A computational investigation of experiments involving the condensation phenomenon in the presence of noncondensable gases was performed. TheRELAP5/MOD3 thermal-hydraulic code was utilized for this analysis. Two separate-effects experiments were studied, which are relevant to actual situations encountered in the industry. The first experiment involved condensation of steam in an inverted U-tube when nitrogen is present. A constant flow of steam was injected into the U-tube and condensed along its surface. The condensing length was a function of the injected nitrogen rate and the secondary temperature. The code predicted an active condensation zone with unimpeded heat transfer and a passive zone with no heat transfer. The lengths of these zones agree with the experimental data. The gas temperatures in the U-tube were favorably predicted except for a discrepancy where the calculated primary temperatures were lower than the secondary temperatures for several cases. Active nitrogen contents in the tube were underpredicted by the code. The second experiment investigated was the Massachusetts Institute of Technology’s steam condensation experiment. This experiment modeled the proposed containment cooling system for advanced reactors. Steam was generated in a vessel in which air was present. The steam in the steam-air mixture condensed on the surface of a cooled copper cylinder. Computational predictions of this experiment revealed that heat transfer coefficients vary with air fraction. Calculated heat transfer coefficients were compared with the data, and it was found that the results were better for higher system pressures than for lower pressures.