Assessment of Terrestrial Radioactivity Distribution in Olkaria Geothermal Field, Kenya

Abstract

Geothermal energy has played a major role in energy supply in Kenya and even overtaking other forces of energy. However, utilization of subsurface fluids need comprehensive examination and the results communicated to the general public. This is because natural radiation is considered critical during earth processes since the gradual disintegration of naturally occurring radioactive elements account for almost half of the energy that brings about volcanology processes. This therefore implies that the slow decay of radioactive elements aids in generation of temperature gradient beneath the earth surface. In this survey, NaI(Tl) gamma-ray spectrometer was employed in determination of the NORMs levels within the Olkaria geothermal field and estimated the hazards indices that arise from the decay of these products in relation to other physico-chemical parameters such as temperature, TOC, pH and specific gravity. The study revealed that 238U, 232Th and 40K had average levels at 66.42±16.02Bqkg-1, 46.92±9.52Bqkg-1 and 512.84±226.49Bqkg-1 respectively while 80.56±17.77nGyh-1, 0.1mSvy-1, 0.47and 172.79±30.37Bq/Kg were the mean values for absorbed dose rates, annual effective dose rate, hazard index and radium equivalent respectively. Also a weak positive correlation between pH, TOC and s.g and the concentration of the three radioactive elements was observed. From the obtained results, the studied hazard indices were below the world acceptable safety limits and therefore human exposure to radiation is within safety levels. Also change in physicochemical parameters does not affect the radionuclide concentrations. This shows that the exploitation of geothermal energy in Olkaria has not affected the activity concentration level of 238U, 232Th and 40K and the hazard indices.