A cooperative Study on Environmentally Assisted Cracking of structural materials of nuclear reactor

确保核电站的安全是世界范围内的一个重要问题。特别是材料在高温水中的环境辅助开裂（EAC）的定量评价至关重要。但是，影响EAC的因素很多，目前对EAC的估计还不够准确。这是一个将项目负责人在EAC方面的基础研究成果与拥有丰富实际核反应堆数据的俄罗斯研究人员的研究成果相结合的合作研究。主要研究成果如下：(1)研究了MnS夹杂物形态与腐蚀疲劳裂纹扩展速率的关系。结果表明，钢中夹杂物的大小分布比总硫含量更重要。日本东北大学对俄罗斯产高含硫量、小颗粒MnS夹杂物分布均匀的反应堆压力容器钢进行了评价。结果表明，单从硫含量上看，裂纹扩展速率没有提高。(2)研究了小缺陷的检测方法。验证了感应电流聚焦电位降（ICFPD）技术和相邻探头直流电位降（DCPD）技术的有效性。今后，双方还将开展一项合作研究项目，研究如何从外表面检测不锈钢焊缝的内部缺陷。这些材料将由俄罗斯中央结构材料研究所准备。评估将在东北大学进行。(3)研究了表面膜老化降解与EAC的关系。交换了薄膜生长过程中接触电阻和其他电学性能的研究结果。根据辐照过程中电性能随薄膜生长的变化，明确了辐照辅助应力腐蚀开裂的关系。(4)对VVER型核电站EAC事故进行了改进调查，并采用了强有力的材料试验方法。提出了缺陷检测和裂纹扩展速率评价方法。(5)对低压缝式汽轮机凝汽桶处的EAC进行了研究。对实验设备和分析提出了切实可行的方案。研究表明，开尔文探针在薄水层条件下的腐蚀评价是有用的。实验已部分完成。少

Assuring the safety of nuclear power plants is an important issue all over the world. Especially the quantitative evaluation of environmentally assisted cracking (EAC) of materials in high temperature water is critical. However, EAC is affected by so many factors that estimation is not accurate enough up to now.This is a cooperative research that combines the fundamental research achievements on EAC of the leader of this project with the research results of Russian researchers who possess rich data of practical nuclear reactors. Main achievements can be summarized as follows :(1) The relation between corrosion fatigue crack growth rate and the shape of MnS inclusions has been studied. It has been shown that the size distribution of the inclusions is more important than the total sulfur content in steel. Reactor pressure vessel steel made by Russian that has high sulfur content but well distributed small particles of MnS inclusions was evaluated in Tohoku University. Results showed that … More the higher crack growth rate expected only from the sulfur content was not observed.(2) Detection method for small defects have been studied. The validities of induced current focusing potential drop (ICFPD) technique and direct current potential drop (DCPD) technique using adjacent probes were confirmed. A cooperative research project on how to detect inside defects in stainless steel welds from the outer surface has been set up for the future. The materials will be prepared by Central Institute of Structural Materials in Russian. The evaluation will be done in Tohoku University.(3) The relation between aging degradation of surface film and EAC has been studied. The research results on contact electric resistance and other electric properties accompanying film growth were exchanged. According to the electric property change with film growth during irradiation, the relation to irradiation assisted stress corrosion cracking has been made clearer.(4) Investigation for improvement for EAC incidents of VVER type nuclear power plants and, strong methods of material test has been done. Defect detection and crack growth rate evaluation have been suggested.(5) EAC at condensation pail of low pressure seam turbine has been researched. A practical plan about experimental facilities and analysis has been suggested. It has been made clear that Kelvin probe is useful for evaluating corrosion in the thin water layer condition. The experiments have been carried out partly. Less