Dose Assessment Of Natural Radioactivity In Fly Ash And Environmental Materials From Morupule A Coal-Fired Power Station In Botswana

ABSTRACT This study has been undertaken to estimate the occupational and public radiation doses due to natural radioactivity at Morupule A Coal-Fired Power Station and its environs. The radiation doses were reconstructed to include 60 year period from 1985 to 2045. Direct gamma ray spectroscopy was used to determine the natural radionuclides Th-232, U-238, and K-40 both qualitatively and quantitatively for fly ash, coal, soil and water (from the fly ash ponds) samples. The average activity concentrations for Th-232, U-238, and K-40 in fly ash samples were 64.54 Bq/kg, 49.37 Bq/kg and 40.08 Bq/kg respectively. In the case of coal, the corresponding average activity concentrations for Th-232, U-238, and K-40 were 27.43 Bq/kg, 18.10 Bq/kg and 17.38 Bq/kg respectively. For soil samples, the average activity concentrations for Th-232, U-238, and K-40 were 10.11 Bq/kg, 6.76 Bq/kg and 118.03 Bq/kg respectively. In water samples, the average activity concentrations for Th232, U-238, and K-40 were 0.79 Bq/l, 0.32 Bq/l and 1.01 Bq/l respectively. These average activity concentrations were generally comparable to the average world activity concentrations in the case of coal samples, but were generally lower than the average world activity concentrations in the case of fly ash, soil and water samples. The average annual effective doses for the study area were estimated as 0.320 mSv, 0.126 mSv, 0.069 mSv and 0.003 mSv for fly ash, coal, soil and water samples respectively. Dose reconstruction modelling estimated the average fly ash annual effective doses for the years 1985, 1995, 2005, 2015, 2025, 2035 and 2045 to be 0.182 mSv, 0.459 mSv, 0.756 mSv, 0.320 mSv, 0.183 mSv, 0.137 mSv and 0.124 mSv respectively. The reconstructed average coal annual effective doses for similar years were 0.070 mSv, 0.182 mSv, 0.303 mSv, 0.126 mSv, 0.070 mSv, 0.060 mSv and 0.046 mSv respectively. The dose reconstruction modelling also estimated the average soil annual effective doses for the same years as above to be 0.048 mSv, 0.091 mSv, 0.136 mSv, 0.070 mSv, 0.048 mSv, 0.041 mSv and 0.039 mSv respectively. Likewise, the reconstructed average annual effective doses for water were 0.0016 mSv, 0.0049 mSv, 0.0083 mSv, 0.0033 mSv, 0.0016 mSv, 0.0011 mSv and 0.0010 mSv respectively. All estimated and reconstructed average annual effective doses are within the recommended public and occupational dose limits of 1 mSv and 20 mSv respectively. The radium equivalent activity, representative level index, external and internal hazard indices for all samples are within recommended international values for their safe use as building materials. Results from this study reveal that there is no significant radiological impact to both the workers and the public within Morupule A Coal-Fired Power Station and its environs.