Abundance Of Uranium Research Articles

Isotopic uranium activity ratios in California groundwater

Whether the uranium MCL is met in California depends on what conversion factor is used.Uranium, a kidney toxicant and a radioactive material, is present at elevated concentrations in groundwater in some states. In 1991 the US Environmental Protection Agency proposed a maximum contaminant level (MCL) for uranium in drinking water of 20 μg/L or 30 pCi/L (1.1 Bq/L). In 1992 California adopted an MCL of 20 pCi/L (0.74 Bq/L). Because California regulations permit analysis of uranium by either mass or radiochemical techniques, a reliable factor that converts values from mass to activity is required to determine compliance with the California MCL and any future federal MCL. The conversion factor for groundwater may differ markedly from that of the natural crustal abundance of uranium. This study compared values determined by three mass measurement techniques and two radiochemical techniques. It is suggested that a conversion factor of 0.79 pCi/μg be used to determine compliance with the California MCL.

Leaching of Spent Fuel in Cladding Segments and After Removal From Cladding

AbstractIn the early 1980s, tests of the leaching behavior of spent light water reactor fuel were conducted in Sweden by SKB and in the USA by the NNWSI Project. Both organizations used fuels with similar burnup, leaching solutions with similar chemical compositions, and conducted the tests at ambient hot cell temperature. Most of the test results were closely similar. The exception was in the recovery of actinide elements at the end of leaching cycles. In the NNWSI tests, the test vessels were stripped with nitric acid at the end of the leaching cycle. When the actinide inventories recovered in the original leaching cycle plus vessel rinse solutions were added to the amount recovered from the acid stripping, the relative abundances of uranium, plutonium, and other actinides were approximately the same as their inventories in the fuel samples. In the SKB tests, the materials recovered from stripping the leaching vessels were low in amount and interpreted to be fine fuel fragments. Only a few percent of the plutonium inventory that would correspond to the uranium recovered in solution was accounted for in the solution samples. To investigate the reasons for this difference in recovery of the actinides, a new test was undertaken using a fuel sample that had been leached for several years using the SKB methods. The fuel was removed from the cladding after a total of a bit more than two years of leaching inside the cladding. The bare fuel was then leached for several cycles using a geometry that simulated the NNWSI tests and a test procedure that was similar to that used in the NNWSI tests. The cladding from which the fuel was removed was also leached in a separate vessel in parallel with the bare fuel leaching. This paper presents the results of the test series and discusses the effects of specimen geometry on the mobility of actinides during leaching. During leaching of spent fuel inside the original cladding, a secondary phase containing Pu seems to form. This phase appears to be less easily dissolved than spent fuel itself.

A model to explain the various paradoxes associated with mantle noble gas geochemistry.

As a result of an energetic accretion, the Earth is a volatile-poor and strongly differentiated planet. The volatile elements can be accounted for by a late veneer ( approximately 1% of total mass of the Earth). The incompatible elements are strongly concentrated into the exosphere (atmosphere, oceans, sediments, and crust) and upper mantle. Recent geochemical models invoke a large primordial undegassed reservoir with chondritic abundances of uranium and helium, which is clearly at odds with mass and energy balance calculations. The basic assumption behind these models is that excess "primordial" 3He is responsible for 3He/4He ratios higher than the average for midocean ridge basalts. The evidence however favors depletion of 3He and excessive depletion of 4He and, therefore, favors a refractory, residual (low U, Th) source Petrological processes such as melt-crystal and melt-gas separation fractionate helium from U and Th and, with time, generate inhomogeneities in the 3He/4He ratio. A self-consistent model for noble gases involves a gas-poor planet with trapping of CO2 and noble gases in the shallow mantle. Such trapped gases are released by later tectonic and magmatic processes. Most of the mantle was depleted and degassed during the accretion process. High 3He/4He gases are viewed as products of ancient gas exsolution stored in low U environments, rather than products of primordial reservoirs.

Antineutrino geophysics with liquid scintillator detectors

Detecting the antineutrinos emitted by the decay of radioactive elements in the mantle and crust could provide a direct measurement of the total abundance of uranium and thorium in the Earth. In calculating the antineutrino flux at specific sites, the local geology of the crust and the background from the world's nuclear power reactors are important considerations. Employing a global crustal map, with type and thickness data, and using recent estimates of the uranium and thorium distribution in the Earth, we calculate the antineutrino event rate for two new neutrino detectors. We show that spectral features allow terrestrial antineutrino events to be identified above reactor antineutrino backgrounds and that the uranium and thorium contributions can be separately determined.

