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This work studied a way to reclaim uranium from contaminated UO oxide scraps as a sinterable UO powder for UO fuel pellet fabrication, which included a dissolution of the uranium oxide scraps in a carbonate solution with hydrogen peroxide and a UO precipitation step. Dissolution characteristics of reduced and oxidized uranium oxides were evaluated in a carbonate solution with hydrogen peroxide, and the UO precipitation were confirmed by acidification of uranyl peroxo-carbonate complex solution. An agglomerated UO powder obtained by the dissolution and precipitation of uranium in the carbonate solution could not be pulverized into fine UO powder by the OREOX process, because of submicron-sized individual UO particles forming the agglomerated UO precipitate. The UO powder prepared from the UO precipitate could meet the UO powder specifications for UO fuel pellet fabrication by a series of steps such as dehydration of UO precipitate, reduction, and milling. The sinterability of the reclaimed UO powder for fuel pellet fabrication was improved by adding virgin UO powder in the reclaimed UO powder. A process to reclaim the contaminated uranium scraps as UO fuel powder using a carbonate solution was finally suggested. [ABSTRACT FROM AUTHOR]

A simulated DUPIC (Direct Use of Spent PWR Fuel in CANDU Reactors) fuel was irradiated at HANARO research reactor of KAERI in 1999. Post-irradiation examinations, such as measurements of γ-scanning, profilometry, density, hardness, microstructure, and fission product distribution were performed on the irradiated simulated DUPIC fuel. In γ-scanning, the intensity along the axial direction was sharply decreased at the areas between the pellets. There was no significant change in the profilometry of SEU-1.47%, but variation was detected in SEU-2.19%+F.P by 67 μm, and the peaks precisely coincided with the ridges of the pellets. The marked difference between SEU-1.47% and SEU-2.19%+F.P pellets after irradiation was the configuration of cracks arised in the pellets. Some large equiaxed grains of 11.1 μm were observed at the center of the SEU-2.19%+F.P pellet, while the grain size near the surface of the pellet was remained almost the same as the original grain size of 5.58 μm. The hardness had no tendency toward change to the direction, but average hardness was increased as much as 10% compared with a fresh simulated DUPIC fuel. [ABSTRACT FROM AUTHOR]

The change of Np oxidation state in nitric acid and the effect of nitrous acid on the oxidation state were analyzed by spectrophotometry, solvent extraction, and electrochemical methods. The Np extraction with 30 vol.% TBP was enhanced by the adjustment of the Np oxidation state using a glassy carbon fiber column electrode system. The knowledge of electrolytic behavior of nitric acid was important because the nitrous acid affecting the Np redox reaction was generated during the adjustment of the Np oxidation state. The Np solution used in this work consisted of Np(V) and Np(VI) but no Np(IV). The ratio of Np(V) in the range of 0.5M∼5.5 M nitric acid was 32%∼19%. The electrolytic oxidation of Np(V) to Np(VI) in the solution enhanced the Np extraction efficiency about five times higher than without electrolytic oxidation. It was confirmed that the nitrous acid in a concentration of less than about 10−5 M acted as a catalyst to accelerate the chemical oxidation reaction of Np(V) to Np(VI). [ABSTRACT FROM AUTHOR]

A new static contactor was developed for solvent extraction using capillary phenomena induced among clearances formed within a highly packed fiber bundle. Feeding two immiscible phases cocurrently into the fiber bundle generated a very large liquid-liquid contact area for mass transfer within the fiber bundle without any flow turbulence or drop phenomena. In order to test the characteristics and stability of the fiber bundle contactor, continuous extraction experiments were carried out using the fiber bundle contactor with a TBP-uranyl ion-nitric acid system. The fiber bundle contactor had the same extraction performance as that of an ideal batch extractor with good reproducibility due to the sufficient liquidliquid contact area generated by the packed fiber bundle. A minimum residence time of the aqueous phase within the fiber bundle contactor was required for the extraction system to reach an extraction equilibrium state. In the TBP-uranyl ion-nitric acid system, the residence time was about 1.9 minutes. This contactor was confirmed to be effective enough to perform solvent extraction and to study the extraction kinetics because of the stable and large static liquid-liquid contact area. [ABSTRACT FROM AUTHOR]