The RELAP5/MOD3.1 computer code is applied to the evaluation of performance of Secondary Condensers. The calculation of condensation heat transfer coefficients in RELAP5/MOD3.1 depends on the node size of the condenser pipe. Therefore, condensation heat transfer coefficients for the laminar and turbulent regions are implemented to modify the condensation subroutine in RELAP5/MOD3.1. And the film Reynolds number, $Re_\Gamma$ is calculated recursively and used to calculate the local averaged condensation heat transfer coefficients at each node. The simulation results of the modified code are independent on the node size. It is found that the performance of SC is very sensitive to the nodal scheme of the SC pool. One pipe model can``t represent the vertical thermal stratification and the natural convection in the pool. The nodal scheme with pipes connected with cross junctions at adjacent axial levels is suitable for the pool modeling.