Abundance of Uranium and Thorium in Rock Salts. Partition of Uranium and Thorium between Solid and Solution Phases in Neutral Environments in Nature.

Uranium and thorium contents of German rock salts were determined by neutron activation analysis. Mean contents of nine samples were 1.07 ppb and 96 ppt for U and Th, respectively. U thus was thought to be depleted and Th was enriched in the solid phase in evaporation of sea water. Similar tendency was observed for other halite samples in nature. These results are consistent with the existence of the stable uranyl tricarbonate anion in the solution phase.

The Background of Regional Lead Isotopic Compositions and Its Application in the Lower and Middle Reaches of the Yangtze River and Neighbouring Areas

AbstractThe paper systematically deals with the background of regional isotopic compositions in the lower and middle reaches of the Yangtze River and neighbouring areas. It is shown that the lead isotopic compositions of different geological formations and units are controlled by the primary mantle heterogeneity, dynamic process of crust—mantle interchange, abundances of uranium, thorium and lead of various layers of the earth and timing. Studies on the background of regional isotopic compositions may offer significant information for geochemical regionalization, tracing of sources of ore–forming materials, and regional prognosis of ore deposits.

Abundance and distribution of uranium in Senonian phosphorites, Arad Basin, southern Israel: D. Gill & Y. Shiloni, Journal of African Earth Sciences, 20(1), 1995, pp 17–28

Abundance and distribution of uranium in Senonian phosphorites, Arad Basin, southern Israel: D. Gill & Y. Shiloni, Journal of African Earth Sciences, 20(1), 1995, pp 17–28

Development of a high-sensitivity inductively coupled plasma mass spectrometer for actinide measurement in the femtogram range

A quadrupole inductively coupled plasma mass spectrometer was modified and developed to achieve very low detection limits, down to a few femtograms in the actinide range. This type of performance was achieved through improvements in the interface pumping system of a conventional ICP-MS instrument, resulting approximately in a 3-fold gain in sensitivity, a 3-fold reduction in background noise, a 2-fold reduction in protenated uranium abundance and a 4-fold reduction in detection limits. A further gain in sensitivity and detection limits, by a factor of 7, was obtained using a high-efficiency desolvating nebulizer which further reduces protenated uranium abundance. The detection limit achieved with good reproducibility, using the high-efficiency desolvating nebulizer on standard solutions, is close to 1.2 fg. The performance of the new instrument is discussed and compared with that of radiometric techniques, with particular reference to plutonium, using standard solutions and real samples. The ‘half-life cut off’ between ICP-MS and alpha-spectrometry is close to 650 years. Intercomparison of plutonium measurements from 300 pg down to 35 fg in 16 environmental samples shows good agreement. The plutonium detection limits in real matrices are greater than those in clean samples and vary from 1.5 to 3 fg. The high-sensitivity ICP-MS system gives access to environmental contamination of other long-lived radionuclides, e.g., 99Tc, 237Np and uranium isotopes, which are sometimes difficult to measure at very low levels using conventional techniques.

Detailed abundances of rare earth elements, thorium and uranium in chondritic meteorites: An ICP‐MS study

Abstract— Inductively coupled plasma mass spectrometry (ICP‐MS) was successfully applied to bulk samples of Allende, Jilin, Modoc, Saint‐Séverin and Atlanta for the determination of rare earth elements (REE) (Y and 14 lanthanoids), Th and U. The results of ICP‐MS showed good agreement with recommended values, and their reproducibilities were high enough to discuss the detailed abundances of lanthanoids and actinoids in chondritic meteorites. For the Allende reference sample issued by the Smithsonian Institution, a positive anomaly of Tm, a fractionation between light REE and heavy REE and a high Th/U ratio were observed in the CI‐normalized abundances of REE, Th and U. These features are common for group II inclusions in Allende, suggesting that the abundances of refractory lithophiles in Allende are somewhat influenced by those in a specific constituent. For the other chondritic meteorites, a zigzag alteration was commonly observed in the heavy‐REE region of their CI‐normalized abundance patterns. It is suggested that such a zigzag pattern is attributable to erratically high abundances of monoisotopic REE (Tb, Ho and Tm) in the CI values. Abundances of REE, Th and U in the bulk samples are also discussed separately in detail.

