Remote visual testing by video cameras is the standard process for inspecting the pressure vessel of nuclear reactors. The inspectors need to find stress corrosion cracking of around several tens of µm wide on a display monitor observed by remote wired cameras in the reactor pressure vessel filled with cooling water. The inside surface of the vessel structure has typically been blasted or grinded during its construction process for smoothing any excess weld metal, and as such, it might contain partly specular areas and partly rough areas. We found that the cracks on such surfaces are hardly distinguished from the boundary of these areas under normal scattered illumination, since the specular area reflects more of the light from the light source outside the path to the camera than the light scattered out by the rough area. To resolve this issue, we propose using two illumination light sources simultaneously, i.e., the bright field illumination and the dark field illumination, to balance the contrast to cracks from both areas. The results of experiments in a simplified condition showed that there was an improvement in the visibility of the cracks using this method.

通过摄像机进行远程视觉测试是检查核反应堆压力容器的标准流程。检查人员需要在充满冷却水的反应堆压力容器中通过远程有线摄像机观察到的显示监视器上发现大约几十微米宽的应力腐蚀开裂。容器结构的内表面通常在其建造过程中经过喷砂或研磨，以平滑任何多余的焊缝金属，因此，它可能包含部分镜面区域和部分粗糙区域。我们发现，在正常散射照明下，这些表面上的裂缝很难与这些区域的边界区分开来，因为镜面反射区域比粗糙区域散射出的光更多地反射了来自到达相机路径之外的光源的光. 为了解决这个问题，我们建议同时使用两个照明光源，即明场照明和暗场照明，以平衡两个区域的裂缝对比度。简化条件下的实验结果表明，使用这种方法可以提高裂纹的可见性。