Physico-chemical analyses and solidification path reconstruction of multi-component oxidic spread melts

In the case of a hypothetical severe core melt accident in a nuclear power plant, scenarios in which a mixture of core materials could melt and mix with the vessel metallic structures and part of the basemat concrete, cannot be fully excluded. In order to study the behavior of this mixture called corium, experiments have been performed in which highly refractory materials have been melted and spread onto a ceramic substrate. This paper describes the physico-chemical analyses made on the corium experimentally obtained from these experiments after cooling. The results show that even if the chemical composition of the corium is homogeneous, variations of crystalline phases are detected along the sample height. These variations are linked to the solidification conditions. The solidification paths followed by the different corium layers are then calculated using a thermodynamic database and software dedicated to corium studies. Finally, a methodology for the estimation of corium physical properties is presented and applied to the different layers of these spreads.