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

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

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.