TITLE:
Assessment of Natural Radionuclides in Fly Ash Produced at Orji River Thermal Power Station, Nigeria and the Associated Radiological Impact
AUTHORS:
Janet A. Ademola, Uzoma C. Onyema
KEYWORDS:
Fly Ash, Natural Radionuclides, Gamma Radiation, Occupational Dose, Absorbed Dose Rate
JOURNAL NAME:
Natural Science,
Vol.6 No.10,
June
20,
2014
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.