234U, 238U, 226Ra, 228Ra and 40K concentrations in feed coal and its combustion products during technological processes in the Upper Silesian Industrial Region, Poland

Abstract

Hard coal is the predominant energy source in Poland. The unavoidable consequence of coal combustion is the production of huge amounts of ash which can be concentrated in radionuclides. The ashes from coal combustion are utilized or stored and may affect the quality of the environment. Therefore, the estimation of radionuclides in hard coal and by-products is of crucial importance. The analyzed samples included ashes produced in ash furnaces, power plants and individual home furnaces operating in the Upper Silesian Industrial Region, Southern Poland, during the hard coal burning. This paper presents radioactivity concentrations of 228Ra, 226Ra and 40K in hard coal, bottom and fly ash samples from Polish coal-fired power plants obtained during various technological coal combustion processes and generated in individual domestic furnaces, determined using the HPGe gamma spectrometry technique. The measurements of 234,238U concentrations were performed after sample preparation using alpha-particle spectrometer. The concentrations of the obtained radionuclides differ greatly in the fly and bottom ash samples. The lowest concentrations of 226Ra, 228Ra, 234U, 238U were observed in bottom ashes from the co-firing of hard coal and biomass in a fluidized-bed furnace, whereas the highest concentrations of 226Ra (163 ± 6 Bq/kg), 228Ra (100 ± 2 Bq/kg) isotopes were found in the ashes from individual household furnaces. This means that both the feed coal type and combustion techniques have a direct impact on the concentration of radionuclides in ash. Hard coal silt samples may be enriched in radionuclides and the radioactive equilibrium between 226Ra and 238U even in the case of coal is not always achieved. The concentrations of the analyzed isotopes in ashes are 5-7-fold higher than in feed coal. Given that combustion by-products are utilized as construction products, it should be noted that for some ash samples, the radiological hazard indices approach or exceed the maximum permitted levels.