Interfacial dynamics of subcooled water jets in liquid lead alloys for lead-cooled fast reactors

Lead-cooled fast reactors (LFRs) are susceptible to steam generator tube rupture (SGTR) incidents, which can cause direct interaction between primary-loop lead-bismuth eutectic (LBE) coolant and secondary-loop high-pressure water, potentially triggering perilous coolant-coolant interactions (CCI) and steam explosions with considerable safety implications. The purpose of this study was to examine the aforementioned phenomena by developing a computational fluid dynamics (CFD) model that utilizes a 2D axisymmetric framework. This model incorporates the VOF method for interface tracking, realizable k-ε turbulence modeling, and the Lee phase change model. The framework was validated by comparing it to the experimental data from LIFUS5. The validated model was used to characterize vapor cavity transport dynamics during initial flash evaporation, capturing transient temperature/pressure distributions and their evolution, analyzing phase-change procedures across CCI stages, and correlating evaporation rates with dimensionless parameters including Reynolds number, turbulent kinetic energy, and Weber number. Evaporation rate dynamics were utilized to establish an improved cover gas pressurization mechanisms and a macro-scale interphase interaction framework to represent the entire CCI process. The findings indicate that the initial vapor cavity experiences continual growth, subsequently resulting in interface fragmentation caused by hydrodynamic instabilities, wake flows, and turbulent fluctuations, which lead to localized steam explosions. Meanwhile, the elevated surface tension of LBE effectively stabilizes vapor films and mitigates bubble collapse, consequently preventing large-scale steam explosions. These findings contribute essential insights for the safety evaluation and design enhancement of lead-cooled fast reactor systems.