Experimental Study of Thermal Stratification in Lead-Bismuth Pools and Development of Predictive Models

Thermal stratification is a common thermal-hydraulic phenomenon in liquid metal cooled reactors, which significantly affects system safety by weakening the natural-circulation driving head and inducing thermal stresses. To predict this phenomenon, thermal stratification experiments were conducted at the MATH (Multi-Application LBE Thermal-Hydraulic test facility). The dimensionless stratification number (STR) was introduced to quantify stratification intensity, and its correlation with the Richardson number (Ri) was analyzed. Experimental results suggest that Ri ≈ 10 indicates the critical threshold for stratification stability under the present experimental conditions: below this value, turbulent mixing dominates, destroying density gradients and interfacial structures; above this value, buoyancy suppresses turbulent mixing, maintaining the stratified state. Based on experimental results and stratified turbulence theory, a predictive model for thermal stratification was developed for the multidimensional system code LIMSAC. Validation results confirm that the model accurately reproduces the evolution of thermal stratification.