[en] Analysis of light water nuclear reactor loss-of-coolant accidents (LOCA) requires that one be able to accurately calculate how two-phase flows split in complex, branching conduits. This paper is intended to provide a more thorough understanding of phase separation phenomena in such systems. In particular, detailed experiments have been performed with air/water mixtures in vertical wyes and tees to provide a data base for the development and verification of analytical models. The dependence of phase separation on different parameters, such as inlet quality, mass flux and separation angle, is discussed. (orig.)