Metallic melt jet fragmentation in a water pool: Experiments and numerical simulations

Abstract

The jet fragmentation is a crucial process during fuel coolant interactions (FCI) which result in droplets dispersed in coolant and may cause a steam explosion. The present work deals with experimental studies of metallic melt jet fragmentation followed by numerical simulations that support the experimental findings. Two test series were carried out at both large and small scales, to achieve significant variation in Weber number (We). It was found that the jet fragmentation patterns followed the R-T and K-H instabilities at lower and higher We, respectively. Various methods were applied to estimate jet breakup length at different scales, due to measurement challenges at larger We (large scale). At smaller scale, an averaged jet breakup length was proposed to consider the dynamic behavior of coherent jet. Early solidification of low superheat melt interacting with water having moderate subcooling was observed in the forms of frozen jet and large-size fragments. The numerical simulations considering only hydrodynamic effects (no consideration of vapor film) reproduced the jet fragmentation patterns but under-estimated jet breakup lengths from the experiments, probably due to the absence of vapor film around the melt jet in simulations, which differs from the reality where vapor film around the melt delay the instabilities development and hence the jet breakup.