[en] I performed an independent assessment of the Transient Reactor Analysis Code, TRAC-PF1/MOD1, using air-water countercurrent-flow limitation data in circular pipes for annular, annular-mist, and stratified flows. Tubes were configurated in the vertical direction with different lengths and diameters and at angles of 60 deg, 40 deg, 20 deg, and 0 deg from the horizontal, respectively. Also, comparisons were made with data from a horizontal tube with an inclined riser at the end that simulated a pressurized water reactor (PWR) hot leg. TRAC-PF1/MOD1 was modified to study the effects of using two different correlations for interfacial shear in the annular-mist flow regime: the Wallis and Bharathan correlations. TRAC-PF1/MOD1 with the Wallis correlation predicts the point of no water penetration (bypass point) in the annular-mist flow regime except for the 40 deg inclined tube. However, for the region of partial water penetration, use of the Bharathan correlation in TRAC-PF1/MOD1 gives better agreement with data. Additional form losses were required at both ends of the tube to predict the flow rate of falling water accurately for the vertical tube. In the stratified-flow regime, TRAC-PF1/MOD1 underpredicts the air velocity which gives the bypass point but gives good agreement for the region of partial penetration. For the case of a simulated PWR hot leg, the code yields similar results to those obtained for the stratified-flow regime. (author)