Numerical study of flow distribution and the effect of unsteady flow of liquid sodium coolant in annular rods scalloped-wall fuel assembly

The core of small sodium-cooled fast reactors is designed to be compact, meeting various regulatory and economic objectives. Heat removal in a compact core can be enhanced by using a tightly arranged annular rod fuel assembly within a scalloped-wall duct. This study investigates the steady and periodic flow of liquid sodium coolant through the triangular tight lattice ( P/D = 1.08) annular rod scalloped-wall fuel assembly. The scalloped wall reduced the temperature difference between the center subchannel and gaps by up to 30% compared to a flat-walled fuel assembly. The flow split between the inner and outer subchannels is 10% – 13% in the fuel assembly. The relationship between the Reynolds number and flow friction resistance aligns with previous results for a light water reactor fuel assembly. Periodic flow intensifies the turbulence distribution within the subchannels. A new correlation was proposed for the flow split between the inner and outer subchannels in the tight triangular-lattice scalloped-wall annular rod fuel assembly.