Abstract. The study presented here, being its main goal to evaluate the behaviour of natural radionuclides in coal combustion, is part of a wider study carried out by CIEMAT and the University of Extremadura (UEX). The research is addressed to the radiological evaluation of the workers and the public as a result of the operation of the four biggest Spanish Coal-Fired Power Plants (CFPPs). Some generally used effects were confirmed in this study, as the difference in concentration of 210 Po in fly and bottom-ashes. Enrichment factors relative to 40 K as defined by UNSCEAR were found to be a little different than expected. 210 Po enrichment was found in gypsum (material obtained as a by-product in the desulphuration process). In order to confirm the assumption considered to explain difference in 232 Th activity concentration between bottom and fly ashes, carbon content was measured, obtaining that it should be reviewed.

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The production of electricity in coal-fired power plants (CFPP) is considered a NORM (Naturally Occurring Radioactive Materials) activity because the coals they burn can present relatively high contents of the naturally occurring radionuclides. In this study, the main radiological impact pathways into the surrounding environments of the four largest coal-fired power plants in Spain were analyzed. These pathways are, first, atmospheric evacuations and wind resuspension and, second, effluent evacuations to nearby rivers or directly to the sea. The atmospheric releases of radionuclides were evaluated by the analyses of soil profiles in the vicinities of the CFPPs. No significant enhancement of radionuclides in the surface soil was observed at the points of maximum deposition of combustion gases, located from 4.3 to 13 km away depending on the considered CFPP. However, an increase of (40)K, (226)Ra, and (232)Th in the surface soils was observed in the first kilometre from the chimney for two CFPPs. This suggested that these radionuclides were released in particulate form. There was also a net influence of the climate in which the CFPPs were located. This was observed in the two CFPPs that were in dry environments, while no increase was observed in the other two, located in more humid environments. The liquid effluents released usually presented an enhancement of dissolved chemical species regarding the initial intake water. Enrichments of the (234,238)U and (226)Ra contents in the water used in the plants' routine procedures were observed, and of (210)Po in the wastewater of just one of the plants. In any case, this enhancement was below the parametric value for the Total Indicative Dose for the hypothetical human consumption of the released waters. As a consequence of these releases of radionuclides, local products destined for human consumption produced in the vicinity of the facilities might incorporate natural radionuclides by these pathways, finding no significant enhancement of the natural radionuclide contents due to the CFPPs.