Bow and twist deformation measurement system of fuel assembly with underwater dual-line structured light

To realize the non-contact on-line measurement of the crucial dimension for the fuel assembly and assist the nuclear power plant to carry out regular maintenance works in the core, we design an underwater fuel assembly deformation measurement system (UFADMS). Based on the principle of dual-optical line laser triangulation, the deformation measurement system integrates two sets of optical units. During the measurement, each optical unit projects two beams of laser to the surface and captures the relevant image for further process, respectively. According to the point clouds obtained by underwater calibration, three-dimensional (3D) reconstruction, and global calibration, we can calculate the relative relationship between the two optical units, and normalize the corresponding measurement data to calculate the bow and twist deformation of the fuel assembly. Benefitting from the novel waterproof design, the dual-optical line laser triangulation principle, and the underwater single-layer refractive geometry, the measurement system has strong environmental adaptability, high measurement accuracy, and short measurement time. Through the underwater field measurement and validation of standard blocks and fuel assembly, the bow deformation measurement accuracy is within 0.4 mm, and the twist deformation measurement accuracy is within 0.15°. What's more, the proposed system allows transient measurement at a certain depth of water, which provides a guarantee for on-line measurement of fuel assembly underwater.