bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preferential Association of Adsorbed Uranium with Mineral Surfaces: A Study Using Analytical Electron Microscopy
Authors: Lumpkin G. R. , Payne T. E. , Fenton B. R. , Waite T. D. 
Published: April 2011

AbstractAnalytical electron microscopy (AEM) has been employed to characterize the distribution of U(VI) on several mineral substrates, including standard kaolinite samples and weathered rock samples from Koongarra, Australia. Results of this study reveal that pre-existing impurity phases play a significant role in the uptake of U(VI) on standard kaolinite samples. Using a natural sample from the weathered zone of the Koongarra uranium deposit, we have also demonstrated that U(VI) sorption is controlled by iron oxyhydroxides (predominantly goethite) which constitute a small fraction of the sample. Limited sorption of U(VI) was observed on the clay minerals of this substrate. Uptake of U(VI) by goethite increases with total uranium content up to the point of uranium precipitation, after which it decreases dramatically. Uranium precipitation is indicated by the appearance of a uranyl oxyhydroxide phase.
Actinide Biocolloid Formation in Brine by Halophilic Bacteria
Authors: Gillow J. B. , Francis A. J. , Dodge C. J. , Harris R. , Beveridge T. J. , Brady P. V. , Papenguth H. W. 
Published: April 2011

AbstractWe examined the ability of a halophilic bacterium (WIPP 1A) isolated from the Waste Isolation Pilot Plant (WIPP) site to accumulate uranium in order to determine the potential for biocolloid facilitated actinide transport. The bacterial cell surface functional groups involved in the complexation of the actinide were determined by titration. Uranium, added as uranyl nitrate, was removed from solution at pH 5 by cells but at pH 7 and 9 very little uranium was removed due to its limited solubility. Although present as soluble species, uranyl citrate at pH 5, 7, and 9, and uranyl carbonate at pH 9 were not removed by the bacterium because they were not bioavailable due to their neutral or negative charge. Addition of uranyl EDTA to brine at pH 5, 7, and 9 resulted in the immediate precipitation of U. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) analysis revealed that uranium was not only associated with the cell surface but also accumulated intracellularly as uranium-enriched granules. Extended X-ray absorption fine structure (EXAFS) analysis of the bacterial cells indicated the bulk sample contained more than one uranium phase. Nevertheless these results show the potential for the formation of actinide bearing bacterial biocolloids that are strictly regulated by the speciation and bioavailability of the actinide.
Incorporation of radionuclides from the electrometallurgical treatment of spent fuel into a ceramic waste form
Authors: Pereira C. , Hash M. C. , Lewis M. A. , Richmann M. K. , Basco J. 
Published: April 2011

AbstractAn electrometallurgical process is being developed at Argonne National Laboratory to treat spent metallic nuclear fuel. In this process, the spent nuclear fuel is electrorefined in a molten salt to separate uranium from the other constituents of the fuel. The treatment process generates a contaminated chloride salt that is incorporated into a ceramic waste form. The ceramic waste form, a composite of sodalite and glass, contains the fission products (rare earths, alkalis, alkaline earth metals, and halides) and transuranic radionuclides that accumulated in the electrorefiner salt. These radionuclides are incorporated into zeolite A, which can fully accommodate the salt in its crystal structure. The radionuclides are incorporated into the zeolite by hightemperature blending or by ion exchange. In the blending process the salt and zeolite are simply tumbled together at >450°C (723 K), but in the ion exchange process, which yields a product more highly concentrated in fission products, the molten salt is passed through a bed of the zeolite. In either case, the salt-loaded zeolite A is mixed with glass frit and hot isostatically pressed to produce a monolithic leach resistant waste form.Zeolite is converted to sodalite during hot pressing. This paper presents experimental results on the experimental results on the fission product uptake of the zeolite as a function of time and salt composition.
Erosion of Magnesium Potassium Phosphate Ceramic Waste Forms
Authors: Goretta K. C. , Singh D. , Tlustochowicz M. , Cuber M. M. , Burdt M. L. , Jeong S. Y. , Smith T. L. , Wagh A. S. , Routbort J. L. 
Published: April 2011

