• Journal of Powder Materials
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• v.4 no.3
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• pp.214-221
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• 1997

The densification and grain growth mechanisms of $UO_{2+x}$ in $H_2$ and in $CO_2$ have been investigated. Uranium dioxide powder compacts were sintered at 1$700^{\circ}C$ in $H_2$ or at 110$0^{\circ}C$ in $CO_2$ for various times from 0.5 h to 16 h. The grain size and density of the specimens were measured. From the measured data, the mechanisms of the densification and grain growth were determined by use of available kinetic equations which express the relations between densification and grain growth. In both atmospheres, it has been found that the densification was controlled by the lattice diffusion and the grain growth by the surface diffusion of atoms around pores. It appears that the surface diffusivity as well as the lattice diffusivity increase considerably with the increase in O/U ratio in the specimen.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.680-688
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• 1998

The macroreticular (MR) type glycidylmethacrylate (GMA)-divinylbenzene (DVB) copolymer (polyglycidylmethacrylate) beads (RG) were prepared by a suspension polymerization using 0~100 vol % of 2,2,4-trimethylpentane (TMP) as a diluent. Macroreticular type cation exchange resins containing phosphoric acid groups (RGP) were prepared by the reaction of GMA-DVB copolymer and poly (glycidyl methacrylate) bead (RG) with phosphoric acid in the presence of benzene. In this study, the effect of degree of crosslinking and the amount of the diluent on physical properties and adsorbability of uranium of RGP resins were investigated respectively. The chemical and physical properties of RGP resins were affected by both of the amount of the diluent and the degree of crosslinking. The effect of degree of crosslinking on the adsorbed amount of uranium for RGP resins were decreased in the order of $$RGP-10(50){\sim_=}RGP-1(50)>RGP-2(50)>RGP-5(50)>RGP-0$$. The effect of the diluent amount were as follows RGP-2(100)>RGP-2(75)>RGP-2(50)>RGP-2(30)>RGP-2(0). The crosslinking degree effect on uranium adsorbability depended on pore structure, cation exchange capability and swelling ratio. On the other hand, the effect of the diluent amount were relied on surface area and pore structure raher than cation exchange capability.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.13 no.4
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• pp.263-269
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• 2015

It is necessary to investigate the electrodeposition behavior of uranium and other elements on the cathode in the electrorefining process to recover the uranium selectively from the reduced metals of the electrolytic reduction process since transuranic elements and rare earth elements is dissolved in the LiCl-KCl eutectic salt. Study on separation factors of U, Ce, Y and Nd based on U and Ce was performed to investigate the deposition behavior of the cathode with respect to the concentration of rare earth elements in LiCl-KCl eutectic salt. After electrorefining with constant current mode by using Ce metal as a sacrifice anode, the contents of U, Ce, Y and Nd in the salt phase and the deposit phase of the cathode were analyzed, and separation factors of the elements were obtained from the analyses. Securing conditions of pure uranium recovery in the elctrorefining process was investigated by considering the separation factors with respect to $UCl_3$ and $CeCl_3/UCl_3$ ratio.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.2792-2800
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• 2022

In the core of the WWR-K reactor, a long-term irradiation of tristructural isotopic (TRISO)-coated fuel particles (CFPs) with a UO₂ kernel was carried out under high-temperature gas-cooled reactor (HTGR)-like operating conditions. The temperature of this TRISO fuel during irradiation varied in the range of 950-1100 ℃. A fission per initial metal atom (FIMA) of uranium burnup of 9.9% was reached. The release of gaseous fission products was measured in-pile. The release-to-birth ratio (R/B) for the fission product isotopes was calculated. Aspects of fuel safety while achieving deep fuel burnup are important and relevant, including maintaining the integrity of the fuel coatings. The main mechanisms of fuel failure are kernel migration, silicon carbide corrosion by palladium, and gas pressure increase inside the CFP. The formation of gaseous fission products and carbon monoxide leads to an increase in the internal pressure in the CFP, which is a dominant failure mechanism of the coatings under this level of burnup. Irradiated fuel compacts were subjected to electric dissociation to isolate the CFPs from the fuel compacts. In addition, nondestructive methods, such as X-ray radiography and gamma spectrometry, were used. The predicted R/B ratio was evaluated using the fission gas release model developed in the high-temperature test reactor (HTTR) project. In the model, both the through-coatings of failed CFPs and as-fabricated uranium contamination were assumed to be sources of the fission gas. The obtained R/B ratio for gaseous fission products allows the finalization and validation of the model for the release of fission products from the CFPs and fuel compacts. The success of the integrity of TRISO fuel irradiated at approximately 9.9% FIMA was demonstrated. A low fuel failure fraction and R/B ratios indicated good performance and reliability of the studied TRISO fuel.

