High Temperature Thrmocouples in the Rover Program

Tungsten/tungsten-rhenium thermocouples have been successfully used for various hydrogen gas temperature measurements in the Kiwi-A reactors of the Rover nuclear propulsion program. The most useful combination for these thermocouples has been tungsten coupled with a tungsten-25 weight percent rhenium alloy. This alloy exhibits a solidus temperature slightly over 3100°C., has considerably more room temperature ductility than tungsten, and yields an electromotive force of about 40 millivolts against tungsten at 2300°C. In one design 60 mil W and W-Re wires are pressed and swaged into a tungsten block. The wires are passed through an insulated pressure seal. The time response of the thermocouple is in the one second range. These thermocouples may be used in an automatic exit gas temperature control system in some subsequent Rover tests.