The electrical conductivity of an 0.085 cm-thick layer of flame-sprayed alumina was examined as a function of temperature and of the specific power of an operating nuclear reactor. It was determined that the electrical conductivity of the alumina can be expressed as The first term on the right is the normal expression for ionic conductivity as a function of temperature. The second term accounts for the impurity conduction in the insulator and the third term assumes an ionized material in which Rutherford scattering plays a dominant role in the mobility of the electron-hole pairs created by photon interactions in the alumina. The assumption of electronic conductivity, a temperature-dependent mobility varying as T3/2, and a density of charge carriers proportional to the reactor specific power P is seen to hold over a temperature range up to 1300°K and up to reactor specific powers to 6 kW liter. An extrapolation of the results to higher specific powers shows the conductivity of Al2O3 adequate for nuclear thermionic systems.