Grade Uranium Research Articles

Selective Leaching and Separation of Uranium from Ochre-Umm Greifat, Red Sea Coast, Central Eastern Desert, Egypt

The Ochre-Umm Greifat area is one of the Red Sea areas with high concentrations of iron and zinc, which is formed from hydrothermal solutions as a result of the structural activity that occurred in the Red Sea Zone during the Pleistocene period. These deposits are also accompanied by deposits of low- to high uranium grade. In addition to Zn, Pb, and Cu anomalies, particularly in fault zones and their branches affecting the study area, although there are numerous zinc minerals in the Ocher-Greifat area, uranium minerals are scarce, with only one mineral, compreignacite, being recorded and the majority of the uranium being present as an adsorbed element on iron and/or clay stones. In addition, uranothorite is extremely rare and occurs as fine grains embedded in rocks. A technological sample was taken from an iron-rich clay area in a fault zone and was found to assay 700-ppm uranium. The leachability of uranium from the used sample was investigated using an alkaline solution based on the chemical and mineralogical composition of the used sample. The selected ore is treated with Na2CO3 and NaHCO3 in the presence of H2O2 as oxidant. Many digestion factors are studied and optimized. Under the optimum leaching conditions, the uranium dissolution efficiency is around 84%. For the uranium separation, the pH of the leach liquor is adjusted at 10, then subjected to a solvent extraction step using 4% Aliquat®336/kerosene in the presence of isodecanol as third-phase prevention. The loaded organic solvent was then treated with NaOH/H2O2 solution as a stripping solution. Finally, the resultant solution is subjected to a precipitation step using ammonia solution.

Ambient Radiological Condition around an Operating Uranium Mill Tailings Disposal Facility at Turamdih, India

Large quantity of the feed forms part of the solid waste (tailings) slurry in the low grade uranium ore processing plant at Turamdih in Singhbhum region of Jharkhand, India. Coarser size fraction of this waste is used for backfilling of the underground uranium mines and fine fraction is discharged into an engineered impoundment system or tailings pond. Since inception of the discharges, field expeditions have been performed as part of the comprehensive radiological monitoring program for the facility. The monitoring program broadly consists of ambient gamma dose rate, atmospheric 222Rn and long lived alpha activity measurement around the facility and the estimation of radionuclide in diverse environmental matrices collected from the adjoining sites. Findings reflect that the radiological conditions are comparable to the pre-existing background level adjoining the tailings pond impoundment. Further, measurements for more than a decade confirm that the atmospheric radon concentration profile just a few meters beyond the embankment is indistinguishable from the background.

Multifractal Characteristics of Uranium Grade Distribution and Spatial Regularities in a Sandstone-Type Uranium Deposit in Xinjiang, China

Based on an analysis of the spatial distribution of uranium grade in 338 boreholes of a uranium deposit in Xinjiang, the enrichment and spatial variation of uranium ore in two stopes of the deposit are discussed using multifractal theory. The distribution characteristics of the uranium ore of the two stopes are studied by multifractal parameters: the scaling exponent of mass τ(q), the scaling exponent α(q) of each sub-set and its corresponding fractal dimension f(α), the fractal dimension D0 and information dimension D1. The differences of uranium distribution in the two stopes can be quantified well by using multifractal spectrum and multifractal parameters such as Δα, Δf and R. After a comprehensive multifractal distribution analysis, 10 m × 10 m is defined as a fence unit, and the window sizes ε=3,6,9⋯,45 are set; the singularity exponents α of the two stopes are calculated by using this element concentration–area method. The results show that the multifractal theory and model can organically combine spatial structure information, scale change information and anisotropy information to obtain low-grade and weak mineral resources information and can effectively distinguish complex and superimposed anomalies. This will provide a basis for the local concentration and spatial variation rules of uranium distribution and the design of the parameters of the leaching uranium mining well site.

