Fabrication of dummy fuel sub-assemblies for PFBR

Dummy fuel sub-assemblies (DFSA) were fabricated for core mechanics experiments, to validate prototype fast breeder reactor (PFBR) core restraint system, design and to check the mechanical interlock along with grid plate sleeve. The purpose of DFSA is to measure the displacement and interaction loads between sub-assemblies. It is planned to insert DFSA vertically in a grid plate sleeve model of diameter 2500 mm, which simulates grid plate (miniature size with 115 sleeves) of PFBR. Fabrication of DFSA at the Central Workshop Division (CWD) was aimed to evolve cost effective robust manufacturing methodology. A mock DFSA was fabricated to standardize and optimize the machining/fabrication parameters and process sequences and a procedure was evolved. Activated flux assisted gas tungsten arc welding (ATIG) technique is employed to join the long seam of hexagonal heaths. 110 DFSAs were manufactured meeting the stringent specifications. This article describes the mechanism and advantage of flux assisted automated ATIG over conventional GTAW and the manufacturing experience gained during fabrication of DFSA. (author)