蒸気発生器伝熱管内蓄水量評価モデルの開発,5; 単管及び複数管実験結果

Study on model development for liquid accumulation in steam generator U-tube, 5; Experimental results on single and multi-channels

山崎 康平*; 大竹 浩靖*; 長谷川 浩司*; 山路 達也*; 小泉 安郎; 大貫 晃*; 金森 大輔*

Yamazaki, Kohei*; Otake, Hiroyasu*; Hasegawa, Koji*; Yamaji, Tatsuya*; Koizumi, Yasuo; Onuki, Akira*; Kanamori, Daisuke*

PWR小破断冷却材喪失事故時に、過渡的な炉心水位低下をもたらすことが懸念されている、蒸気発生器上昇流側U字管内冷却水滞留を調べることを目的として、凝縮を伴う垂直管内気液対向流の蓄水挙動を実験により調べた。複数管の相互作用による影響を調べるため、単管実験と並列4本管実験の2種類の実験を行った。実験は、内径18mm、長さ4mの垂直円管を試験流路とし、蒸気と水を用いて圧力0.1MPaの下で行われた。並列4本管の実験の場合の管内蓄水量の方が単管の場合の蓄水量より多い結果となった。並列4本管実験では、上方に流れるにつれ蒸気凝縮量は減じる条件であったが、単管実験では流れ方向均一蒸気凝縮の条件であった。この実験条件の違いが、4本並列管実験で管路上方での蓄水量を少なくしたものと考えられる。

Experiments of condensing counter-current two-phase flow in a vertical pipe were performed. This study was intended to examine water accumulation in the up-flow side of steam generator U-tubes of a PWR during the reflux cooling stage of a small break LOCA. It has been apprehended that the water accumulation may result in temporary core liquid level depression. Two kind experiments were performed; single channel experiments and parallel four channel experiments. The inner diameter and the length of the test flow channels were 18 mm and 4 m, respectively. The experiments were performed by using steam and water at 0.1 MPa. It was confirmed that even if water on the inner surface of the test pipe could not flow downward at the lower portion of the test pipe, a part of water became to flow downward at the upper portion of the test pipe since steam velocity decreased because of condensation. Thus, two-phase mixture level was formed in the upper portion of the test pipe, which resulted in the water accumulation in the pipe. The water accumulation in the test pipe in the four channel experiments was smaller than in the single channel experiments. In the four channel experiments, the condensing rate of steam decreased as steam flowed upward although the steam condensing rate was uniform along the channel in the single channel experiments. This difference in the experimental condition between the two kind experiments might result in smaller water accumulation in the four channel experiments than in the single channel experiments.