A study of the technologically modified sources of 222Rn and its environmental impact in an Indian U mineralised belt

222Rn Exhalation Flux Rate and 226Ra in the Soils of a Copper-Mineralised Area

Uranium-series radionuclides exist in trace quantities in all soils and rocks on earth in variable concentrations. Among these, 222Rn gas exhaled by the soil of a geological location is the main contributor to the environmental radioactivity. A 222Rn exhalation flux study was carried out in the heavily mineralised area of the Singhbhum Copper Belt of Jharkhand, India. A significant seasonal variation in the soil gas exhalation was observed, which is attributable to the seasonal atmospheric parameters of the study area. The average 222Rn exhalation flux from the soil was estimated to be in the range of 4.5-$20.1\ \mathrm{Bq}\ {\mathrm{m}}^{-2}\ {\mathrm{s}}^{-1}$ with a mean of $10.1\pm 3.9\ \mathrm{mBq}\ {\mathrm{m}}^{-2}\ {\mathrm{s}}^{-1}$ and geometric mean (GM) of $9.5\ \mathrm{mBq}\ {\mathrm{m}}^{-2}\ {\mathrm{s}}^{-1}$. Also, 20 soil samples collected from the study area were analysed by the emanometric method, which estimated the 226Ra specific activity in the soils in the range of 9-$63\ \mathrm{Bq}\ \mathrm{k}{\mathrm{g}}^{-1}$ and a mean value of $39\pm 16\ \mathrm{Bq}\ \mathrm{k}{\mathrm{g}}^{-1}$.

Indoor and Outdoor Exposure to Radon, Thoron and Thoron Decay Products in a NORM Area with Highly Elevated Bedrock Thorium and Legacy Mines

Radon (²²²Rn) and thoron (²²⁰Rn), and especially their short-lived decay products, are major contributors to dose received by the public from naturally occurring radioactive material (NORM), particularly in areas with elevated levels of naturally occurring radionuclides. Mining in such areas can involve ventilation of high amounts of these gases, which may influence outdoor levels. In this work, we assessed indoor and outdoor levels of ²²²Rn, ²²⁰Rn and ²²⁰Rn decay products (TnDP) in close proximity to an area with elevated bedrock levels of thorium (²³²Th) and a NORM legacy mining site with high natural ventilation. We assess municipal buildings at distances from a few hundred meters to 2 km from the NORM legacy mines. In some buildings, high indoor levels of ²²²Rn were observed in winter, as expected for temperate areas. In summer, high indoor levels of ²²²Rn and ²²⁰Rn were observed in some buildings, and very low associated levels of TnDP in actively ventilated buildings may suggest entry by ventilation and an outdoor source. Outdoor levels of TnDP increased with decreased distance from the legacy mines, suggesting dispersal from these during both summer and winter.

Outdoor thoron and progeny in a thorium rich area with old decommissioned mines and waste rock

Radon (²²²Rn), thoron (²²⁰Rn) and their decay products may reach high levels in areas of high natural background radiation, with increased risk associated with mining areas. Historically, the focus has mostly been placed upon radon and progeny (RnP), but recently there have been reports of significant contributions to dose from thoron progeny (TnP). However, few direct measurements of TnP exist under outdoor conditions. Therefore, we assessed the outdoor activity concentrations of radon, thoron and TnP in an area of igneous bedrock with extreme levels of radionuclides in the thorium decay series. The area is characterized by decommissioned mines and waste rock deposits, which provide a large surface area for radon and thoron emanation and high porosity enhancing exhalation. Extreme levels of thorium and thoron have previously been reported from this area and to improve dose rate estimates we also measured TnP using filter sampling and time-integrating alpha track detectors. We found high to extreme levels of thoron and TnP and the associated dose rates relevant for inhalation were up to 8 μSvh^-1 at 100 cm height. Taking gamma irradiation and RnP into account, significant combined doses may result from occupancies in this area. This applies to recreational use of the area and especially previous and planned road-works, which in the worst case could involve doses as large as 23.4 mSv y^-1. However, radon and thoron levels were much more intense on a hot September day than during time-integrated measurements made the subsequent colder and wetter month, especially along the ground. This may be explained by cold air observed flowing out from inside the mines through a drainage pipe adjacent to the measurement stations. During warm periods, activity concentrations may therefore be due to both local exhalation from the ground and air ventilating from the mines. However, a substantially lower level of TnP was measured on the September day using filter sampling, as compared to what was measured with time-integrative alpha track detectors. A possible explanation could be reduced filter efficiency related to the attached progeny of some aerosol sizes, but a more likely cause is an upwards bias on TnP detectors associated with assumed deposition velocity, which may be different in outdoor conditions with wind or a larger fraction of unattached progeny. There is thus a need for better instrumentation when dealing with outdoor TnP.

