AN ANALYTICAL MODEL OF THE SWIRL VANE STEAM SEPARATOR FOR BOILING WATER-REACTORS

Currently, no comprehensive mechanistic model for the two-phase flow t hrough a swirl vane steam separator is available. Therefore, an attemp t has been made to develop an analytical model, using fundamental flui d 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 re gions. the standpipe region, the swirl vane region, the transition reg ion, and the free vortex region. In each region, the vapor and liquid components are treated separately and the behavior of individual dropl ets is determined from the drag force induced by the vapor continuum. The analytical model is used to first determine the vapor velocities t hroughout the separator. The drag force on the droplets is then determ ined, and the droplets are tracked through the separator in order to d etermine the exit position of each droplet. Separator performance can then be determined from this final position in terms of the fraction o f droplets removed from the flow stream. In order to assess the validi ty of this model, the computer code SEPARATOR was developed. Among oth er capabilities, the code is capable of determining separator performa nce in terms of carryover, carry under, and exit quality. However, due to the simplicity of the single-phase fluid treatment of the vapor co ntinuum and the lack of data related to the average droplet diameter f or flows of this nature, the results are not of significant quantitati ve value. The investigation performed does, however, suggest that the developed methodology, upon refinement of the single-phase fluids trea tment, will yield quantitatively accurate results for nearly all separ ator operating conditions of interest.