Thermal fluid dynamics analyses on single- and two-phase flows in helical pipes of steam generators to be used in Generation III and IV nuclear reactors have been performed. The study concerned with experimental activities as well code simulations carried out in the framework of a collaboration between the Department of Energetics of the Polytechnic of Torino and the Department of Energy of the University of Palermo. The goal was the validation of models implemented in Relap5/Mod3.2 beta thermal-hydraulic advanced code to simulate the hydrodynamic behaviour of helical pipe components in spite of the one-dimensional nature of the code. It is shown that much of the experimental data obtained at several national and international research laboratories are well predicted by this modified RELAP5 code for the examined helical pipe geometries.