• Title/Summary/Keyword: U3O8

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Ultrasonic-assisted dissolution of U3O8 in carbonate medium

  • Chenxi Hou;Mingjian He ;Haofan Fang;Meng Zhang;Yang Gao;Caishan Jiao;Hui He
    • Nuclear Engineering and Technology
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    • v.55 no.1
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    • pp.63-70
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    • 2023
  • Ultrasound-assisted dissolution of U3O8 powder in carbonate solution was explored to determine if and how ultrasound act during the dissolution. The variation of U3O8 solid particles and uranyl complexes under ultrasound treatment and magnetic stirring was observed in carbonate media. The results show that the use of ultrasound can increase the solubility and dissolution rate of U3O8 powder than that under magnetic stirring. The crush of U3O8 particles and the reduction of the activation energy (Ea, kJ/mol) of U3O8 dissolution reaction were observed, which both play an important role in the ultrasonic-assisted dissolution of U3O8 in carbonate-peroxide solution. Meanwhile, there is no observation of the ultrasound effect on the distribution of uranyl species and hydrolysis of uranyl complexes during the ultrasound treatment in carbonate-peroxide solution. Although the generation of ·OH radicals under ultrasound (22 ± 2 kHz) was observed, the oxidation of ·OH had little effect on the dissolution of U3O8 in the carbonate-peroxide solution system.

The exploration of U(VI) concentration improvement in carbonate medium for alkaline reprocessing process

  • Chenxi Hou;Mingjian He;Meng Zhang;Haofan Fang;Hui He;Caishan Jiao
    • Nuclear Engineering and Technology
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    • v.56 no.2
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    • pp.419-425
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    • 2024
  • The purpose of this study is to improve the concentration of U(VI) in carbonate solution reasonably, which to improve the application potential of the alkaline reprocessing processes. The dissolution behavior of U3O8 in carbonate peroxide solutions was investigated under different conditions, including pH, carbonate concentration, and solid-liquid ratio. The results showed that the dissolution rate of U3O8 increased with the increase of pH from 8 to 11 in the mixed carbonate solution containing 0.5 mol/L H2O2. The role of carbonate ions in the dissolution of U3O8 was further elucidated by observing the dissolution of UO4⋅4H2O in carbonate solutions. Furthermore, the concentration of U(VI) in 3 mol/L Na2CO3 solution was successfully increased to 350 g/L under ultrasonic-assisted conditions at 60 ℃ and a solid-liquid ratio at 1/2 g/mL. Meanwhile, it is suggested that increasing the concentration of carbonate ions can improve the stability of the dissolved solution containing uranyl peroxycarbonate complex.

Chlorination of TRU/RE/SrOx in Oxide Spent Nuclear Fuel Using Ammonium Chloride as a Chlorinating Agent

  • Yoon, Dalsung;Paek, Seungwoo;Lee, Sang-Kwon;Lee, Ju Ho;Lee, Chang Hwa
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.20 no.2
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    • pp.193-207
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    • 2022
  • Thermodynamically, TRUOx, REOx, and SrOx can be chlorinated using ammonium chloride (NH4Cl) as a chlorinating agent, whereas uranium oxides (U3O8 and UO2) remain in the oxide form. In the preliminary experiments of this study, U3O8 and CeO2 are reacted separately with NH4Cl at 623 K in a sealed reactor. CeO2 is highly reactive with NH4Cl and becomes chlorinated into CeCl3. The chlorination yield ranges from 96% to 100%. By contrast, U3O8 remains as UO2 even after chlorination. We produced U/REOx- and U/SrOx-simulated fuels to understand the chlorination characteristics of the oxide compounds. Each simulated fuel is chlorinated with NH4Cl, and the products are dissolved in LiCl-KCl salt to separate the oxide compounds from the chloride salt. The oxide compounds precipitate at the bottom. The precipitate and salt phases are sampled and analyzed via X-ray diffraction, scanning electron microscope-energy dispersive spectroscopy, and inductively coupled plasma-optical emission spectroscopy. The analysis results indicate that REOx and SrOx can be easily chlorinated from the simulated fuels; however, only a few of U oxide phases is chlorinated, particularly from the U/SrOx-simulated fuels.

