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Airborne radon and its progeny levels in the coal mines of Godavarikhani, Andhra Pradesh, India
Abstract
In India, out of about 0.7 million miners, nearly 0.5 million persons are
directly engaged in coal operations. Radon and its progeny levels have been
quantified in the coal-mining environment of Godavarikhani, Andhra Pradesh,
India using solid-state nuclear track detectors. Seasonal and mine depth
variations in radon levels have been recorded resulting in the
identification of locations with a high radon level as areas with no mining
activity, active mining operational zones and return air ventilation paths.
All these radon levels were below the permissible levels. The average
concentrations of radon and its progeny levels were found to be 144±61 Bq m-3 and 20±11 mWL (working level) respectively in the
two-incline mine, and these values for the five-incline mine are recorded
as 315±71 Bq m-3 and 30±9 mWL respectively.
... Therefore, radon progeny concentration within underground mines depends on the fresh air exchange rate and ventilation. Monitoring and measuring radon concentration in dwellings,public areas and underground workplaces have been the expert's concern foryears [5][6][7][8][9][10][11][12]. ...
Background
The European Union council has introduced the basic safety standards (EU-BSS) for protection against the dangers arising from exposure to ionizing radiation by laying down a new radon reference level at workplaces. In this regard, all European state members must establish a national reference level based on all pre-defined requirements. After implanting the directive 2013/59/Euratom by European state members, new challenges have been revealed to mitigate radon appropriately in underground workplaces due to the exciting limitations (e.g., ventilation system, dust dispersion, air injection, etc.). Therefore, a conceptual design of an environmental radiological survey was defined and implemented by examining the hypothesis to find practical solutions following EU-BSS. The main objectives of this study were to identify the potential radon entry paths, utilize an optimized ventilation system, and carry on long-term radon monitoring in an operational underground manganese mine.
Results
The mullock rocks (the geological structure of the mine walls) contained a small amount of Ra-226 (2–4 Bq kg⁻¹). On the other hand, the mine ore (black shale, underlayer black shale, and carbonate ore) has shown the highest concentration of Ra-226 (12–16 Bq kg⁻¹) and the highest radon exhalation (1.2–1.6 mBq s⁻¹ m⁻²). The surface radon exhalation from the mine walls was in the range of 0.7 ± 0.1 and 1.5 ± 0.2 mBq m⁻² s⁻¹. It was found that shortly after mining activity was undertaken, radon concentration increased dramatically with an average of about 5900 ± 420 Bq m⁻³ near the freshly broken walls. The optimized mobile mitigation system reduced radon concentration to 250 ± 41 Bq m⁻³ on average.
Conclusion
Apart from the fact that aged walls were involved in the radon accumulation, considering the mine ventilation performance and the total active surface area, the exhaled radon from the aged walls could not be the primary potential source of high radon concentration when mining activity was undertaken. According to the obtained results, the ores, recently fragmented during the course of mining operations, were the primary path. Therefore, after successfully identifying the radon entry path, radon concentration could be reduced to meet the EU-BSS requirement by implementing the developed mitigation system.
... Number of coal mine included at the study Radon concentration (Bq m À3 ) Source Poland 71 740 (0e7000) Chruscielewski et al.., 1984 Brazil 1 1650 (170e6100) Veiga et al.., 2004 Britan 12 74 (22e518) Duggan et al., 1968 India 2 145 (46e354) Vishnuprasad Rao et al.., 2001 Iran 10 320 (146e520) Ghiassi-Nejad et al.., 2002 Pakistan 6 192 (121e408) Qureshi et al.., 2000 Turkey 5 (31e48) Yener and Kücüktas 1998 D.E. Tchorz-Trzeciakiewicz, T. Parkitny / Journal of Environmental Radioactivity 149 (2015) 90e98 93 correlation coefficient amounts to 0.95 and is similar to Pearson correlation coefficient defining the relationship between seasonal variations of temperature and radon concentration, which is 0.98 (Fig. 4). ...
A worldwide review of radon exposure in non-uranium mines was conducted. Based on the reported radon measurements in a total of 474 underground non-uranium mines, the average radon concentration in underground non-uranium mines was calculated to be 570 Bq m-3 (varied from below detection limit to above 10,000 Bq m-3), and the average equilibrium factor between radon and its short-lived progeny was 0.34 (varied from 0.02 to 0.9). Using the average values from the review, annual effective radon doses to workers in Canadian non-uranium mines were estimated. For underground workers, the estimated annual effective radon dose to non-uranium miners was 3.8 mSv with the possibility of varying from 0.22 to 10 mSv depending on ventilation and other operation conditions. In Canada, the majority of mines are open-pit surface mines; only a small portion of the workforce in non-uranium mines physically work underground where radon concentration can be elevated. Averaged over the entire mining workforce, occupational exposure to radon in non-uranium mines is estimated to be 0.9 mSv. The results of this study indicate that there is potential for workers in non-uranium mines to reach or exceed Canadian thresholds for mandatory monitoring and reporting radiation doses, at least for underground operations.
