Assessment of Natural Radionuclides in Fly Ash Produced at Orji River Thermal Power Station, Nigeria and the Associated Radiological Impact

Abstract

Coal fired power plants produce significant amounts of ashes, which are quite often being used as additives in cement and other building materials. Coal contains trace quantities of 226 Ra, 232 Th and 40 K. The concentrations of these radionuclides are usually low in the coal, but enriched in fly ash. The activity concentrations of natural radionuclides in fly ash and soil samples in the vicinity of Orji River thermal power station in Nigeria was determined by gamma ray spectroscopy method using NaI(Tl) detector. The mean activity concentrations of 226 Ra, 232 Th and 40 K in the fly ash were 40.8 ± 11.6, 49.1 ± 9.3 and 321 ± 17 Bq•kg −1 , respectively. Coarse fly ash collected from the dump site had mean activity concentrations of 28.2 ± 8.3, 37.6 ± 5.0 and 335 ± 32 Bq•kg −1 , respectively for 226 Ra, 232 Th and 40 K. Soil samples collected at about distances of 10 m from the dump site had 32.7 ± 4.3, 40.0 ± 4.2 and 298 ± 15 Bq•kg −1 , respectively. Those collected at about distances of 100 m from the dump site had 39.1 ± 11.2, 34.1 ± 5.2 and 257 ± 19 Bq•kg −1 , respectively. Occupational dose received by workers due to exposure to the fly ash ranged between 33.0 and 61.2 µSv•y −1 with a mean value of 47.1 ± 8.4 µSv•y −1 , which is below the intervention exemption level of 1 mSv•y −1. The radium equivalent activity concentration, external and internal hazard indices of the fly ash were below the recommended maximum values for building materials. The mean outdoor absorbed dose rate and the annual effective dose obtained in the vicinity of the plant were 49.7 ± 4.0 nGy•y −1 and 0.30 ± 0.02 mSv (dump site), 51.7 ± 3.6 nGy•y −1 and 0.32 mSv (soil 10 m from dump site), 49.4 ± 4.9 nGy•y −1 and 0.30 ± 0.03 mSv (soil 100 m away from dump site), which are lower than the world average. The results obtained in this study show that there is no significant radiological impact of the fly ash on both the workers and the public from radiation protection point of view.

Radionuclide concentration: The coal ash effect

“…Finally, the external and internal indices of the three samples of coal ash, mixed soil and non-mixed soil were below the standard of 1 which is the acceptable international standard (Solehah et al, 2016). Thus, there is no significant risk posed by the coal ash and nonmixed soil as similarly observed by Kolo et al (2016) and Ademola and Onyema (2014). On the other hand, immediate radiological risk exists for mixed soil due to soil and coal ash interaction (Kolo et al, 2016).…”

Radiological Hazard Assessment for Fly Ash and Environmental Materials From Morupule a Coal - Fired Power Station in Botswana

“…The average Ra eq values for all the fly ash, coal, soil and water samples are below the internationally accepted value of 370 Bq/kg. The average values of H ext and H int for all the fly ash, coal, soil and water samples are also below the internationally accepted value of unity [Ademola and Onyema, 2014]. The average values of for all coal, soil and water samples are also below the the internationally accepted value of unity [Harb et al, 2008].…”

“…Radiological hazard assessment Soil and fly ash from the study area may be used as building material. Fly ash is an excellent substitute for concrete, cement and clay [Ademola and Onyema, 2014]. The radium equivalent activity concentration (Ra eq ), external hazard (H ext ) and internal hazard (H int ) indices are used to assess the radiological hazard due to natural radioactivity from the fly ash, coal, soil and water which may be used as construction material.…”

“…Ra eq index basis is on the estimation that the same gamma dose rate is produced by 1 Bq/kg of 226 Ra, 0.7 Bq/kg of 232 Th and 13Bq/kg of 40 K. In order to ensure that bulding materials are safe to use with respect to radiation, the maximum Ra eq for these materials must not exceed 370 Bq/kg. The maximum allowed values for H ext and H int are unity and dimensionless [Ademola and Onyema, 2014]. The representative level index I γr is a radiation index hazard that is used to esimate the level of γ radiation hazard [Harb et al, 2008;NEA-OECD, 1979] due to natural radionuclides in samples and is represented by Equation 4 below:…”

Assessment of the Radiation Hazard Indices from Terrestrial Radiation in Mining Sites in Benue State, Nigeria

“…The AEDE can give a clue on indication radiological contamination in an outdoor environment which may result to inhalation of high level of radon gas emitted and its progeny from the mining activity that can lead to lung cancer from accumulated doses [15]. absorbed gamma dose rates were used to calculate the annual effective dose equivalent (AEDE) received by individuals within and around the selected mining fields.…”