中文摘要：

核反应堆压力容器接管安全端异种金属焊接接头在服役中通常会产生高温高压水环境中的应力腐蚀裂纹扩展。目前减轻和修复这种裂纹的技术是在安全端管接头外表面堆焊一层更抗腐蚀的镍基合金（Alloy52M）材料。本文通过三维结构的有限元断裂力学分析，计算得到了堆焊修复结构的“先漏后断”（Leak—before—break，LBB）~线和韧带失稳线，并分析了堆焊层厚度对LBB安全边际的影响。结果表明，堆焊修复后结构的LBB曲线和韧带失稳线在没有堆焊层结构的曲线上方，且随堆焊层厚度的增加，LBB曲线和韧带失稳线上移，表明堆焊修复及堆焊层厚度的增加使安全端结构的LBB安全边际增大。

英文摘要：

Background： Primary water stress corrosion cracking （PWSCC） is commonly produced in the dissimilar metal welded joints for connecting the pipe-nozzles of nuclear reactor pressure vessels to the safe ends. The technology to repair and mitigate PWSCC is usually to make the weld overlay of higher corrosion resistant Alloy52M on the pipe joints. Purpose： We need to assess the integrity of the welded overlay structures, and to make Leak-before-break （LBB） analyses. The effect of the weld overlay thickness on the LBB behavior needs to be studied. Methods： Based on the three-dimensional finite element fracture mechanics analyses, the ABAQUS software was applied to construct the LBB curves and ligament instability lines of the dissimilar metal welded overlay structures. The effects of the weld overlay thickness on the LBB curves and ligament instability lines were analyzed. Results： The results show that the LBB curves and ligament instability lines with the weld overlay are located above those without the weld overlay. With increasing weld overlay thickness, the LBB curves and ligament instability lines both shift upward. Conclusion： The weld overlay can increase the LBB safe margin of the dissimilar metal welded joints. With increasing weld overlay thickness, the LBB safe margin of the joint structure can be further increased.