Metric Tons Of Uranium Research Articles

Comparison of uranium complexes with methyl-glutarimidedioxime vs. glutarimidedioxime: A methyl change generates different consequences in thermodynamic equilibria and coordination modes

Nuclear power serves as an important source of alternative energy. However, land uranium resources are limited. In contrast, seawater contains an estimated total of 4.5 billion metric tons of uranium, which is more than a thousand times as much as that found in terrestrial ores. Therefore, developing techniques for uranium extraction from seawater is attracting research attention. Amidoxime-functionalized polymer fibers are the most widely utilized sorbents for this purpose. On the surface of amidoxime-based sorbents, cyclic glutarimidedioxime (H2A) is the preferred configuration for sequestration of uranium from seawater. Methyl-glutarimidedioxime (H2Q) forms if a methyl group attaches to the piperidine ring of H2A. The binding strength of uranyl complexes with H2Q and the enthalpy of complexation were investigated via potentiometry and microcalorimetry, respectively. The coordination mode was further revealed by single-crystal X-ray diffraction. It was expected that H2A and H2Q should be identical in terms of coordination as tridentate ligands. However, our investigation revealed that a methyl group attached to the piperidine ring not only altered the chelating mode but also lowered the binding strength of oxime groups. These findings show that developing a mechanism for optimizing molecules that would be formed on fiber surfaces remains challenging, even a methyl structural change would result in major consequences.

Estimation of External Contamination and Exposure Rates Due to Fission Product Release

In the event of a radiological incident, the release of fission products into the surrounding environment and the ensuing external contamination present a challenge for triage assessment by emergency response personnel. Reference exposure rate and skin dose rate calibration data for emergency response personnel are currently lacking for cases where receptors are externally contaminated with fission products. Simulations were conducted to compute reference exposure rate coefficients and skin dose rate coefficients from photon-emitting fission products of radiological concern. To accomplish this task, simplified mathematical skin phantoms were created using surface area and height specifications from International Commission on Radiological Protection Publication 89. Simulations were conducted using Monte Carlo radiation transport code using newborn, 1-y-old, 5-y-old, 10-y-old, 15-y-old, and adult phantoms for 22 photon-emitting radionuclides. Exposure rate coefficient data were employed in a case study simulating the radionuclide inventory for a 17 × 17 Westinghouse pressurized water reactor, following three burn-up cycles at 14,600 MWd per metric ton of uranium. The decay times following the final cycle represent the relative activity fractions over a period of 0.5-30 d. The resulting data can be used as calibration standards for triage efforts in emergency response protocols.

Extracting Uranium From Seawater

If, like most scientists, you haven’t thought much about the composition of seawater, it may come as a surprise that the oceans contain uranium. In fact, they hold a staggering quantity of the heavy element. “It’s estimated that more than 4 billion metric tons of uranium are dissolved in the Earth’s oceans,” according to Benjamin P. Hay, a distinguished scientist at Oak Ridge National Laboratory (ORNL). That quantity is roughly 1,000 times greater than all known terrestrial sources combined—enough to fuel the world’s nuclear power industry for centuries, even if the industry grows aggressively. World production of uranium in the past decade has ranged from 40,000 to 50,000 tons per year. But as nuclear-fuel scientists point out, tapping the ocean’s uranium for industrial use means coming up with an economically viable, long-term, and large-scale method of extracting an extremely dilute supply of uranium under challenging marine conditions. A number of ...

Spectroscopic and diffraction study of uranium speciation in contaminated vadose zone sediments from the Hanford site, Washington state.

Contamination of vadose zone sediments under tank BX-102 at the Hanford site, Washington, resulted from the accidental release of 7-8 metric tons of uranium dissolved in caustic aqueous sludge in 1951. We have applied synchrotron-based X-ray spectroscopic and diffraction techniques to characterize the speciation of uranium in samples of these contaminated sediments. UIII-edge X-ray absorption fine structure (XAFS) spectroscopic studies demonstrate that uranium occurs predominantly as a uranium(VI) silicate from the uranophane group of minerals. XAFS cannot distinguish between the members of this mineral group due to the near identical local coordination environments of uranium in these phases. However, these phases differ crystallographically, and can be distinguished using X-ray diffraction (XRD) methods. As the concentration of uranium was too low for conventional XRD to detect these phases, X-ray microdiffraction (microXRD) was used to collect diffraction patterns on approximately 20 microm diameter areas of localized high uranium concentration found using microscanning X-ray fluorescence (microSXRF). Only sodium boltwoodite, Na(UO2)(SiO3OH) x 1.5H20, was observed; no other uranophane group minerals were present. Sodium boltwoodite formation has effectively sequestered uranium in these sediments under the current geochemical and hydrologic conditions. Attempts to remediate the uranium contamination will likely face significant difficulties because of the speciation and distribution of uranium in the sediments.

