Ponente
Descripción
Exposure to light particles and neutrons bombardment can create activation or microstructure damage in plasma-exposed materials, compromising properties conservation and functionality. This is particularly significant for the divertor components, where the most intense particles (He, hydrogen isotopes, neutrons) and thermal flux are expected, and for which tungsten (W) is the first-choice material thanks to its low sputtering yield, low HI retention and high melting point. Plasma-wall interactions could jeopardize conservation of these key properties throughout long-pulse operation, triggering concerns for the reactor efficiency and safety as soon as tritium (T, hydrogen radioactive isotope) is used: notably, incident He particles can drastically affect the surface, with the formation of dislocation loops, bubbles or W-fuzz. Surface properties play a major role on hydrogen isotopes (HI) retention/permeation, a crucial process for reactor efficiency and safety if enhanced mobility of hydrogen isotopes allow tritium access to structural materials such as Eurofer and potentially its release to the environment; it is therefore of prime importance to characterize both material ageing with hydrogen isotope behavior in the materials envisioned for future fusion power plants
The presentation will tackle activities carried out at CEA-IRFM (Research Institute for Magnetic Fusion, CEA Cadarache) to anticipate material behavior in fusion-relevant conditions. First, evolution of W divertor-tiles from the WEST tokamak is addressed: pre/post mortem studies allow a unique insight on material migration, microstructure evolution and impact on fuel retention throughout the various experimental campaigns, via a large scale multi-technique analysis, with a particular focus on the He campaign impact. In a second part, we will address laboratory studies carried out to anticipate hydrogen trapping and permeation for both the reactor materials (tungsten, Eurofer) and the tritium plant piping (stainless steel), thanks to a coupling between experiments and modelling. Characterizing the behaviour of H isotopes in the materials relies on a large range of experiments, with the rare insight of isotopic behaviour. H and D behaviour studies are based on gas-driven permeation experiments coupled to Thermal Desorption Spectrometry (TDS) measurements of deuterium-loaded samples to get an understanding of both transport and trapping. On the other hand, T behaviour is specifically investigated at the Saclay Tritium Laboratory. These experiments take into account the distinct properties of tritium such as its β decay, which brings us closer to actual tokamak conditions. They also allow us to access experimental conditions that are out of reach with H or D measurements thanks to the high sensitivity of tritium measurements. Finally, experimental activities are performed in the triple beam facility JANnus in Saclay to mimic 14 MeV neutrons irradiation and collect important data to feed CEA-modelling tools on retention/permeation on relevant fusion materials.