Numerical analysis of sodium experiment for thermal stratification in upper plenum of fast reactor

Multi-dimensional transient thermal hydraulic analyses for a sodium experiment are carried out in order to validate the applicability of basic simulation methods to a typical thermal stratification behavior in a reactor upper plenum region. Simulation predictability of the behavior is evaluated after the results of an existing experiment in a simple geometry are reviewed and important fundamental characteristics of the behavior are quantified. The investigation places one of focuses on the applicability of the RANS type standard k-ε turbulence model, the RNG k-ε model and of the Reynolds Stress Model. As for the basic simulation methods, the effect of mesh size and of discretization scheme is also examined. The results clarify that CFD codes provide good prediction for fundamental phenomena of steep temperature gradient and gradual rising behavior of the stratification interface under the condition of adopting appropriate mesh size, higher-order discretization scheme, and the RANS turbulence model. (author)