Radiation doses of inhaled ash from the lignite power plants

The coal-fired thermal power plants in Macedonia use lignite obtained by surface mining. The lignite contains traces of thorium-232, uranium-238 and uranium-235, which are long-lived natural radioactive isotopes. After lignite combustion, the concentration of these isotopes in the ash is increased. Due to long age of fossil materials, the decay products are basically grouped in three radioactive chains that are in a semi-steady state, resulting in equal activity of all isotopes from the chain. Among the members of each chain there are α and β emitters, which are also γ quanta emitters. The energies of the α and β particles are important for determining the effective dose. The γ quanta provide information about the chain activity and isotope types. Gamma-spectroscopy studies of the ash samples from the power plants in the region of the City of Bitola in Macedonia have continued the presence of several radioactive decay products from the uranium and thorium radioactive chains. Using measurements of the radioactivity of the ash in the Bitola region, the total dose from ash inhalation for the population in the Bitola region was calculated and presented in this paper. Also, analysis of the procedure for determining the maximum allowable dose from radioactive contamination of the environment, is described in this paper. (author)