Modeling intrinsic- and displacement-damage-driven retention 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 can act 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 input parameters for rate equation modeling of HI transport in displacement-damaged EUROFER are determined by fitting recently obtained thermal desorption spectroscopy (TDS) data. During these simultaneous fits of all TDS data the input parameters were constrained as much as possible by using literature data and measured HI concentration depth profiles. A comparison of gas phase loading at low pressures with literature data on solubility suggested the presence of a surface limit for D uptake from the gas phase. However, while modeling plasma loading with energetic particles this surface limit results in an overestimation of the D uptake. The only way to reconcile the lack of D loading from the gas-phase at low pressures and match the measured uptake of D during plasma loading, was to introduce a removal process for chemisorbed D from the surface by the energetic particle impact from the plasma. With this surface model and the fitted trapping parameters it is possible to simulate the measured TDS data and the observed lack of gas loading at low pressures. The so configured rate equation model can now be used for prediction of D transport and retention in EUROFER.

Keywords

• Hydrogen
• Retention
• EUROFER
• Displacement-damage
• Diffusion-trapping- modeling
• Surface-limits