Experimental study on flux allocation characteristics of annular fuel bundle channel

Annular fuel allows coolant to flow on both the inner and outer sides of the fuel, thereby enlarging the surface area-to-volume ratio for heat transfer and increases the power density. Due to the different resistance characteristics of the inner and outer channels, the flux allocation ratio varies with the change in inlet velocity, which directly affects the heat transfer efficiency of the annular fuel assembly. This study used the Particle Image Velocimetry (PIV) technique and the rotation integration method to directly measure the flux in the inner and outer channels of a 5 x 5 annular fuel bundle. The results show that the flux allocation ratio initially decreases rapidly, then more slowly, and finally increases as the inlet velocity increases. Under pulsating flow conditions, the flux allocation ratio exhibits a periodic variation. The pulsating acceleration and the flux allocation ratio are approximately linearly correlated.