大規模シミュレーションによる稠密炉心内気液二相流特性の解明,2; 2チャンネル流体混合実験への適用

Investigation of water-vapor two-phase flow characteristics in a tight-lattice core by large-scale numerical simulation, 2; Experimental analysis of 2-channel fluid mixing tests

永吉 拓至*; 吉田 啓之  ; 大貫 晃; 秋本 肇

Nagayoshi, Takuji*; Yoshida, Hiroyuki; Onuki, Akira; Akimoto, Hajime

稠密格子燃料集合体内の気液二相流の流体混合現象のシミュレートを目指し、改良界面追跡法を用いた気液二相流解析コードTPFITを開発した。TPFITの検証作業の一環として、大気圧・水-空気を用いた2チャンネル流体混合実験の解析に適用し、チャンネル間のクロスフローによる単一スラグの変形・分裂挙動やチャンネル間差圧の時間変化を比較した。その結果、スラグ上昇速度を過小評価する傾向はあるが、クロスフローによるスラグの変形・分裂挙動をTPFITが良好に予測できることを確認した。水と流路内壁との接触角など気液界面と流路壁面との相互作用の取り扱いに検討の余地が残るが、TPFITが狭隘ギャップを介した気液二相の流体混合挙動を予測できる見通しを得た。

A detailed gas-liquid two-phase flow analysis code based on an advanced interface-tracking method has been developed. It is expected that the developed code would be able to simulate two-phase cross flow behavior within tight-lattice fuel bundles without relying on any empirical correlations. In order to verify the applicability of the code to simulate two-phase cross flow behavior in such situations, numerical analyses of 2-channel model tests were conducted to compare the air slug deformation and separation behavior caused by cross flow through a narrow interconnection between channels. Although the code underestimated the ascending velocity of the slug, the calculated slug deformation and separation behavior were shown to be quite similar to those observed by a high-speed video camera. Moreover the minimum differential pressure between the subchannels through the interconnection, causing channel-to-channel air transfer to occur could be predicted to within 20Pa. However, further studies of modeling and implementation related to the interface-channel wall interaction, such as a contact angle of a gas-liquid interface at the channel wall, are required for prediction improvements. Nevertheless, the qualitative capability of the developed code to simulate two-phase cross flow phenomena was demonstrated.