Radioactivity assessment of Uranium Isotopes concentration in water sources near selected former uranium mines in the West-Rand area of Johannesburg

Mohlala, Nthabiseng
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This dissertation investigated the activity concentration levels of uranium isotopes in water samples collected in the West Rand-area of Johannesburg. One of the primary goals was to determine if the public dose limit of 1.0 mSv/y was not exceeded. Dose rates were calculated according to the National Nuclear Regulator [1] RG-002, consumption rate for different age groups and dose conversion factors published in IAEA General Safety Requirements Part 3 were used. Dose was modeled for various age groups to ascertain the contribution of the uranium isotopes to the total dose of a person consuming the water on a regular basis. Measurements of uranium isotopes were conducted by using Alpha Spectroscopy system from Canberra with Passivated Implanted Planar Silicon (PIPS) detector and Inductively Coupled Plasma Mass Spectrometer (ICP-MS) technique for measurement of isotopic elements. Based on the results presented for the water samples collected for this study, the quality of water from mining areas varied with fairly high activities measured in some surface water samples from the gold mine areas. The highest activity of 1300±24.7 mBq/l being measured from Blyvooruitzich (Bly4) sampling point collected in June 2019. Downstream of Gold mining operations of Driefontein sampling point recorded marginally lower activity concentration of 142±8 mBq/l was observed in March 2020. The ratio of 234U/238U was found to be equal to one, which indicate that the water was impacted by the mining activities. The estimated annual effective dose for all the age groups were well below the National Nuclear Regulator dose constraint of 0.25 mSv/a. The current study found that the annual ingestion dose of 234U, 235 and 238U were less than the World Health Organization recommended levels of 1 Bq/l and 1 Bq/l and 10 Bq/l,in drinking water [2]. From June 2019 through March 2020, average values of annual effective dose for uranium isotopes were 3.62E-02 mSv/a, 3.51E-02 mSv/a, 3.41E-02 mSv/a and 2.91E-02 mSv/a respectively. Bly4 measured the highest annual effective dose of 9.17E-02 mSv/a in sample collected June 2019 (Winter season) iii for 15 years age groups. Uranium 238 levels exceeded the Target Water Quality Range (TQWR) of 0.89 Bq/l as provided by the Department of Water and Sanitation for all the sample collected at Blyvooruitzich (Bly4), Blyvooruitzich combination and Peter Wright outlet. This means the annual cancer risk is less than one in a million. All the other sampling points were lower than the TQWR, this implies that there is no significant effects. There is no statistical significance in comparing the mean values of two groups.
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2022