Assessment of radon and gamma in Kurday mining site, Kazakhstan.
Master thesis
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Date
2012-09-20Metadata
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- Master's theses (IPM) [204]
Abstract
The present work is based on the data obtained from expeditions to Kurday, Kazakhstan in
2006 performed by Joint Norwegian- Kazakhstan – Kyrgyzstan- Tajikistan project in
collaboration with the NATRO RESCA project. The former uranium mining and processing
site Kurday, located in Zambyl region in southern Kazakhstan is rich in naturally occurring
radioactive materials (NORMs) and technologically enhanced naturally occurring radioactive
materials (TENORMs). It has been recognized as one of the earliest uranium legacy
production sites in Central Asia. In addition, the area is not only contaminated with uranium
and its daughters, but also from associated trace metals which may pose a risk to man and the
environment.
The objectives of the thesis were to use the available outdoor and indoor radon concentrations
as well as gamma dose rates/doses to estimate public annual effective doses from gamma and
radon exposure in selected area of the site. The corresponding doses estimated from gamma
and radon obtained in Kurday, Kazakhstan and Taboshar, Tajikistan were also compared. The
risk of human stochastic effects (excess cancer) from the estimated total doses was also
evaluated.
The absorbed gamma dose rates in air were measured at every sampling sites and also in the
dwellings, using different dosimeters like Geiger Muller type (DKS-96 Automess) and
scintillation type (SRP-68, Radiagem) dosimeters. For every measurement points, the
detectors were positioned 1m above the ground and occasionally at ground. In addition,
simulteneous outdoor and indoor radon concentrations measurements were conducted around
the Pit Lake, at the hills around the lake and in a grid pattern at the mountain plateau. Radon
detectors were also placed indoor in the dwellings of Kurday, and outdoor in the garden of
the dwellings. Indoor and outdoor concentration of Rn in air were measured using both active
and passive devices. The screenings of preliminary level of radon concentration were done by
RAMON-01, RRA AND PRM-145. The track detectors were then placed for a longer period
(2-9 months). All the data were analyzed using windows office EXCEL 2007 and minitab 16.
For all analyisis, p values <<0.05 were considered statistically significant. Annual average
effective doses were estimated by extrapolating the abosorbed doses in air over the measured
period and using the conversion factor 1 Sv/Gy. Indoor occupancy of 6000 hours per year was used, while 350 hours and 700 hours per year were applied for tailing piles and for
gardens of houses, respectively, to estimate doses. In case of radon doses, equilibrium factor
0.4 was used, while the dose conversion factor applied was 9 nSv/Bq/m3/hour. The
occupancy factor used in radon calculations was similar to that of gamma doses for
corresponding locations. Similarly, the risk of developing cancer in human was estimated
using the risk factor of 5×10-2 per Sv.
As a summary, the gamma dose rates were found to vary within the studied areas; highest at
the Pit lake (0.11-1.07 μGy/h) and waste rock piles (0.7-1.05 μGy/h), inside dwellings
(0.131-0.254 μGy/h) and lowest in the gardens (0.07-0.21 μGy/h). The calculated mean
annual effective doses of gamma radiation at different areas of Kurday were; Pit lake
(0.31±0.26 mSv), waste rock piles (0.36±0.05 mSv) inside room (1.40±1.80 mSv) and garden
(0.11±0.02 mSv). One way ANOVA analysis showed the variation of mean dose rates for all
the four areas investigated. The mean dose rate measured in waste rock piles was
significantly higher (p<<0.05) than that in Pit Lake, inside dwellings and in gardens. The
radon concentrations also varied according to the sites investigated. Peak radon
concentrations were found in the living rooms and bedrooms of two selected houses
exceeding 1000 Bq/m3. The mean radon concentrations of indoor environment (inside rooms)
were found to be significantly higher (p<<0.05) than that in outdoor conditions (gardens).
The regression analyses of outdoor gamma dose rate and outdoor radon concentrations, and
indoor gamma dose rates and indoor radon concentrations conditions showed that both of the
combinations have p<<0.05 and R2 around 76%. The mean effective doses due to outdoor
radon exposures at Kurday area was found to be 0.13±0.05 mSv whereas, the mean effective
dose due to indoor radon exposure was estimated to be 3.91±1.80 mSv. Similarly, the mean
concentration of uranium in drinking water from Muzbell dwelling area was found to be 26
μg/L and the annual effective dose was estimated to be 0.25 mSv. The total dose calculated
was 6.31 mSv/year where indoor radon was the largest dose contributor. The dose could
potentially contribute to health injuries to the individuals to develop one cancerous case to
ionizing radiation- at a risk factor of 5×10-2 per Sv.
In conclusion, the present study based on the summary report obtained in the NATO RESCA
project and JNKKT project showed that the Kurday area of Kazakhstan represent sources of
potential contamination of the living environment i.e. gamma radiation, radon exposure and
the uranium concentration in drinking water sources. The outdoor gamma dose rates (0.078- 1.226 μGy/h) were found to be higher than the indoor gamma dose rates (0.013-0.69 μGy/h),
whereas the indoor radon concentrations inside dwellings (70-330 Bq/m3) were recorded to
be higher than the outdoor radon concentrations (30-90 Bq/m3). The values of outdoor
gamma dose rates, indoor and outdoor radon concentrations are considerably higher than
global average corresponding values. The mean uranium concentration in drinking water
from Muzbel dwelling area (26 μg/L) was also found to be higher than the recommended
value by WHO. The highest dose contribution to humans was obtained from indoor radon
concentration (0.18-7.13 mSv) in the houses of Kurday area. The doses from indoor gamma
radiation was also significantly high (0.14-4.14 mSv), while that from drinking water (0.25
mSv) was quite low (within the recommended value) compared to indoor radon and gamma
radiation doses.
The outdoor annual gamma doses obtained in Kurday, Kazakhstan were found to be similar
to the outdoor gamma doses observed in Taboshar, Tajikistan (around 0.6 mSv). However,
the outdoor radon in Taboshar was found to be five times higher than that in Kurday, both the
values were lower than the global recommended values. Similarly, the indoor radon dose and
indoor gamma dose in Kurday and that in Taboshar were in the comparable range. However,
the peak values for indoor gamma doses were found to be higher in Kurday than those in
Taboshar region. The radiological risk to human (cancer) from the total dose was estimated to
be one cancerous case in Kurday with 3000 population. Therefore, on the basis of the present
findings, it can be recommended that interventions should be made at the high doses sites in
Kurday region in order to minimize the probability of human stochastic effects and thereby
limit the public doses as low as reasonably achievable.