Alteration of monazite and zircon and lead migration as geochemical tracers of fluid paleocirculations around the Oklo–Okélobondo and Bangombé natural nuclear reaction zones (Franceville basin, Gabon)

Large-scale light rare earth element (LREE), uranium, lead and phosphorus migration has been evidenced in the FA Lower Proterozoic sandstones of the Franceville basin (Gabon) hosting Oklo natural nuclear reaction zones (RZ) in relation with extensive accessory mineral alteration by highly saline diagenetic brines (28.7 wt.% NaCl eq. to 30 wt.% CaCl 2 eq.) at about 140°C and 1 kbar. Monazite is the most severely altered accessory mineral in the coarse-grained sandstones of the basal FA formation. Detrital monazite crystals are altered to Th–OH silicate microcrystalline phase with very low concentrations of U and LREE. The Th/La ratio increase from non-altered (Th/La∼0.27) to altered sandstones (Th/La∼1.14) shows that about 76% of the LREE was leached. This corresponds to the leaching of 2.01×10 9 metric tons at the scale of the FA formation in the Franceville basin. Similarly, the Th/U increase from monazite (Th/U=18.6) to the Th-silicate phase (Th/U=88.7) is interpreted as a result of an alteration by oxidizing brines with leaching of U together with LREE and P. It corresponds to the leaching of 9.06×10 6 metric tons of uranium. This amount of uranium largely exceeds the known uranium reserves from the Franceville basin. In zircon crystals, the cores are generally homogeneous, weakly fractured and well preserved as attested by the Archean ages (2867±24 and 2865±51 Ma) obtained by ionic microprobe analysis on zircon of the FA Formation, respectively, from the marginal and central parts of the basin. Their composition corresponds to the pure end-member (Zr,Hf)(SiO 4), poor in Th and U (Th/U∼1). At the contrary, their rims, which present several growth zones with cracks fillings, are enriched in REE, P, Th and U with higher Th/U ratios (5–10). Both altered monazite and altered zircon contain galena as numerous inclusions in the outer growth zones and as crack fillings. For example, in zircon, the Pb of galena crystals (3–23 wt.%) largely exceeds the amount of Pb (maximum 0.1 wt.%) that would have been produced in situ by radioactive decay in this mineral. Nearly all the lead were introduced into altered zones of accessories. Dissolution of accessory minerals occurred at 2000 Ma, producing a porous and distorted crystal structure which has allowed a later incorporation of Pb. Galena inclusions in altered zircons located in the vicinity of reactor zones have radiogenic lead compositions. Altered zircon rims and galena inclusions in altered zircon located far from reactor zones have non-radiogenic Pb isotopic compositions, confirming the external origin of lead. Pb isotopic evolution models indicate a crystallization age sometime after 1000 Ma, both for galena located close to and far from U mineralizations and reactor zones, which may be synchronous with a regional extension event contemporaneous with intrusion of dolerite dyke swarms, between 1000 and 750 Ma, at the scale of the Franceville basin. The present study also illustrates the different retention capacities of accessory mineral for elements representing analogs of the radiotoxic nuclides in the relatively extreme natural conditions created by the circulation of moderately hot and chloride-rich fluids during the diagenesis of a sedimentary basin.

