Study on Electrochemical Corrosion Potential of Stainless Steel in High Temperature Water under Irradiation of Ionizing Radiation

控制电化学腐蚀电位（ECP）对于减轻核反应堆结构材料不锈钢的应力腐蚀开裂（SCC）非常重要。本研究旨在探讨影响ECP的各种因素。据报道，控制ECP的关键因素是氧化性物质，主要是由反应堆水的辐射分解产生的H_2O_2和O_2。利用目前已确定的输入参数，对沸水堆水均相系统进行了辐射分解反应动力学模拟。结果表明，氧化组分主要为H_2O_2和O_2。然而，我们发现在某些特定条件下，OH自由基的贡献是不可忽略的。基于混合电位法计算ECP时，水与金属相界面反应的评价是至关重要的。建立了一种新的近似模型，不仅考虑了扩散，而且考虑了扩散中的辐射分解，在界面处形成了更多的层，后者在以前的模型中被忽略。利用该模型计算了不同条件下化学物质的浓度分布。澄清的是，如果考虑扩散层内的辐射溶解，则阴极反应的极限电流密度在某些条件下比根据先前模型计算的密度增加一个数量级以上。用实验得到的阳极极化曲线进行ECP计算。据推测，这些曲线在很大程度上受到表面氧化层性质的影响，但细节尚不清楚。阳极极化曲线的测量是用预先处理过的金属试样进行的，以获得表面氧化层。结果表明，与磁铁矿（Fe_3O_4）和铁氧体（MFe_2O_4）组成的氧化层相比，以赤铁矿（Fe_2O_3）为主的氧化层显著降低了极化曲线钝化区的电流密度，导致ECP升高。为了研究辐射对表面氧化层的影响，在以赤铁矿为表面氧化物的金属试样的光照射下，研究了其极化行为。实验结果表明，光照射导致阳极极化的ECP减小，无源电流密度增大。这些结果是在赤铁矿层作为n型半导体在光照射下产生激子行为的基础上定性解释的。贵金属的加入被认为是控制ECP的有效方法，本文对氧化膜中Pt的性质进行了澄清研究。少

Control of electrochemical corrosion potential (ECP) is very important for mitigating stress corrosion cracking (SCC) of stainless steels used as structural materials in nuclear reactors. This study aims at investigating various factors affecting ECP.It has been reported that key factors controlling ECP are oxidizing species, mainly H_2O_2 and O_2, which are produced by radiolysis of reactor water. Simulation on reaction kinetics of radiolysis was carried out using currently established input parameters for homogeneous systems relating to reactor water of BWR. It was confirmed that the major oxidizing species are H_2O_2 and O_2. However, it was found that the contribution of OH radical is not negligible under some specific conditions.Evaluation of the interfacial reactions between water and metal phases is essential for the calculation of ECP based on mixed potential method. A new approximation model was developed to consider not only diffusion but also radiolysis within the diffusion … More layer formed at the interface, the latter being neglected in the previous model. Using this model the concentration profiles of chemical species were calculated under the various conditions. It was clarified that if the radiolysis within the diffusion layer is taken into account the limiting current densities for the cathodic reactions increase under some conditions by more than one order of magnitude compared to those calculated according to the previous model.Anodic polarization curves derived from experiments are used for the ECP calculation. These curves are presumed to be largely affected by the property of surface oxide layers formed, but the details are not yet clear. Measurements of anodic polarization curves were carried out with metal specimens previously treated to give surface oxide layers. It was found that oxide layers comprising mainly hematite (Fe_2O_3) reduces significantly the current density in the passive region of the polarization curve in comparison with those composed of magnetite (Fe_3O_4) and ferrites (MFe_2O_4), and results in the increase in ECP.In order to investigate the effect of radiation on surface oxide layers, the polarization behaviors are examined under the light irradiation with the metal specimens provided with hematite as surface oxide. The experimental results show that the light irradiation induces the decrease in ECP and increase in the passive current densities for the anodic polarization. These results were qualitatively explained on the basis of the behavior of excitons produced by the light irradiation in the hematite layer as n-type semi-conductor.In relation to noble metal addition proposed as an effective method to control ECP a study was carried out to clarity the properties of Pt taken into oxide films. Less