Evaluation, Characterization and management of Naturally Occurring Radioactive Materials and disused radioactive waste in Water and Soil Samples
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Date
2017-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
AAU
Abstract
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.
Description
Keywords
Radioactive Materials, radioactive waste, Water, soil