AbstractPhosphate-based chemically bonded ceramics were formed from magnesium potassium phosphate (MKP) binder and either industrial fly ash or steel slag. The resulting ceramics were subjected to solid-particle erosion by a stream of either angular Al2O3 particles or rounded SiO2 sand. Particle impact angles were 30 or 90° and the impact velocity was 50 m/s. Steady-state erosion rates, measured as mass lost from a specimen per mass of impacting particle, were dependent on impact angle and on erodent particle size and shape. Material was lost by a combination of fracture mechanisms. Evolution of H2O from the MKP phase appeared to contribute significantly to the material loss.
Surface features and alteration products of natural zirconolite leached in silica-saturated solutions
Authors: Helean K. B. , Lutze W. , Ewing R. C. 
Published: April 2011

AbstractZirconolite, CaZrTi2O7, has been proposed as an immobilization phase for the disposition of excess weapons Pu and other actinides (e.g., 235U). Due to actinide incorporation, zirconolite is expected to sustain α-decay event damage and become aperiodic (=metamict) over time. The leaching behavior of metamict zirconolite is, therefore, of interest. Because groundwater in a variety of geologic settings contains up to saturation concentrations of silicic acid, H4SiO4, silica-saturated solutions were used. Natural, metamict (> 1026 α-decay events per mn3) zirconolite grains, nominally (Ca, Th)ZrTi2O7 (U.S. National Museum sample #B20392, Walawada, Sri Lanka) were leached in two separate silica-saturated solutions at 150 °C for 60 days. Surface features and alteration products were examined using scanning electron microscopy (SEM) and quantitative energy dispersive X-ray spectroscopy (EDS). Secondary electron (SEI) images of the surfaces of the leached grains from both experiments revealed pores, probably due to the accumulation of He-bubbles from α-decay events, of approximately 4% as estimated by contrast enhanced gray-scale analysis of digital images. SEI of the zirconolite surface before leaching showed a smooth surface. The pores not only increase the surface area of the metamict zirconolite, but also act as nucleation sites for alteration phase growth. One experiment was conducted in a silica-saturated solution containing approximately 100 ppm P as measured by atomic absorption spectroscopy (AAS). The main alteration phase was euhedral, monoclinic cheralite, (Th, Ca, Ce)(P, Si)O4 (monazite group). The second experiment was conducted in the absence of P. The main alteration phase was subhedral cubic thorianite, ThO2.
A study of alteration phases on glass-bonded zeolite and sodaiate using the vapor hydration test
Authors: Sun Donglin , Wronkiewicz D. J. , Simpson L. J. 
Published: April 2011

AbstractThis paper focuses on the reaction of glass-bonded zeolite and sodalite ceramic waste forms, naturally occurring sodalite, and their respective alteration phases that formed after reaction in a Vapor Hydration Test (VHT). Scanning electron microscope (SEM) analysis of the glass-bonded zeolite and sodalite samples indicate that NaCI is the major alteration phase present, along with KCI, Na-Al-Si, and Na-K-Ca-Al-Si phases. The order of precipitation of salt crystals from ceramic waste form occurred in the sequence NaCl ⇒ KC1 ⇒ CaCl2 and MgCl2. We also found aluminum silicate phases containing Ca, Mg, K-Na-Ca, K-Mg, Na-K-Mg, K-Ca-Na-Mg, as well as CaCO3, SiO2. The ratio of Si/Al in the alteration phases was noted to increase from approximately 1.5 to 5 during the progressive alteration of the samples. This trend indicates a relative increase in the contribution of silicon from the relatively Si-rich glass regions of the samples over time. Phases enriched in Cs, Ba and rare earth elements (RE) were also observed on the altered samples. Alteration phases initially appeared along the micro-fractures during the early stages of alteration. The number of micro-fractures, density of alteration phase cover, and grain size of alteration phases increased with reaction time and temperature.
Intergrowth Structures in Synthetic Pyrochlores: Implications for Radiation Damage Effects and Waste Form Formulation
Authors: Buck E. C. , Chamberlain D. B. , Gieré R. 
Published: April 2011

AbstractTitanate-based ceramic waste forms are currently under development for the immobilization of excess weapons plutonium. Both Hf and Gd are added to the ceramic formulation as neutron absorbers in order to satisfy a defense-in-depth concept for the waste form. The introduction of significant amounts of hafnium may be responsible for the presence of zirconolite-2M crystals in pyrochlore-based ceramics and the formation of zirconolite lamellae within pyrochlore. The zirconolite grows epitaxially on { 111 }planes of pyrochlore. Although the zirconolite lamellae within pyrochlore are non-cubic, any volume expansion due to radiation damage in the pyrochlore should still be isotropic; in addition, the presence of these intergrowths may allow some stress relief in the ceramic.
Behavior of simulated hanford slurries during conversion to glass
Authors: Darab John G. , Meiers Eve M. , Smith Peter A. 
Published: April 2011

