Multidimensional thermal-hydraulic characteristics in the secondary side of a steam generator (SG) are simulated by way of flow-boiling models. These models essentially belong to the so-called first-principle models that are derived from the conservation laws. The calculated results can provide the whole picture of thermal-hydraulic phenomena and the localized distributions of velocity, pressure, enthalpy, and void fraction, etc. in the secondary side of the SG. In addition, with the help of these localized flow characteristics, the forcing sources can be estimated for predicting flow-induced vibration (FIV) damage suspected in the tube bundles around the U-bend region. These calculated results can provide important information to help the FIV prediction for SG U-tubes and to find where the most possible FIV damage is located.