Abstract: The successful operation and safety of the Very-High-Temperature Nuclear Reactors (VHTR) extremely depend on the quality of the TRISO nuclear fuel coated particles. Hence, the fuel coating technology of TRISO particles, based on chemical vapor deposition (CVD) process, performed in gas-solid spouted beds, is of utmost importance. However, the deposition of the coating layers surrounding the kernel is a delicate process, and impacted by the hydrodynamics of spouted beds. Therefore, in this work, we have applied an advanced non-invasive gamma-ray computed tomography (CT) technique for the first time to investigate the hydrodynamics of spouted beds. In particular, we study the effect of particle density, particle size, bed size, and superficial gas velocity on the gas-solid cross-sectional distributions of spouted beds. The color distributions of the cross-sectional images clearly identified the three regions of spouted beds: the spout, the annulus, and the fountain regions. Interesting results and findings are presented, discussed and analyzed in the article. For example, the results demonstrated that the summation that operating spouted beds at stable spouting state would lead to achieving uniform coating layers of the particles in the TRISO fuel coating process is not adequate. Further, it has been found that increasing the superficial gas velocity much higher above the minimum spouting velocity increases the gas holdup in the annulus above the gas holdup value at the loss-packed bed state, contrary to common assumptions presented in the literature. This study represents an original experimental investigation required both for advancing the understanding of TRISO particles spouted bed and providing benchmark data to validate computational fluid dynamics (CFD).