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Energy & Fuels 2008, 22, 428–432
Radiological Characterization around the Afsin-Elbistan Coal-Fired Power Plant in Turkey Ugur Cevik,*,† Nevzat Damla,† Bahadır Koz,‡ and Selim Kaya† Department of Physics, Karadeniz Technical UniVersity, 61080 Trabzon, Turkey, and Department of Biology, Giresun UniVersity, Giresun, Turkey ReceiVed July 3, 2007. ReVised Manuscript ReceiVed October 10, 2007
A radiological characterization of soil samples around the Afsin-Elbistan coal-fired thermal power plant in the Mediterranean region of Turkey was carried out. Moreover, activity concentrations and chemical analyses of coal samples used in this power plant and fly ash and slag samples originating from coal combustion were measured. For this purpose, coal, fly ash, slag, and soil samples were collected from this region. The analysis shows that the samples include relevant natural radionuclides such as 226Ra, 232Th and 40K. The mean activity concentrations of 226Ra, 232Th, and 40K were 167, 44, and 404 Bq · kg-1, respectively. Obtained values shows that the average radium equivalent activity, air-absorbed dose rate, annual effective dose, and external hazard index for all samples are 258 Bq · kg-1, 121 nGy · h-1, 148 µSv · y-1, and 0.7, respectively. The environmental effect of natural radionuclides caused by coal-fired power plants was considered to be negligible because the Raeq values of the measured samples are generally lower than the limit value of 370 Bq · kg-1, equivalent to a gamma dose of 1.5 mSv · y-1. A comparison of the concentrations obtained in this work with other parts of the world indicates that the radioactivity content of the samples is not significantly different.
1. Introduction Fossil fuels such as coal and lignite play an important role in electric power generation worldwide. Coal, lignite, and their combustion residues (fly ash and bottom-ash or slag) contain trace elements, including the naturally occurring radionuclides such as 238U, 226Ra, 210Pb, 232Th, and 40K. The fractions of the combustion residues collected at different points following their pathway inside the power plant have different radiological characteristics, such as natural radioactivity content and radon exhalation rate. Since the produced ashes may be either disposed off, or further utilized in other applications such as the building materials industry, it is very important to study in detail the radiological characteristics of their various fractions. Furthermore, a detailed knowledge of the radiological characteristics will allow for a better determination of the radiation exposure, both occupationally and publicly, caused by the produced ashes.1 Moreover, when coals are burned in coal-fired power plants, the remains such as coal slag and fly ash become 3–5 times more enriched in naturally occurring radionuclides than the coals themselves. The majority of the ash is the so-called bottom ash or slag that can be kept under control. But some small proportion of the ash, called the fly ash, is discharged through the stacks to the environment without any control.2 As natural radionuclides from fly ash are finally incorporated into the soil, their presence should be carefully investigated in order to assess their impact on people living in the vicinity of coal-fired power plants. Coal plays an increasingly important role to cover the energy needs of Turkey. Turkey has significant coal reserves especially * Corresponding author. Tel.: +904623773591. Fax: +904623253195. E-mail address:
[email protected]. † Karadeniz Technical University. ‡ Giresun University. (1) Karangelos, D. J.; Petropoulos, N. P.; Anagnostakis, M. J.; Hinis, E. P.; Simopoulos, S. E. J. EnViron. Radioact. 2004, 3, 233–246. (2) Papp, Z.; Dezsö, Z.; Daröczy, S. J. EnViron. Radioact. 2002, 59, 191–205.