AbstractMixtures of simulated Hanford low-activity aqueous waste and glass precursor additives were heat treated at various temperatures up to 1000°C and characterized using X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, gas chromatography mass spectroscopy, and inductively coupled plasma – mass spectroscopy. It was found after heating the simulant mixture up to 700°C, the majority of the sodium nitrite present in the original waste reacted with the silica and perhaps boron species in the additives to form C– and N-containing gases, oxygen gas, and lower melting phases which contributed to the observed batch volume expansion beginning at these temperatures. Elemental analyses of minor components in the simulant mixture showed that I, Cl, and S exhibited significant losses during heating, presumably due to volatilization or entrainment. For the case of I, nearly 90% on an elemental basis was lost from the simulant mixture after processing to 1000°C, whereas Re exhibited less than 40% loss.
Processing of large-Scale radwaste-containing blocks using exothermic metallic mixtures
Authors: Ojovan M. I. , Petrov G. A. , Stefanovsky S. V. , Nikonov B. S. 
Published: April 2011

AbstractThe parameters of processing of large-scale (50-100 kg) radwaste-containing blocks were studied. Batches consisted of exothermic mixture, oxidizer, mineral additive, and radwaste surrogate. Such mixtures provide process temperature up to ˜2400 K. In the present work exothermic mixtures composed of Ca-Fe silicide, zirconium, silicon, and boron were intermixed with oxidizer (mixture of KMnO4 and V2O5), natural zircon concentrate as mineral additive, and cerium oxide (actinide surrogate). Tests were carried out in a bench-scale plant. Burning of the reaction mixture was remotely initiated from electric supply unit. Melt formation started in the nearbottom area sustained upwards frontally, The melt temperature ranged between 1600 and 1900 K. The melt formation rate during the tests ranged between 0.7 and 2.5 kg/s. Melt cooling after reaction completion was kept for about 15-18 hours. Volatile aerosols were essentially retained in the bulk. The initial volume of the mixture was reduced after reaction by factors of 2 to 3. The densities of the blocks were ranged between 3.2 and 3.9 kg/dm3.Samples of the materials obtained were examined by optical microscopy, X-ray diffraction, and scanning electron microscopy. The product consisted of glass-like body with metallic spheres (˜0.5-1.5 mm) distributed within. The base was composed of glass (˜60-80 vol.% of total) and crystalline phases (mainly zirconia). Monoclinic baddeleyite was found to be the major crystalline phase. The minor phase was tetragonal zirconia. Cerium (actinide surrogate) was partitioned among the glass and zirconia. The Ce2O3 concentration in glass ranged between ˜0.4 wt.% and ˜0.8 wt.% whereas its content in zirconia was found to be lower (up to ˜0.3 wt %). The metallic constituent consisted of vanadium and Fe-V-Si alloy whose average composition wasFe7O2V19.3Mn1.1 Si9.4.
Nonisothermal kinetics of spinel crystallization in a HLW glass
Authors: Casler D. G. , Hrma P. 
Published: April 2011

AbstractNonisothermal kinetics of spinel crystallization in a high-level waste (HLW) glass was predicted using Mehl-Avrami-Johnson-Kolmogorov equation coefficients from isothermal data. The volume fraction of spinel was determined as a function of time, temperature, and cooling rate. The results were verified experimentally. Also predicted was the spatial distribution of spinel in a HLW glass canister. Finally, a parameter study was performed, and an empirical equation was proposed relating the final spinel volume fraction in glass to dimensionless numbers for cooling rate, phase equilibrium, and crystallization kinetics.
Partitioning of plutonium between glass, secondary phases, and contact refractories
Authors: Muller I. S. , Buechele A. C. , Perez-Cardenas F. , Gan H. , Pegg I. L. 
Published: April 2011

