Uranium carbides structure

Uranium. tetrathiocyanatotetrakis[tris-(dimethylamino)phosphine oxide]-structure, 1.87 Uranium carbide nuclear fuels dissolution, 6, 928 Uranium complexes, 3,1131-1215 carbamic acid... 

It was shown [33] for uranium (U), possessing a related electronic structure ([Rn] 5f 1 ) to gadolinium ([Xe] Af 5d 6s ), that after CO adsorption two features appear one structure at 2.4 eV binding energy is due to C 2p emission from uranium carbide (UC) and the other one at 2.2 eV from U caused by the existence of oxygen. 

The structure of a typical coated particle is shown in Fig. 5.4. The fuel kernel is a sphere of uranium carbide with a diameter in the range of 100-400 pm. The innermost coatihg consists of a layer of pyrolytic carbon laid down by deposition from hydrocarbon gases in a high-temperature fluidized bed. This inner layer absorbs fission fragment recoils and is made relatively porous to provide voidage for the accommodation of fission gases. The next layer is made up of silicon carbide, which is particularly effective in the... 

The deposition of pyrolytic graphite in a fluidized bed is used in the production of biomedical components such as heart valves, ] and in the coating of uranium- and thorium-carbides nuclear-fuel particles for high temperature gas-cooled reactors, for the purpose of containing the products of nuclear fission.fl" The carbon is obtained from the decomposition of propane (CgHg) or propylene (CgHg) at 1350°C, or of methane (CH4) at 1800°C. Its structure is usually isotropic (see Ch. 4). 

The high-temperature gas-cooled reactor (HTGR) is a thermal reactor that produces desired steam conditions. Helium is used as the coolam. Graphite, with its superior high temperature properties, is used as the moderator and structural material. The fuel is a mixture of enriched uranium and thorium in the form of carbide particles clad with ceramic coatings. 

To elucidate the nature of chemical bonding in metal carbides with the NaCl structure, the valence electronic states for TiC and UC have been calculated using the discrete-variational (DV) Xa method. Since relativistic effects on chemical bonding of compounds containing uranium atom become significant, the relativistic Hamiltonian, i.e., the DV-Dirac-Slater method, was used for UC. The results... 

Jones, D.W., McColm, I.J., Yerkess, J., Clark, N.J., Carbon Species in the Crystal Structures of Uranium-Transition-Element Carbides, UMC2 , 7. Solid State Chem., 74, 304-313 (1988) (Crys. Stmcture, Experimental, 27)... 

UC2 is a carbide of uranium, which has a high melting point and a high thermal conductivity. UC2 has a body-centered tetragonal (BCT) crystal structure up to the transformation temperature of 1820 20°C, where it transforms to a face-centered cubic (FCC) structure, similar to that of UO2 (Frost, 1963). Frost (1963) has indicated that UC2 has always been found in hypostoichiometric forms such... 

Two fuel forms have the potential to satisfy the GFR requirements (1) a ceramic plate-type fuel element and (2) a ceramic pin-type fuel element. The reference material for the structure is reinforced ceramic comprised of a sUicon carbide composite matrix ceramic. The fuel compound is made of pellets of mixed uranium-plutonium-minor actinide carbide. A leak-tight barrier made of a refractory metal or of Si-based multilayer ceramics is added to prevent fission products from diffusing through the clad [1]. 

---