Study on model development for liquid accumulation in steam generator U-Tube, 3; Flow observation

Yamaji, Tatsuya*; Koizumi, Yasuo; Yamazaki, Kohei*; Otake, Hiroyasu*; Hasegawa, Koji*; Hasebe, Yoshiaki*; Onuki, Akira*; Nishi, Hiroaki*

Experiments of counter-current two-phase flow of upward steam flow and condensing downward film flow in a pipe were performed. The experiments were intended to examine water accumulation in steam generator U-tubes during intermediate and small break loss-of-coolant accidents of a pressurized water reactor. The inner diameter and the length of a test flow channel used in the experiments were 18 mm and 4 m, respectively. A transparent polycarbonate tube was used as the test tube since flow observation was mainly intended. When the vapor velocity was low, condensate flowed down on the inner wall of the test tube and flowed out from the bottom inlet of the test tube. As the vapor velocity was increased, slug flow came out at the intermediate elevation of the test tube and the condensate flowed up and flowed out from the top outlet of the test tube. At the lower elevation, the condensate flowed down and flowed out from the bottom outlet. This state have not been observed in the water-air experiments. The unique state for the water-vapor condensing counter-current two-phase flow was found out.