Uranium separation behavior

Oxo Ion Salts. Salts of 0x0 anions, such as nitrate, sulfate, perchlorate, iodate, hydroxide, carbonate, phosphate, oxalate, etc, are important for the separation and reprocessing of uranium, hydroxide, carbonate, and phosphate ions are important for the chemical behavior of uranium ia the environment (150—153). 

Experiments on the sky. Two experiments have been carried out at the sky, using two laser installations built for the American and French programmes for Uranium isotope separation, respectively AVLIS at the Lawrence Livermore Nat l Lab (California) in 1996 and SILVA at CEA/Pierrelatte (Southern France) in 1999. The average power was high pa 2 x 175 W, with a pulse repetition rate of 12.9 and 4.3 kHz, a pulse width of 40 ns and a spectral width of 1 and 3 GHz. Polarization was linear. The return flux was < 5 10 photons/m /s (Foy et al., 2000). Thus incoherent two-photon resonant absorption works, with a behavior consistent with models. But we do need lower powers at observatories ... 

Uranium and thorium are actinide elements. Their chemical behavior is similar under most conditions. Both are refractory elements, both occur in nature in the +4 oxidation state, and their ionic radii are very similar (U+4 = 1.05 A, Th+4 = l.lOA). However, uranium can also exist in the +6 state as the uranyl ion (U02 2), which forms compounds that are soluble in water. Thus, under oxidizing conditions, uranium can be separated from thorium through the action of water. 

Tn reviewing the chemistry of the actinides as a group, the simplest approach is to consider each valence state separately. In the tervalent state, and such examples of the divalent state as are known, the actinides show similar chemical behavior to the lanthanides. Experimental diflB-culties with the terpositive actinides up to plutonium are considerable because of the ready oxidation of this state. Some correlation exists with the actinides in studies of the lanthanide tetrafluorides and fluoro complexes. For other compounds of the 4-valent actinides, protactinium shows almost as many similarities as dijSerences between thorium and the uranium-americium set thus investigating the complex forming properties of their halides has attracted attention. In the 5- and 6-valent states, the elements from uranium to americium show a considerable degree of chemical similarity. Protactinium (V) behaves in much the same way as these elements in the 5-valent state except for water, where its hydrolytic behavior is more reminiscent of niobium and tantalum. 

Monazite ubiquitously exhibits this type of behavior. Backscattered electron images and yttrium, thorium, and uranium X-ray maps nearly always reveal complex zonation (e.g., Parrish, 1990 DeWolf et al., 1993 Zhu et al., 1997 Zhu and O Nions, 1999 Williams et al., 1999 Pyle et al., 2001 Townsend et al., 2001 Williams and Jercinovic, 2002 see Figures 27 and 28), and several studies have demonstrated significant age differences between these chemically distinct domains (e.g., DeWolf et al., 1993 Zhu et al., 1997 Zhu and O Nions, 1999 Williams et al., 1999 Townsend et al., 2001 Figures 27 and 28). Extreme compositional and age heterogeneity implies that the analysis of a bulk mineral separate or even of a single grain is not very useful... 

The most practical reason for interest in the chemistry of the early actinides is their technological importance. In particular, the importance of uranium and plutonium in applications ranging from nuclear power to radiothermal generators for deep space missions. The production and use of nuclear materials in nuclear weapons from the 1940s has also driven the development of a great deal of the chemistry of these metals, from their separation and isolation to investigations of their behavior under biologically relevant conditions. 

The sucessful experiments for the retention of plutonium onto alumina from TTN0 -HF solution gave enough confidence to recomend the proposed method to separate traces of plutonium from waste solutions in the presence of macroamounts of uranium (VI). Of course, only macroamounts of thorium, uranium (IV) and rare earths are serious interfering ions, since they precipitate with HF. The behavior expected for neptunium in the same system should be similar to plutonium, thorium and rare earths. The retention of neptunium from HNO - HF solutions is in progress. The sorption yield for Pu was around 95%. The sorption mechanism is not well established. Figure 3 shows the proposed flowsheet for recovery of Pu traces from reprocessing waste solutions. 

Some of the pyrochemical processes have more potential for being proliferation resistant because of the great similarity of the chemistry of uranium, plutonium, and some of the fission products in the chosen systems. Ordinary processes are designed to maximize differences in chemical behavior in order to separate constitutents. For some of the pyrochemical processes the chemical equilibria are such that partial separations are possible but complete separations are thermodynamically limited. For example, excess uranium can be separated from plutonium by precipitation in a molten metal such as zinc only until both are present in about equal quantities in solution, but no further ( 3, 4). Likewise, the solubility of fission products is selectively limited. Only a portion of elements such as ruthenium will stay in solution and be removed 05). The majority of the ruthenium precipitates with the actinides. A complete separation is again thermodynamically limited. As a result only a modest dependence needs to be placed on process equipment and facility design for proliferation resistance. 

