Reactor Vessel Integrity in Severe Accidents (REVISA)

The REVISA project, which addressed the issue of the vessel integrity in severe accident project, has produced new results in the characterisation and modelling of high temperature deformation and damaging behaviour of various vessel steels: above 900°C, their ductility is very large, whereas necking occurs for 1% elongation, when temperature is close to 600°C. The creep behaviour of the various steels in the austenitic domain is similar to the one of pure metals and presents a marked difference with the behaviour below the transformation point. There is almost no size effect on the maximum tensile stress and on the uniform elongation of smoother tensile specimens tested at room temperature if material inhomogeneity is accounted for. Interpreting validation (RUPTHER) experiments through computational models has underlined the necessity to account for the various non-linearities (plasticity and viscoplasticity, large displacements and strains, conservative pressure) involved and to reflect the global and local deformation behaviour in order to produce predictive analyses even if one uses models with coupled damage variables.