[en] Safety injection water is injected into the reactor vessel downcomer directly in Korean Next Generation Reactor(KNGR). Due to the adoption of direct vessel injection(DVI) method, thermal hydraulic phenomena different from existing cold leg injection plants can be occurred during large break loss of coolant accidents (LBLOCAs). Therefore, safety evaluation against LBLOCA has been performed for KNGR using TRAC-M/F77 code. One of the important phenomena is steam-water condensation in the upper downcomer. In the paper, heat transfer correlation of TRAC code is evaluated through the comparison between the correlation and the experiment results for steam-water heat transfer in vertical rectangular channel. As a result, TRAC code predicts the heat transfer coefficient larger than those of experiment results. Therefore, in LBLOCA analysis using TRAC code, the sensitivity studies for heat transfer in upper downcomer should be performed to evaluate the uncertainty