Indian Test Blanket Module in ITER - Development of RAFM Steel and Fabrication Technology

Abstract

A detailed and comprehensive programme is undertaken in India to fabricate Indian Test Blanket Module (TBM) to be tested in ITER. Development of India-specific Reduced Activation Ferritic/Martensitic (RAFM) steel has been realized through melting and physical and mechanical properties characterization of several heats of 9Cr-RAFM steel with varying tungsten and tantalum contents. The RAFM steel having 1.4 wt. % tungsten and 0.06 wt. % tantalum is found to possess better combination of strength and toughness and is considered as India-specific RAFM steel. Different joining processes for fabrication of TBM have been assessed. Hot Isostatic Pressing (HIP) has been demonstrated to fabricate the first wall of TBM. To avoid channel collapse during HIPing, leachable ceramic cores were inserted in the channels. Electron Beam (EB) and Laser Welding processes are used for fabrication of breeder cassettes and hence, these welding procedures have been developed. Tungsten Inert Gas (TIG), Narrow Gap TIG (NG-TIG) and Laser Hybrid welding processes are being considered for integration of the various components such as first wall, back plate, bottom plate, breeder assembly and flow dividers into TBM. RAFM steel welding consumables have also been developed and qualified. Procedure for laser hybrid welding has also been developed. Necessary technologies for inspection and quality assurance of the fabricated TBM are also being developed. Use of ultrasonic C-Scan imaging to examine the bond integrity of the HIP joint has been demonstrated. Phased Array technique that would enable inspection of welds by longitudinal movement of the probe from an optimised lateral distance of the weld without the requirement of lateral movement has also been developed. The challenges in developing the India-specific RAFM steel and the fabrication and inspection technologies for fabrication of Indian TBM are presented.