Effect of azimuthal injection angle on the direct ECC bypass in a DVI system

The direct ECC bypass fraction is strongly dependent on the relative ECC injection angle because the wake region of hot leg has the characteristics of ECC penetration due to the stagnant vortex behind the hot leg while the cold leg suction zone has the characteristics of ECC bypass (Kwon et al., 2002). Thus the azimuthal injection angle from the broken cold leg is most important parameter. In the APR1400, the DVI nozzles are located at the cold legs with the relative angle of 15 degrees. Therefore, the ECC film is formed at near a suction zone of the broken cold leg. If the relative angle between the cold leg and the DVI nozzle is increased to 45 degrees from the current relative angle of 15 degrees, the ECC film is also shifted to the upper region of the hot legs wake instead of the suction zone of the broken cold legs. Thus the ECC penetration will be increased with the relative azimuthal injection angle increasing. In this study, the effect of the azimuthal injection angle on the direct bypass has been investigated by air-water test