Air-water two-phase swirling flows in a downscaled model of a steam separator for a boiling water nuclear reactor have been measured while paying attention to the effects of pick-off-ring (POR) shape on separation performance. As a result, the following conclusions are obtained. (1) In an annular swirling flow, the ratio Ws* of the separated liquid flow rate to the total liquid flow rate increases with JG and does not depend on JL and POR shape so much. (2) Separation performance becomes lower and does not depend on POR shape so much when the liquid film thickness becomes larger than the size of the gap between the barrel wall and the POR wall. The gap size should be determined so as to be smaller than the maximum film thickness. (3) The POR shape strongly affects the separation performance when the liquid film thickness is smaller than the gap size.