Towards a Mineral Systems Model for Surficial Uranium Mineralization Based on Deposits in the Erongo District of Namibia

Surficial deposits in Namibia’s Erongo district contain substantial but low-grade resources of uranium and vanadium (nearly 500 Mlb U3O8), hosted in palaeochannels. This review attempts to develop a mineral systems model for the deposit type, but it is emphasised that research into this important class of deposit has been minimal since the nineteen eighties, largely as a result of a limited investment in uranium exploration. The deposits are the result of groundwater movement in aquifers developed within Cenozoic palaeochannels. The source of uranium was probably granitic rocks traversed by these palaeodrainages, particularly black-quartz rich pegmatites similar to those that make up the hard-rock alaskite deposits of the region. Transport of uranium is generally assumed to have occurred in aqueous uranium species after palaeochannels became filled with sediment. U-enriched clasts within the palaeochannels have yet to be investigated as a local source of uranium. The localised deposition of uranium occurred after regionally extensive carbonate cementation of the palaeochannel sediments, which was the result of climate change (aridification). Pre-uranium calcite may have acted as a chemical buffer (pH) and probably influenced palaeochannel hydrology, restricting groundwater flow to the deeper portions. Uranium is paragenetically related to Mg clays and dolomite, suggesting that the groundwater evolved to a more Mg-rich composition during uranium deposition, probably as a result of more extreme evaporation. The controls on the localisation of mineralisation remain unclear and unpredictable, as are the controls on uranium grade—the fundamental determinant of economic viability. There are few absolute age determinations for any of the deposits, but none occur in rocks likely to be older than the Miocene. This reflects low preservation potential. For example, the Langer Heinrich deposit is incised by active drainage with attendant erosion and probable removal of mineralised material.

Feasibility studies on the detection of third phase formation in the solvent extraction equipment during reprocessing of fast reactor spent fuels

Fast reactor spent fuel plants reprocess plutonium rich fuel discharged from fast reactors. Centrifugal extractor or mixer settler solvent extraction equipments are employed for the selective recovery of nuclear grade uranium and plutonium from fission products. 30% (v/v) TBP/NPH is used as the solvent in PUREX process. Plutonium rich spent fuel has disadvantage of third phase formation during process upsets. Third phase can leads to flooding thereby prone for nuclear criticality or explosion hazard in evaporators. Hence, the solvent extraction equipments should be continuously monitored to detect onset of third phase. Studies are carried out by placing electrical conductivity probe in the organic outlet of a single stage mixer settler. This study measured electrical conductivity in different runs. 12 M feed nitric acid run and 15.8 M nitric acid feed acidity run indicated the conductivity at organic outlet is beyond 1035 μS/cm, indicated severe flooding as well as two phases in organic collecting container. Uranous in nitric acid run indicated when the A/O change was initiated loaded organic phase (8–11 μS/cm) conductivity at organic outlet decrease to 2.06 μS/cm as well when probe inserted at the organic and aqueous interface jumped to 190 μS/by forming Third phase. The results of this study indicated it is feasible to detect online of third phase in solvent extraction equipment such as mixer settler.

Experimental validation of a CeBr3gamma-ray logging probe MCNP model

Orano Mining has relied on Nuclear Measurement Laboratories for several years to estimate calibration factors for borehole radiometric probes. The total gamma count rate recorded with a NaI(Tl) scintillation detector (NGRS probe) is converted into equivalent uranium grade using a calibration coefficient in s-1.ppmU-1units, estimated thanks to different calibration blocks ranging from 0 to 10,000 ppm of uranium, at Orano CIME calibration facility in Bessines, France. Recently, Orano Mining embarked on an update of its measurement means by associating gamma spectrometry directly in the wellbore. Therefore, Orano Mining has recently tested a CeBr3probe designed and developed by ALT (Advanced Logic Technology) to qualify a patented borehole spectroscopic method based on energy bands recently developed by CEA and Orano. In this context, we have implemented a fine Monte Carlo modelling of this new probe in order to correct the calibration coefficients as a function of different parameters such as the drilling diameter, the presence of a casing, the density of the mineralization, the distance of the probe with respect to the well or casing walls, etc. In the present work, we have simulated the CeBr3probe in the concrete calibration blocks of Orano CIME. The MCNP model of the probe has been validated through a comparison with experimental data. The calibration coefficient determined by simulation is 11.6 s-1.ppm-1> 10 % in total gamma counting, which is in good agreement with the one measured in Bessines, i.e. 10.6 s-1.ppm-1. The calculation vs. experiment agreement is also satisfactory (i.e. within 10 %) for spectroscopic energy bands used to characterize the uranium grade in case of disequilibrium in the uranium chain, when total count rate does not apply. This method recently developed for samples and boreholes will be tested in future work with this new CeBr3probe.

