The paper describes a passive method of determining the radioactivity level in the emission plumes of atomic power plants (APP) by the secondary emission of radiation from the plume. The emissions have been analyzed from the APPs that exploit the most common types of reactors, and the main beta-radionuclides involved in the emission have been determined. Taking into account the process of electron breeding in the atmosphere, the total energy spectrum of electrons has been obtained. Basic physicochemical reactions were considered resulting in the atomic hydrogen formation in the zone of the emission plume. The spatial distribution of atomic hydrogen concentration in the plume was calculated and the power of emission at 1420 MHz frequency from the volume was estimated. It has been shown that in estimating the radiation impact on the atmosphere we should consider many electron generations because they have mean energy values far exceeding the ionization potentials for atoms and molecules of the air components. It was found that the power emitted by 1 km3 volume at 1420 MHz frequency in the APP emissions can reach ~ 10-13 W. The comparison has been carried out with the results of field experiments based on detecting radiation at 1420 MHz from the emission plume of a nuclear reprocessing plant, from whence it follows that the above method enables one to reliably detect the total radioactivity of the APP emissions.