Characterization of a gas elliptic jet in a nuclear safety scenario

► We study a subsonic jet expanding in a tube bundle from an axial-type tube breach. ► The scenario is key to assess retention of radioactivity in SGTR nuclear accidents. ► PIV characterized the flow between the breach & the closest tubes for ReD=8–27×104. ► Jet expansion in a tube-free space and with other type of breach was also analyzed. ► It shows tophat profiles & asymmetric entrainment highly influenced by the tubes. This paper summarizes the major insights gained into the aerodynamics of a subsonic gas jet expanding across a bundle of tubes from an axial-type tube breach. This scenario is highly relevant in nuclear safety since it determines the potential retention of radioactive aerosol particles during a severe accident Steam Generator Tube Rupture (SGTR) sequence. A scaled-down mock-up with representative dimensions of a real shell and tube heat exchanger of a nuclear power plant was used in the experiments. Two dimensional (2D) PIV technique was used to characterize the flow field in the space between the breach and the neighbor tubes in the Reynolds range investigated (ReD=0.8–2.7×105). The free jet case (i.e. jet expansion in a “tube-free” space) was used as a reference to compare the “in-bundle” jet case. By comparing with previous results obtained with an axisymmetric radial tube breach, the effect of the type of breach in the nearby flow field across the bundle has been also analyzed. Results show that an axial tube breach generates an elliptic jet with “quasi top-hat” velocity profile. The presence of tubes distorts the jet shape, reduce its penetration and its gas entrainment with respect to a “tube-free” space. The type of breach drastically affects the jet evolution in the surroundings of the breach. Particularly, different velocity profiles and jet flow entrainments have been found for the same upstream conditions. Results are being applied in the development of aerosol retention models of severe accident SGTR sequences.