Widely present in the primary circuit of Nuclear Power Plants (NPP), Dissimilar Metal Welds (DMW) are inspected using Ultrasonic nondestructive Testing (UT) techniques to ensure the integrity of the structure and detect defects such as Stress Corrosion Cracking (SCC).In a previous collaborative research, CRIEPI and CEA have worked on the understanding of the propagation of ultrasonic waves in complex materials. Indeed, the ultrasonic propagation can be disturbed due to the anisotropic and inhomogeneous properties of the medium and the interpretation of inspection results can then be difficult. An analytical model, based on a dynamic ray theory, developed by CEA-LIST and implemented in the CIVA software had been used to predict the ultrasonic propagation in a DMW. The model evaluates the ray trajectories, the travel-time and the computation of the amplitude along the ray tube in a medium described thanks to a continuously varying description of its physical properties. In this study, the weld had been described by an analytical law of the crystallographic orientation. The simulated results of the detection of calibrated notches located in the buttering and the weld had been compared with experimental data and had shown a good agreement.The new collaborative program presented in this paper aims at detecting a real SCC defect located close to the root of the DMW. Thus, simulations have been performed for a DMW described with an analytical law and a smooth cartography of the crystallographic orientation. Furthermore, advanced ultrasonic testing methods have been used to inspect the specimen and detect the real SCC defect. Experimental and simulated results of the mock-up inspection have been compared.

翻译：核电站一回路中广泛存在的异种金属焊缝（DMW）采用超声无损检测（UT）技术进行检验，以确保结构完整性并检测应力腐蚀开裂（SCC）等缺陷。在前期合作研究中，CRIEPI与CEA共同致力于理解超声波在复杂材料中的传播特性。由于介质各向异性及非均匀性质，超声传播可能受到干扰，进而导致检测结果判读困难。基于动态射线理论的分析模型（由CEA-LIST开发并集成于CIVA软件）已被用于预测DMW中的超声传播。该模型通过连续变化的物理特性描述介质，评估射线轨迹、传播时间及沿射线管的振幅计算。本研究中，焊缝的晶粒取向采用解析律描述。对位于缓冲层和焊缝中的校准刻槽的检测模拟结果与实验数据进行了比较，两者吻合良好。本文所述的新合作项目旨在检测靠近DMW根部的真实SCC缺陷。为此，针对采用解析律和平滑晶粒取向分布图描述的DMW开展了模拟研究。同时，采用先进超声检测方法对试件进行检测并识别真实SCC缺陷。最后，对模拟件检测的实验结果与模拟结果进行了比较。