Thermal conductivity of neptunium dioxide

The thermal diffusivity of neptunium dioxide was measured in the temperature range from 473 to 1473 K by using a laser flash method. The thermal diffusivity slightly decreased with increasing temperature in the temperature range investigated. The heat capacity of NpO₂ was measured in the temperature range from 334 to 1071 K by using a drop calorimetry method. The heat capacity of NpO₂ determined in this study was slightly larger than that of UO₂ and about 7% smaller than that of PuO₂. The thermal conductivity of NpO₂ was determined from the thermal diffusivity, the heat capacity and the bulk density. It was found that the thermal conductivity of NpO₂ from 873 to 1473 K lay between those of UO₂ and PuO₂