Investigations on separated two-phase flow concerned with LOCA of LWR

The separated two phase flow of liquid and gas may occur in a duct of large diameter at the time of loss of coolant accident (LOCA) in a light water reactor (LWR). As one of the unsteady phenomena, the generation of slugging was studied with pressure variation and flow variation. The experimental apparatus has two main test channels, one is 31.5 mm wide, 43.3 mm high and 2420 mm long, and the other is 40 mm wide, 50 mm high and 4800 mm long. The schematic diagram of this test apparatus and the instrumentation system are presented. As for the experimental results, the photograph of slugging flow changing from wavy flow, the relation between wave length and wave propagation velocity, the condition of generating slugging, the transient states of pressure and water level in relation to time, the air velocity distribution above water surface and the power spectrum of water level variation are explained. These experimental results were evaluated in comparison with other studies. Based on the experimental evaluation, the experimental results as to air-water two phase flow are expressed as the equation. (Nakai, Y.)