Annealing of hydrogen trap sites in displacement-damaged EUROFER

Abstract

For future fusion power plants, the reduced activation ferritic/martensitic (RAFM) steel EUROFER is considered to be the primary choice as a structural material for plasma facing components (PFC) of the first wall, such as the blanket modules. Its exposure to high energy fusion neutrons will lead to creation of radiation-induced defects, which could act as trapping sites for hydrogen isotopes (HI) and consequently, strongly affect HI diffusion and retention. For predictive simulations of HI retention, the concentration of these trap sites needs to be known as a function of the temperature. In this work, EUROFER samples are irradiated by 20 MeV W-ions at 290 K to create displacement damage. Subsequently, they are exposed to deuterium (D) plasma at 370 K to decorate the created defects. Partial thermal desorption spectroscopy (TDS) is conducted in 50 K steps up to 620 K. D depth profiles are determined by nuclear reaction analysis (NRA) after each partial-TDS step. Following this analysis, the defects are again decorated with D and the D depth profiles are measured again by NRA to monitor the evolution of the concentration of trap sites. Most of the D is lost already at 470 K due to thermal de-trapping. Full recovery of the displacement damage is reached at 620 K.