Neutron-Irradiation + Helium Hardening & Embrittlement Modeling of 9%Cr-Steels in an Engineering Perspective (HELENA)

Abstract

This report provides a physically–based engineering model to estimate the radiationhardening of 9%Cr–steels under both displacement damage (dpa) and helium. The modelis essentially based on the dispersed barrier hardening theory and the dynamic re–solutionof helium under displacement cascades. However, a number of assumptions andsimplifications were considered to obtain a simple description of irradiation hardeningand embrittlement primarily relying on the available experimental data. As a result, twocomponents were basically identified, the dpa component that can be associated withblack dots and small loops and the He–component accounting for helium bubbles. Thedpa component is strongly dependent on the irradiation temperature and its dependencelaw was based on a first–order annealing kinetics. The damage accumulation law wasalso modified to take saturation into account. Finally, the global kinetics of the damageaccumulation kept defined, its amplitude is fitted to one experimental condition. Themodel was rationalized on an experimental database that mainly consists of ~9%Cr–steels irradiated in the technologically important temperature range of 50 to 600°C up to50 dpa and with a He-content up to ~5000 appm, including neutron and proton irradiationas well as implantation. The test temperature effect is taken into account through anormalization procedure based on the change of the Young's modulus and the anelasticdeformation that occurs at high temperature. Finally, the hardening–to–embrittlementcorrelation is obtained using the load diagram approach.Despite the large experimental scatter, inherent to the variety of the materials andirradiation as well as testing conditions, the obtained results are very promising.Improvement of the model performance is still possible by including He–hardeningsaturation and high temperature softening but unfortunately, at this stage, a number ofconflicting experimental data reported in literature should first be clarified