AbstractA wide variety of plutonium-containing wastes have been generated from both defense and commercial nuclear programs. The Advanced Mixed Waste Treatment Project (AMWTP) involves the privatized treatment of 65,000 m3 of mixed TRU and low-level waste that is in storage at DOE's INEEL site. BNFL Inc. leads the commercial team including GTS Duratek, Inc., that has been selected to design, construct, and operate a facility to perform that service. Since vitrification is a potential treatment option, the current study was conducted to investigate issues surrounding the incorporation of the approximately 700 kg of plutonium that is present in the AMWTP waste. A series of glasses were prepared with plutonium (0.5 wt%), with cerium (as a potential surrogate), with both, and with neither. Scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDS) and optical analyses confirmed that both elements were completely dissolved into the as-melted glasses. Heat treatments forced the formation of secondary phases, which were analyzed for Pu and Ce incorporation. Plutonium-containing glasses were spiked with sulfates and remelted to force the formation of a sulfate salt phase, which was analyzed to determine partitioning of Pu and Ce. Coupons of Monofrax K-3 glass contact refractory were exposed to melts of these glasses for six days at 1208°C using both standard and modified versions of ASTM procedure C621-84. Thickness loss, microstructural alteration, and the extent to which Pu and Ce were incorporated into the material were then determined by methods employing SEMEDS\ wavelength dispersive x-ray spectroscopy (WDS). Extreme heat treatments were found to lead to the formation of small amounts (< 0.1 vol%) of either (Pu, Ce)O2, or PuO2, depending upon whether Ce was present or absent, respectively. The Pu level in the sulfate phase was at least a factor often below that of the parent glass, and no tendency to concentrate Pu in the K-3 refractory above the level in the parent glass was found.
The Effects of Uranium on the Structure of Iron Phosphate Glasses
Authors: Badyal Yaspal , Karabulut Mevlut , Marasinghe Kanishka , Saboungi Marie-Louise , Haeffner Dean , Shastri Sarvjit , Day D. E. , Ray C. S. 
Published: April 2011

AbstractBecause of their high chemical durability and waste loading capacity, iron phosphate glasses are a natural candidate for a nuclear waste disposal medium. We have studied the effects of uranium on the structure of iron phosphate glasses with both neutron and high-energy x-raydiffraction. The results of neutron scattering, which is mostly sensitive to pair correlations involving light atoms i.e. O-O, Fe-O and P-O, indicate the main structural features of the base glass are largely unaffected by the addition of UO2. The nearest-neighborbour P-O, Fe-O and O- O peaks remain at the same position in real space and their intensities scale approximately with concentration. These findings are consistent with earlier results using Raman scattering and EXAFS on the Fe-K edge, where in both cases the spectra remain similar to the base glass. The results of high-energy x-ray scattering, which is sensitive to correlations involving the heavier atoms and thus complements the neutron measurements, are also consistent with the overall picture of uranium occupying interstitial sites in the relatively undisturbed base glass structure. Combining the neutron and x-ray data for a 10 mol% UO2 glass suggests the intriguing possibility of a U6+ uranyl ion configuration although further work is needed to establish the precise local structure and valence state of uranium in these glasses.
Fundamental and Technological Aspects of Actinide Oxide Pyrochlores: Relevance For Immobilization Matrices
Authors: Raison P. E. , Haire R. G. , Sato T. , Ogawa T. 
Published: April 2011

AbstractPolycrystalline pyrochlore oxides consisting of selected f elements (lanthanides and actinides) and Zr and Hf have been prepared and characterized. Characterization to date has been primarily by X-ray diffraction, both at room and at elevated temperatures. Initial studies concentrated on selected lanthanides and the Np, Pu and Am analogs (reported here) but have been extended to the other actinide elements through Cf. Data from these studies have been used to establish a systematic correlation regarding the fundamental materials science of these particular pyrochlores and structurally related fluorite-type dioxides. In addition to pursuing their materials science, we have addressed some potential technological applications for these materials. Some of the latter concern: (1) immobilization matrices; (2) materials for transmutation concepts; and (3) special nuclear fuel forms that can minimize the generation of nuclear wastes. For f elements that display both a III and IV oxidation state in oxide matrices, the synthetic path required for producing the desired pyrochlore oxide is dictated by their pseudo-oxidation potential the stability of the compound towards oxygen uptake. For the f elements that display an oxidationreduction cycle for pyrochlore-dioxide solid solution, X-ray diffraction can be used to identify the composition in the oxidation-reduction cycle, the oxygen stoichiometry and/or the composition. This paper concentrates on the Np, Pu and Am systems, and addresses the above aspects, the role of the crystal matrix in controlling the ceramic products as well as discussingsome custom-tailored materials.
Chemistry of Rare Earth Oxalate Vitrification
Authors: Vienna J. D. , Peeler D. K. , Darab J. G. , Zamecnik J. R. , LI H. , Marra J. E. 
Published: April 2011

