Novel approach to plasma facing materials in nuclear fusion reactors

A novel material design in nuclear fusion reactors is proposed based on W-nDiamond nanostructured composites. Generally, a microstructure refined to the nanometer scale improves the mechanical strength due to modification of plasticity mechanisms. Moreover, highly specific grainboundary area raises the number of sites for annihilation of radiation induced defects. However, the low thermal stability of fine-grained and nanostructured materials demands the presence of particles at the grain boundaries that can delay coarsening by a pinning effect. As a result, the concept of a composite is promising in the field of nanostructured materials. The hardness of diamond renders nanodiamond dispersions excellent reinforcing and stabilization candidates and, in addition, diamond has extremely high thermal conductivity. Consequently, W-nDiamond nanocomposites are promising candidates for thermally stable first-wall materials. The proposed design involves the production of WAV-nDiamondAV-Cu/Cu layered castellations. The W, W-nDiamond and W-Cu layers are produced by mechanical alloying followed by a consolidation route that combines hot rolling with spark plasma sintering (SPS). Layer welding is achieved by spark plasma sintering. The present work describes the mechanical alloying processsing and consolidation route used to produce W-nDiamond composites, as well as microstructural features and mechanical properties of the material produced Long term plasma exposure experiments are planned at ISTTOK and at FTU (Frascati)

Influence of gas environment on synthesis of silicon carbide and some carbides and carbonitrides of d-group transition metals through reaction between metal powders and amorphous carbon powders in a solar furnace at P.S.A. (Plataforma Solar de Almería)

Refractory carbides and carbonitrides including silicon carbide SiC, tungsten carbide WC, titanium carbide TiCx (0.5<x<l) and titanium carbonitride TiCxNy (0.5<x+y<l) were synthesised from compacted pellet composed of metal powders and amorphous carbon powders through heating in a solar furnace under controlled atmosphere (Ar or N2). Under irradiation of the solar energy flux 1,350 kW/m2 (ca. 1650°C in terms of measured temperature) for 30 min in Ar atmosphere, Si, W and Ti were converted to SiC, WC and TiCx, respectively. By the similar reaction undertaken in N2 atmosphere, Si and W were converted to SiC and WC, respectively, but carbonitride TiCxNy formed from Ti. No special influence of atmosphere was detected on the WC formation, but conversion to SiC from Si was somewhat retarded in N2 atmosphere. In either Ar or N2 atmosphere, progress of graphitisation of amorphous carbon was not detectable by X-ray diffraction analysis in the reaction with Si and Ti but graphitisation of amorphous carbon appeared to be significantly accelerated in the reaction with W

LOW-TEMPERATURE NITRIDING OF VA -GROUP METAL POWDERS (V, Nb, Ta) IN FLOWING NH 3 GAS UNDER HEATING WITH CONCENTRATED SOLAR BEAM AT PSA

Abstract Over the last two decades, we have been using concentrated solar beam as the reaction heat source for synthesizing carbides and nitrides of d-group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or gas. In recent works [1,2] nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH 3 gas with suppressed extent of dissociation (uncracked NH 3 ) was attempted under heating with concentrated solar beam. It was demonstrated that mono-nitride -MoN of Mo and sub-nitride -Fe 2 N of Fe that are known to be impossible to synthesize in N 2 gas environment even at elevated pressure p(N 2 ) were successfully synthesized by the reactions of these metals in stream of NH 3 gas under heating with concentrated solar beam up to 800ºC. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH 3 gas under irradiation of concentrated solar beam. By up to 90 min heating in uncracked NH 3 under concentrated solar beam up to 800ºC, reaction products were identified by X-ray diffraction (XRD) analysis to be consisted of mono-nitride MN co-existent with sub-nitride M 2 N