Development and Validation of a Compressible OpenFOAM Solver for Simulating Steam-Water Jets and Liquid Metal Interactions in Advanced Nuclear Systems

Coolant–coolant interactions (CCIs) between water and liquid metals represent significant safety challenges in advanced nuclear systems, including Generation IV liquid metal fast reactors and water-cooled lead–lithium (WCLL) fusion breeding blankets. Accidental water ingress into a hot liquid metal pool can cause rapid vapor generation, pressure transients, and potentially steam explosions. Accurate numerical simulation of these phenomena requires resolving multiphase flow, compressibility, and phase change, including the complex interfaces between liquid droplets, vapor, and liquid metal. This work investigates the development and validation of a computational fluid dynamics solver based on OpenFOAM, aiming to improve the prediction of water–liquid metal interactions. The Volume of Fluid (VoF) solver icoReactingMultiphaseInterFoam was selected for its interface-capturing capabilities and phase-change modeling. Its evaporation models were first validated against analytical solutions of the one-dimensional Stefan problem and two-dimensional horizontal film boiling, showing good agreement with reference solutions. The solver was subsequently assessed against experimental measurements of a subcooled water jet plunging into a molten lead–bismuth pool, obtained using high-frame-rate neutron radiography. A systematic investigation of mesh resolution, time-step sensitivity, and boundary conditions identified a configuration yielding promising preliminary results. Despite not yet accounting for compressibility, the simulations reproduced the main hydrodynamic features, including jet instabilities, penetration depth, and multiphase cloud formation, with improved agreement with experimental data compared with previously published simulations. These findings suggest that compressibility may have a limited influence during the initial transient under the investigated conditions, although its inclusion remains essential for a comprehensive physical description. Compressibility models have therefore been integrated into the solver and are undergoing dedicated validation. The resulting tool is expected to support more accurate safety analyses of water–liquid metal interactions in advanced nuclear reactors.