5. The limitations of the model

The proposed model was established on the basis of an experimental base in which the tests are carried out for monotonic stresses: (i) tensile tests on pre-irradiated materials under isothermal conditions; creep, irradiation (and swelling) tests in isothermal conditions for a constant flow. However, this law must be used to simulate the behavior of tank internals under real conditions; that is to say with variable flows and temperatures.

Thermal cycling induces cyclic mechanical loading. The equations of the model, written in differential form, make it possible to manage variable temperatures and flows but some physical effects are not taken into account. This is for example the case of kinematic work hardening, which could occur during thermal cycling. To our knowledge, there are no cyclic traction/compression tests on irradiated materials. Other questions may also arise: (i) what is the radiation creep behavior of a pre-irradiated material (at a different temperature and/or under stress)? (ii) is there a coupling between radiation creep and plasticity?

Swelling is treated as an irreversible volume deformation. However, it is the appearance of cavities that can grow under tensile stress (or even be filled under compressive stress but this remains very hypothetical). However, this harmful effect, since the void rate increases more quickly, is not taken into account.

The field of use of the model in terms of temperature, fluence and creep stress is specified in the note HT-26/05/045/A for materials 304 and 316. However, it is possible to use such a model in the context of a calculation with Code_Aster for any material other than these. In this case, it is the responsibility of the user of the code to ensure that the material coefficients he uses are in accordance with the field of validity of his calculation.