This paper presents a concise description of a model developed for the prediction of the thermal, hygral and mechanical response of concrete elements at high temperature. The model can be applied to the analysis of behaviour of concrete structures exposed to fire, but the attention in this paper is focused on nuclear reactors vessels where thermal spalling can occur in high temperature conditions. It is the result of different co-existing thermo-hygro-chemical and mechanical processes strongly coupled one with another. These situations should not be modelled by considering thermo-mechanical processes alone. Heat and mass transfer within the concrete body has to be taken into account, including phase changes, hydration/dehydration, aging creep, shrinkage processes and material degradation. Mechanical damage alone is not sufficient, and thermally induced deterioration due to strains at material meso-scale and due to concrete dehydration, called thermo-chemical damage (with an appropriate modification of the stress-strain curves at elevated temperature) has been introduced in a framework of the isotropic non-local damage theory. An example, concerning a concrete containment of nuclear reactor vessel, showing the hygro-thermal and mechanical performance of concrete the structure in these conditions is shown and discussed.
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