Investigation of phase separation models in RELAP 4/MOD 6

Calculation of blowdown processes with the RELAP 4/MOD 6 code and various phase separation models was investigated using Dementev's blowdown experiment and different bubble rise velocities (VBUBs) and bubble density gradients (ALPHAs). Results of the parametric study show that the cases with a relatively low bubble rise velocity (VBUB = 0.5 and 1.0 ft/sec) and ALPHA = 1.0 give the closest agreement with the test for pressure, total mass, early void fraction and mixture level evolution. The results with the Wilson bubble rise model are not satisfactory because the Wilson model used VBUBs which were too high for the Dementev experiment.