Visualization of flow impinged on a vertical plane wall

In the early high pressure phase during a large-break loss-of-coolant accident (LBLOCA), the emergency core cooling (ECC) water is supplied from the safety injection tank (SIT) of the direct vessel injection (DVI) system in the APR 1400 (Advanced Power Reactor 1400 MWe). After the SIT is depleted, the in-containment re-fueling water storage tank (IRWST) subsequently supplies coolant to the DVI system through the safety injection pump (SIP). During this process, velocity of the injected flow varies with time. The initial velocity exceeds 10 m/s, but is decreased to about 2 - 3 m/s in the late phase of reflood. During the injection the flow behavior exhibits a complex mode involving impingement, bypass, entrainment, sweepout and condensation in the annular downcomer. This work is particularly concerned with impingement among these phenomena. The impingement relates to the ECC water being injected into the reactor downcomer striking the inner vessel wall. Accordingly, the water generates a film in the form of ridge on the vessel wall, which then flows down the downcomer due to gravity. This has an important bearing on the bypass and sweepout mechanisms. Use is made of the method of visualization to phenomenologically investigate the exact flow behavior. The visualization is achieved by tracing the fluorescent particles on a vertical plane wall. The velocity vectors are obtained using the digital and high speed cameras in the darkroom. A first-principle based computational tool is developed to analyze the flow behavior on a vertical plate. The flow behavior was captured on the computer screen, and the velocity distributions were compared against the predicted values. (author)