ENEA and Ansaldo Nucleare S.p.A. (EA) have been deeply involved in the European International Thermonuclear Experimental Reactor (ITER) research and development activities for the manufacturing of high-heat-flux plasma-facing components and in particular for the inner vertical target (IVT) of the ITER divertor.
These components have to be manufactured by using both armor and structural materials whose properties are defined by ITER. Their physical properties prevent the use of standard joining techniques. The reference armor materials are tungsten and carbon/carbon fiber composite (CFC), and for the cooling pipe, the materials are a copper alloy (CuCrZr).
During the last years EA have jointly manufactured several actively cooled mock-ups and prototypical components of different lengths, geometries, and materials by using innovative processes: hot radial pressing (HRP) and prebrazed casting (PBC).
The HRP technique is based on radial diffusion bonding between the cooling tube and the armor material obtained by pressurizing only the cooling tube while the joining zone is kept in vacuum and at the required bonding temperature. The heating is obtained by a standard air furnace.
The PBC process is used for the CFC armor tile preparation. A soft copper interlayer between the tube and armor is necessary to mitigate the stress at the joint interface, and it is obtained by pure copper casting that follows the activation of the CFC surface by a standard brazing alloy.
The optimization of the processes started from the successful manufacturing of both tungsten and CFC small-scale mock-ups and successful testing under the worst ITER operating condition (20 MW/m2) through the achievement of record performances obtained from a medium-scale vertical target CFC and tungsten armored mock-up: After ITER-relevant heat flux fatigue testing (20 MW/m2 for 2000 cycles, CFC part, and 15 MW/m2 for 2000 cycles, tungsten part), it reached a critical heat flux of 35 MW/m2 at ITER-relevant thermal-hydraulic conditions.
Based on these results EA participated in the European program for the qualification and manufacturing of the divertor IVT, according to the Fusion for Energy (F4E) specifications. A divertor IVT prototype (400-mm total length) with three plasma-facing-component units was successfully tested at ITER-relevant thermal heat fluxes (20 MW/m2 for 3000 cycles, CFC part, and 15 MW/m2 for 3000 cycles, tungsten part).
Now, EA are ready to face the challenge of the ITER IVT production, transferring to an industrial production line the experience gained in the development, optimization, and qualification of the PBC and HRP processes.