[en] Heat transfers by sodium natural convection above and below the internal core catcher in SUPER PHENIX and below the core support structure are evaluated. Results of a 1/20 water mock-up experiment and results of an experimental study of sodium natural convection heat transfer from a downward-facing horizontal plate with uniform heat flux are presented. The evaluation is also based on other correlations and theoretical work found in the literature. It is considered that the heat transfer coefficient in laminar regime below the core catcher (the most important for evaluation of the core catcher performance) is determined from this evaluation to within +- 25%