Flash expansion morphologies of subcooled water upward injecting into high-temperature oil pool

Abstract

Flash expansion of subcooled water injecting into high-temperature liquid pool is a ubiquitous phenomenon in steam generator tube rupture (SGTR) accidents in lead-cooled fast reactors (LFRs). In this study, a series of visual experiments were conducted to investigate the evolutions of jet flow pattern and jet flash expansion characteristics with different oil temperatures, water injection pressures, and hole diameters. It was found that the injection process includes the initial jet cavity formation stage and the jet cavity expansion–contraction stage. The jet can be classified into two flow patterns: a significant expansion jet dominated by flash evaporation of water, which only occurs at low oil temperatures; and a confined expansion jet dominated by steam escape, which only occurs at higher oil temperatures. Meanwhile, the expansion–contraction mechanism of the jet cavity can be elucidated as a competition between the flash evaporation of water and steam escape. Furthermore, predicted correlations for jet cavity width and jet expansion period based on the Reynolds number, Jacob number, dimensionless heating coefficient and dimensionless hole diameter were proposed with high accuracy. Finally, geometric estimations on the steam cavity volume and its volume expansion rate were conducted, which enriched the quantitative analysis of the flash expansion morphologies. This research is promising to enhance the understanding and cognition of the jet flash expansion behavior after SGTR accidents in LFRs, and to provide valuable reference and guidance for subsequent numerical simulation research.