核电站安全端焊接接头高温高压水环境应力腐蚀特性及机理

Stress corrosion cracking (SCC) in the safe-end weld joint of the primary circuit has been one of the key issues for the safe and economic operation of the pressurized water reactor (PWR) nuclear power plant. Solving the issue requires clarifying the characteristic and mechanism of SCC in association with establishing a theoretical basis for evaluation and prediction of SCC. This project focuses on a study of SCC in domestically-fabricated safe-end weld joint of PWR. Following microstructure analyses and electrochemical studies of the corrosion behavior of the weld joint, slow strain rate tension and stress corrosion crack growth rate tests on the weld joint in simulated primary water of PWR will be conducted to reveal the SCC characteristics under combinations of microstructure and water chemistry. Composition and microstructure of the oxide formed under various combinations of microstructure and water chemistry in the tip area and on the path of SCC will be analyzed by high-resolution transmission electron microscopy, in order to reveal the effect of the interaction between microstructure and water chemistry on corrosion and SCC. As a result, the mechanism for the effect of microstructure and water chemistry on SCC will be clarified. Finally the mechanism for SCC of different materials and structures in the weld joint will be clarified according to the microstructure characteristic of the oxide and material at the tip area of SCC. Results of this research will provide a basis for developing theoretical methods for evaluation of SCC in the safe-end weld joint.

压水堆核电站一回路安全端焊接接头的应力腐蚀开裂(SCC)已成为影响在役电站运行安全性和经济性的关键问题之一，需要通过揭示SCC的特性和机理，建立预测和评价SCC的理论基础加以解决。本项目以国产压水堆一回路安全端焊接接头为研究对象，采用材料表征和电化学实验手段明确焊接接头的微观结构和高温高压水环境腐蚀特性，在此基础上采用高温高压水环境的慢应变速率拉伸试验及裂纹扩展速率试验，揭示焊接接头中不同部位材料在残余应变分布与水化学等因素耦合条件下SCC的萌生与扩展特性。采用高分辨率透射电子显微镜分析不同材料结构和水化学耦合条件下形成的SCC尖端区域的材料与腐蚀产物组成、分布与结构特征，分析材料与水化学交互作用与腐蚀及SCC的关系，进而揭示材料结构与水化学对SCC的影响机理。在此基础上基于SCC尖端区域材料与腐蚀产物的结构特征等完整阐明焊接接头SCC的机理，为开发焊接接头SCC行为的理论评价方法提供基础

安全端焊接接头的应力腐蚀开裂（SCC）是影响压水堆核电站长期运行的可靠性、安全性和经济性的关键问题之一。由于焊接接头组成与结构的特异性及复杂性，焊接接头中不同部位的SCC行为及机理也会不同。本项目采用微观分析，高温高压腐蚀与SCC试验等手段，研究了焊接接头微观结构、高温高压水环境腐蚀特性和高温高压水环境SCC特性，明确了焊接接头不同部位SCC的萌生敏感性、SCC萌生的位置与取向等特征及规律，发现焊接接头各个位置的SCC敏感性顺序为：镍基52M合金隔离层>316L不锈钢热影响区>不锈钢侧镍基52M合金稀释区>镍基52M合金，通过建立SCC敏感性及扩展速率与微观组织结构的关联，阐明了焊接接头SCC的机理，可为开发焊接接头SCC行为的理论评价方法提供基础。