Development and Scale-up of Chemical Process for Conversion of Impure Sodium Diuranate to Uranium Peroxide

Abstract Uranium mills following the sulfuric acid leaching route produce Uranium Peroxide (UP) as uranium ore concentrate (yellow cake), which is then refined to produce nuclear grade uranium products. Whereas the mills processing ores by alkaline leaching route generate Sodium Diuranate (SDU) as yellow cake, which commonly contains impurities viz. Zr, SiO2, Mo, Organic Carbon (OC). These impurities form muck, interfacial crud and acid insolubles during digestion and solvent extraction (SX) stages in refining process. Hence, SDU needs to be pre-treated before processing in the uranium refinery. India has substantial U reserves (>50%) hosted in carbonate minerals matrix which obviously need alkaline processing for extraction of U. In the present study, the origin of impurities in a SDU produced in an Indian Uranium mill was traced back to the mineralogical composition of the ore, chemical reactivity of minerals to the reagents,and build-up of impurities in process streams due to existence of multiple recycle streams in the milling process flowsheet. A process scheme has been developed for converting SDU into highly pure Heat Treated Uranium Peroxide (HTUP). The scheme involves digestion of SDU in sulfuric acid medium followed by separation of insolubles from the liquor which is later subjected to pH controlled U-peroxide precipitation process. The U-peroxide formed was heat treated to drive-off active oxygen and water of crystallization. A HTUP product assaying about 91% U3O8 was produced from an impure SDU assaying 74% U3O8. Process has been demonstrated at large scale (about 100 kg/batch) and engineering data and scale up parameters have been generated.

Synthesis of a New Chelating Iminophosphorane Derivative (Phosphazene) for U(VI) Recovery.

A new synthetic chelating N–hydroxy–N–trioctyl iminophosphorane (HTIP) was prepared through the reaction of trioctylphosphine oxide (TOPO) with N–hydroxylamine hydrochloride in the presence of a Lewis acid (AlCl3). Specifications for the HTIP chelating ligand were successfully determined using many analytical techniques, 13C–NMR, 1H–NMR, FTIR, EDX, and GC–MS analyses, which assured a reasonable synthesis of the HTIP ligand. The ability of HTIP to retain U(VI) ions was investigated. The optimum experimental factors, pH value, experimental time, initial U(VI) ion concentration, HTIP dosage, ambient temperature, and eluents, were attained with solvent extraction techniques. The utmost retention capacity of HTIP/CHCl3 was 247.5 mg/g; it was achieved at pH = 3.0, 25 °C, with 30 min of shaking and 0.99 × 10−3 mol/L. From the stoichiometric calculations, approximately 1.5 hydrogen atoms are released during the extraction at pH 3.0, and 4.0 moles of HTIP ligand were responsible for chelation of one mole of uranyl ions. According to kinetic studies, the pseudo–first order model accurately predicted the kinetics of U(VI) extraction by HTIP ligand with a retention power of 245.47 mg/g. The thermodynamic parameters ΔS°, ΔH°, and ΔG° were also calculated; the extraction process was predicted as an exothermic, spontaneous, and advantageous extraction at low temperatures. As the temperature increased, the value of ∆G° increased. The elution of uranium ions from the loaded HTIP/CHCl3 was achieved using 2.0 mol of H2SO4 with a 99.0% efficiency rate. Finally, the extended variables were used to obtain a uranium concentrate (Na2U2O7, Y.C) with a uranium grade of 69.93% and purity of 93.24%.

Arbitrary estimation of uranium ore reserves in Qattar–V, North Eastern Desert, Egypt using geographic information system

The qattar - V (G-V) uranium occurrence occurs at the contact areas between Gabal Qattar (G - Qattar) granite and Hammamat sedimentary rocks. The aim of this study is to estimate uranium ore reserves using a geographic information system by analyzing all the exploration data sets at G-V. Several geological investigations, including field and mineralogical observations, geochemical and radiometric surveys, have been performed for this uranium occurrence. Integrate these investigations with new radiometric and geochemical measurements to cover all the investigated areas has been done in this study. Using GIS it is possible to visualize the results and to extract the spatial features indicative of uranium mineralization's over G-V uranium occurrence. Our methodology involves the generation of prediction maps for the favorable host rock, structure control of uranium mineralization, alterations in intimate association with uranium, radiometrical and geochemical measurements. Combining all these spatial features leads to the differentiation between the areas with economical and for grades of uranium and the generation of a potential uranium map. From this map, the estimation of uranium ore quantity and quality at G-V uranium occurrences can be calculated using cuboids of constant widths, different lengths, and heights. This method gave arbitrary but reasonable estimates of uranium in selected blocks.

