LAUSR

Abstract To meet the requirement of passive safety, natural circulation has been applied in cooling the nuclear reactor core. In comparison with the great successes in predicting subcooled boiling in simple geometries such as pipes, annuli and rectangular channels, few researches have been performed for rod bundle. We performed subcooled boiling heat transfer experiments in a vertical 3 × 3 rod bundle under upward natural circulation flow condition. The experiments were performed under pressure from 0.2 MPa to 1.0 MPa, mass flux from 162 to 411 kg/m2/s, heat flux from 31 to 271 kW/m2, local subcooling from 0 to 25 °C and thermodynamic vapor quality from −0.05 to 0. The experimental results were compared with the predictions of 14 subcooled boiling correlations. The comparisons showed that the new Shah correlation and Thom correlation can accurately predict the heat transfer coefficient of natural circulation flow in the rod bundle within a deviation of 30%. The average deviations of new Shah correlation and Thom correlation are 3.98% and 2.54% respectively. According to the discussion of three kinds of correlation, we found that empirical correlations can better predict the subcooled boiling than semi-empirical correlations.