Abstract: A new topaz color-alteration device suitable for reactors with plate fuel is developed. The physical and structural safety features have been analyzed. With porous medium model in CFD, the flow and temperature field were got, also the factor limiting the reactor operating power. The device improvement of enhancing the function material cladding's cooling capacity were done. The results shows that the color-alteration experiment could be done at rated power after device improvement. The hydrodynamic characteristic experiment and CFD simulation data by the operation differential pressure were compared, with -3.6%-1.9% difference. The device washing test shows good ability to collect topaz residue, and the flow channel blockage is avoided.