Devi Prasad Mishra

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.

An improved mathematical model for prediction of air quantity to minimise radiation levels in underground uranium mines

Ventilation is the primary means of controlling radon and its daughter concentrations in an underground uranium mine environment. Therefore, prediction of air quantity is the vital component for planning and designing of ventilation systems to minimise the radiation exposure of miners in underground uranium mines. This paper comprehensively describes the derivation and verification of an improved mathematical model for prediction of air quantity, based on the growth of radon daughters in terms of potential alpha energy concentration (PAEC), to reduce the radiation levels in uranium mines. The model also explains the prediction of air quantity depending upon the quality of intake air to the stopes. This model can be used to evaluate the contribution of different sources to radon concentration in mine atmosphere based on the measurements of radon emanation and exhalation. Moreover, a mathematical relationship has been established for quick prediction of air quantity to achieve the desired radon daughter concentration in the mines.

A comprehensive review on sources of radon and factors affecting radon concentration in underground uranium mines

This paper presents an extensive literature review on the various sources of radon such as ore body, backfill mill tailings, broken ore and mine water in underground uranium mines. This review also comprehensively investigates the influence of intrinsic factors such as ore grade, 226Ra content, water content, porosity and surface area of the materials and the extrinsic factors such as barometric pressure, temperature and ventilation on radon concentration in uranium mines. The objectives of this review are to identify the major sources of radon and the parameters significantly affecting radon concentration in underground uranium mine environment. The review demonstrated that backfill mill tailings are the major source of radon in underground uranium mines. A comparison of radon exhalation rates of different rock types and backfill tailings revealed that porosity has more pronounced effect on radon exhalation process than the ore grade/226Ra content of the materials. The radon exhalation rate from the moist materials is comparatively higher than the dry and saturated tailings. Reduction of barometric pressure in mine environment increases the radon exhalation rate from porous rocks, backfill mill tailings and broken ore piles. The contribution of mine water on radon contamination of mine atmosphere mainly depends on the dissolved radon content and flow rate of water. The current knowledge of the factors affecting radon exhalation process has also been reviewed in this paper.

One-Dimensional Consolidation of Sedimented Stowed Pond Ash and Pond Ash-Lime Mixture Deposits—A Comparative Study

The present study investigates the influence of slaked lime addition on the one-dimensional consolidation properties of sedimented stowed pond ash (Class F category). The effects of step incremental consolidation pressure, lime addition, and curing time on the one-dimensional consolidation characteristics such as rate of settlement, consolidation coefficients, and void ratio, of the sedimented stowed pond ash and pond ash-lime mixture deposits are investigated using a fixed ring consolidometer. The study revealed that the void ratios of both the stowed pond ash and pond ash-lime mixture deposits decrease with the applied pressure. Comparatively, the stowed pond ash-lime mixture deposit demonstrated a higher void ratio than the stowed pond ash deposit. A decrease in coefficient of consolidation (Cv) values with the increase in consolidation pressure and curing time is also observed in the case of both deposits, thereby indicating a decrease in their compressibility. Owing to the addition of lime, an improvement in the consolidation characteristics in terms of increase in Cv values and decrease in final settlement of the sedimented stowed pond ash-lime mixture deposit is generally observed at higher consolidation pressures and longer curing time.

Comprehensive Characterization of Pond Ash and Pond Ash Slurries for Hydraulic Stowing in Underground Coal Mines

In this study, the physicochemical and self-heating characteristics of pond ashes from Talcher Thermal Power Station (TTPS), located in the Angul district of the Indian state of Odisha are studied. The study revealed that the TTPS pond ashes belong to Class F fly ash category consisting mainly of SiO2, Al2O3, and Fe2O3, with a small amount of CaO. The presence of mineral phases, namely, quartz, mullite, magnetite, and hematite in the pond ash are confirmed by x-ray diffraction. Based on the pond ash properties, various properties of the slurries of one representative pond ash, namely, density, volume concentration, and viscosity are determined by varying the ash concentration from 45% to 65% with an increment of 5%. As well, the critical deposition velocities of slurries as a function of slurry concentration and pipe diameter are determined. The results showed that the slurry viscosity increases exponentially with increase in solid content and the critical velocity increases linearly with increase in slurry concentration and pipe diameter. The relationships generated through regression analysis can be used to quickly predict the critical velocity of similar types of ash slurries for any known slurry concentrations and pipe sizes.