Monazite, an orthophosphate mineral of the lanthanides (Ln) and the actinides (An) U and Th, is a model for an ideal synthetic mineral waste form for geologic disposal of long-lived nuclear waste actinides. Natural monazites are known to have survived many of the conditions that might be inflicted on a nuclear waste repository by geological disruptions. High Th and U monazites with compositions typical of nuclear wastes have been synthesized with a routine calcination-pelletization-crystallization procedure. Charge balance for the Th4+ → Ln3+ substitution can be provided by either an equimolar Ca2+ → Ln3+ or Si4+ → P5+ substitution. For U4+ → Ln3+, only the Ca2+ → Ln3+ substitution resulted in a phase-pure monazite. Unit cell parameter data were obtained for each nuclear waste monazite phase. 相似文献
Transuranic (TRU) waste generated by the handling of plutonium during research on or production of U.S. nuclear weapons will be disposed of in the Waste Isolation Pilot Plant (WIPP). This paper describes the physical and radiological properties of the TRU waste that will be deposited in the WIPP. This geologic repository will accommodate up to 175,564 m3 of TRU waste, corresponding to 168,485 m3 of contact-handled (CH-) TRU waste and 7079 m3 of remote-handled (RH-) TRU waste. Approximately 35% of the TRU waste is currently packaged and stored (i.e. legacy) waste, with the remainder of the waste to be packaged or generated and packaged in activities before the year 2033, which is the closure time for the repository. These wastes were produced at 27 U.S. Department of Energy (DOE) sites in the course of generating defense nuclear materials. The radionuclide and nonradionuclide inventories for the TRU wastes described in this paper were used in the 1996 WIPP Compliance Certification Application (CCA) performance assessment calculations by the Sandia National Laboratories/New Mexico (SNL/NM). 相似文献
The NZP structure is a candidate for immobilization of certain types of nuclear waste. It will incorporate 137Cs, 90Sr, and a range of other nuclides. The leach resistance of CsZr2(PO4)3 appears to be comparable with that of other phases under consideration for radio-Cs immobilization. This phase can be formed by sintering at ~850°C; it is reasonably refractory, and it is compatible with monazite, a favored immobilizing agent for waste actinides. 相似文献
Hard template-based fabrication of mesoporous carbon unavoidably goes through the removal process of the template to generate template-free carbon replica, including troublesome disposal of template waste often accompanied by toxic etchant, which not only increases the fabrication cost of materials but also raises serious environmental concerns. As a novel strategy to overcome such problem, a direct in situ synthesis approach using silica waste in carbon/silica nanocomposite as a silica source and cetyltrimethylammonium bromide as a porogen under basic condition is reported in this study for the generation of a new composite composed of mesoporous MCM-41 silica and hollow carbon capsule. The resultant MCM-41/carbon capsule composite offers a 3-D interconnected multimodal pore system, which discloses a wide pore range of ordered uniform mesopores (ca 2.3?nm) resulting from MCM-41 silica and disordered uniform mesopores (ca 3.8?nm) and macropores (ca 300?nm) from hollow mesoporous carbon, respectively. The composite has a high specific surface area (ca 909?m2/g) and large pore volume (ca 0.73?cm3/g). The in situ transformation approach of silica waste into valuable mesoporous silica is considered as a promising scalable route for efficient new multi-functional composites useful for a wide range of applications such as adsorption of volatile organic compounds and radioactive wastes produced in a nuclear facility. 相似文献
This study successfully recycled alum sludge with either lithium slag or bottle glass to make high purity zeolite LTA beads. The basic synthesis approach was to fuse the waste material with sodium hydroxide then complete hydrothermal crystallization. Separate fusion of individual wastes promoted zeolite LTA formation compared to combined fusion. Preferred synthesis conditions were: 10 Na2O:Al2O3:2.5 SiO2:300 H2O; hydrothermal temperature = 80 °C; time = 5 h. Zeolite LTA purity was between 80 and 85 wt% from the two waste combinations. Use of pseudoboehmite and carboxymethyl cellulose favoured granulation/extrusion/spheronization of zeolite LTA powder. However, the beading process decreased calcium exchange capacity (CEC) from 99.5 to 37 mg Ca2+/g for alum sludge + lithium slag and from 64.5 to 37 mg Ca2+/g for alum sludge + waste glass. Additionally, when using 20 wt% pseudo-boehmite as a binder the ion-exchange equilibrium time increased from 60 to 300 min. The importance of not only making zeolite powder from waste materials but also to extend studies to shaped forms was evident. It is recommended that future studies should also focus on making extrudates or beads as these are the forms used commercially. 相似文献
