To accurately predict the critical condition at the upstream of the fuel assembly outlet and improve the reliability of safety analysis,this paper uses the CFD method to study the flow mixing between subchannels of rod bundles.A geometric model for the rod bundles is established,the SST model for calculation is selected,the mesh sensitivity analysis is completed,and the temperature distribution of subchannels at different axial po-sitions under rated operating conditions is obtained.Using the subchannel analysis program in conjunction with the numerical simulation data,the mixing coefficients at different axial positions of rod bundles are determined.The calculation results indicate that if the mixing phenomenon at the entrance is considered as local mixing,it can be observed that when the influence of local mixing weakens,the mixing coefficient shows a trend of ap-proaching 0 with the increase of axial length.There is no significant difference in the axial mixing coefficient cal-culated by selecting 16 central channels and selecting all subchannels.The mixing at the entrance is caused by the development of the thermal boundary layer,not by the flow distribution at the entrance.
numerical modelingaxial mixing coefficientsubchannel analysis program
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