No abstract available

[en] This invention relates to an improved continuous calcining apparatus for consistently and controllably producing from calcinable reactive solid compounds of uranium, such as ammonium diuranate, uranium dioxide (UO₂) having an oxygen to uranium ratio of less than 2.2. The apparatus comprises means at the outlet end of a calciner kiln for receiving hot UO₂, means for cooling the UO₂ to a temperature of below 100 deg C and conveying the cooled UO₂ to storage or to subsequent UO₂ processing apparatus where it finally comes into contact with air, the means for receiving cooling and conveying being sealed to the outlet end of the calciner and being maintained full of UO₂ and so operable as to exclude atmospheric oxygen from coming into contact with any UO₂ which is at elevated temperatures where it would readily oxidize, without the use of extra hydrogen gas in said means. (author)

[en] This invention concerns a dry process method for the fabrication of UO₂ uranium oxide and a system to use this process. It makes it possible to obtain in a reproducible manner uranium oxide having the requisite physical qualities for easy sintering. The first stage of the process consists in making gaseous uranium hexafluoride with steam in one part of a vessel and the second stage in submitting the UO₂F₂ oxyfluoride obtained in the first stage to a reduction in another part of the same vessel in order to obtain UO₂ uranium oxide

No abstract available

No abstract available

[en] Results are presented of a new theoretical survey of the energetics of fission Xe in UO₂, in which improved gas-lattice potentials are employed, and calculations performed for a range of temperatures. Single gas atom trapping and migration and their solution from underpressurised bubbles is concentrated on. (author)

[en] In order to study densification characteristics of ATR (Advanced Thermal Reactor) type fuel, irradiation experiments have been performed by means of OWL-1 loop in JMTR (Japan Materials Testing Reactor). The experimental results obtained are compared with that obtained from EEI/EPRI, which have performed densification tests under simulated LWR conditions. (orig.)

[en] The reprocessing of scrap in the production of UO2 pellets, is important from an economical view-point of the fuel cycle. The recovery method by means of a humid process, tested for UO2 scrap, includes the dissolution of the pellets in a nitric media at boiling point, the precipitation of ammonium diuranates (ADU) and its conversion into UO2 at 600 deg C. The microestructural results and the sintering density of the pellets produced in these tests are compared. It is shown that, although the addition of said UO2 powders impaires the performance of the original mixture produced by the factory, the results thus obtained are, nevertheless, within specifications. This facts show that the mixture would then be able for production. (M.E.L.)

[en] Quantum–mechanical techniques were used to determine the charge distribution of U atoms in UO_2+x (x ⩽ 0.25) and to calculate activation-energy barriers to oxygen diffusion. Upon optimization, the reduction in unit-cell volume relative to UO₂, and the shortest 〈U–O〉 and 〈O–O〉 bond-lengths (0.22 and 0.24 nm, respectively) are in good agreement with experimental data. The addition of interstitial oxygen to the unoccupied cubic sites in the UO₂ structure deflects two nearest-neighbor oxygen atoms along the body diagonal of uranium-occupied cubic sites, creating lattice oxygen defects. In (1 × 1 × 2) supercells, the partial oxidation of two U⁴⁺ atoms is observed for every interstitial oxygen added to the structure, consistent with previous quantum–mechanical studies. Results favor the stabilization of two U⁵⁺ over one U⁶⁺ in UO_2+x. Calculated activation energies (2.06–2.73 eV) and diffusion rates for oxygen in UO_2+x support the idea that defect clusters likely play an increasingly important role as oxidation proceeds

[en] Results are presented of calculations of formation energies of small aggregates, or bubbles, of Xe atoms in UO₂. This is followed by a study of the energetics of resolution of gas atoms from bubbles into the UO₂ lattice. (author)