Abundance and distribution of uranium in Senonian phosphorites, Arad basin, southern Israel

The Senonian phosphorites in the Arad basin contain significant amounts of uranium. The average uranium concentrations in the Ghareb Formation, and the phosphate-lean and phosphate-rich beds of the Mishash Formation are 22, 47 and 106 ppm, respectively, and the average uranium/phosphate ratios in these units are 7.4, 5.5 and 4.5. It is estimated that the Mishash and Ghareb Formations contains about 3,900 and 350 tons of uranium per square kilometre, respectively. The abundance of uranium and its relations to the concentration of phosphate is examined in various subpopulations defined by stratigraphic position and/or phosphate content. There exists a high positive correlation between the concentrations of uranium and phosphate (R=0.9 for individual samples and R=0.98 for means). The regression line between the two variables is Uppm=9.0+4.0(phosphate%). The positive intercept indicates the existence of excessive amounts of uranium, over and above the concentrations which can be attributed to the uranium which is incorporated in francolite. Since independent uranium minerals are found in association with the phosphorites, the extra uranium is most likely due to secondary uranium minerals, formed by the leaching of uranium from the phosphorites. The possible remobilization of uranium out of phosphorites poses obvious potential environmental hazards for land use and the toxic contamination of groundwater resources.

Risks From Radon Progeny Exposure: What We Know, and What We Need to Know

Scientific interest in radon spans 90 years since it was first discovered by Dom (1) in 1900 and detected in air by Elster & Geitel (2) in 1901. It is an inert radioactive gas that occurs naturally in the environment. Although there are 25 known isotopes of radon, only three occur naturally in the environ­ ment. These isotopes, 219Rn, 220Rn and 222Rn, arise as a result of radioactive decay series beginning with either uranium or thorium isotopes. From dosimetry and risk perspectives, 219Rn is unimportant because of its very low concentrations in air, due mainly to the scarcity of its parent radionuclide, 235U, and its very short half-life (3 .9 seconds). Radon-220 (thoron) is a radioactive progeny (or daughter) of naturally occurring 232Th, as is 222Rn, a progeny of 238U. Radon-220 and 222Rn are produced in similar quantities worldwide because of the similarities in the crustal abundances of uranium and thorium (about 25 Bq/kg earth) (3). However, differences in half-lives and aerosol properties between the two isotopes produce about a fivefold

Radioelement distribution in U, Th, Mo, and rare-earth-element pegmatites, skarns, and veins in a portion of the Grenville Province, Ontario and Quebec

Gamma-ray spectrometer measurements were obtained at and in the vicinity of 104 of the 124 U, Th, Mo, and rare-earth-element (REE) occurrences examined in the Central Metasedimentary Belt of the Grenville Province. Spatial, temporal, mineralogical, and geochemical relationships among granitic pegmatites, phlogopite – scapolite – Ca pyroxene skarns, and fluorite – apatite – calcite veins hosting U, Th, Mo, and REE minerals indicate a common magmatic–hydrothermal origin. Quartz–feldspar gneisses in the Central Metasedimentary Belt (n = 54) have low abundances of uranium (1–7 ppm) and thorium (4–27 ppm) suggesting that partial melting, fractional crystallization, and volatile phase separation were responsible for the enrichment of uranium (2–37 ppm) and thorium (5–102 ppm) in uncontaminated granitic pegmatites (n = 163) derived during ultrametamorphism. The U/Th ratio is probably inherited from the source quartz–feldspar gneiss protolith and enhanced during fractionation.Average U and Th concentrations and U/Th ratios at numerous localities show significant positive correlations among pegmatites, skarns, and veins, providing further evidence for a related origin. The interaction of the pegmatite-derived hydrothermal fluids with host rocks produced a spectrum of types and styles of alteration, which include (i) hybridization and (or) endoskarnification along pegmatite margins; (ii) marble- and clinopyroxenite-hosted exoskarn; and (iii) fluorite–apatite–calcite veins. The deposition of U, Th, Mo, and REE from the evolving hydrothermal fluid is responsible for the heterogeneous distribution of U, Th, and REE minerals and molybdenite within pegmatites, skarns, and veins at each locality. Secondary enrichment of uranium in association with hematitized sheared pegmatites and veins may be responsible for the observed large variation in U/Th ratios at some sites.

