TOPAZ‐II single cell thermoinic fuel element (TFE) electric insulation parameters under testing with electric heating were measured. TFE electric design schematic, experimental procedure and measurements results are described. Collector resistance was measured in helium at 420–890 K. Metal ceramic ceals insulation properties were measured in vacuum P=10−4 Pa and in cesium vapor P=10−1−260 Pa, at 420–730 K. Results of separate TFE are compared with the data; that were measured during nuclear power system (NPS) Ya‐21U test. Based upon this data NPS power losses were estimated.
