Study on thermalhydraulics of thermal striping phenomena. Evaluation of transfer characteristics of temperature fluctuation based on conjugated numerical simulation in triple-parallel jet geometry

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing between hot and cold fluids causes thermal fatigue in structural components, is of importance for reactor safety. It is necessary for the quantitative evaluation to investigate occurrence and propagate processes of temperature fluctuation, e.g., decay of temperature fluctuation near structures and transfer of temperature fluctuation from fluid to structures. Deceases of temperature fluctuation intensity in these processes should be considered for reasonable evaluation of temperature fluctuation. In this study, sodium and water experiments of parallel triple jets configuration were performed. For these experiments, numerical simulations were carried out to evaluate the transfer characteristics of temperature fluctuation from fluid to structure. The analysis code, called Trio- U, used in the study has been developed at the CEA in France. The large eddy simulation (LES) model is incorporated in the code. Furthermore, the code can calculate fluid and structural domains simultaneously. In the simulations, the calculated time-averaged temperature distributions in fluid and structure were close to the experimental results in sodium and water. The power spectrum densities of temperature fluctuation in fluid and structure were also in good agreements between the experiments and calculations. Furthermore the calculated decay characteristics of temperature fluctuation from fluid to structure were in good agreements with the experimental results. (author)