1. Introduction

Finite element calculations carried out as part of studies on serious accidents in nuclear reactors have highlighted the need to use damage models in order to predict the ruin of a structure such as the tank subjected to severe and complex thermal conditions (high temperatures up to fusion, high temperatures up to fusion, strong thermal gradients in space or time, etc.) that corium would impose on it [bib1].

The major advantage of this choice lies in the fact that the value of the damage variable at breakage (or at cracking) can be considered as an intrinsic parameter of the material which is accessible, although difficult and delicate, by physical measurements (ultrasound, diffraction \(X\), etc.). The criterion for breaking with the theory of damage is then more « physical » than the maximum deformation criteria sometimes used in viscoplastic calculations without damage or the criteria for uncoupled damage (rule for the accumulation of time actually spent under certain conditions \((\sigma ,T)\) divided by the ruin time for these same conditions).

The model implemented in Code_Aster is a viscoplastic behavior model with viscosity-multiplicative work hardening coupled with isotropic damage (model due to Chaboche [bib2]).

Note Bene:

Reference [bib3] provides a detailed description of the capabilities of the model, a methodology for identifying parameters, and the values of these parameters for 22MonicR37 steel.