Extension wire for high temperature irradiation resistant thermocouples

In an effort to reduce production costs for the doped molybdenum/niobium alloy high temperature irradiation resistant thermocouples (HTIR-TCs) recently developed by the Idaho National Laboratory, a series of evaluations were completed to identify an optimum compensating extension cable. Results indicate that of those combinations tested, two inexpensive, commercially-available copper-nickel alloy wires approximate the low temperature (0 °C to 500 °C) thermoelectric output of KW-Mo (molybdenum doped with tungsten and potassium silicate) versus Nb-1%Zr in HTIR-TCs. For lower temperatures (0 °C to 150 °C), which is the region where a soft extension cable is most often located, results indicate that the thermocouple emf is best replicated by the Cu-3.5%Ni versus Cu-5%Ni combination. At higher temperatures (300 °C to 500 °C), data suggest that the Cu-5%Ni versus Cu-10%Ni combination may yield data closer to those obtained with KW-Mo versus Nb-1%Zr wires.