On the modification of wire wrapping process for fast Breeder reactor fuel Pins: Replacing hydraulic crimping with resistance spot welding

In this communication we report a modification in the conventional design of wire wrapping process for fast reactor fuel pins and related results. The fuel pins for sodium cooled fast reactors are wire wrapped helically along the length of the pin. In the conventional design of wire wrapping the end of the wire is mechanically crimped prior to Tungsten Inert Gas (TIG) spot welding with the end plug. In the modified design, we have incorporated resistance spot welding (RSW) of the wire with the plug in place of the hydraulic crimping operation prior to TIG spot welding. The quality of the welds were evaluated by metallography and tensile testing. Digital Image Correlation (DIC) studies were carried out for strain mapping during tensile testing. The modified design resulted in enduring ∼ 23% more load than the conventional design before fracture. The failure location during tensile pull test of spacer wire was observed at the resistance weld location. DIC studies during tensile testing showed that maximum strain was experienced by the resistance spot weld. Incorporation of modified design will ease the bottom end plug welding and wire wrapping process in addition to substantial cost reduction in fabrication of end plugs.