بررسی فنی فعالیت تحقیق و توسعه در برنامه ریزی منابع انسانی در فرآیند تولید

ENEA and Ansaldo Nucleare S.p.A. have been deeply involved in the European International Thermonuclear Experimental Reactor (ITER) R&D activities for the manufacturing of high heat flux plasma-facing components (HHFC), and in particular for the inner vertical target (IVT) of the ITER divertor. This component has to be manufactured by using both armour and structural materials whose properties are defined by ITER. Their physical properties prevent the use of standard joining techniques. The reference armour materials are tungsten and carbon/carbon fibre composite (CFC). The cooling pipe is made of copper alloy (CuCrZr-IG). During the last years ENEA and Ansaldo have jointly manufactured several actively cooled monoblock mock-ups and prototypical components of different length, geometry and materials, by using innovative processes: HRP (hot radial pressing) and PBC (pre-brazed casting). The history of the technical issues solved during the R&D phase and the improvements implemented to the assembling tools and equipments are reviewed in the paper together with the testing results. The optimization of the processes started from the successful manufacturing of both W and CFC armoured small scale mockups thermal fatigue tested in the worst ITER operating condition (20 MW/m2) through the achievement of record performances obtained from a monoblock medium scale mockup. On the base of these results ENEA-ANSALDO participated to the European programme for the qualification of the manufacturing technology to be used for the procurement of the ITER divertor IVT, according to the F4E specifications. A divertor inner vertical target prototype (400 mm total length) with three plasma facing component units, was successfully tested at ITER relevant thermal heat fluxes. Now, ANSALDO and ENEA are ready to face the challenge of the ITER inner vertical target production, transferring to an industrial production line the experience gained in the development, optimization and qualification of the PBC and HRP processes.

The ITER operation programme foresees for the IVT strike point region, a steady state thermal flux of 10 MW m−2 and shorter transients during which the heat flux can reach up to of 20 MW m−2. The plasma facing units are identified as the plasma facing components that have to deal with these high thermal and particles loads. Such high heat fluxes can be sustained only by components designed and manufactured accordingly. The technical design solutions have to guarantee a reasonable lifetime and to be affordable. The lifetime is limited mainly by thermal fatigue caused by cyclic thermal loads that induce high mechanical stresses to these components. The technical solutions considered today for the PFU of the ITER divertor IVT are mainly based on carbon or tungsten as plasma facing materials and copper alloys for the heat sink [1]. The selection of these materials is based on ITER physical and thermo-mechanical requirements [1]. Tungsten is a refractory metal with an extremely high melting point (3410 °C) and a RT thermal conductivity of approx. 140 Wm−1 K−1. Its brittle behaviour will not impact its fatigue performances because it is used as functional armour material. Similar considerations can be applied to carbon materials, like carbon-fibre reinforced carbon matrix composite (CFC), when used in IVT because it can withstand very high-heat loads without the risk of melting. However, sublimation of carbon at elevated temperatures (T > 2200 °C) and tritium retention has to be considered as important issues. Different requirements are foreseen for the heat sink. It has been identified in general terms as a precipitation hardened copper alloy structure that, by means of pressurized water coolant, is able to remove the incoming thermal load. To reduce stresses thermally induced by the thermal gradient during plasma exposure and enhanced by the mismatch of the CTE of the plasma facing (armour) and the heat sink materials, a pure copper compliant layer is used between them two.

It can be stated that the present design of the ITER divertor has reached a technically mature level. That has been made possible by an intense collaboration among ITER Organization, F4E, the EURATOM Associations, other international partners and with industry during the past few years. The ITER design has requested to all these entities a big effort to keep up with its evolution. This effort has been supported by an intense R&D programme to which ENEA and ANSALDO have participated too. Design improvements, qualification of the materials for the plasma facing armour and for the heat sink have been transferred to the manufacturing processes (HRP and PBC) by keeping a high level of reliability still fulfilling the ITER requirements. These achievements were obtained by the production of numerous small-scale mockups which were benchmarked by non-destructive analyses and extensive qualification HHF tests. Following the experienced skill coming from all these activities, including the qualification prototypes production, ANSLDO NUCLEARE and ENEA are ready to scale-up towards the full scale prototyping by continuing their R&D activity on the ITER divertor.