Radon‐222 Concentration and Aquifer Lithology in North Carolina

AbstractThe presence of the radioactive gas radon (Rn‐222) in many ground water supplies is a potentially significant source of public exposure to ionizing radiation. A wide range of radon concentrations has been measured in ground water in North Carolina, including some far in excess of national average concentrations. North Carolina is, however, geologically complex and ground water radon concentrations vary considerably among the state's aquifers. The highest average radon concentrations occur in areas underlain by granites (geometric mean 5910 pCi/l), and the lowest occur in the Atlantic Coastal Plain region (48 pCi/l). Average radon levels intermediate between these extremes are characteristic of the large areas of North Carolina underlain by gneisses, schists and metavolcanic rocks. Relative average radon concentrations in ground water from the rock types surveyed are consistent with relative abundances of uranium, the parent element of radon, in these rocks. Although other geologic and hydrologic factors also have an effect, aquifer lithology is a useful predictor of the concentration of radon in ground water. The occurrence of high radon concentrations in certain aquifer types; such as granites, shows that geologic factors should be considered in estimates of population exposure to radon, and that knowledge of aquifer geology can help to predict ground water radon concentrations in areas where field sampling has not been done.

Determination of the uranium abundance in the Ap star 73 Dra using the line U II ? 3859.58

The uranium abundance in the atmosphere of the Ap star 73 Dra has been determined by the method of synthetic spectra using four spectrograms in the interval 3858.5-3860.5 A containing the line UU II lambda 3859.58. As a preliminary, the spectrum of Procyon was used to check the oscillator strengths of the lines in this interval; there was found to be a discrepancy between the theory and the observed central depth of the strong line Fe I lambda 3859.91, which did not disappear even after the model of the atmosphere of Procyon had been augmented by a model of the chromosphere and allowance made for the enhanced ionization of the Fe I atoms due to deviation from local thermodynamic equilibrium. Analysis of the line U II lambda 3859.58 confirmed the high uranium abundance found for 73 Dra from an ultraviolet spectrum obtained at the Astron station. From the average over the four spectra, which corresponded to the phases phi = 0.375, 0.88, 0.19, and 0.77, the uranium abundance was found to be log epsilon(U) = 4.1, this exceeding by four orders of magnitude the value log epsilon(U) = 0.1-0.2 found from meteorites.

African anorogenic alkaline magmatism and mineralization — a discussion with reference to the Niger-Nigerian Province

The close of the Pan-African was characterized by a change from subduction and arc related magmatism to post tectonic alkaline magmatism in Saudi Arabia and West Africa. For the remainder of the Phanerozoic, folding and tectonism was more restricted in Africa than on any other continent and was limited to the Caledonian, Hercynian and Alpine orogenies in the extreme north, and the Cape fold belt at the southern tip of the continent, with an equivalent orogenic belt on the extreme east of the Arabian peninsula. Thus Phanerozoic magmatism was dominantly anorogenic in nature and alkaline in character throughout the African Plate. Such magmatism was initiated by reactivation of deep-seated lineaments with the peak of activity during the Mesozoic, which can be correlated with fragmentation of Gondwanaland. The Phanerozoic alkaline magmatism is characterised by small centres of subvolanic to plutonic nature often in the form of ring complexes. These can be subdivided into two separate associations consisting of Provinces dominated by centres of oversaturated magmatism such as Nigeria and Sudan. There are also provinces with undersaturated complexes and carbonatites with oversaturated magmatism such as in Namibia, Angola, and the East African rift system. Despite the contrasting nature of undersaturated and oversaturated magmatism many comparisons can be drawn between carbonatites and granitic complexes. Such comparisons include the source of the magmas, the mechanisms of emplacement, the cause and effect of alkali metasomatism and processes of hydrothermal alteration, the trace element geochemistry, the abundance of zircon, uranium, thorium and complex Ti-Zr silicates, the importance of columbite, pyrochlore, fluorine, and rare earth enrichment in mineralization, and in their current and future economic potential. The common feature is the development and reactivation of deep-seated lineaments which were not only controlled the emplacement of anorogenic complexes but also acted as channelways for hydrothermal mineralizing fluids. The development of a fluid phase during crystallisation occurred in both undersaturated and oversaturated alkaline rocks. Subsequent hydrothermal modifications, subsolidus reactions, geochemical variations and mineralization were dependent upon whether this fluid phase was retained or expelled.

