A hydrodynamic fragmentation model based on boundary layer stripping

Fuel Coolant Interactions (FCIs) are important issues in nuclear reactor severe accident analysis, which have drawn much attention by experts all over the world for many years. The boundary layer stripping is one of the mechanisms that result in hydrodynamic fragmentation during FCIs, and has been studied for many years. However, the results and trends predicted by the existing fragmentation rate models based on such a mechanism are still very different from the experimental data. In this study, in order to develop a fragmentation rate model of a liquid droplet, induced by boundary layer stripping, a new velocity distribution in boundary layer is proposed, which covers two very significant parameters. Then, based on theoretical modeling and experimental data, semi-empirical correlations which can predict the fragmentation rate and the average size of fragments are established, which are verified by typical experimental data and are compared with previous model predictions. The result shows that the fragmentation rate calculated by the present model and the certain range of average fragment size are in good agreement with the experimental data, which proves that the two new parameters involved can reflect the velocity distribution in boundary layers of both the melt and coolant more appropriately and reliably. With the help of the model from IFCI and CULDESAC codes, there is reason to believe the present hydrodynamic fragmentation model could be applied in FCI codes in the future.