Quantification of radionuclides and associated radiological risk estimation of coal combustion residues from a South African coal-fired power plant

Background: Radionuclides occur in coal combustion residues, such as fly ash and bottom ash, which are by-products of coal combustion. They pose potential radiological risks to people present in the surrounding areas. Materials and Methods: Gamma spectrometry was performed to determine the radionuclide activity concentrations in a coal-driven power plant located in the Limpopo province, South Africa, to assess the radiological impacts of the ash stored in ash dumps adjacent to the plant. Results: The mean (+/- SD) activity concentrations were found to be 144.3 +/- 4, 62 +/- 2.1, and 315.9 +/- 4.9 Bq/kg for Ra-226, Th-232, and K-40, respectively, which are comparable to those found in previous studies. The radium equivalent activity was determined to be 258.43 Bq/kg. The average values of internal and external hazard indices were 1.09 and 0.70, respectively. With the exception of the internal hazard index, all the other indices were within the prescribed ranges indicated by the literature. Furthermore, the mean total annual effective dose received by plant workers was found to be 0.070 mSv/y, which is within the limit of 1.0 mSv/y prescribed by the IAEA. The average excess lifetime cancer risk value was 0.49 x 10(-3), which is higher than the UNSCEAR precautionary limit of 0.29 x 10(-3) but lower than the ICRP limit of 0.05 for low-level radiation. Conclusion: Ash dust inhalation was identified as the most significant exposure pathway among plant workers. However, the results demonstrated that storing of ash at this plant does not constitute any radiological threat to people in the adjacent regions.