The influence of duct wall shape on mass redistribution in supercritical water-cooled reactor fuel assembly

•Different shapes of duct wall around fuel bundle are established.•The influences of duct wall shape on mass redistribution are discussed.•The effective solution to control mass redistribution phenomenon is proposed.•The influences of duct wall on heat transfer and circumferential non-uniformity are compared. Based on the fuel assembly of supercritical water-cooled reactor, a 19-rod bundle with triangular arrangement is established and different shapes of duct wall are used to adjust the hydraulic diameter of the external sub-channel. The Reynolds stress model (RSM) and enhanced wall treatment were employed to simulate the fluid flow and heat transfer phenomena of supercritical water and the mass redistribution in fuel assembly. The result shows that the hydraulic diameter difference between internal and external sub-channels and the physical properties of supercritical water are the main factors affecting the mass redistribution phenomenon. The mass redistribution can be effectively controlled by adjusting the hydraulic diameter of the external sub-channel. As the hydraulic diameter of the external sub-channel decreases, the fluid accumulation to the external sub-channel gradually weakens and then reverses to the internal sub-channel accumulation. Meantime, comparing with the primary model, the overall heat transfer effect of internal and external sub-channel can be balanced and kept at a high level by weakening the mass redistribution. Besides, the circumferential non-uniformity of the outermost fuel rod is affected by the local hydraulic diameter and the mass redistribution. Mass redistribution is the dominant factor and the local hydraulic diameter can only start to affect the circumferential wall temperature until the mass redistribution is weakened to a certain extent.