AbstractMixtures of rare earth and actinide oxalates will be vitrified into boro-aluminosilicate-based glasses for intermediate term stabilization according to current plans. The reaction chemistry involved with converting these oxalate feed stocks into glass products determines the potential for foaming, redox, and other melt and off gas related phenomena associated with this process. We've undertaken a detailed study of this conversion process using a variety of complementary techniques. A closed quartz crucible contained in a vertical furnace equipped with a quartz window and video camera was used to study volume expansion of the feed/melt during heating while monitoring the off-gas using a gas chromatograph-mass spectrometer. Simultaneous thermogravimetric and differential thermal analyses were conducted on small samples of feed and frit mixtures. Samples containing Ce were analyzed using established wet chemical techniques to determine Ce3+/Ce4+ ratio (redox) as a function of temperature. We evaluate the results and provide a description of the reaction chemistry of these oxalate feeds during vitrification.
NMR Characterization of Simulated Hanford Low-Activity Waste Glasses and its use in Understanding Waste form Chemical Durability
Authors: Darab J. G. , Linehan J. C. , McGrail B. P. 
Published: April 2011

AbstractMagic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy has been used to characterize the structural and chemical environments of B, Al, and Si in model Hanford low-activity waste glasses. The average 29Si NMR peak position was found to systematically change with changing glass composition and structure. From an understanding of the structural roles of Al and B obtained from MAS-NMR experiments, we first developed a model that reliably predicts the distribution of structural units and the average 29Si chemical shift value, δ, based purely on glass composition. A product consistency test (PCT) was used to determine the normalized elemental release (NL) from the prepared glasses. Comparison of the NMR and PCT data obtained from sodium boro-aluminosilicate glasses indicates that a rudimentary exponential relationship exists between the 29Si chemical shift value, and the boron NL value.
Effects of Halides and Sulphates in Synroc-C
Authors: Vance E. R. , Hartman J. S. 
Published: April 2011

AbstractHalides can be retained in bellows hot-pressed Synroc-C. Loadings of 0.2 wt% of fluoride or 2 wt% of sulphate did not appear to exert deleterious effects on the aqueous durability of the Synroc, but 0.2 wt% of chloride or 0.5 wt% of fluoride increased the Cs leach rate by a factor of ˜10. Fluoride was present principally as CaF2 in both calcined and hot-pressed Synrocs containing (a) ˜2 wt% of F as the only waste or (b) ˜2 wt% of F plus 20 wt% of simulated PW-4b Purex reprocessing waste. The speciation of Cl- in Synroc is not clear, though there was some evidence of CsCl from nmr and a compound giving a similar X-ray pattern to that of TiCI3. Iodine can retained in the hot-pressed Synroc containing the full complement of fission products, probably as insoluble Ag, Cr or Pd group iodides.
α-Radiolysis and α-Radiation Damage Effects on uo2 Dissolution Under Spent Fuel Storage Conditions
Authors: Rondinella V. V. , matzke Hj. , Cobos J. , Wiss T. 
Published: April 2011

Abstractα-decay will constitute almost entirely the radiation field in and around spent nuclear fuel after a few hundred years in a geological repository. Pellets of UO 2 containing ˜0.1 and ˜10 wt. % 238Pu were fabricated using a sol-gel method and characterized, comparing their properties to those of undoped UO2. The α-radiation fields of different types of commercial LWR spent fuel are of the same order of magnitude as the fuel with the lower Pu-concentration used in this work. The results of static batch leaching tests at room temperature in demineralized water under anoxic atmosphere showed that the amounts of U released during leaching were higher in the case of UO2 containing 238pu than for undoped UO2. Relatively large amounts of Pu were released after the longest leaching times. Lattice parameter measurements using XRD and hardness measurements by Vickers indentation showed a relatively rapid build-up of α-decay damage in the material stored at ambient temperature with the higher concentration of dopant, while for the material with ˜0.1 wt. % Pu no clear variations were detected during the same time intervals.