Technologically enhanced natural radioactivity level in fly ash produced in lignite-fired thermal power plant and assessment of radiological hazards

Abstract

Lignite coal is the primary local energy source in Türkiye. The inevitable result of the utilization of lignite coal in thermal power plants for electricity generation is the formation of large amounts of ash (bottom ash and fly ash) as industrial solid waste. These wastes contain technologically enhanced natural radionuclides in the uranium (238U) and thorium (232Th) decay series and radio-potassium (40K). Seyitömer lignite-fired thermal power plant (4 × 150 MW) located in the Central Western Anatolia Region of Türkiye produces approximately 1.6 million tons of siliceous fly ash per year. In this study, the utilization of these fly ashes in the construction industry and their storage in ash landfill areas were assessed by estimating radiological parameters and using the RESRAD Onsite 7.2 computer code. For this, the enhanced natural radioactivity levels of fly ash samples were determined by gamma-ray spectrometry with a high-purity germanium detector. The average activity concentrations of the natural radionuclides measured in fly ash samples were 621 ± 25 (40K), 150 ± 7 (226Ra), and 96 ± 3 (232Th) Bq/kg. The assessment results confirm that the studied fly ash samples are radiologically safe to be used in cement and concrete production in accordance with international and national standards without significant effects of radiological hazards. The RESRAD simulation results revealed that the total annual effective dose rate in the uncovered ash storage area reached its maximum (0.11 mSv/y) at 18.97 years, and the covering of the protective materials on top of the area significantly attenuated the gamma radiation in the decreasing order: concrete > soil > PVC > zeolite.