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The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials programme is to develop structural and armor materials in combination with the necessary production and fabrication technologies for reactor concepts beyond the International Thermonuclear Experimental Reactor. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on ''Materials Science and Modelling.'' This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on materials research, fabrication, joining, high heat flux testing, plasticity studies, modelling, and validation experiments.Corresponding author. Michael Rieht

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Scanning electrochemical microscopy ͑SECM͒ is used to image variations in electrochemical activity over the surface of an aluminum-based metal matrix composite ͑MMC͒ in contact with buffered or unbuffered neutral solutions. The composite consists of an Al-13.5% Si-9% Mg alloy matrix and reinforcing silicon carbide particles (SiC p ). Feedback-mode SECM imaging using ferrocenemethanol as a redox mediator in 0.1 M NaCl solution and in buffer solution ͑pH 6.8͒ revealed that the SiC particles are electrochemically active. The data suggest that the electronic conductivity at these sites is higher than that of the Al 2 O 3 film covering the alloy matrix surface. The reduction of dissolved oxygen on the silicon carbide particles was investigated by in situ SECM images of samples and current vs. tip-substrate distance curves. The results with samples of SiC p /Al composites immersed in distilled water alone or in either 0.1 M NaCl or boric acid/borax buffer containing ferrocenemethanol as mediator demonstrate that the silicon carbide particles are conductive and act as local cathodes for the reduction of oxygen.

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Stress corrosion cracking (SCC) of stainless steel components in boiling water reactors (BWR) can threaten their structural integrity and leads to costly maintenance operations. A low electrochemical corrosion potential (ECP) can reduce the susceptibility of stainless steel to SCC. Injecting hydrogen into the reactor feed water lowers the ECP. The efficiency of hydrogen injection is improved in presence of catalytically active noble metals. Therefore, platinum (Pt) compounds are added to the reactor feed water and then deposit on the water-wetted surfaces. To understand the parameters affecting the application and mitigation processes, stainless steel coupons in as-received or pre-oxidized condition were exposed in a high-temperature water loop to simulated BWR water conditions with addition of Pt. Coupons were placed at three locations: i) in an autoclave with quasi-stagnant flow conditions (few mm/s), ii) in a specimen holder with a flow velocity of 0.10 m/s, iii) and in another with a flow velocity of 0.52 m/s. Independently of parameters such as Pt injection rate or water chemistry, coupons exposed to a transitional flow regime showed a lower Pt loading than the coupons exposed to a turbulent flow or suspended in the autoclave under quasi-stagnant flow.

Electrodeposited nickel and nickel-yttrium oxide composite samples were studied in situ using scanning electrochemical microscopy (SECM). The monitored probe currents in phosphate-citrate buffer (pH 4.2) in the presence or absence of normalRufalse(NH3)63+ as an oxidizing mediator near the Ni surface show that the SECM is a useful tool for studying the electrochemical activity of heterogeneous metal surfaces at micrometer scales. The SECM ultramicroelectrode probe tip provides information about the shape, activity, and location of particles, such as Y2O3 introduced (codeposited) in the Ni matrix of the composite. Experiments show that the Ni matrix in the composite coating is more active than the pure Ni coating. This fact is expected, because of texture changes in the Ni structure upon introduction (by codeposition) of Y2O3 particles. In the absence of a mediator in the solution, the electrochemical activity of heterogeneous metal surface at a microlevel is investigated by using O2 concentration changes. The rate of reaction for O2 reduction was found to vary locally at electrodes floating at the open-circuit potential (OCP) when compared to an electrode potentiostatically polarized at a more positive potential than the OCP. This behavior suggests that local anode and cathode regions are being observed at the OCP sample. © 2002 The Electrochemical Society. All rights reserved.