Irradiation effects: modelling and experiments
Work-package WP3 aims at better understanding the microstructural evolution of austenitic stainless steels under irradiation. Such alloys will be used in GenIV prototypes (e.g. ASTRID) for both structures (316 L(N) steels) and cladding (AIM1-type steels). While the structure materials will receive a low irradiation flux and dose during a long time, the core components and the fuel cladding tubes will receive very high irradiation fluences, that in the temperature range of interest (300–700°C) produce new microstructure features, such as new families of precipitates, solute segregations at structural defects, point defect clusters and voids, leading to dimensional changes of the components (swelling). In addition, cladding materials are exposed to higher operating temperatures than structure materials, which brings about an aggravation of corrosion issues in the short term, and a concomitant need for protective coatings. Swelling, corrosion and mechanical issues limiting the lifetime of these materials are strongly related to their microstructure. It is then of prime importance to be able to predict their microstructure evolution.
The objective of the first three tasks of WP3 is to build thermodynamic and kinetic models for Fe-Ni-Cr model alloys able to accurately describe their phase diagrams, their diffusion properties and the kinetics of segregation and ordering. This is the first necessary step for a reliable and sound modelling of the microstructure evolution under irradiation in austenitic stainless steels. The composition range of the ternary model alloy will be chosen to encompass those of 316 L(N) and AIM1 steels, and we will focus more closely on the foreseen operating temperatures for GenIV fast reactors (around 500 °C). Inter-diffusion experiments in Fe-Ni-Cr multi-layers during isothermal annealing and under ion irradiation will be performed to assess the validity of the atomistic kinetic models and to investigate the effect of temperature, chemical composition and irradiation on their thermodynamic and nanoscale inter-diffusion properties.
In the last task of WP3, ion irradiation will be used as a surrogate of neutron irradiation to obtain valuable information on the effect of radiation damage on the microstructure of selected alumina forming alloys, surface modified layers and coatings and on their mechanical properties (stiffness and hardness). The most promising materials will be selected for the irradiations based on inputs coming from WP1 (processing) and WP4 (environmental testing).
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