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Abstract
AREVA group produces reactor coolant pumps (RCP) for nuclear power plants (NPP) worldwide. AREVA and partners aim at improving its mechanical performances in agreement with the lifetime extension politics of NPP. Initially made by casting and machining, the RCP impeller could be now obtained by forging and machining. Despite it is bringing an improvement of mechanical characteristics, this solution requires extensive machining of up to 80% of a 4 ton ingot. HIPPI project aims at developing the manufacturing sequence and elaborating large dimension impellers by implementing powder metallurgy and HIP. It also aspires at acquiring sufficient data to justify the introduction, in a NPP, of a new super-austenitic steel grade enhancing mechanical properties and corrosion resistance of impellers. Moreover, a specific NDE tool is being developed to simultaneously check the health of the part and get its full dimension inside the container. Finally, an economic study is engaged to assess the interest of this solution.
I-Introduction
The national and international contexts of the metallurgy industry are in profound evolution with, in particular, a globalization of its businesses and a reinforcement of the competitive context. To maintain the competitiveness of the metallurgy industry in France it seems indispensable to promote now a real strategy of development centered on innovation and medium and long-term profitability. The manufacturing of large parts with complex shapes, close to the final dimensions, is a crucial point for high-technology industries such as the nuclear power and the aeronautics. In particular, the homogeneity of the microstructure and the acceptable surface finishes are the main quality criteria for the manufacturers of heavy components.
Large components with complex shapes, such as impellers, were traditionally manufactured by casting. However, in the last years, alternative approaches consisting of machining impellers from a forged ingot have appeared in the market place. Of course, this solution offers an improvement of the mechanical characteristics but, in the case of a Reactor Coolant Pump (RCP) impeller, it is necessary to start with a 4000 kg ingot to finish with a 700 kg impeller, resulting in the scrapping of 80% of the material. This observation is also valid in the field of aeronautics where impellers for gas turbines are elaborated by a forging/machining process with a mass ratio of 10...