Fuel rod simulator fabrication requires creative joining techniques

Laser welding and furnace brazing techniques have been used to join subassemblies for fuel rod simulators (FRSs) that have survived up to 100 h steady-state operation at 700 to 11000C cladding temperatures and over 5000 thermal transients, ranging from 10 to 1000C/s. A pulsed-laser welding procedure uses small-diameter filler wire to join one end of a resistance heating element to a tubular conductor. The other end of the heating element is laser welded to an end plug, which in turn is welded to a central conductor. Before these welding operations the intermediate material conductor (either tubular or rod) are vacuum brazed to matching copper leads. On room-temperature tensile testing, 10 of 11 brazements between copper and nickel rods failed in the copper rather than the brazement