Background: High speed rotate of the flow in gaps around upper flywheel of the reactor coolant pump may create the phenomenon of Taylor vortex

which causes the fluid to be well-mixed.Purpose: Provide the input of thermal analysis for the whole structure.Methods: Make model of the flow around the lower flywheel

then use CFX program to perform Computational Fluid Dynamic（CFD） analyses of the flow and thermal fields.The influence of speed of flywheel and the size of radial gap are also discussed for the flow of Taylor vortex in the report.Results: Effective thermal conductivity and heat source can be calculated.Conclusions: Rotate speed and size of radial gap can be used to control the temperature distribution of upper flywheel.