Abstract:
The adoption of geothermal energy in Kenya for electricity generation has grown and become an
adorable part of the substitute energy blend and from the current rate of geothermal installation it
may soon overtake hydro as the leading source of energy. Despite the fact that geothermal energy has
been described as clean energy, uncertainty associated with the exploitation of deep subsurface
fluids need intensive assessment and dissemination within the community and with the public.
Radioactive decay assists in production of a high temperature gradient in the subsurface for
geothermal energy production since the slow decay of radioactive elements produces
approximately half of the heat that drives earth processes such as continental drift, ocean
spreading and plate tectonics. This may lead to an elevated concentration of radioactive elements
in a geothermal setting. In this research activity concentrations of radioactive elements of natural
origin in Olkaria geothermal field was measured in relation to other physico-chemical parameters
such as temperature, TOC, pH and specific gravity, estimated the absorbed dose rate, annual
effective dose rates and the hazards index. Activity concentrations was determined by use of
NaI(Tl) gamma-ray spectrometer, the soil pH using pH meter, the Total Organic Carbon using
wet chemistry technique, in situ temperature obtained by use of a thermometer and specific
gravity was determined by use of Water Pycnometer. The study reported that the activity
concentrations in rock samples for
238U, 232Th
and
xiv
4°K
were 66.42±16.02Bq/kg,
46.92±9.52Bq/kg and 512.84±226.49Bq/kg while in sediment, the levels were
64.62±15.17Bq/kg, 48.69±9.28Bq/kg and 525.86±21 l.54Bq/kg respectively in Olkaria
geothermal field. In the control samples (from Ongata Rongai, over 1 OOkm away), the activity
levels of radionuclides were 364.3±2.97Bq/kg, 52±1Bq/kg and 34.64±0.99Bq/kg for,
4°K, 238U
and
232Th
in rock samples and 350.36±3.82Bq/kg, 37.08±1.34Bq/kg and 35.11±0.52Bq/kg in
sediments respectively. The mean absorbed dose rates in rocks from both Olkaria geothermal and
Ongata Rongai samples were 80.56±17.77nGy/h and 70.82±1.72nGy/h respectively. In
sediments, the average absorbed dose rates in both the samples were 81.35±16.88nGyh-1 and
54.26±2.05nGyh-1 respectively. The mean AEDR for rocks samples in the two areas were
O. lmSv/y and 0.086mSv/y while the same parameter for sediments samples was O. lmSv/y and
0.067mSv/y respectively in the two areas. The mean hazard index (Hex) obtained for rock
samples from both Olkaria geothermal and control site samples were found to be 0.47 and 0.42
while the mean for sediments for samples from the two sites were found to be 0.47 and 0.32.
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. This shows that the
exploitation of geothermal energy in Olkaria has not affected the activity concentration level of
238U, 232Th
and
4°K
and the hazard indices