The findings of the EU 'Materials Assessment Group' (MAG), within the 2012 EU Fusion Roadmap exercise, are discussed. MAG analysed the technological readiness of structural, plasma facing and high heat flux materials for a DEMO concept to be constructed in the early 2030s, proposing a coherent strategy for R&D up to a DEMO construction decision.A DEMO phase I with a 'Starter Blanket' and 'Starter Divertor' is foreseen: the blanket being capable of withstanding ≥2MW.yr.m -2 fusion neutron fluence (~20 dpa in the frontwall steel). A second phase ensues for DEMO with ≥5MW.yr.m -2 first wall neutron fluence.Technical consequences for the materials required and the development, testing and modelling programmes, are analysed using: a systems engineering approach, considering reactor operational cycles, efficient maintenance and inspection requirements, and interaction § Corresponding author. Address as 1. email: derek.stork@btinternet.com *Manuscript Click here to view linked References with functional materials/coolants; and a project-based risk analysis, with R&D to mitigate risks from material shortcomings including development of specific risk mitigation materials.The DEMO balance of plant constrains the blanket and divertor coolants to remain unchanged between the two phases. The blanket coolant choices (He gas or pressurised water) put technical constraints on the blanket steels, either to have high strength at higher temperatures than current baseline variants (above 650ºC for high thermodynamic efficiency from He-gas coolant), or superior radiation-embrittlement properties at lower temperatures (~290-320ºC), for construction of water-cooled blankets. Risk mitigation proposed would develop these options in parallel, and computational and modelling techniques to shorten the cycle-time of new steel development will be important to achieve tight R&D timescales. The superior power handling of a water-cooled divertor target suggests a substructure temperature operating window (~200-350ºC) that could be realised, as a baseline-concept, using tungsten on a copper-alloy substructure. The difficulty of establishing design codes for brittle tungsten puts great urgency on the development of a range of advanced ductile or strengthened tungsten and copper compounds.Lessons learned from Fission reactor material development have been included, especially in safety and licensing, fabrication/joining techniques and designing for in-vessel inspection. The technical basis of using the ITER licensing experience to refine the issues in nuclear testing of materials is discussed.Testing with 14MeV neutrons is essential to Fusion Materials development, and the Roadmap requires acquisition of ≥30 dpa (steels) 14MeV test data by 2026. The value and limits of pre-screening testing with fission neutrons on isotopically-or chemically-doped steels and with ion-beams are evaluated to help determine the minimum14 MeV testing programme requirements.

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The purpose of this paper is to review the lessons learnt on the use of advanced materials on the design and operation of components in fission reactors and to consider how these lessons can be employed to benefit the use of advanced structural and, to a certain extent, coolant channel materials in the design and qualification of the in-vessel and containment vessel components for the DEMO fusion reactor. The focus is on lessons learnt on methodologies that need to be applied, and a number of specific recommendations are made.

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