J.M. Seiler’s major contributions to the understanding and modeling of corium – ceramic and concrete interactions

• Summary of the development of J.M. Seiler’s Transient Interface Model. • A generic model of corium interaction with concrete or ceramic. • Strong coupling between physico-chemistry and thermal-hydraulics. • Model consistent with results of corium-concrete interaction experiments. In the 80s and 90s, the inconsistencies between predictions of Molten Core-Concrete Interaction (MCCI) models and experimental observations on large-scale tests pushed J.M. Seiler to propose the foundations of a new modelling approach. This approach, formalized under the form of the Transient Interface Model (TIM), is based on strong physical grounds and simplifying assumptions obtained from order-of-magnitude analyses. This paper summarizes the development of this model. The inconsistencies of previous approaches are recalled before presenting J.M. Seiler’s main contributions with the introduction of first-order thermochemical phenomena into the classical thermohydraulic modelling. J.M. Seiler demonstrated that the strong coupling between physico-chemistry and thermal-hydraulics during the final phases of severe accidents is of paramount importance for quantitative prediction of severe accident consequences and scaling of recovery systems. The wide implications of this approach on the temperatures of the mixtures, their compositions, their physical properties (viscosity in particular) and the interaction with ceramics are highlighted. One of the important contributions of the TIM approach lies in the global physical consistency of the model and its consistency with the observed experimental evidence. Such consistency is essential for the credibility of the calculations used for safety demonstrations.