Abstract
As a low Prandtl number fluid, the numerical simulation of liquid sodium is different from the typical numerical simulation, because the turbulent Prandtl number is no longer a constant and the turbulent Prandtl number model must be developed. In this study, a novel numerical model is used to carry out the steady-state numerical simulation of a 7-pin sodium-cooled fast reactor wire-wrapped fuel bundle. The turbulent Prandtl number of liquid sodium is no longer approximate to the default value of 0.85. Kays model is used as a UDF of Fluent to modify the turbulent Prandtl number. The novel numerical model is computationally economical and can ensure the accuracy of the calculation. Numerical simulations in five different working conditions are performed (104 < Re < 105).
Comparing the CFD results with the experimental correlation, it is found that the numerical model with Prt = 0.85 which used the same geometry would overestimate the heat transfer performance by 9% compared to the novel numerical model, and the novel numerical model is closer to the experimental correlation. In addition, the analysis of the flow field and temperature field shows that the axial velocity changes periodically along the axial direction due to the influence of wire wraps. The period equals one-quarter of the wire pitch. In the different cross sections, the cross flow which is induced by the wire wraps forms vortices in the subchannels. The surface temperature of fuel rods on the windward side is different from that on the leeward side due to the blockage of wire wraps. And the maximum surface temperature occurs at the location of the gap between fuel rod and wire wrap. The conclusions of this study provide effective suggestions for the optimization of numerical simulation and the prediction of the hot spot of the sodium-cooled fast reactor wire-wrapped fuel bundle.
