Transient analysis of a condensation experiment in the noncondensable gas-filled closed loop using an inverted U-tube

Two-phase transient phenomena in the noncondensable gas-filled closed loop was investigated numerically using the RELAP5IMOD3 code. Analyses for three different . modes observed in the inverted U-tube experiment, i.e., reflux condensation, natural circulation, and oscillatory mode between these two modes were performed. Major thermal-hydraulic phenomena were predicted well, however, system pressure and pressure drop at the U-tube riser side were overpredicted than experimental data. Higher frequent flow oscillation than the data was also predicted