Modélisation de la Stratification du Corium dans ICARE/CATHARE

M. Salay et F. Fichot. MASCA Seminar - June 2004 - Aix en Provence (France)

A comprehensive modelling to predict the stratification of oxides and metals in a corium pool is presented. It consists in a series of models that take into account both thermochemical and thermalhydraulic aspects. The model is designed to be used on a 2D/3D meshing. Therefore, the corium pool is assumed to be non homogeneous in temperature and composition. Only local thermochemical equilibrium is assumed (in each mesh).

A simplified thermochemical model provides the equilibrium compositions of the oxide and metal phases. It is consistent with MASCA experimental results. It is also consistent with computational results obtained by using IRSN thermochemical database. All the local physical properties, and particularly the densities, are calculated from the local compositions and temperature. The relative motion of the two phases is calculated with a drift flux model. This provides the velocities of the materials in the pool and, therefore, the global transport of species. Fission products are also transported, assuming, for each fission product, a pre-defined local equilibrium distribution between oxide and metal phases.

The model is implemented in a test-version of ICARE/CATHARE V2.0. Comparisons of the code results with selected MASCA tests show a good agreement. The OECD MASCA program was dedicated to the study of the thermochemical interactions between typical corium materials in a molten pool. A one-dimensional transient with successive steel additions is presented to demonstrate the existence of a transient ``3-layer'' configuration. In such configurations, the oxide pool is surrounded by two metallic layers with different compositions. It corresponds to a global non-equilibrium situation which may remain for a significant time, depending on species transport process across the oxide pool. A reactor configuration used to study the effects of the progressive melting of lower plenum steel structures in a two-dimensional corium pool is also presented.