Protective and structural materials for fusion reactors: Main challenges, long-term materials development needs, differences and commonalities with fission

Full text: Developing plasma-facing and structural materials with Low nuclear Activation (LA), high heat and radiation resistance, is a challenge that the materials community has to address to enable reliable development and safe operation of fusion reactors in the future. This requires scientific innovation, new knowledge, and the exploration of a range of new materials. To address this challenge, the EU fusion programme has set up a Fusion Materials Topical Group to strengthen coordination of long-term fusion materials development for DEMO, and to undertake physically based modelling of radiation induced microstructure and degradation of mechanical properties required to guide the experimental developments. In this paper we describe main radiation effects induced by the intense flux of 14 MeV neutrons in the reference structural materials (i) for Tritium-Breeding Blanket (TBB) modules, LA Ferritic/Martensitic Steel EUROFER, Oxide Dispersion (ODS) EUROFER and ODS ferritic steels, and, (ii) for the divertor, W and W-alloys. Specific issues concerning the peculiar microstructure induced by the impact of α particles on the surface of tungsten, foreseen as a reference protection material, will also be discussed. Modelling radiation effects in EUROFER under fusion reactor relevant conditions is the first priority for the programme, in order to inter-correlate the data obtained with various neutron spectra, contribute to the definition of the irradiation matrix in the future intense source of 14 MeV neutrons, IFMIF, and bring comprehensive understanding and extrapolation capabilities towards the very large range of DEMO operating conditions. Formulating and developing predictive modelling tools is therefore a task of prime significance. Particular care has been taken (i) to focus the modelling effort on the scale where physics can be mastered, i.e. on the scale of the chemical bond, which is triggered by electronic correlation in the case of Fe-Cr system and body cubic centred steels, and, (ii) to validate model prediction at the relevant scale and on the adequate system. The paper will present modelling results based on ab-initio calculation and the development of kinetic tools describing (i) phase stability of Fe-Cr alloy system taking magnetic effects explicitly into account, (ii) point defects energetics in transition metals and their recovery in α-Fe (iii) He and dpa accumulation, and (iv) dynamical properties of dislocations in α-Fe at low and high temperatures. Based on the successful progress of the currently on-going research programme, the Strategic Objectives defined for the next period 2010-2015 (http://www.efda.org/eu_fusion_programme/scientific_and_technical_publications.htm) will be presented and briefly discussed. (author)