HIGH TEMPERATURE GAS TURBINE FOR NUCLEAR GAS COOLED REACTORS: MATERIALS NEEDS AND LIFETIME MODELLING

摘要

Recent advances in the design of turbomachinery, recuperators and magnetic bearings provide the potential to develop a High Temperature nuclear Reactor (HTR) cooled with helium and directly coupled to a high-capacity helium turbine. The helium temperature at the core outlet is limited to 850°C. This constitutes a very high thermal load for the materials of the primary circuit components. Among these components, the turbine is the most heavily loaded one. CEA has launched research programs to evaluate high-temperature metallic alloys for the turbine disks and blades. High temperature corrosion, irradiation effect and long creep life will be the key issues to be considered for the selection of the materials. Materials issued from the aircraft and the land-based gas turbines industries constitute potential candidates but an extension of their qualification is needed for the prediction of their properties for long service times under helium and nuclear environment. Directionally solidified and single crystal nickel-based alloys with protective coatings are considered to be the best candidates for the blades. The large size of the disk required the use of a powder metallurgy material to avoid segregation phenomena occurring during the solidification of large highly alloyed ingots. Recent results obtained on a powder metallurgy Udimet 720LI material are given in terms of creep deformation mechanisms, and long term thermal stability. This material may be suitable for HTR application.