Underwater 3D measurement using sheet of light systems for nuclear fuel assemblies

As the demand for high-precision underwater measurements of nuclear fuel assemblies (NFA) continues to rise, there is a concurrent improvement in underwater optical measurement technology. The sheet of light, an optical measurement technology based on a straightforward principle, has progressively emerged as a focal point of research. However, the process of conducting high-accuracy measurements underwater presents significant challenges due to the impact of scattering, refraction, and intense radiation. This paper presents the development of a reflective underwater sheet of light system. It proposes an enhanced refraction correction method, utilizing ray tracing. Additionally, it suggests an improved center extraction method for underwater laser lines, based on the grayscale center of gravity, to mitigate random speckle interference. The comprehensive experimental results demonstrate that the system achieves an underwater measurement accuracy of 0.2mm to 0.4mm at a distance of 850mm from the NFA. These measurements confirm the effectiveness of the underwater measurement system and provide a methodical verification for the safety assessment of NFA.