Foam formation in oxidic pool with application to MCCI real material experiments

Void fraction is an important parameter in molten core concrete interaction (MCCI) study of PWR since it controls the swollen level of the corium pool, the interaction surface between the pool and the concrete and, in turn, the concrete erosion velocity. In recent MCCI real material experiments (OECD-MCCI, VULCANO), it seems that very high void fraction (higher than 50%) might have been obtained leading to low erosion velocity of concrete (e.g. CCI-4) and significant concrete erosion of the upper part of the test section (e.g. CCI-2 and CCI-4). Such void fraction cannot presently be predicted with classical void fraction correlations (e.g. Zuber and Findlay), so that a different phenomenon related to the formation of foam in oxidic pool during core concrete interaction could be considered. The main purpose of this paper is to propose an analysis of MCCI experiments taking into account the foam formation resulting from gas released from concrete in corium pool with SiO2 and CaO. The first part of this paper is devoted to a review of the available experimental and modeling work performed in the frame of the metallurgical industry R&D. Two of these models have been implemented in the TOLBIAC-ICB code (CEA/EDF) which has then been used to simulate real material MCCI experiments of the OECD-MCCI project, CCI-2 and CCI-3. In the second part of this paper, it will be seen that foam formation could explain some of the phenomena observed in these experiments such as the strong ablation of the upper part of the cavity in Limestone Common Sand (LCS) concrete tests.