High-Precision Experiment and Model Development for Local Thermal Hydraulic Phenomena

To improve the prediction capability of safety analysis code for the phenomena occurring in the advanced safety system of new nuclear plant, the local physical model should be developed based on the fine scale of experimental data for the key phenomena. The current study performed high-precision experiment and constructed database for key phenomena for the boiling induced natural convection inside cooling tank and tube inside condensation of heat exchanger of passive auxiliary feedwater injection system, dynamic multi-dimensional behaviour of ECC water inside downcomer from DVI system and passive injection system. To achieve local high-precision experimental data, measuring technique was newly developed or improve the applicability of the conventional instrument such as optical probe, laser optics including PIV, LDV and LIF, and ultrasonic measuring techniques. The bubble departure diameter on curved heated surface, condensation heat transfer inside heat exchanger tube and interfacial shear on the liquid film were uniquely developed in this study. The boiling phenomena is very important for the heat transfer and thermal margin evaluation of reactor safety. experiment for high heat flux condition was performed using high resolution of visualization. From the visualization, the boiling structure and mechanism near CHF condition was analyzed. As one of the key boiling parameter, a bubble departure size model was newly developed based on balance equation of heat transfer. Also, experimental DB and equations were setup for the multi-D turbulence in the rod bundle geometry. The experimental database and unique mechanistic physical models developed in this study, will enhance the brand value and the accuracy of the prediction capability of the domestic safety analysis code, which will contribute to the nuclear plant export.