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The multi-phase code AFDM (Advanced Fluid Dynamics Model) of the SIMMER family of codes has two dimensions and addresses highly transient flows of three components in three velocity fields. Its development was supported by US-NRC, PNC Japan, CEA France, JRC Ispra, and the Forschungszentrum Karlsruhe (FZK). The code allows to track one component in the solid, liquid, and vapor state, a second component in the liquid and vapor state, and a third component in the vapor state. The of-the-shelf version models the following processes: Multi-component, multi-velocity, multi-phase compressible fluid flow, heat and mass transfer, melting, freezing, evaporation, condensation, interfacial areas dependent of space and time with source terms. The numerical solution method with its predictor-corrector method allows to add user-defined explicit models. The DCH-version models steam generation in RPV, flow through a breach, breach ablation, jet disintegration, entrapment of liquid on cavity walls, entrainment of liquid, crust formation and ablation, vapour-liquid thermal and chemical interaction (hydrogen generation), and contains a simplified hydrogen combustion model.


The code aims at modelling the physical phenomena governing the molten core/concrete interaction. WECHSL models one-dimensional as well as two-dimensional melt/concrete interactions in axisymmetrical concrete cavities. The one-dimensional concrete cavity may consist of an additional layer composed of concrete and metals. The code performs calculations from the time of initial contact of a hot molten pool to the start of solidification processes, including the long-term basemat erosion over several days with the possibility of basemat penetration. It is assumed that there is an underlying metallic melt layer which is covered by an oxide layer. Alternatively, a single oxide layer is modelled, which may contain a homogeneously dispersed metallic phase. Internal energy can be produced by decay heat or by exothermic chemical reactions. Energy is transferred to the melting concrete and to the upper containment by thermal radiation or evaporation of sump water, possibly flooding the surface of the melt.

Simulates the free surface flow (Spreading of core melts)
The CORFLOW code simulates the free surface flow of an incompressible fluid in a 3-dimensional geometry. In addition to the fluid, several structure materials can be considered as hydrodynamic obstacles or thermodynamic heat sources. The fluid is assumed to possess Newtonian or non-Newtonian rheology. The free surface is determined by an equation which results from the free interface kinematic boundary condition and an integration of the continuity equation in the vertical direction. The free interface is represented as a height function either as a step function or a second-order polynomial. Internal heat transport by conduction and convection as well as heat generation (decay heat) and heat transfer to the surroundings are modelled. The material properties, except the surface tension, may depend on temperature. A discrete phase transition model is available to simulate solidification and melting of the fluid and phase transition of the structure materials. The influence of the solidification process on the spreading is modelled by an increase of the viscosity. The increase of the viscosity in the thermal boundary layer of the melt can eventually lead to a stop of the melt front.