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

Janet A. Ademola, Uzoma C. Onyema

Department of Physics, University of Ibadan, Ibadan, Nigeria.

DOI: 10.4236/ns.2014.610075                

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.

Keywords

Fly Ash, Natural Radionuclides, Gamma Radiation, Occupational Dose, Absorbed Dose Rate

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Kant, K., Rashmi, Kuriakose, S., Sonkawade, R.G., Chauhan, R.P., Chakarvarti, S.K. and Sharma, G.S. (2010) Radon Activity and Exhalation Rates in Indian Fly Ash Samples. Indian Journal of Pure & Applied Physics, 48, 457-462.
[2]	Yeledhalli, N.A., Prakash, S.S. and Ravi, M.V. (2008) Concentration of Heavy Elements and Radionuclides in Crops Grown on Coal Fly Ash Amended Red and Black Soils. Karnataka Journal of Agricultural Science, 21, 125-127.
[3]	Papastefanou, C. and Charalambous, S. (1979) On the Radioactivity of Fly Ashes from Coal Power Plants. Zeitschrift für Naturforschung, 34a, 533-537.
[4]	Pandit, G.G., Sahu, S.K. and Puranik, V.D. (2011) Natural Radionuclides from Coal Fired Thermal Power Plants— Estimation of Atmospheric Release and Inhalation Risk. Radioprotection, 46, S173-S179. http://dx.doi.org/10.1051/radiopro/20116982s
[5]	Ademola, J.A. and Olatunji, M.A. (2013) Evaluation of NORM and Dose Assessment in an Aluminium Industry in Nigeria. World Journal of Nuclear Science and Technology, 3, 150-154. http://dx.doi.org/10.4236/wjnst.2013.34025
[6]	Mustapha, A.O., Mbuzukongira, P. and Mangala, M.J. (2007) Occupational Radiation Exposure of Artisans Mining Columbite-Tantalite in the Eastern Democratic Republic. Journal of Radiological Protection, 27, 187-195. http://dx.doi.org/10.1088/0952-4746/27/2/005
[7]	Weiss, D., Biesold, H., Jovanovic, P., Juhàsz, L., Laciok, A., Leopold, K., Michalik, B., Moravanská, H., Poffijn, A., Popescu, M., R?dulescu, C., Szerbin, P. and Wiegand, J. (2005) Natural Occurring Radioactive Materials (NORM IV). Proceedings of an International Conference, Szczkyrk, 17-21 May 2004, 147-155.
[8]	Kumar, V., Mathur, M., Sinha, S.S. and Dhatrak, S. (2005) Fly Ash: An Environment Saviour. Fly Ash India 2005, New Delhi, Fly Ash Utilization Programme (FAUP), TIFAC, DST, New Delhi 110016, IV 1.1-IV 1.4.
[9]	Beretka, J. and Mathew, P.J. (1985) Natural Radioactivity of Australian Building Materials, Industrial Wastes and By-Products. Health Physics, 48, 87-95. http://dx.doi.org/10.1097/00004032-198501000-00007
[10]	Lu, X.W. and Zhang, X.L. (2008) 226Ra, 232Th and 40K Activities in Soil of Cuihna Mountain National Geological Park, China. Environmental Geology, 56, 353-357. http://dx.doi.org/10.1007/s00254-007-1170-3
[11]	Ademola, J.A. (2008) Assessment of Natural Radionuclide Content of Cement Used in Nigeria. Journal of Radiological Protection, 28, 581-588. http://dx.doi.org/10.1088/0952-4746/28/4/010
[12]	Stranden, E. (1976) Some Aspects on Radioactivity of Building Materials. Health Physics, 8, 167-177.
[13]	UNSCEAR (2000) Sources, and Effects of Ionizing Radiation. United Nation Scientific Committee on the Effect of Atomic Radiation. United Nations, New York.
[14]	Veiga, R., Sanches, N., Anjos, R.M., Macario, K., Bastos J., Iguatemy, M., Aguiar, J.G., Santos, A.M.A., Mosquera, B., Carvalho, C., Baptista, F.M. and Umisedo, N.K. (2006) Measurement of Natural Radioactivity in Brazilian Beach Sands. Radiation Measurements, 41,189-196. http://dx.doi.org/10.1016/j.radmeas.2005.05.001
[15]	UNSCEAR (1988) Sources, Effects and Risk of Ionizing Radiation. United Nation Scientific Committee on the Effect of Atomic Radiation. United Nations, New York.
[16]	Sam, A.K. and Awad Al-Geed, M.M. (2000) Radiological Evaluation of Gold Mining Activities in Ariab (Eastern Sudan). Radiation Protection Dosimetry, 88, 335-340. http://dx.doi.org/10.1093/oxfordjournals.rpd.a033053
[17]	IAEA (1996) International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115. IAEA, Vienna.
[18]	IAEA (2003) Assessing Radiation Doses to the Public from Radionuclides in Timber and Wood Product. IAEA- TECDOC-1376 Vienna, Austria.
[19]	Degrange, J.P. and Lepicard, S. (2005) Natural Occurring Radioactive Materials (NORM IV). Proceedings of an International Conference, Szczkyrk, 17-21 May 2004, 230-239.
[20]	ICRP (1999) Protection of Public in Situation of Prolonged Radiation Exposure. ICRP Publication 82. Ann. ICRP 29 (1-2), Pergamon, Oxford.
[21]	ICRP (1991) 1990 Recommendations of International Commission on Radiological Protection. ICRP Publication 60. Ann. ICRP, 21(1-3), Pergamon, Oxford.