Ceramic precursors of Zirconolite (CaZrTi2O7) family have a remarkable property of substitution on Zr4 + cationic sites. This makes them potential material for nuclear waste management in ‘synroc’ technology. In order to simulate the mechanism of partial substitution of zirconium by tetravalent actinides, a solid phase of composition CaZr0.95U0.05Ti2O7 has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and nitrates of uranium and zirconium respectively. Solid state synthesis has been carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050°C. The polycrystalline solid phase has been characterized by its typical powder diffraction pattern. Step analysis data has been used for ab initio calculation of structural parameters. The SEM and EDAX analysis also confirm that zirconolite acts as a host material for uranium. The powder diffraction data of 3500 points between 2θ = 10–80° has been analysed by GSAS (general structure analysis system) software to obtain the best fit of the observed data points. The uranium substituted zirconolite crystallizes in monoclinic symmetry with space group C2/c (#15). The following unit cell parameters have been calculated: a = 12.4883(15), b = 7.2448(5), c = 11.3973(10) and β = 100.615(9)°. The calculated and observed values of the intensities, lattice parameters and density measurement shows good agreement. The Rietveld analysis and GSAS based calculations for bond distance Ti—O, Ca—O, Zr—O, and O—M—O bond angles have been made. The structure was refined to satisfactory completion.The and Rp and Rwp are found to be 7.48 and 9.74 % respectively. 相似文献
Host matrices for actinides prepared by self-propagating high-temperature synthesis are studied. The matrices consist of a pyrochlore or fluorite phase and metallic molybdenum. The factor determining the structural type of the crystal lattice of the target phase is the ionic radius ratio. When the difference in the ionic radii is insignificant, as in the case of Y3+ (r 0.102 nm) and Zr4+ (r 0.084 nm), the oxide Zr1-xYxO2-0.5x with a fluorite structure is formed, in which the cations occupy the eight-coordinate sites. This structure permits incorporation of heavy lanthanides and tetravalent actinides: U4+ (r 0.10 nm), Np4+ (r 0.098 nm), and Pu4+ (r 0.096 nm). When the difference in the ionic radii is more considerable, as in the case of Y3+ and Ti4+ (r 0.061 nm), a pyrochlore-related structure is realized. In this case the cations occupy different (eight- or six-coordinate) sites. The pyrochlore structure is preserved if the radii of ions occupying different structural sites change in parallel. This structure is typical of zirconates of trivalent actinides and light REEs. The decision on the major host phase for actinides is determined by the waste composition. At low content of light REEs and americium an oxide with a fluorite-related structure shows promise. At high content of these elements, zirconates and titanates with the pyrochlore structure are more stable. 相似文献
A three-dimensional flower-like NiCo2S4 formed by two-dimensional nanosheets is synthesized by a facile hydrothermal method and utilized as the anode for sodium-ion batteries. Studies have shown that materials can achieve the best performance under the ether-based electrolyte system with voltage ranging from 0.3 to 3 V, which could effectively avoid the dissolution of polysulfides and over-discharge of the material. Here, sodium storage mechanism and charge compensation behaviors of this ternary metal sulfide are comprehensively investigated by ex situ X-ray diffraction. Moreover, ex situ Raman spectra, ex situ X-ray photoelectron spectroscopy and transmission electron microscopy measurements are used to related tests for the first time. Additionally, quantitative kinetic analysis unravels that sodium storage partially depends on the pseudocapacitance mechanism, resulting in good specific capacity and excellent rate performance. The initial discharge capacity is as high as 748 mAh·g−1 at a current density of 0.1 A·g−1 with the initial coulomb efficiency of 94%, and the capacity can still maintain at 580 mAh·g−1 with the Coulomb efficiency close to 100% after following 50 cycles. Moreover, by the long cycle test at a high current density of 2 A·g−1, the capacity can still reach at 376 mAh·g−1 after over 500 cycles.
