CFD Simulation of Flashing Boiling Flow in the Containment Cooling Condensers (CCC) System of KERENA™ Reactor

Abstract

The flashing boiling phenomenon occurring inside the Containment Cooling Condensers (CCC) passive system of KERENA™ reactor was simulated by using the CFD (Computational Fluid Dynamics) code ANSYS CFX. The steam generation was assumed to be caused by thermal phase change, which is controlled by interphase heat transfer. In general, the model setup is able to capture the generation and disappearance of steam and the fluctuation of pressure and temperature observed during the flashing. However, since the nucleation and bubble growth process was neglected in the simulation, the initialization of evaporation was found to be a key issue, which depends on the prescribed bubble size sensitively. In order to get a satisfying agreement with the experimental data, a relatively large size has to be assumed for the selected test case (db>10 mm). The CFD results are qualitatively comparable to those obtained by using the system code ATHLET, except that the mass transfer rate is higher and the fluctuation frequency and altitude is lower. In addition, the assumption of constant bubble size might introduce significant error. The change of bubble size as well as the effect of nucleation and bubble growth should be investigated in the future work. For this purpose, however, further experimental data such as evaporation rate, phase and bubble size distribution, phase velocity are required.