Dr. Dirk Lucas

Head Computational Fluid Dynamics
Phone: +49 351 260 2047

CFD-calculation of a hot channel of a fuel rod bundle

Boiling is a very effective heat transfer mechanism. Liquid cooling including phase transfer very large heat fluxes can be established. Exceeding the critical heat flux however, the heat transfer coefficient suddenly decreases, the temperatures increases leading to possible damaging of construction material. The critical heat flux not only depends on fluid properties but also on flow conditions and on geometric circumstances.

For the case of a fuel rod, the permissible heat flux can be influenced by the geometrical design. Especially the spacer grids equipped with mixing vanes play an important role to increase the permissible heat flux. The verification of design improvements and their influence on the critical heat flux require very expensive experiments. Therefore, the supplementation ore even the replacements of expensive experiments by numerical analyses are of relevant interest in fuel assembly design.

The figure shows the flow condition in a hot channel between four rods (axial shortened presentation). The mixing vanes generate a strong swirl in the actual calculation given as inlet condition. The overall vapour generation can be decreased. The streamlines show vapour bubbles moving in the centre of the channel caused by the centrifugal forces. The colours present the temperatures of the metal surface.

Brennelement-Heißkanal mit Swirl


Main publications

  • Krepper, E., Koncar, B., Egorov, Y., 2007, Modelling of subcooled boiling – concept, validation  and application to fuel assembly design, Nuclear Engineering and Design 237 (2007) 716-731
  • Krepper, E.; Egorov, Y.; Koncar, B., 2006. Towards CFD modelling of critical heat flux in fuel rod bundles; International Congress on Advances in Nuclear Power Plants (ICAPP06), 04.-08.06.2006, Reno, USA
  • Burtak, F.; Krepper, E., 2005. Can we predict critical heat flux in fuel assemblies by CFD methods?, Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
  • Krepper, E., Egorov, Y., 2005. CFD-Modelling of Subcooled Boiling and Application to Simulate a Hot Channel of a Fuel Assembly, 13th International Conference on Nuclear Engineering, Beijing, China, May 16-20 2005, ICONE 13-50245
  • Koncar, B., Krepper, E., Egorov, Y., 2005. CFD Modelling of Subcooled Flow Boiling for Nuclear Engineering Applications, International Conference “Nuclear Energy for New Europe” Bled, Slovenia, September 5-8, 2005, Paper 140
  • Krepper, E., CFD modelling of subcooled boiling, The 10th International Topic Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-10, Seoul, Korea, October 5 - 9, 2003