Model development and transient analysis of thermal stratification phenomenon in pool-type sodium-cooled fast reactors

•The three-dimensional system analysis model is established, which takes into account accuracy and calculation efficiency.•The accuracy of 3D thermal–hydraulic analysis model and the capability of thermal stratification analysis for SFR were fully verified, and the number of numerical grids required by the method established is only 0.004% of CFD method.•The location with maximum temperature gradient of the upper plenum in the sodium pool can be suggested in the process of thermal stratification with the three-dimensional system analysis method. Thermal stratification of pool-type SFR under transient accident conditions has a very significant impact on the performance of key components of the primary loop and the establishment of natural circulation of the residual heat removal system. In this paper, combined with the mechanism of thermal stratification, a three-dimensional (3-D) system analysis model is developed, which takes into account the energy source model, the 3-D convection model and the large space inlet-effect model. Based on the model development, the accuracy of 3-D thermal–hydraulic analysis model and the capability of thermal stratification analysis for SFR were fully verified. The validation results show that the method established in this paper takes into account accuracy and calculation efficiency. It can greatly reduce the amount of numerical grid, take up very little computing resources and greatly improves analyzing efficiency. And it can accurately simulate the thermal stratification phenomenon in the sodium pool. At the same time, the location with maximum temperature gradient of the inner barrel wall can be suggested in the process of thermal stratification. Furthermore, this study provides an important analytical method for the transient safety analysis of SFR, and has a great academic value and engineering significance.