Cfd Analysis of a Thermal Mixing in a Subcooled Water Pool under a High Steam Mass Flux

A CFD (Computational Fluid Dynamics) benchmark calculation for a steam blowdown test was performed for 30 seconds to develop the methodology for a numerical analysis of the thermal mixing between steam and subcooled water and to apply it to APR1400 (Advanced Power Reactor 1400MWe). In the CFD analysis, the steam condensation phenomenon by a direct contact was simulated by the so-called condensation region model. Thermal mixing phenomenon in the subcooled water tank was treated as an incompressible flow, a free surface flow between the air and the water, a turbulent flow, and a buoyancy flow. The comparison of the CFD results with the test data showed a good agreement as a whole, but a small local temperature difference was found at some locations. The commercial CFD code of CFX4.4 together with the condensation region model can simulate the thermal mixing behavior reasonably well when a sufficient number of mesh distributions and a proper numerical method are adopted. Introduction The experimental and CFD research for an unstable steam condensation in a DCC (Direct Contact Condensation) which may be developed in the IRWST (In-containment Refueling Water Storage Tank) of APR1400 were performed [1-6]. An unstable steam condensation may damage into the IRWST wall [7-9]. The reason of unstable steam condensation may be the fluctuation of the interface between the steam and the condensed water when the temperature of an entrained water flowing into the steam was increased [4,8]. Therefore, the prediction of the entrained water temperature and thermal mixing pattern is important. The thermal mixing experimental program was performed to understand and to generate data for the thermal mixing phenomena induced by a steam ejection into the subcooled water in the APR1400 IRWST to prevent an unstable steam condensation being developed due to the locally increased water temperature [1-3]. In the CFD analysis, the numerical methodology which can predict the local and global thermal mixing in the tank was developed based on a comparison of the CFD results with test data. The present commercial CFD codes do not have the model of the DCC [10], and the development of a numerical model for the DCC has been restricted to an ideal flow [11]. Thus, a steam condensation region model was developed based on the water temperature data around a steam jet to simulate the DCC [4-6,12]. The calculated temperature and velocity of the condensed water and the entrained water from the condensation region model were used as the boundary conditions for a thermal mixing CFD analysis [4-6].