Modelling of binary mixture phase change : Assessment on RASPLAV-SALT experiments

International Topical Meeting on Nuclear Thermal-Hydraulics (NURETH-11), Avignon, Octobre 2005

Patrick Roux, S. De Pierrepont, Florian Fichot, D. Gobin, B. Goyeau, M. Quintard(1).

In the context of severe accident of Pressurized Water Reactors (PWR), corium evolution in the lower plenum is a crucial issue.
Modelling corium behaviour is necessary in order to evaluate the possibility to cool it before the vessel breaks.
Many investigations have been done, but few of them account for all the complexity of the problem. In particular, only a few works have dealt with multicomponent mixtures, which is a pecularity of corium.
A macroscopic model of columnar solidification of binary alloys was developed in IRSN for that application. It is meant to be used as a stand-alone module but might also, in the future, be included in numerical codes for severe accidents. The model accounts for the coupled effects of energy, mass, species and momentum transfers.
It was validated on several experiments of binary alloy solidification. The main results of this validation are presented. The model is also applied to calculate Rasplav-salt experiment, in a hemi-cylindrical geometry which is more prototypic of a reactor vessel.
The main results are shown and compared with experimental data. Despite some uncertainties on the physical properties of the NaF-NaBF4 mixture, a reasonable agreement is found, in particular in the prediction of crust thickness.

(1) : Uv. Toulouse