High temperature materials and their welding for nuclear and thermal power plants

As India makes efforts to reduce carbon emission from power plants, there is interest in adopting Fast Breeder Reactor (FBR) technology for nuclear and Advanced Ultra Super Critical (AUSC) technology for fossil-fuel plants for power production. This necessitated indigenous development of improved high-temperature materials and associated welding technologies for fabrication of components for FBRs and AUSC plants. For FBRs, Alloy D9 (15Cr-15Ni-2Mo-Ti SS) for fuel clad-tubes, 316L(N) SS (0.08%N max.) for most reactor structures and Grade-91 steel for steam generators have been chosen. For future FBRs, Alloy D9I with improved radiation swelling resistance, 316L(N) SS with enhanced nitrogen (0.12%) for improved high-temperature mechanical properties, and Grade-91 steel with controlled boron and nitrogen addition for improved Type-IV cracking resistance were developed along with appropriate welding consumables and technologies for these materials. For AUSC power plants India-specific 304HCu SS and Alloy 617M boiler-tubes, appropriate welding consumables, and procedures for manual and automated orbital TIG welding of their similar and dissimilar joints were developed. Also, Alloy 617 forgings for turbine-rotor, Alloy 625 castings for turbine-casing, their welding consumables, and procedure for dissimilar welding of 10%Cr-steel and Alloy 617M forgings by hot-wire narrow-gap TIG welding of upto 400 mm diameter turbine rotors were developed. (author)