Geological Feature Modeling and Reserve Estimation of Uranium Deposits Based on Multiple Interpolation Methods

Uranium resource distribution and accurate reserve evaluation are important references for mineral investment and production. Eight kinds of interpolation methods in the Groundwater Modeling System (GMS), including ordinary kriging (OK), are used in this study to predict the spatial distribution of reserve-related parameters, such as uranium grade, ore thickness and uranium content per square meter. The present study draws the following conclusions: (1) Cross-validation found that the uranium grade value using the spherical method is the closest to the actual value. The spherical method has the best interpolation effect. (2) The relative error, which is +3.62%, between the uranium reserves that is calculated by the spherical interpolation method and that by the traditional calculation value is the smallest. (3) The setting of the number of interpolation grids is related to the actual number of boreholes. The ratio between the two will affect the accuracy of reserve estimation, and different interpolation methods have different degrees of influence on reserve estimation. This method is applicable to all in-situ leaching sandstone uranium mines. Further study needs to be carried out toward heterogeneity of three-dimensional space, which will make the estimation more accurate.

Reactive transport numerical modeling of CO<sub>2</sub>+O<sub>2</sub> <italic>in-situ</italic> leaching in sandstone-type uranium ore

The CO2+O2 in situ leaching (ISL) technique represents the third generation of in situ uranium leach mining in China. The key point of CO2+O2 ISL is the interaction between the complex hydrodynamic behavior and geochemical reactions. To deal with hydrodynamic evolution, leaching solutions-rock interaction, and reactive kinetics of uranium minerals during ISL uranium mining, a CO2+O2 ISL reactive transport numerical simulation implemented in TOUGHREACT is proposed herein in Qianjiadian uranium deposit. In this study, we developed a chemical thermodynamic database suitable for sandstone-hosted uranium deposits and a method for modeling the kinetic uranium dissolution under the control of oxygen (O2(aq)) and bicarbonate (HCO3–). We conduct a sensitivity analysis to assess the effect of the uncertainties associated with the modeling parameters on the simulation results. The reactive transport simulation successfully reproduced the behavior of dynamic uranium recovery. The sensitivity analysis showed that the initial volume of uranium (uranium grade) and injecting oxygen concentration were very sensitive to changes in the leaching concentration of uranium. This study provides technical support for accurate simulation and dynamic regulation of the CO2+O2 leaching process at a large mining area.

Tectono-Sedimentary Evolution of the Uranium Deposits of the DASA Graben, Northern Niger

This study presents the structural evolution of the N70° trending Paleozoic-Mesozoic DASA graben, which is considered a sub-basin of the Tim Mersoï basin, and is located in northern Niger. The DASA graben is a uranium-rich trough discovered in recent exploration surveys. A tectono-sedimentary analysis of the DASA graben was implemented with a combined use of satellite imagery, field observations, borehole data analysis and available literature. This graben was affected from the Carboniferous to the Early Cretaceous by two major tectonic periods. The first period was an uplifting stage, which prevailed during the Carboniferous-Permian times and the second, ranging from the Triassic to the Early Cretaceous, corresponds to a rifting episode. The particularity of the DASA graben is that the sediments contain very high uranium grades. Lithological and tectonic factors controlled the emplacement of the uranium mineralization in the graben. The successive fracturing phases that affected the DASA graben were associated with a greater circulation of hydrothermal fluids and would have favoured higher grades of uranium mineralization.

Radiochemical technique as a tool for determination and characterisation of El Sela ore grade uranium deposits

ABSTRACT The present study is an application of a radiochemical procedure for the determination of 238U, 235U and 234U as well as uranium isotopic ratios in El Sela ore grade samples that located at the Southeastern Desert of Egypt. This procedure is consisting of several steps include sample preparation, chemical separation and source preparation followed by counting using alpha-particle spectrometry technique. Radiochemical determination of various uranium isotopes contents indicated that El Sela uranium deposits are considered as a recent deposit where there was a large difference between radiochemically and radiometrically determined uranium. The measured 234U/238U activity ratios for most samples were approximately unity, indicating that secular radioactive equilibrium was established between 238U and 234U in the El Sela mineralised rocks. On the other hand, 238U and 234U might be equally leached due to the effect of rock-water interactions during the pluvial time by the action of surficial or underground water. The 238U/235U activity ratios of the studied mineralised granites were significantly shifted from the natural ratio 21.7, indicating that the redox conditions and alteration processes played an important role in the fractionation of 238U from 235U. The values of 234U/235U ratios in the studied granites varied between 23.08 and 34.70 in different samples, suggesting 235U migration out due to the prevailing conditions.

