Some French pressurized water reactors (PWRs) include double containments vessel with the inner one made of a pre-stressed reinforced concrete wall. Leak tightness of the latter is a fundamental safety requirement for the reactor building. Within the framework of the level 2 probabilistic safety assessments (PSA), studies of the inner containment vessel behavior subjected to severe accident conditions have been performed by IRSN. The loading scenario lies in the total loss of the electrical sources, which led to the core meltdown and then, to the breakthrough of the reactor vessel by the corium. In this context, mechanical simulations with a three-dimensional model have been carried by IRSN with the objective of assessing the behavior of the containment under inner pressure and thermal loads. The results show that, for extreme temperatures, damage develops firstly in the dome. Then, damage penetrates over 50% of the wall thickness from the outer face to the inner face without causing the breakthrough of the wall. The thermal computations show that temperature in the beams of the dome might rise over 100°C whereas the temperature evolves slightly less in the major part of the thickness of the dome wall. The differential thermal expansion between the beams of the dome might explain the increase of damage.