The thermal turbulence phenomenon of underwater fuel assembly based on image processing

When measuring fuel assemblies that have just been removed from the reactor core, residual heat in fuel rods causes the uneven temperature gradient field, which subsequently leads to irregular variations of refractive index. Consequently, inevitable thermal turbulence occurs, impacting the measurement accuracy of bow and twist deformation. A multi-layer refractive model is adopted for direct underwater calibration to accurately identify camera parameters. Field simulated turbulence experiments are carried out to qualitatively and quantitatively demonstrate the presence of thermal turbulence. Compared to normal conditions, these image processing experiments show that underwater thermal turbulence induces image fluctuations and temporal fluctuations, affecting image positions and image distributions and ultimately impacting the accuracy of optical line laser center extraction.