Impacts of gamma ray emissions of materials containing 232U on safety, security, and safeguards

The introduction of 232U to uranium materials is a possible technique to reduce the material attractive of the material for weapons purposes. In order to implement 232U in civilian nuclear fuel cycles, its impacts on safety, security, and safeguards must be considered. This study will utilize an initial mixture of 0.03 at.% 232U with natural uranium, enriched to approximately 3, 5, 20, and 90 at.% 235U. The mixture with natural uranium, 3, 5, and 20 at.% 235U represent uranium isotopic vectors that would be commonly found within civilian nuclear fuel cycles. The 90 at.% 235U isotopic vector represents weapons grade uranium. The security and safeguards results from each isotopic vector will be compared to results from a corresponding isotopic vector that does not contain 232U, but has the same 235U/238U ratio. Considering 232U’s daughter products contribute significantly to the gamma ray emissions over time, the isotopic vectors will be evaluated at three time intervals: fresh, 0.5 year, and 10 years. When compared to standards put in place by U.S. Nuclear Regulatory Commission, the dose rates produced by the uranium isotopic vectors containing 232U indicate the need for additional safety protocol to shield workers from this increased dose rate. These gamma ray emissions produce a significant increase in detectability in the weapons grade uranium isotopic vector with 232U even in the presence of lead shielding. A common safeguards technique used to verify 235U enrichment was shown to be useless in the presence of 232U and its daughter products. This would require the use of a different technique in order to verify the 235U enrichment.

Gene expression response of mutagenic breeding of Acidithiobacillus sp. FJ2 to different concentrations of uranium low grade ore

Acidithiobacillus ferrooxidans ( At. f ) is a bacterium involved in the bioleaching process . In the present study, we investigated the effects of Acidithiobacillus sp. FJ2 induced with diethyl sulfate (DES) as mutagen on the bioleaching of low grade uranium ore. The comparison was carried out within 5, 10, 15, 25 and 50% uranium ore pulp densities in the bioleaching system. The impact of the induction of Acidithiobacillus sp. FJ2 was determined by Eh and pH values, concentrations of Fe 2+ and uranium extraction rates at 24 h intervals. The results showed that DES with 0.8% may lead to an obvious change on bacteria leading to improvement of bioleaching capability in 5, 10, 15% pulp densities. However, the bioleaching activity of the original bacteria was more efficient than DES-induced bacteria at 25 and 50% pulp densities. The gene expression results in 0.8% DES treated bacteria indicated that the bacteria attempt to adjust in the bioleaching systems (with different pulp densities) through decreased cyc2 and increased rus , cyc1 and coxB levels. These results suggest that uranium may induce oxidative stress in the wild and treated strains in the high pulp density, while the bacteria tried to survive and gain more energy from the iron oxidation. However, when the amount of uranium increased, the mutants couldn’t cope up woth the enhanced stress in 25 and 50% pulp densities. It may be due to inhibitory effect of uranium toxicity on adaptive processes which may change the trends.

Study on leaching systems and recovery for PALUA–PARONG low grade uranium sandstone ores

The study on treatment of Palua-Parong uranium low grade ores by different techniques: agitation leaching, strong acidic pugging and curing, and heap leaching was carried out on laboratory and pilot scales. The experimental conditions during the leaching process for uranium recovery from ore such as time, ground particle size, acid influence and temperature effect were investigated. The bench scale experiments developed in a laboratory were tested in pilot with 100 kg of ore sample for each batch. From the experimental results, the heap leaching method was proposed to treat this ore on large scale. The uranium recovery efficiency at pilot scale reached over 80%. The concentration and purification of uranium leached liquor was examined by anion exchange method using Amberlite IRA-420 and INDION GS300 resins. Uranium loading on INDION GS300 resin was approximately 85% that of Amberlite IRA-420.

The effects of U-232 on enrichment and material attractiveness over time

The effect of 232U on enrichment and material attractiveness provides a significant firewall against proliferation. Mixing 232U with natural uranium creates major obstacles to the weaponization process. The decay heat of 232U is significant and increases over time by a factor greater than 5 through the decay of 232U daughter products. The dose rate also becomes significant as 208Tl builds up and emits an energetic gamma ray of 2.615 MeV. These factors, along with the bare critical mass and spontaneous fission neutron rate are used to determine the material’s attractiveness through a Figure of Merit analysis. Considering 232U is lighter than 235U, attempting to enrich a mixture of natural uranium and 232U to weapons grade will also increase the concentration of 232U and thus increase the material’s unattractiveness. This study simulates natural uranium with a 232U concentration of 0.03 at.% being enriched to weapons grade and determines the attractiveness of the resulting uranium vector. The results show that the material becomes unattractive within a year of initial separation. In addition, the alpha decay of 232U in gaseous UF6 will result in the decomposition of UF6 molecules. The rate of this decomposition in the initial natural uranium mixture, the mixture enriched to 3 at.% 235U, and this mixture enriched to 90 at.% 235U is calculated. These rates are notable and may pose a significant firewall to obtaining weapons grade uranium.

