3.5. Materials Development and Test Introduction Materials R&D for ...

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Review of the ITER Technology R&D 3.5 Materials Development and Test The study of the different W grades at thermal fatigue and disruption simulation has been performed by the RF HT [49]. All tested tungsten grades show good thermal fatigue performance at proper armour design up to heat flux of 15 MW/m 2 . Rolled tungsten with texture orientation perpendicular to heat flow direction shows tendency of delamination at heat fluxes higher than about 5 MW/m 2 . Disruption simulation tests show that nearly all tungsten grades suffer from surface cracking except for single crystal tungsten. Thermal fatigue test at 20 MW/m 2 of mock-up after disruption simulation demonstrated that there is severe crack formation in almost all materials except for W-5Re-0.1ZrC alloy and W-0.02 Re single crystal alloy. Typically for bcc metals, neutron irradiation leads to an increase in the ductile-to-brittle transition temperature (DBTT) [44]. Based on the available data it could be concluded that all W grades have the problem of brittleness, at the expected fluence of 0.1-0.5 dpa in the region near the heat sink, for an irradiation temperature less than ~ 500°C. One of the findings from the R&D results is that the key issue is the proper design of the W armour (size of tiles and grain orientation). The recommended grain orientation is parallel to the direction of the heat flow, in which case possible delamination is not so critical. Based on the results of R&D the pure sintered W is recommended as reference material for divertor components. 3.5.3.3 Carbon Fibre Composites The R&D activity has been performed in EU and JA HTs and has been focused on the following directions [50]: - development of the new advanced CFCs (including doped) with improved properties, - characterisation of these new materials, Fusion Engineering and Design Page 18
Review of the ITER Technology R&D 3.5 Materials Development and Test - study of the critical issues as neutron irradiation and thermal shock/disruption. Significant progress has been achieved by the EU HT in the development of the new CFCs. Several new grades as Dunlop, 3D CFC Sepcarb ® NB31, silicon doped CFC with improved resistance to chemical erosion Sepcarb-inox NS31 have been developed [51, 52]. The key property for CFCs is thermal conductivity, for Sepcarb ® NB31 it is in a range 320 W/mK at room temperature. JA HT has developed new advanced 3D CFC NIC-01 with thermal conductivity ~ 540 W/mK at room temperature [53]. These new developed materials have been widely studied in comparison with existing grades with regards to effect of the neutron irradiation and thermal shock effect. For ITER condition (damage ~ 0.1-0.3 dpa and irradiation temperature 150-1200°C) the changes in properties are not expected to be crucial except for the thermal conductivity. CFCs with high initial thermal conductivity retain high conductivity after irradiation, but at low irradiation temperatures (less than 300°C) the thermal conductivity could be ~ 3-5 times lower than the unirradiated CFC [44]. The performances of mock-ups using the Sepcarb ® NB 31 and NIC-01 armour tiles have been studied including irradiation effects. Generally, the performance was as expected (higher temperature due to the loss of thermal conductivity). The decrease in the thermal conductivity due to neutron irradiation leads to an increase in thermal erosion under disruption conditions and this may have to be taken into account during the erosion lifetime assessment. Fusion Engineering and Design Page 19
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3.5. Materials Development and Test Introduction Materials R&D for ...

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