Currently, no comprehensive mechanistic model for the two-phase flow through a swirl vane steam separator is available. Therefore, an attempt has been made to develop an analytical model, using fundamental fluid mechanics, which is capable of predicting separator performance over a wide range of conditions. The developed model subdivides a typical boiling water reactor swirl vane steam separator into four distinct regions: the standpipe region, the swirl vane region, the transition region, and the free vortex region. In each region, the vapor and liquid components are treated separately and the behavior of individual droplets is determined from the drag force induced by the vapor continuum. The analytical model is used to first determine the vapor velocities throughout the separator. The drag force on the droplets is then determined, and the droplets are tracked through the separator in order to determine the exit position of each droplet. Separator performance can then be determined from this final position in terms of the fraction of droplets removed from the flow stream. In order to assess the validity of this model, the computer code SEPARATOR was developed. Among other capabilities, the code is capable of determining separator performance in terms of carryover, carryunder, and exit quality. However, due to the simplicity of the single-phase fluid treatment of the vapor continuum and the lack of data related to the average droplet diameter for flows of this nature, the results are not of significant quantitative value. The investigation performed does, however, suggest that the developed methodology, upon refinement of the single-phase fluids treatment, will yield quantitatively accurate results for nearly all separator operating conditions of interest.