Abstract
The return line of the passive residual system (PRS) of ACP100 is connected to the direct injection nozzle of the pressure vessel. It is a non-isolated dead pipe containing coolant, and there is no insulation layer. The temperature difference between the two sides of the pipe is large, which is prone to thermal stratification. This paper uses FloEFD software to carry out CFD simulation analysis and research on the thermal stratification phenomenon of the pipeline in normal operation and accident conditions. The scope of the return line analysis in this paper begins with the isolation valve at the outlet and ends with the direct injection nozzle on the pressure vessel. The finite volume method is used to solve the model, and the standard k-ε two-equation model is used for turbulence simulation. The pipeline system adopts a mesh refinement strategy according to the flow channel and wall thickness in the pipeline to obtain a reasonable mesh distribution. The results show that during normal operation, there is obvious thermal stratification at the exit of the PRS isolation valves, and there is a certain vortex in the tube, which can promote the heat exchange between the reactor pressure vessel and the PRS return pipeline; When PRS put into operation, a large temperature gradient is generated at the interface of the annular cavity of the pressure vessel, and the influence of thermal stress and cyclic thermal shock needs to be considered, and an obvious vortex will be formed nearby to promote the rapid heat exchange of cold and hot water in the nearby area. The result of this paper can provide input for PRS return line thermal stress and thermal cycling impact analysis.
