Environmental Engineering

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Browsing Environmental Engineering by Author "Abubeker, Yimam (Asst. Prof.)"

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    Evaluation, Characterization and management of Naturally Occurring Radioactive Materials and disused radioactive waste in Water and Soil Samples
    (AAU, 2017-12) Belete, Derib; Abubeker, Yimam (Asst. Prof.)
    In this study radiological hazards to members of the public and workers from exposure to natural radioactivity as a result of mining activities from Kenticha Tantalum Mines in Ethiopia, have been studied through several exposure pathways using direct gamma spectrometry to determine 238 U, 232 Th, 40 K, 226 Ra and 222 Rn in tantalum ore, soil, waste, waste tailing and water samples. Additionally, cancer risk assessment associated with NORM was estimated. The average activity concentrations of 238 U, 232 Th, 40 K, 226 Ra and 222 Rn in tantalum ore were 78.653±1.431Bq/kg, 24.945±0.492 Bq/kg, 603.170±55.013 Bq/kg, 69.478±31.0 Bq/kg and 112.554±50.249 kBq/m 3 , respectively. In soil the activity concentrations were 69.354±1.081 Bq/kg, 15.479±0.231 Bq/kg, 718.880±65.531Bq/kg, 68.923±1.7Bq/kg and 111.655±2.681 kBq/m 3 , respectively and in solid waste samples 110.496±1.907 Bq/kg, 15.009±0.274 Bq/kg, 607.269±55.375 Bq/kg, 98.300±38.6 Bq/kg and 159.246±62.607 kBq/m 3 respectively. The values were generally above the worldwide average activity concentrations in all samples, except thorium-232.This might be due to the high contents of 238 U decay families and 40 K in the granite – pegmatite rocks of Kenticha area. The corresponding average external dose rate at 1m above the ground in air for tantalum ore, soil and solid waste samples were 76.407 nGy/h, 71.337 nGy/h, 85.408 nGy/h, respectively which were above worldwide average value of 60 nGy/h. The annual equivalent doses were also estimated as 0.021±0.003 mSv, 0.020±0.001 mSv and 0.023±0.004 mSv for ore, soil and solid waste samples, respectively and were found to be lower than the worldwide average of 2.42 mSv/y. Likewise, the radon emanation coefficient which is the fraction of radon generated within the grains of materials and escaped to the pore space, varied from 82±2% to 85±2% for ores, from 82±2% to 84±2% for soil, and from 53±15% to 83±15% for solid waste samples. Also, the radon exhalation rate varied in the range of 41.7±25.7 to 87.3±25.7 mBq/m 2 .s for ores, from 56.2±1.4 to 58.1±1.4 mBq/m 2 s for soil and from 53.3±32.1 to 120.2±32.1 mBq/m 2 s for solid waste, respectively. The radium equivalent activity, external hazard index, internal hazard index and representative gamma index, for all samples were estimated and generally found to be within recommended international values. Annual effective dose was evaluated from only external gamma dose rate. However, the relatively high values in all the other parameters measured implies that the Kenticha tantalum mine and its environments shown the significance of naturally occurring radioactive material. Therefore, the results from this study will ignite in decisionmaking for future set-up of further research for the management of NORM wastes in Kenticha tantalum mine and for the emerging mining industry in Ethiopia. Radioactive material containing Cs-137, Ra-226, Co-60, Sr-90 and Am-241 were treated using the developed method. In the method different type of materials (cement, sands, concrete, etc.) were tested for absorption of radiation emitted from the source as well as suitability of the material for storage for long time. It was found that the best materials to be used in radioactive waste treatment is Concrete, where the surface dose reduced from 150 to 3 µsave/h. In addition, design of storage container was proposed (with specification). Finally, based on indications of the present research findings and scientific background, recommendations were forwarded to help on amending nuclear waste management problems or indicate for other possible alternatives such as radiation map of Ethiopia.