Numerical Analysis Of Hydraulic Characteristic Of Wire-wrapped Rod Bundle Assembly Under Low Reynolds Number

The safe discharge of waste heat from the core of a nuclear power plant is one of the most important safety issues for large reactors after an emergency shutdown caused by power failure or stuck main pumps.After the emergency shutdown of sodium-cooled fast reactor,the flow state of the sodium liquid in the flow passage of the core assembly gradually changes from turbulent to laminar and transition flow.The flow rate and its distribution in the component,as well as the distribution of global and local temperature and pressure,will undergo complex changes.The thermal-hydraulic characteristics of low Reynolds number flow of wire-wrapped assembly after emergency shutdown are studied.It is of great significance to design the passive residual heat removal system reasonably and ensure the safety of fast reactor.In this context,the thermodynamic characteristics of the low Reynolds number flow of the wire-wound rod bundle assembly are investigated in this paper using the commercial CFD software STAR-CCM+.Firstly,the geometric modeling of the wire-wrapped 37-pin bundle assembly was carried out using SCDM software.In order to generate a qualified mesh,the paper adopts a way to embed the wire into the fuel rod,so that the position relationship between the two changes from tangent to intersection,which solves the problem of not being able to generate a qualified mesh on the wire structure.Then,using the automatic mesh generation technology of STAR-CCM+software,five sets of hexahedral meshes of different sizes were divided and analyzed for mesh irrelevance,and the most suitable set of meshes was selected.The surface uniform heat flow density was used to simulate the heat release from the fuel rod.Finally,two experimental conditions with heating power of 5432.36 W/m³ and 3551.86 W/m³ were selected to compare the simulation results.The prediction errors of the laminar flow model,k-εlow Reynolds number model and SST k-ωmodel were close to each other and the maximum error did not exceed 10%,among which the maximum error of the SST k-ωmodel was less than6%.The SST k-ωmodel was finally selected as the physical model for numerical simulation.The velocity,pressure and temperature distributions of the components,as well as the frictional resistance and flow distribution of sub-channels are studied by numerical simulation.The results show that the velocity distribution inside the component is uniform,and the velocity of the side sub-channel adjacent to the component box is the largest.The pressure distribution shows that the pressure near one side of the hexagonal box is the lowest and the opposite side is the highest,and the pressure increases gradually from the lowest wall to the highest wall.The temperature distribution shows the law of"cold outside and hot inside",and the more central the location,the higher the temperature.Under the same flow condition,the Reynolds number of the edge sub-channel is the largest,and that of the corner sub-channel is the smallest.At the same Reynolds number,the friction coefficient of the interior sub-channel is the largest,and that of the corner sub-channel is the smallest.The flow split factors show a reasonable order of averaged values for each subchannel type,where X₂>X₁>X₃（X₂>1 and X₁,X₃<1）.With the rotation around the wire（2）,X_i of the interior sub-channel shows three periodic changes.Compared with the interior sub-channel,the change trend of edge sub-channel X_i is less regular,and the change rule of corner sub-channel X_i is the simplest.