Results are reported for effective thermal conductivity measurements performed in situ and in core samples of illite marine sediment. The measurements were obtained during a recent oceanographic expedition to a study site in the north central region of the Pacific Ocean. This study was undertaken in support of the U.S. Subseabed Disposal Project, the purpose of which is to investigate the scientific feasibility of using the fine-grained sediments of the sea floor as a repository for high-level nuclear waste. In situ measurements were made and 1.5-m-long hydrostatic piston cores were taken, under remote control, from a platform that was lowered to the sea floor, 5844 m below sea level. The in situ measurement of thermal conductivity was made at a nominal depth of 80 cm below the sediment surface using a specially developed, line-source, needle probe. Thermal conductivity measurements in three piston cores and one box core (obtained several kilometers from the study site) were made on shipboard using a miniature needle probe. The in situ thermal conductivity was approximately 0.91 W · m–1 · K–1. Values determined from the cores were within the range 0.81 to 0.89 W · m–1 · K–1.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A. 相似文献
We describe a facile in situ hydrothermal fabrication of graphene–MoO3 nanorod bundle composites utilizing sodium salicylate. The structure, morphology and composition of graphen–MoO3 composites were investigated by means of field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and thermogravimetric-differential scanning calorimetry (TG-DSC). FESEM and TEM studies show that the presence of ordered MoO3 nanorod bundles in composites, the characterization results of XRD, Raman spectra and TG-DSC analysis confirm the reduction of graphite oxide (GO) to graphene accompanying by the formation of MoO3 nanorod bundles in the hydrothermal process. Due to characteristics of MoO3 and graphene–MoO3 composites, our findings may have implications in the synthesis and fabrication of well-defined functional graphene–MoO3 hybrid materials. It may also provide a general approach for the preparation of graphene–metal oxide hybrid materials. 相似文献
Scrupulous design and fabrication of advanced electrode materials are vital for developing high-performance sodium ion batteries. Herein, we report a facile one-step hydrothermal strategy for construction of a C-MoSe2/rGO composite with both high porosity and large surface area. Double modification of MoSe2 nanosheets is realized in this composite by introducing a reduced graphene oxide (rGO) skeleton and outer carbon protective layer. The MoSe2 nanosheets are well wrapped by a carbon layer and also strongly anchored on the interconnected rGO network. As an anode in sodium ion batteries, the designed C-MoSe2/rGO composite delivers noticeably enhanced sodium ion storage, with a high specific capacity of 445 mAh·g-1 at 200 mA·g-1 after 350 cycles, and 228 mAh·g-1 even at 4 A·g-1; these values are much better than those of C-MoSe2 nanosheets (258 mAh·g-1 at 200 mA·g-1 and 75 mAh·g-1 at 4 A·g-1). Additionally, the sodium ion storage mechanism is investigated well using ex situ X-ray diffraction and transmission electron microscopy methods. Our proposed electrode design protocol and sodium storage mechanism may pave the way for the fabrication of other high-performance metal diselenide anodes for electrochemical energy storage.
The total stability constants of Th4+, U4+, Np4+, Pu4+, Am4+, Cm4+, Ce4+, Tb4+, Pr4+, Tb3+, and Pr3+ complexes with P2W17O6110? heteropolyanion in 1 M sodium salt solutions at pH ≥ 5.5 (i.e., when the anion is not protonated; so-called “absolute” constants), were determined experimentally or calculated from published data. Plots of constants vs. ionic radius of the f element were considered for solutions with ionic strength 1 (1 M acid or sodium salt solutions at pH ≥ 5.5). The correlations found confirm that the interaction of counterions in the complex is predominantly electrostatic. At the same time, different contributions of the covalent interaction for actinides and lanthanides were suggested. 相似文献
Pertechnetate oxyanion (TcO4−), which is highly soluble in water and readily mobile in the environment, can be immobilized through an ion exchange /adsorption process and chemical reduction followed by adsorption and/or precipitation. Previous studies have focused on the separation and removal of 99TcO4− from high-level waste streams; however, little information is available for 99TcO4− removal from only slightly contaminated groundwater. This paper describes treatment of 99TcO4−-contaminated groundwater with both batch and column flowthrough experiments. Synthetic resins and sponges, and zero-valence iron filings were used to evaluate their capacities and the rates of 99TcO4− removal. The toxicity characteristic leaching procedure (TCLP) was applied to evaluate the leachability of 99Tc adsorbed or co-precipitated on iron. Results suggest that both iron and synthetic resins remove 99TcO4− from groundwater and that at a high flow rate (with residence time of less than 1 min), 99TcO4− removal capacity is greater for iron filings than for the synthetic resins on a volume basis. Additionally, the rate of 99TcO4− sorption on the sponge is slow (approximately 3 days), and the capacity is relatively low. No appreciable amount of 99Tc can be leached out from the spent iron filings by the TCLP test. Overall, zero-valence iron filings provide fast reaction and high removal capacity for 99TcO4− in groundwater. The high removal efficiency, low cost, and the small waste production of zero-valence iron are attractive for remediation of 99TcO4−-contaminated groundwater. 相似文献
Designing high-efficient and low cost of electrodes with seamless integration of substrate and electrocatalyst particles is of significant concern for electrocatalytic water splitting. In this study, we actualized in situ growth of Co3O4 nanoneedles on titanium (Ti) mesh (denoted as Co3O4@Ti) by a simple combination of hydrothermal approach and subsequently calcination treatment under relatively low temperatures. The as-prepared Co3O4@Ti samples were evaluated as anodes for electrocatalytic oxygen evolution reaction (OER) in alkaline electrolyte. It demonstrates that the optimized Co3O4@Ti electrode displayed good OER activity with a small overpotential of 416 mV at a current density of 20 mA cm?2, which is on a par with commercial RuO2 catalyst (overpotential of 403 mV at 20 mA cm?2). The satisfactory OER performance of Co3O4@Ti electrode is largely attributed to the seamless integration of conductive Ti mesh substrate and the direct growth of Co3O4 nanoneedles on Ti mesh with sufficient active sites. This study suggests the potential application of Co3O4@Ti electrode as preeminent OER catalyst.