Ore petrography of a sedimentary uranium deposit, Live Oak County, Texas

Samples from the McLean 5 open-pit uranium mine, a small high-grade deposit located along a normal fault in the Miocene Oakville sandstone of Live Oak County, Texas, have been studied for uranium abundance, distribution, and nature of occurrence on the microscopic level. The host sandstone is composed of quartz, feldspars, and volcanic rock fragments, cemented by sparry calcite. Authigenic minerals include iron disulfide minerals (dominantly pyrite and some marcasite) and small amounts of clays, Ti oxides, and opal. High-grade ore (to 3% U) occurs along the fault, decreasing to less than 1,000 ppm within 10 m from the fault. The ore mineral is amorphous pitchblende and exhibits botryoidal morphology.The microscopic occurrence of uranium, documented by fission-track mapping of petrographic thin sections, is presented in detail. Uranium occurs abundantly as grain coatings and fillings in intergranular spaces in samples with high uranium content, where calcite cement has been partially or totally leached as mineralization proceeded. Lesser amounts are adsorbed onto leucoxene (microcrystalline anatase), mud clasts, and altered igneous rock fragments. Adsorbed uranium is the major mode of occurrence in samples, with lower uranium contents farther from the orebody.Textural relations indicate that iron sulfides formed both before and after mineralization. Initial mineralization was by adsorption onto aggregates of fine particles of Ti oxide and clay minerals of various origins. With dissolution of cement and continued uranium influx, uranium precipitated as grain coatings and pore fillings.

Thorium and uranium abundances in the Jilin H5 chondrite

Thorium and uranium abundances have been measured in the Jilin H5 chondrite by radiochemical neutron activation analysis. Although the abundances of (35.8 ± 1.5) ppb Th and (14.9 ± 0.9) ppb U are within the range of literature values, the ratio Th/U is about 25% lower than the average value for H chondrites. Terrestrial addition of uranium appears to be the most likely explanation.

Some observations on the geochemistry and isotopic composition of uranium in relation to the reprocessing of nuclear fuels

In order to determine whether or not uranium depleted in 235U and derived from the British Nuclear Fuels Ltd (BNFL) nuclear fuel reprocessingg plant at Sellafield, Cumbria, UK can be detected in environmental samples, we have investigated the isotopic composition of uranium in ammonium carbonate leachates from marine and terrestial samples from near Sellafield. Some show a depletion in 235U and the presence of 236U which unequivocally identifies the presence of uranium derived from BNFL. The 234U/ 238U activity ratio and total uranium content of samples are not significantly different from those of natural uranium abundances. The highest concentrations of uranium are found in anaerobic organic-rich silts and the lowest in sandy silts and coarse-grained sands.

Helium on Venus: Implications for Uranium and Thorium

Helium is removed at an average rate of 10(6) atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on Earth, suggesting comparable abundances of crustal uranium and thorium.

Uranium in Igneous Rocks of Central Davis Mountains, West Texas: ABSTRACT

The central Davis Mountains are remnants of a Tertiary eruptive center composed of layered extrusives and a few shallow intrusions. Rock types range from basalts to trachyandesites, latites, trachytes, syenites, and rhyolites. Delayed-neutron counting was used to determine uranium abundance in 102 rock samples representative of all rock types. Thin sections of 72 samples, 30 with fission-track data, were analyzed for petrography, mineralogy, and uranium distribution and mode of occurrence. Major-element analyses for 23 samples were obtained for comparison with trends in uranium abundance. Uranium abundance increases in general with SiO2 and K2O content, and ranges from a mean of 1 ppm in basalts and andesites to 7 ppm in rhyolites. Uranium is most abundant in welded tuffs, in contrast to lava flows and shallow intrusions. Hydrothermal alteration redistributes uranium; unaltered rocks have significantly more uranium than altered rocks of all types. Glassy rocks contain up to one-third more uranium than their crystalline counterparts. In a vertical section through three rhyolitic-welded tuff units, uranium increases progressively from the oldest unit to the youngest; within each of two of these units, uranium also increases upsection. Further, rhyolitic-welded tuffs from the southwest part of the area contain 50% more uranium than those from the eas ; the eruptive source, however, has not been located. Within a given rock type, uranium occurs preferentially in accessory minerals, in areas surrounding hydrothermally leached zones, and in vein fillings. Coarse-grained rocks have more localized concentrations of uranium than aphanitic or glassy rocks. Ground-water leaching of uranium from igneous rocks of the central Davis Mountains is not considered an effective mechanism for uranium redistribution and enrichment because of the low permeability of the rocks and the nature of occurrence of uranium. Therefore, the probability of occurrence of large secondary uranium deposits in the area is not high. End_of_Article - Last_Page 545------------