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

Abstract

Robust manufacturing technology for Sodium-cooled Fast Reactor (SFR) components necessitates development of various research-backed innovative welding technologies. Prior to the start of construction of the 500 MWe Prototype Fast Breeder Reactor, extensive technology development was planned and implemented for development of welding consumables, procedures and technologies for fabrication of components with stringent specifications. With close interaction amongst design, materials and non-destructive evaluation engineers, materials and welding consumable manufactures, and the fabrication industries, it has been possible to overcome the challenges and establish robust manufacturing technologies for fabrication of all the structural components. Extensive welding is involved in the fabrication of reactor vessels, steam generators, fuel sub-assemblies etc. Further, Activated Tungsten Inert Gas (A-TIG) welding process, along with activated flux developed in-house, has been successfully implemented on various SFR-related components. Also, a computational-intelligence based welding system for online monitoring and control during welding has been developed for obtaining near defect-free welded components. Plasma Transferred Arc Welding process has been deployed for deposition of the chosen nickel-base alloy for hardfacing of SFR components, which require improvement in resistance to high temperature wear, especially galling, of mating surfaces in liquid sodium. To reduce carbon footprint substantially, India has initiated a national mission programme of design, development and establishment of 800 MWe Advanced Ultra Supercritical (AUSC) power plant having steam parameters of 710°C / 720°C / 310 bar. Materials and fabrication technologies play decisive roles in the success of such mission project. For this purpose, two important India-specific high-temperature tube materials, 304HCu austenitic stainless steel (304HCu SS) and modified Alloy 617M, as also large cylindrical forgings of Alloy 617M of up to 800 mm diameter for turbine rotors have been indigenously developed. Development of welding consumables and welding procedure has also been established for TIG welding of the tubes, including the 304HCu SS/Alloy 617M dissimilar joint. Based on the tensile and creep tests properties, welding consumables for the tubes and their dissimilar joint have been finalized. Technology for dissimilar metal welding between Alloy 617M and 10Cr-steel forgings for turbine rotors has also been developed. Using narrow-gap TIG welding process, the dissimilar metal weld between 200 mm Alloy 617M and 10Cr-steel have been produced by directly welding the two forgings using Alloy 617 filler wire. The weld exhibited no lack-of-penetration defects and passed dye-penetrant, radiographic and ultrasonic examinations. Similarly procedure for NG welding of superheater headers has also been demonstrated. The details of the Indian efforts towards development and deployment of welding technologies for application to the fabrication to components for the Indian programmes for SFR-based nuclear power and AUSC thermal power plant are presented and discussed.