Behaviour of Si, Al, Fe and Mg during oxidative sulfuric acid leaching of low grade uranium ore: A kinetic approach

This paper deals with the behavior of reactive micaceous gangue minerals like chlorite and biotite during the oxidative sulfuric acid leaching of uranium ores taking case study of a typical low grade Indian uranium ore hosted by chlorite-biotite-muscovite-quartzo-feldspathic schist. The progress of the gangue minerals chemical reactivity was monitored kinetically by analyzing the concentration of Si, Al, Fe and Mg ions in the leach liquor and through SEM-EDS analysis of feed and leach residue. The kinetic plots were analysed using shrinking core model and the rate equations deduced for all the aforementioned four elements constituting the gangue indicated significant role played by concentration of sulfuric acid, redox potential, temperature of reaction and particle size in the diffusion controlled process, which is also substantiated from the thermodynamic parameters computed. The results indicated decreased particle size, increased sulfuric acid concentration, longer contact time, higher rate of agitation and increased redox potential results in higher concentration of Si, Al, Fe, Mg and U.

Sequence and sedimentary characteristics of upper Cretaceous Sifangtai Formation in northern Songliao Baisn, northeast China: Implications for sandstone-type uranium mineralization

Sequence and sedimentary characteristics play an important role in the mineralization of sandstone-type uranium deposit. Two third-order sequences, including four system tracts namely lowstand system tract (LST), transgression system tract (TST), highstand system tract (HST) and regression system tract (RST), and two sedimentary facies, including braided-meandering river and meandering river are identified in the Upper Cretaceous Sifangtai Formation in northern Songliao Basin. Sandstones with better porosity and permeability formed in LST are good uranium reservoir, and the compacted fine-grained deposits in TST are good confining layers. They form a reservoir-confining assemblage that is beneficial to uranium mineralization. The uranium is mainly hosted in the braided-meandering river depositional system, the channel bar ore-hosting sandstones are connective and have good reservoir property, the maximum porosity and permeability are 42% and 1140 mD, respectively. Suitable thickness and sand percentage of sand bodies are beneficial to uranium enrichment, the industrial grade uranium deposits mainly occur in areas with sand percentage of 0.6–0.8 and sand body thickness of 8–12 m. Organic matter and sulfur act as adsorbents and reducing agents in the progress of uranium mineralization, braided-meandering river with strong hydrodynamic conditions bring a large amount of terrestrial carbon debris, which creates conditions for the formation and adsorption of sulfur and uranium. A sequence and sedimentation uranium metallogenic model of Sifangtai Formation has been established, large and high grade uranium deposits are formed in braided-meandering river sand bodies of LST, which have good reservoir properties, suitable thickness, sufficient organic matter and reducing sulfur content, and regional confining bed.

Modelling the dispersion of radionuclides in dust from a landform covered by low uranium grade waste rock

The dispersion of radionuclides in dust and inhalation dose rates to the public from the planned remediation of the Ranger uranium mine in the wet-dry tropics of Australia was modelled using RESRAD-OFFSITE. Dust inhalation dose rates were predicted to be highest on the remediated site and decrease with an approximate inverse square to inverse cubic dependence with distance from the site. The annual dose above natural background to a hypothetical individual permanently occupying the remediated site (representing the worst case scenario for radionuclide in dust exposure) was estimated to be 5.3 × 10−3 mSv. The estimated doses from exposure to radionuclides in dust were two to three orders of magnitude lower than those from exposure to 222Rn. A sensitivity analysis showed that source-related and receptor-related model parameters had direct proportional influences on dust inhalation dose rates. Four transport-related model parameters (atmospheric stability class, deposition velocity of particulates, precipitation and wind speed) were also influential and generally had an increasing influence with distance from the source. The results of this study may provide general guidance to similar sites elsewhere on the relative importance of dust versus gaseous 222Rn transport pathways and the relative influence of dispersion modelling parameters on predicted exposures and doses.