Development and Deployment of Welding Technologies for the Indian Sodium-Cooled Fast Reactor and Advanced Ultra-supercritical Thermal Power Programmes

Robust manufacturing technology for sodium-cooled fast reactor (SFR) components required development of various innovative welding technologies backed by thorough research. Construction of the 500 MWe Prototype Fast Breeder Reactor at Kalpakkam was preceded by extensive technology development which included planning and implementation of R&D on welding consumables and procedures and also technologies for fabrication of components with stringent specifications. To take on the challenges and establish robust manufacturing techniques for fabrication of all the structural components of the SFR, a close interaction among design, materials and non-destructive evaluation engineers, materials and welding consumable manufactures, and the fabrication industries had to be facilitated. Fabrication of SFR reactor vessels, steam generators, fuel sub-assemblies, etc., requires extensive welding. Activated tungsten inert gas (A-TIG) welding process together with activated flux was developed in-house. The same was successfully implemented on various SFR components. Online monitoring and control during welding was developed based on a computational intelligence methodology and deployed for obtaining near defect-free welded components. Plasma transferred arc welding process was used for deposition of a nickel-base alloy for hardfacing of SFR components, with improved resistance to high-temperature wear, especially galling of mating surfaces in liquid sodium environment. In order to substantially reduce carbon footprint, India has initiated a national mission programme for design, development and establishment of a 800 MWe Advanced Ultra-supercritical (AUSC) power plant having steam parameters of 710ºC/ 720ºC/ 310 bar. Success of this program heavily banks on development of materials and fabrication technologies that can sustain the extreme in-service conditions. Two important India-specific high-temperature tube materials were developed for the purpose, namely, 304HCu austenitic stainless steel (304HCu SS) and modified Alloy 617M. In addition, large cylindrical forgings of Alloy 617M of up to 800 mm diameter for turbine rotors were indigenously developed. R&D activities included development of welding consumables and welding procedure for TIG welding of tubes, including the 304HCu SS/Alloy 617M dissimilar joint. Based on the tensile and creep tests results, welding consumables for joining the tubes and their dissimilar joints were also finalized. Technology development also