Numerical calculation of fluid flow within a large-diameter piping with a short-radius elbow in JSFR

大口径ショートエルボ管内流動の数値解析

相澤 康介 ; 山野 秀将   ; 小竹 庄司; 藤又 和博*

Aizawa, Kosuke; Yamano, Hidemasa; Kotake, Shoji; Fujimata, Kazuhiro*

FBRサイクルの実用化研究開発(FaCT)で設計検討が進めているナトリウム冷却大型炉では、プラント建設費を削減するため、2ループ構成の主冷却系及びショートエルボ大口径配管を採用している。この設計概念は、10以上の高レイノルズ数域における配管内の流動励起振動挙動が課題になる。本報告では、STAR-CDコードを用いて定常解析を実施し、適切な解析モデルを選定することで、別途実施したホットレグ配管を模擬した1/3縮尺試験の流動特性(逆流を含んだ剥離域など)を再現できることを確認した。また、その検証された解析モデルを用いて、冷却材物性及び配管スケールの影響を調べるとともに、実機におけるホットレグ配管の入口境界における乱れなどの条件を考慮して流動特性の検討を実施した。その結果、実機で想定されるホットレグ配管吸込み部での乱れを考慮すると、剥離域が小さくなる可能性が示された。

The present study has numerically investigated using the STAR-CD code the fluid-flow characteristics within a large-diameter piping with a short-radius elbow, which is adopted in an advanced large-sized sodium-cooled fast reactor (named JSFR). This study reports the result of numerical steady-state calculations of the 1/3-scale experiment with 9.2m/s of velocity performed at the first step. Since the experiments have revealed that dominant fluctuating pressures were generated at the boundary of flow separation and reattachment point on the pipe wall, this study focused on the flow separation size as one of the flow characteristics. The calculation has reproduced the flow characteristics, such as the measured velocity profile in the flow separation region, by specifying appropriate analytical models and conditions. With the validated models, the effect of the coolant viscosity has also been investigated as well as the piping scale. In order to examine the disturbance at the piping inlet, the flow dynamics within the reactor vessel were also calculated by modeling an entire upper sodium plenum region including various components within the reactor vessel in the JSFR design. This upper plenum calculation had to reduce the spatial resolution within the hot-leg piping because of numerous computational meshes needed in this calculation. The plenum calculation has shown several vortexes and flow distortion at the hot-leg inlet. The hot-leg inlet flow condition obtained in the plenum calculation was interpolated for the calculation simulating the hot-leg piping, where the spatial resolution was better than in the plenum calculation. The numerical calculation under the reactor condition involving the inlet disturbance has indicated the flow separation size became smaller than that in no disturbance case. This calculation implies that the inlet disturbance may play an important role to mitigate the flow-induced vibration force in the flow separation region.