Radionuclides in mineral coal and related rocks are of great concern to the human health, among them the radon gas, as it has been considered the second largest cause of lung cancer by the World Health Organization (WHO). This paper describes a field and laboratorial study focusing this noble gas in the Amando Simões PI-08 coal mine, Figueira city, Paraná State, Brazil. The average ²²²Rn activity concentration inside the mine was ~ 227 Bq/m³, whereas the average annual effective dose received by the workers was 1.4 mSv/year, suggesting that it does not offer radon-risks to the human health.
Radon and its progeny are prevalent everywhere on the lithosphere especially in the mining environment. Coal exists in the Salt Range that passes through Pakistan. The aim of the present study was to measure radon concentration and assess the associated radiological hazard in the coalmines developed in that portion of the Salt Range which passes through the district of Chakwal in Pakistan. Among the various coalmines in the coalfield, five were selected for radon survey. A passive integrated technique consisting of SSNTDs (solid state nuclear track detectors) was employed for the measurement of radon concentration in these coalmines. Box type dosimeters containing CN-85 detectors were placed for three months at six locations in every selected coalmine. After removing the dosimeters, the CN-85 detectors were etched in alkaline solution to enlarge the alpha tracks in the detectors and counted under an optical microscope. The track densities were converted to radon concentration. The average concentration of radon in the coalmines varied in the range 50-114 Bq m(-3). Radon exhalation rates from the samples of coal and shale collected from the coalmines were determined to be respectively 934 (830-1010) and 1302 (1020-1580) mBq m(-2) h(-1). The radiation dose and corresponding health risk for the mine workers were also estimated.
Monitoring of radon in underground mines is important in order to assess the radiological hazards to occupational workers. Radon concentration levels in three underground lignite mines (Tunçbilek, Omerler and Eynez) of Turkey were obtained in this study. For this reason, atmospheric radon level measurements were carried out in mines using CR-39 track detectors. Chemical etching of the detector tracks and subsequent counting were performed at Cekmece Nuclear Research and Training Center. The obtained results were evaluated according to the International Commission of Radiation Protection and the Turkish Atomic Energy Authority whose radon action levels for workplaces are 500-1500 and 1000 Bq(-3), respectively. The radon gas concentrations in the lignite mines were determined to be between 50 +/- 7 and 587 +/- 16 Bq m(-3). The results obtained in these experiments are far under the action levels. The computed radon doses for the mine workers of Tunçbilek, Omerler and Eynez lignite mines are 1.23, 2.44 and 1.47 mSv y(-1), respectively.
The main source of radiation exposure in most underground mining operations is radon and radon decay products. The situation of radon exposure in underground mining in Brazil is still unknown, since there has been no national regulation regarding this exposure. A preliminary radiological survey in nonuranium mines in Brazil indicated that an underground coal mine in the south of Brazil had high radon concentration and needed to be better evaluated. This paper intends to present an assessment of radon and radon decay product exposure in the underground environment of this coal mining industry and to estimate the annual exposure to the workers. As a product of this assessment, it was found that average radon concentrations at all sampling campaign and excavation sites were above the action level range for workplaces of 500-1500 Bq m(-3) recommended by the International Commission on Radiological Protection--ICRP 65. The average effective dose estimated for the workers was almost 30 times higher than the world average dose for coal miners.
Radon measurements were carried out in Kozlu, Karadon and Uzülmez underground coal mines of Zonguldak bituminous coal basin in Turkey. Passive-time integrating method, which is the most widely used technique for the measurement of radon concentration in air, was applied by using nuclear etched track detectors (CR-39) in the study area. The radon concentration measurements were performed on a total of 42 points in those three mines. The annual exposure, the annual effective dose and lifetime fatality risk, which are the important parameters for the health of workers, were estimated based on chronic occupational exposure to the radon gas, which is calculated using UNCEAR-2000 and ICRP-65 models. The radon concentrations at several coal production faces are higher than the action level of 1000 Bq m(-3). It is suggested that the ventilation rates should be rearranged to reduce the radon concentration.
