The improvement of RELAP5/MOD3.1 code predictive capability for steam condensation on an inclined surface is investigated. In modeling the secondary condensers with RELAP5, two problems were encountered with respect to condensation in vertically stacked tube walls: the capability for turbulent film condensation and the effect of the wall node size on the prediction of condensation heat transfer coefficients (HTCs). The code original model based on the Nus-selt model for laminar film condensation is extended to the turbulent film condensation by introducing two previously developed models into the code. The code is further improved to properly take into account the condensation length over many nodings. To eliminate the dependence on the node size in predicting the condensation HTC of the code, film Reynolds numbers at each node are calculated recursively to track the growing condensate film thickness along the condensation length. The modified version is tested under idealized boundary conditions and with the simulation of secondary condensers and is compared with an analytical solution and the original code. It turns out that the simulation results by this modified version are independent of the node size and are in better agreement with the analytical solution than those by the original one.
