A circumferentially non-uniform heat transfer model for subchannel analysis of tight rod bundles

The non-uniformity of circumferential heat transfer is small in conventional PWR core but becomes significant with tight-lattice core design for advanced reactors. Predicting the circumferentially non-uniform heat transfer behavior can be challenging given the considerable heterogeneity of the subchannel geometry and the drastic change of property with supercritical fluids. In this paper, a circumferentially non-uniform heat transfer model for subchannel analysis has been developed to predict the circumferential distributions of heat transfer coefficient, wall temperature and wall heat flux. In the model, the sources of the heat transfer non-uniformity are considered to be the circumferentially non-uniform flow area and the fluid property variation. To account for these two effects, new correlation with a non-uniform factor is developed. A series of tests using CFD method was performed for determining the empirical coefficients of the non-uniform factor. Furthermore, a two-dimensional fuel heat conduction model is also added to the subchannel analysis code. The new model was validated by comparing the prediction results with available experimental data of a 2 × 2 square rod bundle with supercritical water. It is demonstrated that the inclusion of circumferentially non-uniform heat transfer model leads to an improvement in the predictive capabilities for current subchannel analysis method and will improve the prediction accuracy of cladding temperatures in the design and safety analysis of reactor fuel elements.