Subchannel Void Fraction Prediction via Drift-Flux Analysis

Void fraction calculations have been performed using the subchannel drift-flux code CANAL. Using void and flow distributions in rod bundle geometry, a value of C₀ has been estimated for bundle-averaged void fraction calculation in one-dimensional approximations. Successful prediction of the average void fraction is observed for the annular rod bundle geometry of the FRIGG experiment. In order to perform subchannel void fraction calculation, a C₀ model has been developed for one-dimensional subchannel geometry. The implicit form of the C₀ model developed accounts for void and flow conditions in the adjacent subchannels existing at the common interfaces, i.e., at the gap spacing between the subchannels. It appears that the magnitude of C₀ varies between subchannels (annular rings of FRIGG geometry) but remains almost constant within each subchannel. Good agreement is observed between prediction and data for subchannel void fractions in axially uniform and nonuniform heated rod bundles.