HTIR-TC Compensating Extension Wire Evaluations

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. As documented in this report, results indicate that of those combinations tested, two inexpensive, commercially-available copper nickel alloy wires approximate the low temperature (0 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 to 150 °C), which is the region where 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 (measured emfs were within 4% at 100 and 150 °C). At higher temperatures (300 to 500 °C), data suggest that the Cu-5%Ni versus Cu-10%Ni combination may yield data closer to that obtained with KWMo versus Nb-1%Zr wires (measured emfs were within 8%)