[en] High-temperature (2200⁰C) compatibilty tests were conducted at the Hanford Engineering Development Laboratory (HEDL) to select proper materials for commercial fabrication of fuel centerline thermocouples for Loss of Fluid Test (LOFT) reactor use. Materials investigated include the following: (a) beryllia (BeO), thoria (ThO₂) and hafnia (HfO₂) insulators, (b) molybdenum 48% rhenium (Mo48Re), tungsten 22% rhenium (W22Re), rhenium (Re), and rhenium/tungsten-augmented (Re/W-augmented) sheaths; (c) tungsten 3% rhenium versus tungsten 25% rhenium (W3Re/ W25Re) and tungsten 5% rhenium versus tungsten 26% rhenium (W5Re/W26Re) thermoelectric wires. Candidate materials had to withstand temperatures of up to 2200⁰C, pressures up to 17.2 MPa and neutron fluences of 7.2 x 10¹⁹ nvt