In this study, the results of atmospheric radon measurements that were performed for the Amasra underground coal mine in Zonguldak
bituminous coal basin (Turkey) are presented. The radon measurements were performed for 40 days between November 2004 and
December 2004 using passive nuclear etched track detectors. The radon concentrations vary from a minimum value 49 Bq m−3 in a site located at +40 m to a maximum value 223 Bq m−3 in a site located at −100 m. Mean concentration is 117 (Bq m−3). This value is well below the action level of 500–1500 Bq m−3 recommended by the International Commission on Radiological Protection (ICRP) (1993). The mean effective dose value for workers
of this mine of 3.4 µSv per day was obtained. This result shows that protection against radiological hazards would not be
necessary for workers of this mine(2).
Radon survey measurements were performed at workplaces not covered by the Radiation Protection Ordinance, i.e. in production mines and caves and show mines open to visitors, underground power stations and the like. About 150 of 170 facilities, excluding coal mines, have been measured for radon, radon daughters, external radiation, humidity ventilation rate. etc. and working times have been calculated to estimate the resulting effective annual dose. High radon concentrations, above 1 kBq.m⁻³ have been found in 40% of all places while 10% still exceed 5 kBq.m⁻³. The highest values at occupied places have been found in visitors mines and caves. The factual radiation exposures have been processed in statistical terms, while actual numbers related to the different operations must be encoded for data protection reasons.
The paper presents the most recent data, collected during 1987-1989, on concentrations of ²²²Rn products in the air of all Polish underground non-uranium mines, and data on the exposure of miners employed there. The exposures of miners were evaluated by using individual etched track dosemeters, worn on helmets of representative groups in every mine. The weighted average annual exposures in coal, metal ore, and chemical raw materials ore mines were 1.07, 0.547 and 0.255 x 10⁻³ J.h.m⁻³ (0.315, 0.161 and 0.075 WLM), respectively. Also, the paper presents expected 'frequency' distributions of individual miner exposure in particular mines, as well as the computer simulations of 'relative frequency' distributions of expected miner exposure with the annual limit of exposure (ALE) adopted at the levels of 17, 12, 8.6, 6.9 and 3.4 x 10⁻³ J.h.m⁻³ (5.0, 3.5, 2.5, 2 and 1 WLM).
Natural radioactivity due to radon and its daughters indoors contributes significantly to the total radiation exposure of man. A number of non-radioactive mines have been found to have high levels of radon and its daughters. Levels of natural radioactivity measured in dwellings and some of the non-radioactive mines in India are presented. The methods employed for these studies, grab sampling and alpha counting, nuclear track detector films and track counting, are briefly described. Indoor radioactivity results are given for dwellings in known elevated natural background areas and around hot springs with high dissolved radium. In general, the levels of natural radioactivity in dwellings have been found to be small fractions of a Working Level. Some of the non-uranium mines have, however, been found to show higher Working Level concentrations. Reasons for these obervations have been discussed. Results for radon in structures built with coal fly ash bricks are also presented.
Measurements of radon exhalation from a gravely sandy loam have been
made in a semi-arid climate by using a combination of closed
accumulation, flow-through accumulation, and 222Rn and
210Pb soil profiles. The meteorological factors that most
affected the instantaneous value of exhalation of 222Rn were
atmospheric pressure and rain. Effects due to other parameters such as
wind or temperature were either comparatively small or undetectable. No
evidence was seen for migration of radon from distant (≫10m) sources
or for an effect on exhalation due to limited nearby seismic activity.
Measurements for 220Rn indicated its exhalation was also
sensitive to pressure variation but to a lesser extent than for
222Rn. While instantaneous exhalation of 222Rn
could easily vary by a factor of 2 or more, time-averaged exhalation was
found to be close to that expected for pure diffusion. There is thus
some indication that the time-averaged effect of cyclic environmental
variables is small for this soil. Comparison with transport equations
indicates that it is difficult to explain the observed variation in
surface flux density solely in terms of the radon concentration gradient
in the top few decimeters of soil. A contribution to transport from
direct flow, perhaps through inhomogeneities such as cracks or channels,
is one possible explanation.
Ten non-uranium mines from various regions of India have been surveyed for airborne radioactivity due to radon daughter products. The average air concentrations of RaA, RaB and RaC in the main ventilation return airways and in some selected areas in different working levels underground were assessed. The average equilibrium equivalent radon values and the RaC to RaB ratios were calculated. In one of these mines activity levels of the order of 500 to 1200 mWL were observed in different working areas. In all other mines the levels observed varied from a few mWL to about 100 mWL. The method of air sampling and analysis is briefly described.
The method is based on measuring the alpha-activity of shift-long respirable dust samples. Activity concentrations of a few
thousandths of a working level are easily measured, and the value obtained is fairly close to a shift average. The sampling
equipment used in trials was the MRE gravimetric dust sampler, which is safe for use in methane-air mixtures, and in British
coal mines the measurements can be made on routine respirable dust samples.