In the framework of the European IVMR project, dedicated to the assessment of In-Vessel Retention (IVR) strategy for high power reactors, VITI-CORMET tests, performed in VITI facility (CEA-Cadarache/PLINIUS Severe Accident Platform), intend to study the interaction between a molten 304L stainless steel droplet and suboxidized solid corium crust, referred to as C-70 ((U 0.54 , Zr 0.46)O 1.74). In the present paper, original experimental results on molten steel penetration through a corium crust are presented. Identification of penetration mechanisms is performed by SEM/EDX analyses, and has shown that molten steel can penetrate through pre-existing cracks or by a dissolution process. The latter is found to be the dominant penetration mechanism and involves material transport from the crust to molten steel. Penetration kinetics is studied by measuring the average penetration length at different exposure times. It is found that the penetration by dissolution decelerates with time, while U and Zr contents tend to reach an equilibrium value within the metallic droplet.

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