Radon emanation from backfilled mill tailings in underground uranium mine

Coarser mill tailings used as backfill to stabilize the stoped out areas in underground uranium mines is a potential source of radon contamination. This paper presents the quantitative assessment of radon emanation from the backfilled tailings in Jaduguda mine, India using a cylindrical accumulator. Some of the important parameters such as (226)Ra activity concentration, bulk density, bulk porosity, moisture content and radon emanation factor of the tailings affecting radon emanation were determined in the laboratory. The study revealed that the radon emanation rate of the tailings varied in the range of 0.12-7.03 Bq m(-2) s(-1) with geometric mean of 1.01 Bq m(-2) s(-1) and geometric standard deviation of 3.39. An increase in radon emanation rate was noticed up to a moisture saturation of 0.09 in the tailings, after which the emanation rate gradually started declining with saturation due to low diffusion coefficient of radon in the saturated tailings. Radon emanation factor of the tailings varied in the range of 0.08-0.23 with the mean value of 0.21. The emanation factor of the tailings with moisture saturation level over 0.09 was found to be about three times higher than that of the absolutely dry tailings. The empirical relationship obtained between (222)Rn emanation rate and (226)Ra activity concentration of the tailings indicated a significant positive linear correlation (r = 0.95, p < 0.001). This relationship may be useful for quick prediction of radon emanation rate from the backfill material of similar nature.

Radon emanation from low-grade uranium ore

Estimation of radon emanation in uranium mines is given top priority to minimize the risk of inhalation exposure due to short-lived radon progeny. This paper describes the radon emanation studies conducted in the laboratory as well as inside an operating underground uranium mine at Jaduguda, India. Some of the important parameters, such as grade/(226)Ra activity, moisture content, bulk density, porosity and emanation fraction of ore, governing the migration of radon through the ore were determined. Emanation from the ore samples in terms of emanation rate and emanation fraction was measured in the laboratory under airtight condition in glass jar. The in situ radon emanation rate inside the mine was measured from drill holes made in the ore body. The in situ(222)Rn emanation rate from the mine walls varied in the range of 0.22-51.84 × 10(-3) Bq m(-2) s(-1) with the geometric mean of 8.68 × 10(-3) Bq m(-2) s(-1). A significant positive linear correlation (r = 0.99, p < 0.001) between in situ(222)Rn emanation rate and the ore grade was observed. The emanation fraction of the ore samples, which varied in the range of 0.004-0.089 with mean value of 0.025 ± 0.02, showed poor correlation with ore grade and porosity. Empirical relationships between radon emanation rate and the ore grade/(226)Ra were also established for quick prediction of radon emanation rate from the ore body.

Study of the distribution of ²²⁶Ra in ground water near the uranium industry of Jharkhand, India

Ground water is the principal source of drinking water in the rural areas of India. With the aim of determining, the contribution of (226)Ra to natural background radiation through drinking water exposure pathway near an operating uranium mining industry at Jaduguda, Jharkhand state of eastern India, the (226)Ra activity concentrations were measured in potable ground water. The water analysed, both tube well and well water, was collected in areas near the uranium industry and away. The (226)Ra concentration was measured by emanometric technique. The (226)Ra level in ground water was ranging between minimum detection limit of 3.5 mBq l(-1) and a maximum of 208 mBq l(-1). The analysis of variance reveals that there is insignificant statistical variation in the median (226)Ra concentration up to a distance of >10 km from the mining complex. Variation in concentration of (226)Ra in sources is attributed to the local geochemistry and environmental factors. The (226)Ra concentration was significantly elevated in natural artesian wells in the vicinity of uranium mineralised hill and it varies from 53.4 to 754 mBq l(-1). The WHO [Guidelines for Drinking Water Quality. Third Edition, Vol. 1, Recommendation (2004)] guideline value of 1000 mBq l(-1) has not been exceeded in any of the sources investigated.

