Thermal-Mechanical Behaviour of the Reactor Pressure Vessel and Corium Molten Pool in a Severe Accident Core Melt Down

The thermal and mechanical behaviour of a PWR vessel in consequence of a severe accident with core melt down and flooding of the reactor pit has been investigated by refined finite element analyses of the vessel and of the corium. Although the large corium mass and high residual power, the external water cooling avoids complete melt of the vessel but a deep thermal attack is observed in the inner part of the wall with a residual thickness of few centimetres. The high temperature gradients that establish through this thickness cause a high stress level and plastic deformations are observed in a large region of the vessel.