Development of new UV-I.I. Cerenkov viewing device

The Cerenkov glow images from BWR and PWR irradiated fuel assemblies are generally used for inspections. However, sometimes it is difficult or impossible to identify the image by the conventional Cerenkov Viewing Device (CVD), because of the long cooling time and/or low burnup. Now a new UV-I.I. (ultra-violet light image intensifier) CVD has been developed, which can detect the very weak Cerenkov glow from spent fuel assemblies. As this new device uses the newly developed proximity focused type UV-I.I., Cerenkov photons are used efficiently, producing better quality Cerenkov glow images. Moreover, since the image is converted to a video signal, it is easy to improve the signal to noise ratio (S/N) by an image processor. The new CVD was tested at BWR and PWR power plants in Japan, with fuel burnups ranging from 6,200-33,000 MWD/MTU (megawatt days per metric ton of uranium) and cooling times ranging from 370 to 6,200 d. The tests showed that the new CVD is superior to the conventional STA/CRIEPI CVD, and could detect very feeble Cerenkov glow images using an image processor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Current Status and Perspectives of Fissile Material Availability in the World through the Year 2000

Using a realistic evaluation of the likely develop-ment of commercial nuclear power, it is projected that some 428 000 MW(electric) of capacity will be in operation by the year 2000 in noncommunist countries. The availability of fissile material to support this program primarily hinges on the viability of two main industries, namely, the production of natural uranium and enrichment.The demand for natural uranium corresponding to this nuclear program is projected to amount to some 940 000 metric tons of uranium (MTU) through the end of the century. Currently defined reserves in the lower cost of recovery category (i.e., up to $80/kgU) amount to 1.75 million MTU so that such reserves can more than adequately cover needs. When the category of reasonably assured resources of some 550 000 MTU are also taken into account, needs can be covered well into the first half of the next century. There is currently a significant overcapacity for the mining and milling of uranium, and presently definable capacity should be able to meet the annual demand on a worldwide basis until the mid-1990s. However, buyer purchasing strategies and the level of prices will be important to ensure that production will remain or be made available when needed.The demand for enrichment services by the year 2000 will amount to some 47 000 metric tons of separative work units (MTSWU)/yr. Production capacity in operation, under construction, and firmly planned will have attained 45 400 MTSWU/yr by 1990. Further expansion of capacity is possible with very modest lead times. Only a very small increase in capacity would in principle be needed to cover demand in excess of the then existing capacity in the last two or three years of the 1990s. Demand could also be met by a very limited amount of preproduction from the excess capacity of previous years. Because of supply diversification considerations on the part of buyers, there will undoubtedly be further, though probably modest, expansion in supply capacity in the 1990s.

The uranium deposit at Kvanefjeld, the Ilímaussaq intrusion, South Greenland, Geology, reserves and beneficiation

The uranium-thorium deposit is located in part of an alkaline intrusion consisting of peralkaline, agpaitic nepheline syenites. The radioactive minerals are steenstrupine, uranium-rich monazite, thorite and pigmentary material. The radio-element content varies from 100 to 3000 ppm U and 300 to 15000 ppm Th. Reasonably assured ore in the main area with a grade of 310 ppm is calculated to 5800 metric tons of uranium in 18.6 million metric tons of ore. Estimated additional reserves with a grade of 292 ppm U are 29.4 million tons of ore with 8700 tons of uranium and 3.5 million tons of ore with a grade of 350 ppm yielding 1200 tons of uranium. Estimates of amounts of thorium ore are 2.6 times those of uranium. A method of recovery of the uranium based on sulphating roasting and subsequent leaching with water is described.

Irradiation Testing of UO2 Fuel Elements Containing Burnable Poison Additions

Two fuel elements containing 0.05 wt% B4 C in 6% enriched UO2, were irradiated in the Saxton reactor to burnups of ∼1000 and 5000 MWd per metric ton of uranium at peak heat ratings of 17.2 and 19.8 kW/ft, respectively. These elements were fabricated by vibratory compaction to densities of 88 ± 2% of theoretical with local boron concentrations maintained within a variation of ∼ ± 20% of the nominal loading. The postirradiation examination revealed no significant dimensional changes in either element and no axial boron redistribution of any consequence. However, the boron migrated radially outward in both irradiated fuel elements. The boron redistribution does not appear to be a function of burnup but depends heavily on the thermal gradient during irradiation. Its effect on core physics was analyzed using the THERMOS program, and the changes in ηf(ratio of neutrons produced to thermal neutrons absorbed) and Δρ (difference in core reactivity) were found to be minimal.