Retention of Tritium will be one of the key issues in the operation of future fusion devices (i.e. ITER and DEMO). The retention as a physical process is associated to the effects of Hydrogen isotopes being trapped in the first wall material. Generally, the retention of insoluble H/D/Ti and He is associated with the presence of imperfections in a crystalline structure which can be various types of lattice defects, such as vacancies, dislocations and grain boundaries, depending on thermo-mechanical treatment of material's grades. Retention is a crucial factor in such effects as: mechanical wall degradation, fuel management and contamination assessment. In the course of exploitation the microstructure of the first wall material will undergo stress-induced modification due to extensive plastic deformation. Hence, the trapping of Hydrogen in the operating conditions is to be addressed by a combination of expertise in plasma wall interaction and condensed matter science. Which is why experiments involving plasma exposure, deposition assessment and subsequent annealing need to be rationalized in terms of physical processes governing the uptake, bulk migration, bubble nucleation and growth to blisters. Naturally, the latter processes are related to initial microstructure, and its evolution within exposure cycle and subsequent thermal fatigue. By understanding the key physical processes determining retention and degradation of mechanical properties of materials as a function of plasma beam, exposure temperature and material's microstructure, it is possible to make step further towards development of 'controlled/predictable' retention grades with desirable characteristics.
Even though Tungsten is the baseline armour and divertor material for ITER, its intrinsic brittleness, even without irradiation, is a principal showstopper. Consideration of the reduced activation Ferritic Martensitic steels (RAFMS) is one of the options that will be explored in the European Fusion programme H2020. However, there is a lack of data about Hydrogen retention in the RAFMS grades, which by now are well characterized in terms of their performance under neutron irradiation.
This thesis will therefore contribute to the experimental studies of RAFMS, and it will focus on the mutual effects of severe plastic deformation and Hydrogen retention under various exposure conditions. Limited study on Tungsten grades will also be performed to provide the reference data.
To ensure the proper embedding of the researcher in the fusion technology environment, the work will be mainly carried out in the two laboratories from Belgium and Kingdom of Netherlands, namely: SCK•CEN (Nuclear Research Centre, Mol) and DIFFER (Netherlands).