Development and qualification of materials for plasma facing and structural applications for DEMO is one the heaviest tasks in the EUROfusion programme within HORIZONT2020 with the total budget exceeding 100ME. Tungsten and tungsten-based composites are presently considered as main candidates for armor and divertor (including structural function) in DEMO. An armor material needs high crack resistance under extreme thermal operation conditions as well as compatibility with plasma-wall interaction phenomena, while a structural material has to be ductile within the operation temperature range. Both material types have also to be stable with respect to high neutron irradiation doses and helium production rates. Design of DEMO divertor remains one of the most challenging tasks in the current Fusion Roadmap.
The plasma facing materials envisaged for ITER application should receive only limited amounts of dpa during their lifetime (~0.1-0.5 dpa), while Tungsten selected as the first wall armour and Tungsten-based composites for structural applications in DEMO are expected to receive doses up to 20 dpa. Under these conditions, the impact of n-irradiation on mechanical and thermal properties is currently unknown ! Four physical degrading process will take place simultaneously: (i) neutron irradiation damage, (ii) heat transients, (iii) plasma gas uptake and (iv) nuclear transmutation. Consequently, the combination of these phenomena will define structural integrity and operational limit of the plasma facing components (PFC).
Although fission irradiation is currently the only option to proceed with the design material database, fission is not fully equivalent to fusion, because of: softer neutron spectra (lack of 14 MeV), high thermal to fast ratio (enhanced W transmutation), lower dose rate (enhanced defect annealing). SCK•CEN launches a large-scale neutron irradiation campaign in support of EUROfusion needs for the baseline and advanced tungsten grades. It is call TUNER (Tungsten Neutron Radiation) project and it involves more than 500 samples to be delivered for Post Irradiation Investigation (PIE) within 2017-2018. Among many others, one of the goal of this programme is to clarify the impact of the neutron irradiation on the microstructure of commercially available tungsten grades and investigate the neutron induced features in a wide range of doses and temperatures. This action will be done by means of (a) post-irradiation campaign involving usage of positron annihilation lifetime spectroscopy (PALS) and transmission electron microscopy (TEM), as well as (b) physically-based computational tool to rationalize microstructure obtained in BR2 conditions. The latter is important part of this scientific traineeship.