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 226Ra, 232Th and 40K. 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 226Ra, 232Th and 40K 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 226Ra, 232Th and 40K. 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.
Highlights
Measurements of radioactivity in Technologically Enhanced Naturally Occurring Radioactive Materials (TENORMs) are important from radiation protection point of view because more than 50% of the total dose to human population from natural sources of radiation is contributed by these materials [1]
Coal is technologically important material used for power generation and its fly ash is used in manufacturing of bricks, sheet, cement, land filling etc
Occurring radionuclides contribute most to environmental radiation. The concentration of these long lived radionuclides is usually low in the coal. When it is burnt in power plant, the fly ash that is emitted through the stack gets enriched in some of the radionuclide [2]
Summary
Measurements of radioactivity in Technologically Enhanced Naturally Occurring Radioactive Materials (TENORMs) are important from radiation protection point of view because more than 50% of the total dose to human population from natural sources of radiation is contributed by these materials [1]. Occurring radionuclides contribute most to environmental radiation The concentration of these long lived radionuclides is usually low in the coal. The combustion of coal results in the release of some natural radioactive elements into the environment and in the redistribution of these radioactive elements in the surface soil in the vicinity of coal-fired power plants. This can modify ambient radiation fields and population exposures [3]. This study seeks to determine the activity concentration of natural radionuclides in fly ash and soil samples collected in the vicinity of the power station and assess the radiological implication
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