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Science and Technology of Nuclear Installations
Volume 2014, Article ID 197267, 16 pages
Research Article

Large Scale Gas Stratification Erosion by a Vertical Helium-Air Jet

Paul Scherrer Institut, 5232 Villigen, Switzerland

Received 5 August 2014; Accepted 25 September 2014; Published 30 November 2014

Academic Editor: Arkady Serikov

Copyright © 2014 R. Kapulla et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Containment conditions after certain postulated severe accident scenarios in nuclear power plants might result in the accumulation of hydrogen in the vessel dome. Inspired by these accident scenarios an experiment for the OECD/NEA benchmark exercise (2014) was carried out in the large scale PANDA facility at the Paul Scherrer Institut in Switzerland. The benchmark experiment was conducted at room temperature and under conditions characterized by an initially positively buoyant jet which becomes negatively buoyant while interacting with a helium layer. The experiment addresses (i) the initial conditions especially at the tube exit and (ii) the details of the entrainment of the helium stratification into the jet and the transport of the mixture towards the lower parts of the vessel. For the tube exit velocity mean and fluctuating quantities we find a reasonable agreement with pipe flow data, but a lack of agreement between past tube exit measurements and our results. It is shown that the axial velocity of the jet experiences a strong deceleration in the vicinity of the helium-rich layer and is finally stopped. Fluid accumulates in this zone and part of this fluid is flowing back in a narrow annular region around the upward flowing jet. Consequently, part of the annular flow is reentrained into the rising jet. During the layer erosion, the flow structure changes from a more downwards oriented annular type to a more horizontally oriented mushroom type of flow. It is found that locations for which we record considerable turbulent kinetic energy extends above the region where the velocity magnitude has decayed to almost zero, indicating that the jet deceleration and redirection introduces considerable turbulence in the helium stratification.