Improving accuracy of CFD modelling for direct contact condensation in a suppression pool

A suppression pool performance depends on its temperature and can deteriorate if a thermal stratification occurs. To predict the thermal stratification, the pool mixing induced by steam jets can usually be predicted using analytical models for jetting. In the aftermath of the Fukushima Daiichi severe accident, the effect of chugging on the pool mixing has been studied. It has been shown that available analytical model for chugging fits experimental data only in some cases. In this work, experimental data on chugging from SIET experiments are presented and it is shown that they do not fit a recent generalisation approach for experimental data. One of authors has previously presented a Rayleigh Taylor instability model, which enabled to rapidly increase the interfacial area and thus to reproduce chugging qualitatively using a CFD simulation. In order to evaluate the effect of chugging on thermal stratification, a quantitative agreement with experiment is needed. This paper examines how a modification of specific closure models (for density of steam and phase interface temperature) and a boundary condition affects the accuracy of the CFD model. Furthermore, it was confirmed that the CFD model does correctly decrease the interfacial area growth rate for higher temperatures and does not predict chugging with temperatures for which bubbling was observed experimentally.