Radiation Dose Reconstruction of Natural Radioactivity in Fly Ash and Environmental Materials from Morupule a Coal-Fired Power Station in Botswana

Dose reconstruction modelling was used in estimating the average annual effective doses due to natural radionuclides to both workers and public members within Morupule A Coal-Fired Power Station and its environs to include the years 1985, 1995, 2005, 2015, 2025, 2035 and 2045. For these years, average fly ash annual effective doses were estimated to be 0.1817 mSv, 0.4591 mSv, 0.7561 mSv, 0.3202 mSv, 0.1826 mSv, 0.1367 mSv and 0.1239 mSv respectively. In the case of coal samples, the values were 0.0695 mSv, 0.1822 mSv, 0.3028 mSv, 0.1258 mSv, 0.0700 mSv, 0.0601 mSv and 0.0462 mSv respectively. For soil samples, they were estimated to be 0.0482 mSv, 0.0907 mSv, 0.1361 mSv, 0.0695 mSv, 0.0484 mSv, 0.0413 mSv and 0.0394 mSv respectively. With regards to water samples, they were estimated to be 1.600 Sv, 4.900 Sv, 8.300 Sv, 3.300 Sv, 1.600 Sv, 1.100 Sv and 1.000 Sv respectively. At the time of sample analysis, the average annual effective doses for the study area were estimated to be 0.320 mSv, 0.126 mSv, 0.069 mSv and 0.003 mSv for fly ash, coal, soil and water samples respectively. All these annual effective doses were due to the natural radionuclides Th-232, U-238 and K-40 in fly ash, coal, soil and water (from the fly ash ponds) samples collected from the study area. All reconstructed average annual effective doses are within the recommended public and occupational dose limits of 1 mSv and 20 mSv respectively. Direct gamma ray spectrometry was used in the initial determination of the above natural radionuclides.