Development of qualification of materials for plasma facing and structural applications for DEMO is one the heaviest work tasks in the EUROfusion programme within HORIZONT2020 with the total budget exceeding 100ME. Tungsten and tungsten-based composites are presently considered as main candidates. 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.
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 of 20 dpa or even higher. Under these conditions, the mechanical properties of the materials are known to degrade radically due to (i) neutron irradiation, (ii) heat transients and (iii) plasma gas uptake. Consequently, the combination of these phenomena will define structural integrity.
The physical origin of the above mentioned effects has been investigated thanks to recent developments of physically-based modelling techniques operating at different time and space scales thus capturing variety of phenomena, such as: H/He permeation and retention, evolution of radiation induced microstructure, plastic flow in the presence of radiation defects, etc. Thus a valuable information regarding the microscopic level effects is present or can be extracted on the basis of currently established expertise (to which SCK-CEN made a significant and world-wide recognized contribution). Thus, the incorporation and overall integration of the microscopic phenomena into full-scale model is the next step. While fine scale descriptions (atomistic and mesoscale methods) should be used for the understanding of fundamental mechanisms of degradation of mechanical properties, reliable full scale (i.e. comparable to experimental size) representation is needed to minimize expensive experimental load and rationalize scarce experimental results to help development and qualification of tungsten for ITER and advanced tungsten-based grades for DEMO applications.