In case of severe accident in a Nuclear reactor, nuclear fuel melting will result in the formation of high temperature (T>2500°C) corium, a complex and aggressive mixture. A means of mitigation is to inject water onto the corium to ensure its cooling, as it was the case during Fukushima Severe Accidents. Whatever the severe accident configuration, oxidation phenomena of the corium surface will form a layer of oxide at solid or liquid state, blocking or not the diffusion of oxygen. These complex and coupled phenomena are today partially modelled, they will depend on the configurations that may exist in reactors.

The VITI experiment on the Severe Accidents Plinius platform at CEA-Cadarache has been developed to simulate these extreme conditions performing oxidation analytical studies of corium melt by steam using températures till 2000°C.The objective of the thesis will be to carry out analytical experiments with materials representative of the nuclear core (fuel, casing and vessel steel), to analyze these experiments (post-test analysis) and to propose a fine modelling usable for severe accident codes.