lignite. The total proven lignite reserves were estimated at about 8.4 billion tons. Lignite is found in almost all regions of the country.3 In this study, we determined the radioactive contamination of soil around the Afsin-Elbistan coal-fired power plant. The coal used in the power plant and the fly ash and slag which were remnants of this coal were also examined. As the fly ash and slag samples are used as additives in cement factories and other building materials in Turkey, it is very important for human health. 2. Experimental Section 2.1. Study Area. The Afsin-Elbistan coal-fired thermal power plant is located near the small Turkish town Afsin, on the high plateau of Elbistan in the southeast of Turkey (Figure 1). About 40% of Turkey’s lignite resources are situated in Afsin-Elbistan basin. The coal reserve is estimated at 2 818 000 000 ton in this region. The plant was built in 1980 in the vicinity of a big coal mine and the spring wells of the river Ceyhan. Afsin-Elbistan is the biggest thermal power plant in Turkey with 4 × 340 MW ABB steam turbines. The power plant consumes 86 400 000 ton coal/y. 2.2. Estimation of Natural Radioactivity Levels by Gamma Spectrometry Technique. Twenty-one soil samples and five fly ashes, slags, and coals were collected from points distributed through the Afsin-Elbistan (Kahramanmaras, Turkey) coal-fired power plant. Soil samples (0–15 cm depth) were collected the south, east, west, and north at distances of 0, 100, 1000, 2000, 3000, and 5000 m from the power plant. The sampling points are given in Figure 1. Various samples (soil, coal, fly ash, and slag) were selected from each station, and measurements were taken after the samples were mixed as a homogeneous group. The coal, fly ash, slag, and soil samples were crushed thoroughly dried at room temperature to constant weight and later crushed to pass through a 2 mm mesh sieve to homogenize them. The samples were then dried by using (3) Oztürk, N.; Ozdogan, Z. S. J. Radioanal. Nucl. Chem. 2003, 259, 233–237.
10.1021/ef700374u CCC: $40.75 2008 American Chemical Society Published on Web 11/30/2007
Afsin-Elbistan Coal-Fired Power Plant
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Figure 1. Map of sampling region.
ovens at 105 °C for 24 h to ensure that moisture is completely removed. About 150 g of sample was used and sealed in gastight, radon impermeable, cylindrical polyethylene plastic containers (5.5 cm diameter and 5 cm height). Each sample was sealed for 30 days to reach radioactive equilibrium where the decay rate of the daughters becomes equal to that of the parent. The activities of 214Pb and 214Bi in equilibrium with their parents were assumed to represent the 226Ra activity, while the activities of 228Ac and 208Tl were assumed to represent the 232Th activity. Gamma spectrometry measurements were made with a coaxial high purity Ge detector of 15% relative efficiency and 1.9 keV resolution at the 1332 keV gamma of 60Co (Canberra, GC 1519 model). The detector was shielded in a 10 cm thick lead well internally lined with 2 mm Cu foils. The detector output was connected to a spectroscopy amplifier (Canberra, model 2025). The energy calibration and relative efficiency calibration of the spectrometer were carried out using calibration sources which contain 133Ba, 57Co, 22Na, 137Cs, 54Mn, and 60Co peaks for an energy range between 80 and 1400 keV. The counting time for each sample and background was 50 000 s. Gamma spectroscopy was used to determine the activities of 226Ra, 232Th, and 40K. The gamma lines employed for the qualification of the radionuclides are listed in Table 1. The activity concentrations of 232Th and 226Ra were calculated assuming secular equilibrium with their decay products. The gamma ray transitions of energies 351.9 (214Pb)
Table 1. Gamma Rays Employed for Quantification element
nuclide
226Ra
214Pb 214Bi
232Th
208Tl 228Ac
40K
half-life
gamma-ray energy (keV)
emission ratio (%)
26.8 min 19.9 min 3.05 min 6.13 h 1.3 × 109 y
351.9 609.3 583.1 911.1 1460.8
37 46 84 28 11
and 609.3 keV (214Bi) were used to determine the concentration of the 226Ra series. The gamma-ray lines at 911.1 (228Ac) and 583.1 keV (208Tl) were used to determine the concentration of the 232Th series. The 1460.8 keV gamma-ray transition was used to determine the concentration of 40K. The activity levels of the samples obtained for 226Ra, 232Th, and 40K are expressed in becquerel per kilogram. The activity concentrations for the natural radionuclides in the measured samples were computed using the following relation: Cs )
Na εPrMst
(Bq · kg-1)
(1)
where Na is the net counting rate of gamma rays, ε is the detector efficiency of the specific gamma ray, Pr is the absolute transition probability of gamma decay, Ms is the mass of the sample (kg), and t is counting time.
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Table 2. Mean Concentrations of Major Components in Coal and Fly Ash Samples coal component SiO2 Fe2O3 TiO2 Na2O MgO K2O Al2O3 CaO SO3 MnO
fly ash
concentration (%) 5.75 0.69 0.10 6.89 3.20 0.38 3.77 12.30 4.28