Molten Nitrate Salt Oxidation Process (10). The reaction of UO2 with molten nitrate salts to form uranates that are sub-sequently reduced to effect a separation of the uranium is being evaluated. The actinide behavior and uranate composition in equimolar sodium-potassium nitrate is being studied to determine the uranate stability and forecasting of cation behavior in subsequent process steps. 

The solubilities of uranium, plutonium, and thorium in magnesium at 650°C are 0.002 wt %, 55 wt %, and 44 wt %, respectively. Thus, assuming no solute interaction, uranium is essentially insoluble in magnesium, while plutonium is quite soluble and good separation may be effected. While precipitation of an insoluble phase from solution would appear to be a straightforward process, the behavior of a solute in a given metal or alloy may differ from its behavior when influenced by the inclusion of other solutes. One element may increase or suppress the solubility of another through coprecipitation or intermetallic compound formation. Such effects must be determined experimentally. 

Our preliminary studies of fission-product behavior show that those fission products that are soluble in the melt remain so during precipitation of the sodium diuranate. Hence, a relatively "clean11 uranium product should be obtained. Again, a liquid (nitrate melt containing soluble fission products) - solid (sodium diuranate) phase separation is required. The melt temperature may be lowered to approximately 275°C for this separation once the diuranate has precipitated. 

It appears that whatever the behavior of uranium is in molten nitrates, the end product is most likely to be an alkali metal uranate. Separation of the alkali metal cation and uranium is perhaps the greatest unknown in the development of a... 

Runs With Technetium-Spiked UO Two continuous uranium fluorination runs were made to determine the behavior of technetium in the pilot-plant fluorination system. Fluidized-bed-produced UO containing 300 jg of technetium per gram of UO was fluorinated and then separated from UF by passing the volatile fluorination products through a static bed of MgF. ... 

If Frisch now glimpsed an opening into those depths he did so because he had looked carefully at isotope separation and had decided it could be accomplished even with so fugitive an isotope as U235. He was therefore prepared to consider the behavior of the pure substance unalloyed with U238, as Bohr, Fermi and even Szilard had not yet been. I wondered— assuming that my Clusius separation tube worked well—if one could use a number of such tubes to produce enough uranium-235 to make a truly explosive chain reaction possible, not dependent on slow neutrons. How much of the isotope would be needed ... 

Adachi, T. Ohnuki, M. Yoshida, N. Sonobe, T. Kawamura, W. Takeishi, H. Gunji, K. Kimura, T. Suzuki, T. Nakahara, Y. Muromura, T. Kobayashi, Y. Okashita, H. Yamamoto, T. (1990). Dissolution Study of Spend PWR Fuel Dissolution Behavior and Chemical Properties of Insoluble Residues. Journal of Nuclear Materials, Vol. 174, No. 1, (November 1990), pp. 60-71, ISSN 0022-3115 Anderson, H. H. (1949). Alkali Plutonium(IV) Nitrates, In The Transuranium Elements, National Nuclear Energy Series IV, Vol. 14B, G. T. Seaborg, J. J. Katz, W. M. Manning, (Eds.), pp. 964-967, McGraw-Hill Book Co. Inc., New York, USA Ebert, K Henrich, E. Stahl, R. Bauder, U. (1989). A Continuous Crystallization Process for Uranium and Plutonium Refinement, Proceedings of 2nd International Conference on Separation Science Technology, pp. 346-352, Paper No. S5b, Hamilton, Ontario, Canada, October 1-4,1989... 

The discovery of the next two transuranium elements, americium (Z = 95) and curium (Z = 96), depended on an understanding of the correct positions in the periodic table of the elements beyond actinium (Z = 89). It had been thought that these elements should be placed after actinium under the d-transition elements. So uranium was placed in Group VIB under tungsten. However, Glenn T. Seaborg, then at the University of California, Berkeley, postulated a second series of elements to be placed at the bottom of the periodic table, under the lanthanides, as shown in modem tables (see inside front cover). These elements, the actinides, would be expected to have chemical properties similar to those of the lanthanides. Once they understood this, Seaborg and others were able to use the predicted chemical behaviors of the actinides to separate americium and curium. 

The enrichment of uranium has to be accomplished by some physical process which depends on differential behavior of the two isotopes of uranium. The great majority of separative work has to date been carried out by the gaseous diffusion process, where the distinguishing feature between the isotopes is the rate at which the molecules of different mass diffuse through a porous barrier under an applied pressure differential. In a sample of uranium hexafluoride gas, the mean kinetic energy of the lighter molecules is equal to that of the heavier, i.e.,... 

Because of the number of variables and the large niunber of uranium solvents, one cannot consider, in a volume of this size, each solvent In the light of each variable. Indeed, the behavioral relation between solvent and the afore-mentioned variables la known for only a few well-studied solvents. The purpose of the present paper Is to provide information on the conditions best-suited for the quantitative extraction of uranium or for the separation of uranium from Interfering elements. This la done as much as possible In graphic or tabular form. 

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