The behavior of actinides (U, Am, Pu) in the course of combustion of radioactive graphite in steam was studied by thermodynamic modeling. Thermodynamic modeling was performed using TERRA program in the temperature interval from 373 to 3273 K to determine the possible composition of volatile actinide species formed in the course of graphite utilization by heating in steam. The modeling shows that the actinides at high temperatures are present in the following forms: U, as UO3 and UO2 vapors and as UO3– and UO2+ ions; Am, as Am vapor; and Pu, as PuO2 and PuO vapors and as ionized PuO+. The main reactions within separate phases and at the interface were revealed, and their equilibrium constants were determined. 相似文献
The boundary resistance between liquid and solid3He and CMN is calculated taking the coupling to be due to the nuclear spin-electron spin dipolar interaction. The boundary resistance is calculated using a relationship betweenRK–1
and the longitudinal relaxation timeT1. We find qualitative agreement with the results of Leggett and Vuorio for the temperature dependence and impurity dependence ofRK–1
. Quantitative agreement with experiment is possible using a number of plausible assumptions. An important insight emerges: the relative rates of motion of the spins in3He and CMN are crucial to their coupling. Solid3He at low pressure is in near synchronism with CNM. As a consequence its boundary resistance should be very low.Supported in part by the National Science Foundation and the A. P. Sloan Foundation. 相似文献
AbstractA novel in situ reactive technique has been employed for preparing 2·0 wt-%TiB2/60Si–Al composite. The kinetic equations and the Arrhenius type equation were applied to compute the coarsening rate constant and the activation energy for grain growth for the composite when it was heated at semisolid state for partial remelting. Experimental results have shown that the in situ TiB2 particles can refine effectively the primary Si phase and restrain the Si phase growth. The cubic coarsening rate constant for the composite was computed to be in the range of 75–148 μm3 min?1 at temperatures in the range of 600–700°C, which was much less than that for the 60Si–Al alloy (1323–4523 μm3 min?1). The value of activation energy for grain growth for the composite was about twice of that for the 60Si–Al alloy. The composite exhibited a higher thermal stability than that of the 60Si–Al alloy, suggesting that the in situ TiB2 particles can effectively pin the grain boundaries and arrest the migration of liquid film in the semisolid state of the composite. 相似文献
The electrical resistivity and specific heat of samples of 241Am and 243Am are reported. The electrical resistivity at room temperature is reduced compared with the value for plutonium, while the power law exponent at low temperatures is increased. The electronic specific heat coefficient is lower than for the lighter actinides. These features lead to the conclusion that americium is the first of the actinides in which the 5 f electrons are essentially localized. Anomalies occur in the electrical resistivity and in the specific heat in the region of 60 K, the cause of which is unknown. 相似文献
Nuclear incineration of long-lived fission products and minor actinides is being investigated as an alternative means of reactor waste disposal. 129I is of particular interest because of its long half-life and high mobility in the environment. Lead iodide targets of 129I for neutron capture cross-section measurements were prepared from 210 l fuel reprocessing waste solution containing 1.3 g l−1 iodine and other fission products. The iodine was separated by oxidation to I2 and extraction into chloroform, reduction to iodide by sodium sulphite and re-extraction into an aqueous phase. Iodide was precipitated using lead nitrate and dried. The chemistry was carried out batch-wise using 400 ml starting solution each time and recycling the chloroform. An extraction efficiency of about 90%, determined by γ-ray spectrometry, was achieved. 相似文献
AbstractThe microstructural stability of Ni nanocrystalline electrodeposits was investigated to verify general principles underlying the suppression of grain growth by microalloying with elements of very low solid solubility. Hf ions at 300 keV energy were implanted in Ni nanocrystalline foils at low (5·8 × 1015 ions cm?2) and high (3·0 × 1016 ions cm?2) doses. Their effects on grain growth at 550°C were studied in situ by transmission electron microscopy at 1·25 MeV and by selected area electron diffraction. Grains roughly doublled in size during implantation, but grain growth during subsequent heat treatment was dose dependent and significantly less than in specimens without implantation. Observation on implanted Ni single crystals revealed clustering and the formation of fine Ni5Hf precipitates. A possible mechanism of grain growth suppression is discussed. 相似文献