Numerical Simulation Of Supercritical Water Thermal-hydraulic Behaviour In4-rod Bundles

Investigation on the thermal-hydraulic behavior in the SCWR fuel bundlesassembly have obtained significant attention in the international SCWR community.However, there is still a lack of understanding to predict the heat transfer behavior ofsupercritical fluid because of the limitation in the experimental measurementtechniques. Hence, most investigations have been carried out by numericalinvestigation using Computational Fluid Dynamics (CFD) codes.In this thesis, the computational fluid dynamics (CFD) code, CFX, is utilized tosimulate the heat transfer experiment of supercritical water in4-rod bundle which hasbeen conducted in Shanghai Jiao Tong University. Performance of turbulence modelis investigated, which shows that the SSG Reynolds stress model capable to accountfor anisotropic effect gives more reasonable prediction than the SST model. The effectof spacer grid, flow direction and pitch-to-diameter ratio is investigated with the SSGmodel. The calculation shows that the spacer significantly changes the velocity profilein the downstream of channel, enhances turbulent mixing and heat transfer.Consequently, the rod wall temperature drops sharply downstream of the spacer gridand the wall temperature appears more uniform in the circumferential direction. At thesame time the peak wall temperature spot is also shifted by the spacer. In thedownward flow condition the mass flow rate distribution in the sub-channel is moreuniform than in the upward case. The non-uniformity of the circumferentialtemperature distribution in a tight lattice with P/D ratio of1.1.8is much stronger thanthat in a wide lattice. In the tight-lattice sub-channel the fluid temperature is higher,while the rod temperature is lower than that in a wide lattice, which indicates that heattransfer can be enhanced in the tight-lattice bundle.