• Nuclear Engineering and Technology
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• v.56 no.10
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• pp.4176-4183
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• 2024

In this study, the groundwater hydrodynamics of two adjacent well sites were simulated under different pumping-injection ratios. The aim is to select an optimal pumping-injection ratio that can ensure the groundwater of the two well sites don't affect each other. In addition, the sulfur isotope composition of groundwater in the two well sites were analyzed to verify the simulated results. The results show that the flow velocity at different points outside the edge drilling hole decreases exponentially with the distance between the point and the edge hole. The streamline gradually extends outside of the borehole with the increase of leaching time. It is found that the optimal pumping-injection ratio is 1.003. In this case, the maximum distance between the moving front and the injection borehole is 28.44 m after leaching for 5 years. This indicates that the groundwater flow fields of the two well sites are well controlled. The significant difference in sulfur isotopes between the two well-sites further proves that the SO₄^2- in the acid mining zone does not affect the groundwater in the zone leached by CO₂+O₂.

• Journal of the Korean Chemical Society
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• v.31 no.4
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• pp.315-321
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• 1987

The ligand, 2,10-dibenzyl-4,6,8-trioxo-3,9-diaza undecane dioic acid(DTDA) for the extraction of uranium was synthesized under dry nitrogen from phenylalanine and 3-oxoglutaric acid. Extraction was performed by stirring a solution of DTDA in dichloromethane for 1 hour with an aqueous solution of $UO_2(ClO_4)_2{\cdot}6H_2O$ at various pH values and at different $DTDA/UO_2{^{2+}}$ molar ratios. Extraction efficiency reaches a maximum when the pH of the aqueous phase was ca 8.0. The extraction percentage was affected by concentration of DTDA and increases with the $DTDA/UO_2{^{2+}}$ molar ratio to complete extraction with a 4 fold excess of DTDA. The high selectivity of the DTDA for uranium was ascertained by competition experiments with other cations. The bound uranyl ion was quantitatively liberated within few minutes from the organic phase by treatment with an aqueous 1M HCI solution and DTDA was recovered very satisfactorily from the organic phase. The values of the over-all formation constants of the complex between uranyl ion and DTDA were determined to be the following : ${\beta}_1=1.20{\times}10^5\;,\;{\beta}_2=1.01{\times}10^8$.

• Polymer(Korea)
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• v.25 no.1
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• pp.49-55
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• 2001

The bi-functional ion exchangers, SAPP-g-(AN/St) were synthesized with mixed vinyl monomers(acrylonitrile and styrene) onto PP fabric by the pre-irradiation grafting with E-beam and its subsequent amidoximination and sulfonation. The degree of grafting of PP-g-(AN/St) was increased with decreasing acrylonitrile composition in the mixed monomers. The water uptake of copolymers increased with decreasing in the amidoxime ratio in the copolymers and increased by sulfonation, but decreased by amidoximation. The $UO_2^{2+}$ adsorption capacity of SPP-g-St, APP-g-AN, and SAPP-g-(AN/St) were 12.4, 34.0, and 38.0 mg/g, respectively and the optimum adsorption time is about 50 hrs. As a result of uranium adsorption, the synthesized ion exchanger, which we obtained have also good affinity toward the adsorption or chelating with $UO_2^{2+}$ ions.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.10a
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• pp.252-253
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• 2005

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.588-592
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• 2004

Effect of the UO$_2$ powder characteristic changes by dynamic milling method on the density was investigated. particle size decreased and its shape was changed from irregular to round form with increasing milling time (0∼8 h), while its specific surface area and O/U ratio increased. It was shown that the sintered density decreased, while green density increased with these powder characteristic changes. It could be considered that this decrement was affected by increased O/U ratio of the UO$_2$ powder during dynamic milling.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.2
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• pp.153-159
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• 2006

It is a serious task to the decommissioning of the uranium conversion plant that the demolition of the lagoon sludge. The main component of the sludge is ammonium nitrate and that is the very explosive material. Therefore, the bio-denitrification is a attractive process to remove the nitrate. In this work, some process variables was tested such as incubation temperature, nitrate concentration, electron donor, C/N ratio, seeding ratio, and pH with an anaerobic bacteria as Pseudomonas halodenitrificans. The results would be used as basic data to the continuous bio-denitrification process.