Simple models for jet breakup length and fraction of particulate debris estimation

Abstract

As molten corium releases to a pre-flooded cavity, the corium jet will be fragmented under fuel-coolant interaction (FCI). Unless the corium is entirely fragmented, hard debris, or cake, is going to be formed on the bottom of the cavity. As cake formation degrades heat removal performance in the cavity, it is required to have sufficient water in the cavity for the complete breakup. Therefore, it is essential to understand the breakup process of corium to predict accurate jet breakup length and cake ratio. In this study, jet breakup experimental data have been collected and analyzed to construct databases. Clearly-identified jet breakup length, shallow pool depth strategy, and a melt mass analysis method are applied for screening the experimental data. Based on the screened database we develop the models for jet breakup length with exponential form. The suggested empirical correlations show 24.70% and 41.42% of the root mean square error (RMSE) for all (non-corium and corium) data and the corium data only, respectively. Regarding conservatism, we suggested using the correlation for all experiment. Also, we validated the KAIST model with the heat transfer coefficient from Epstein correlation against FARO fraction of particulate debris data. The proposed model gives 37.83% of RMSE, and ASTEC and COMETA code do 33.75% and 39.32% of RMSE, respectively.