U metal

World annual uranium requirements in 1993 were estimated at about 58,382 t natural uranium equivalent. Reactor-related requirements are expected to rise about 1015 t/yr on the average, reaching 75,700 t U total requirements in the year 2010. The cumulative aggregate world uranium requirements for the period 1993—2010 are estimated to be about 1.185 X 10 t U metal (29). 

Atomic- Vapor Laser Isotope-Separation. Although the technology has been around since the 1970s, laser isotope separation has only recently matured to the point of industrialization. In particular, laser isotope separation for the production of fuel and moderators for nuclear power generation is on the threshold of pilot-plant demonstrations in several countries. In the atomic vapor laser isotope-separation (AVLIS) process, vibrationaHy cooled U metal atoms are selectively ionized by means of a high power (1—2 kW) tunable copper vapor or dye laser operated at high (kHz) repetition rates (51,59,60). 

Gash, V.U. "Metal Chelates and Process of Preparing Same," US Patent 2,976,285(1961). 

Persmark, U. Metal Catal. Lipid Oxid., SIK (Sv. Inst. Konserveringsforsk.)... 

Proceeding from thorium to plutonium along the actinide series, the vapor pressure of the corresponding iodides decreases and the thermal stability of the iodides increases. The melting point of U metal is below 1475 K and for Np and Pu metals it is below 975 K. The thermal stabilities of the iodides of U, Np, and Pu below the melting points of the respective metals are too great to permit the preparation of these metals by the van Arkel-De Boer process. 

As with Th and Pa metals, ultrapure U metal can in principal be obtained by such methods as zone melting and solid-state electro-... 

Fig. 10. The full photoelectron spectrum (direct and inverse photoemission) of the conduction band of U metal (from Ref, 56)...

Spurious effects due to incompletely removed oxides layers are very likely to be recorded and misinterpreted in photoemission experiments from the very oxidizable U-metal surface. However, considering only high resolution XPS and UPS data for clean surfaces as well as the measurements using synchrotron radiation , it can be... 

Table 2. Summary of valence band structures of a-U metal as reported by different authors (AE is the experimental resolution)...

Fig. 11. The valence band spectrum of a-U metal, as measured in XPS a), from Ref. 56 is compared with two one-electron density of states calculations (6) from Ref. 68, (c) from Ref. 69...

By summing up all these observations, and considering that theoretical calculations firstly, provide different results and, seeondly, describe less well the experiments on U metal than those on Th, the conclusion can be drawn that a fully 5 f band-like description may not be completely suitable An interpretation based on a locahzed behaviour (as for Nd) is, however, also unsuited (and not expected from other physical measurements and band-theory results). We conclude from this analysis, that the strong emission just below and beyond Ep originates manifestly from itinerant 5 f states. 

Resonance photoemission measurements have been recently made for U metal , and show indeed a resonant enhancement of the satelUte at 2.3 eV only for the threshold energy (5 A i2. hv = 94 eV) (Fig. 15). In addition the main peak at Ep shows the expected off-resonance behaviour. Further support for such an interpretation of the satellite is given by the analysis of the photon excited Auger emission. This is shown to be composed of two different bands also separated by 2.3 eV and due to the two screening channels by 5 f or 6 d states ... 

However, the 4fy/2 core level response of U metal does not show a poorly screened satellite, but only a pronounced asymmetry. This is somewhat in contrast with the greater localization predicted by theory ° when proceeding across the actinide series. 

The most important information (by Baer and Schoenes ) obtained when using the combined XPS/BIS method is the Coulomb interaction energy Uh that we have discussed in Part II. For UO2, Uh = 4.6 0.8 eV has been obtained. This large separation between the two final states (2(5f ) —> 5f + 5f ) is in itself a hint to the localized character of the 5 f states in UO2. Baer and Schoenes compared the value for Uh with theoretical values they found an agreement with Uh = 4 eV as calculated by Herbst et al. for a U" " metal core. As discussed in Chap. A, intraatomic calculations of Uh in metals possibly underestimate screening by conduction electrons nevertheless, they should be valid in the case of an insulating solid as UO2. 

C on Hanford N (ninth) reactor corroding U-metal fuel particles do not generate studtite. If the fuel in a geological repository is held at temperatures above 60 °C, it is unlikely that there will be significant H202 build-up, and thus there will be little or no studtite formation. 

Ref 2) insol in w dil acids sol in coned acids. Prepd by hydrofluorination of UOa, which, in turn, is obtd from fluid bed reduction of higher oxides by hydrogen. Used for prepn of U metal and UF6 Refs 1) Gmelin-Kraut Syst Number 55(1936),... 

U is also found in the Soviet Union where there are sources in Karelia, near Dnepropetrovsk, the Kirghiz Soviet Republic and in Transcaucasia Whereas once U ores were processed for their Ra content, Ra has now lost its commercial importance and it is considered a contaminant. Only two U ores have been processed extensively, pitchblende and carnotite. The general procedure is to solubilize the U with an acid, convert the ion to a complex carbonate (thereby removing the Fe, A1 and Mn), ppt the Pb and Cu as the sulfide, and finally, to recover the U as the ammonium uranate and hence, as the oxide U metal can be obtained from the oxide or the halide by reduction with alkali metals or alkaline earth metals. U, being highly electropositive, cannot be deposited electrolytically from aq solns. Thermal decompn of the tetra-iodide is possible (Ref 1)... 

Not all reactions leading to carbonylate anions require strong reducing agents. Some involve reduction of the meta by carbon monoxide already present in the metal carbonyl or disproportionation of the complex In fact, the first synthesis of u metal carbonylate involved the former procedure ... 

The U(VI) can be prepared by dissolving UO3 in acid or U metal in HNO3. Solutions of the uranyl ion show a characteristic yellow-green color and are very... 

Schindewolf U. Metal-Ammonia Solutions. Lagowski JJ, Sienko MJ eds. London Butterworth, 1970 199-218. 

Murugkar, A. Padhye, S. Guha-Roy, S. Wagh, U. Metal complexes of Taxol precursor 1. Synthesis, characterization and antitumor activity of the copper complex of 10-deacetylbaccatin thiosemicarbazone. Inorg. Chem. Commun., 1999, 2 545-548. 

Once enriched, the UFg needs to be reduced to either uranium metal or UO2 to be formed into fuel pins. A variety of methods can be used to accomphsh the conversion to the oxide however, the predominately used technique involves reduction of the UFe to U metal fully, using Ca at high temperatures, followed by burning in oxygen. Once formed, the UO2 is pressed into pellets, which are then fed into fuel rods. 

Not every actinide element has known or well-developed organometallic chemistry. By far the most research has been done on thorium and uranium compounds, a consequence of favorable isotope-specific nuclear properties and, at least until recently, the commercial availability of key starting materials such as Th metal, anhydrous ThCLi, U metal, and anhydrous UCL. Thorium chemistry is dominated by the -F4 oxidation state and has some similarities to the chemistry of the heavier group 4 metals. For uranium, one can access oxidation states from d-3 to 4-6 in organic media. Although there are some similarities to the chemistry of the heavier group 6 elements, for example, tungsten, there are also some remarkable differences made possible by the availability of the 5f valence orbitals. 

U-metal No data No data No data No data No data 270 496 299,117 3,159 0... 

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