Radiation dose to members of public residing around uranium mining complex, Jaduguda, Jharkhand, India

Uranium mining activities in the Jaduguda region of Jharkhand state, India have been carried out for the last five decades. Radioactive releases from mines, ore processing facility and tailings pond may increase the natural radiation dose to members of the public residing around the complex. It is, therefore, imperative to investigate the radiological condition around the uranium mining complex and assess the dose received by them. In the present study, it was estimated that the average radiation dose from all exposure pathways to the public living in villages around the mining complex is 2.5 mSv y(-1) and around 50 % contributed due to inhalation of radon and its progeny. The external radiation dose due to terrestrial and cosmic activity is estimated to be 1.1 mSv y(-1), which is 40 % of the total dose and ingestion dose contributes only 3% to the total dose.

Radon in the environment and in dwellings in a uranium mining area in eastern India: an overview

Radon has been extensively studied in the Singhbhum Thrust Belt (STB) of eastern India where mining and processing of uranium ore has been in progress for over four decades. Emanation from the soil is the main natural source of environmental radon. Releases from mine and emanations from waste rocks and tailings are the technological sources. Rn studies in the environment, dwellings and ground waters in STB are reviewed in this paper.

Spatial distribution of gamma radiation levels in surface soils from Jaduguda uranium mineralization zone, Jharkhand, India, using γ-ray spectrometry, and determination of outdoor dose to the population

The concentrations of natural radionuclides in surface soil samples around selected villages of Jaduguda were investigated and compared with the radioactivity level in the region. Concentrations of ²³⁸U, ²³²Th, and ⁴⁰K were determined by a gamma ray spectrometer using the HPGe detector with 50% relative efficiency, and the radiation dose to the local population was estimated. The average estimated activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K in the surface soil were 53.8, 44.2 and 464.2 Bq kg⁻¹ respectively. The average absorbed dose rate in the study area was estimated to be 72.5 nGy h-1, where as the annual effective dose to the population was 0.09 mSv y-1. A correlation analysis was made between measured dose rate and individual radionuclides, in order to delineate the contribution of the respective nuclides towards dose rate. The radio-elemental concentrations of uranium, thorium and potassium estimated for the soils, in the study area, indicated the enrichment of uranium series nuclide. The results of the present study were subsequently compared with international and national recommended values.

Geographic variability in radon exhalation at a rehabilitated uranium mine in the Northern Territory, Australia

In this study, dry season radon flux densities and radon fluxes have been determined at the rehabilitated Nabarlek uranium mine in northern Australia using conventional charcoal canisters. Environmental background levels amounted to 31+/- 15 milli Becquerel per m(2) per second (mBq m(-2) s(-1)). Radon flux densities within the fenced rehabilitated mine area showed large variations with a maximum of 6500 mBq m(-2) s(-1) at an area south of the former pit characterised by a disequilibrium between (226)Ra and (238)U. Radon flux densities were also high above the areas of the former pit (mean 971 mBq m(-2) s(-1)) and waste rock dump (mean 335 mBq m(-2) s(-1)). The lower limit for the total pre-mining radon flux from the fenced area (140 ha) was estimated to 214 kBq s(-1), post-mining radon flux amounted to 174 kBq s(-1). Our study highlights that the results of radon flux studies are vitally dependant on the selection of individual survey points. We suggest the use of a randomised system for both the selection of survey points and the placement of charcoal canisters at each survey point, to avoid over estimation of radon flux densities. It is also important to emphasize the significance of having reliable pre-mining radiological data available to assess the success of rehabilitation of a uranium mine site.

Radon and 'King Solomon's Miners': Faynan Orefield, Jordanian Desert

Concentrations of 222Rn were measured in ancient copper mines which exploited the Faynan Orefield in the South-Western Jordanian Desert. The concentrations of radon gas detected indicate that the ancient metal workers would have been exposed to a significant health risk and indicate that any future attempt to exploit the copper ores must deal with the hazard identified. Seasonal variations in radon concentrations are noted and these are linked to the ventilation of the mines. These modern data are used to explore the differential exposure to radon and the health of ancient mining communities.