Study on thermal striping phenomena in triple-parallel jet; Transfer characteristics of temperature fluctuation in sodium and water based on conjugated numerical simulation

平行三噴流によるサーマルストライピングに関する研究; 流体-構造連成解析によるナトリウム/水流動場での温度変動伝達挙動の評価

木村 暢之; 上出 英樹 ; Emonot, P.*; 長澤 一嘉*

Kimura, Nobuyuki; Kamide, Hideki; Emonot, P.*; Nagasawa, Kazuyoshi*

温度の異なる流体の混合により発生する温度変動に起因する高サイクル熱疲労現象を評価するために、流体-構造連成解析を実施した。ナトリウムと水を作動流体とした同形状の平行三噴流試験体系を対象とした解析により、構造材表面での温度変動強度の減衰を定量的に明らかにするとともに、温度変動の伝達挙動について、作動流体の違いを評価した。

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. In Japan Atomic Energy Agency, an innovative sodium cooled fast reactor has been designed. The transfer characteristics of temperature fluctuation from fluid to structure in sodium are quite different from that in water. In order to realize the sodium cooled fast reactor, the clarification of the transfer characteristics of temperature fluctuation is of importance for the rational design against the thermal striping phenomena. 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 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.