Analytical prediction of blowdown system experiments using DRUFAN

The significant physical phenomena observed during HDR and Battelle blowdown experiments are correctly predicted by the thermal-hydraulic system code DRUFAN-02. The DRUFAN model for the HDR-test V31.1 included 21 control volumes, 21 flow paths, and 15 heat conductors. There was good agreement between measured and calculated results during the initial blowdown phase (1 s), especially with the mass flow rate, density, pressure, and temperature behavior at different locations. This agreement was achieved by modifying the evaporation and condensation models assuming the number of nucleations for bubbles or droplets per unit volume is a function of void fraction. Results of the entire blowdown phase (200 s) have also shown good agreement between measured and predicted values. Noticeable superheating of the vapor phase at high levels in the pressure vessel was calculated at the end of blowdown. The DRUFAN model for the Battelle Steam Line Rupture Test DL-3 simulated 3 loops with 23 control volumes, 28 flow paths, 20 heat conductors, 3 pumps, and 4 valves. A mixture-level tracking model was use for control volumes inside and outside the core barrel. Correct calculation of pressure differences across the core barrel was only possible by using the drift-flux model in air flow paths in the presence vessel