied.The high temperature molten salt corrosion resistance of 304,316,316L,316LN and 316H stainless steel were compared,and the factors of corrosion behavior of 304 and 316H stainless steels in molten salt were discussed.The influence of SO42-ions on the corrosion behavior of 316L stainless steel in molten salt was studied.The effect of adding Zr2+ in molten salt on the corrosion behavior of high temperature resistant stainless steel 316H was studied.The main results and conclusions are as follows:The order of the high temperature molten salt corrosion resistance of these stainless steels in the molten fluoride salts at 700℃ from low to high is:304(the worst),316,316L,316LN,316H(the best).Because of the existance of the Mo element,a Mo-containing compound can form on the grain boundary,and the diffusion rate of Cr on the grain boundary decreaced.So the corrosion resistance of the Mo-containing stainless steel is enhanced,and the high temperature molten salt corrosion resistance of 316 stainless steel is better than 304 stainless steel.Cr and A1 nitride precipitation phase layers are found on the surface of the stainless steel after corrosion.The precipitates will hinder the diffusion of Cr in the alloy,which can slow down the corrosion rate of the alloy in the molten salt.The corrosion rate of 316L stainless steel in LiF-NaF-KF salt increases almost linearly with the increase of SO42-ion content in salt.The investigation shows that Cr element in the alloy reacts with SO42-ions to form Cr2O3 and S element,then S element reacts with Mn element in the alloy to form MnS.C2O3 and MnS can melt in the molten salt to accelerate the corrosion of the alloy.The addition of Zr2+ ions in LiF-NaF-KF salt can effectively reduce the corrosion rate of 316H stainless steel in molten salt.Zr2+ is unstable in high-temperature molten salt and can easily form stable Zr4+.Zr is more active than Cr in the alloy,so Zr2+ is preferentially oxidized into Zr4+ in the molten salt,thereby consuming the impurity ions in the molten salt to slow down the corrosion rate of the 316H stainless steel.In this paper,the differences of corrosion resistance of different stainless steels in high temperature molten salt environment were concluded,and the corrosion mechanism of stainless steel in molten salt were discussed.The influence of the precipitation of Cr,Al nitride and grain boundary Mo compounds on the corrosion of stainless steel in the molten salt environment was revealed,and the effect of the addition of SO42-and Zr2+ in the salt on corrosion of stainless steel was clarified.This research is very important for stainless steel to be applied in molten salt reactor.更多还原