Influence of hydrogen isotopes on displacement damage formation in EUROFER

Abstract

The reduced activation ferritic martensitic steel EUROFER is one of the foreseen structural materials for future fusion reactors. The exposure to energetic fusion neutrons will generate displacement damage in the steel which acts as trapping sites for hydrogen isotopes (HIs). For predictive simulations of HI retention the concentration of the trap sites and HI trap-binding energies are needed. In this work the potential influence of HIs present during displacement damage on the resulting trap site concentration is investigated. EUROFER samples are exposed to multiple sequences of displacement damage by MeV W-ions and subsequent loading by D-ions from a low temperature plasma. After each of these damage/loading sequences the D depth profile in the surfaces is measured by nuclear reaction analysis (NRA) using a 3He beam. These depth profiles show a clear increase in the trap site concentration when the displacement damaging step is performed on a sample already containing trapped D. The presence of 3He in analysis spots from previous NRA-depth profiling also results in a strong increase of local retention due to traps formed by the implanted 3He. Thermal desorption spectra show that in EUROFER retention is dominated by the bulk, even in the presence of displacement damage in the near surface. These results suggest that the presence of D and He in EUROFER will result in increased retention compared to pure EUROFER under displacement damage.