Simulation of a gas jet entering the secondary side of a steam generator during a SGTR sequence: Validation of a FLUENT 6.2 Model Original Research Article

This paper summarizes the major insights gained as a result of gas jets entering a tube bundle from either a guillotine or a fish-mouth breach of a steam generator tube. This scenario is highly relevant in nuclear safety since it determines the potential retention of radioactive particles during risk-dominant sequences, the so-called Steam Generator Tube Rupture (SGTR) sequences. The scenario has been modeled with the FLUENT 6.2 code and its predictions have been proven to be grid independent and consistent with the experimental data available. The topology of the jets and the influence of the inlet mass flow rate (from 75 to 250 kg/h) have been studied in terms of velocity profiles. The results show that the breach shape heavily determines the jet topology. Both jets initially describe a quasi-parabolic trajectory, which is affected by the presence of the tubes. A guillotine breach generates a jet with azimuthal symmetry, which vanishes for the fish-mouth breach configuration. In this case, jet expands azimuthally in a pseudo-triangular way with a small angle. This fact diminishes the momentum loss across the bundle, so that for the same inlet mass flow rate the fish-mouth jet penetration is higher than the guillotine one. The normalized maximum radial and axial velocities of the jet from the guillotine breach are found to be self-similar with respect to inlet mass flow rate along the tube row position and axial distance to the breach, respectively. However, in absolute terms higher penetrations are found at higher mass flow rates.