Occurrence of Radioactive Minerals and U-Th Geochemistry of the Weolaksan and Sokrisan Granite in the Central Ogcheon Belt (중부 옥천대 월악산과 속리산 화강암의 방사성 광물 산출상태와 U-Th 지구화학)

  • Hwang, Jeong
    • The Journal of Engineering Geology
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    • v.32 no.2
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    • pp.295-310
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    • 2022
  • The Weolaksan and Sokrisan granites yield high SiO2 and alkali (Na2O+K2O) contents and low CaO and P2O5 contents. The Al saturation index is ≥1.3, which indicates that the granites are peraluminous. The mean U and Th contents are 8.3 and 39.3 ppm, respectively, higher than typical Mesozoic granites in South Korea and about twice the global mean for granitic rocks. The causes of such high radioelement contents are related to high degrees of fractionation and the crustal origin of the granites. U- and Thbearing radioactive minerals occur in the granites include zircon, thorite, monazite, xenotime, fergusonite and uraninite. The fact that the mean Th/U ratio of the granites (5.4) is similar to the global average crustal value suggests that the radioelement contents of granite were controlled by the crustal source material. Given the correlation of Zr, Y, and heavy rare earth elements for U and Th, radioelements are more likely hosted by xenotime than zircon and monazite.

The conversion of ammonium uranate prepared via sol-gel synthesis into uranium oxides

  • Schreinemachers, Christian;Leinders, Gregory;Modolo, Giuseppe;Verwerft, Marc;Binnemans, Koen;Cardinaels, Thomas
    • Nuclear Engineering and Technology
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    • v.52 no.5
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    • pp.1013-1021
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    • 2020
  • A combination of simultaneous thermal analysis, evolved gas analysis and non-ambient XRD techniques was used to characterise and investigate the conversion reactions of ammonium uranates into uranium oxides. Two solid phases of the ternary system NH3 - UO3 - H2O were synthesised under specified conditions. Microspheres prepared by the sol-gel method via internal gelation were identified as 3UO3·2NH3·4H2O, whereas the product of a typical ammonium diuranate precipitation reaction was associated to the composition 3UO3·NH3·5H2O. The thermal decomposition profile of both compounds in air feature distinct reaction steps towards the conversion to U3O8, owing to the successive release of water and ammonia molecules. Both compounds are converted into α-U3O8 above 550 ℃, but the crystallographic transition occurs differently. In compound 3UO3·NH3·5H2O (ADU) the transformation occurs via the crystalline β-UO3 phase, whereas in compound 3UO3·2NH3·4H2O (microspheres) an amorphous UO3 intermediate was observed. The new insights obtained on these uranate systems improve the information base for designing and synthesising minor actinide-containing target materials in future applications.

RECYCLING PROCESS OF U3O8 POWDER IN MnO-Al2O3 DOPED LARGE GRAIN UO2 PELLETS

  • Oh, Jang Soo;Kim, Dong-Joo;Yang, Jae Ho;Kim, Keon Sik;Rhee, Young Woo;Koo, Yang-Hyun
    • Nuclear Engineering and Technology
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    • v.46 no.1
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    • pp.117-124
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    • 2014
  • The effect of various process variables on the powder properties of recycled $U_3O_8$ from MnO-$Al_2O_3$ doped large grain $UO_2$ pellets and the effect of those recycled $U_3O_8$ powders on the sintered density and grain size of MnO-$Al_2O_3$ doped large grain $UO_2$ pellets have been investigated. The evolution of morphology, size, and BET surface area of the recycled $U_3O_8$ powders according to the respective variation of the thermo-mechanical treatment variables of oxidation temperature, powder milling, and sequential cyclic heat treatment of oxidation and then reduction was examined. The correlation between the BET surface area of recycled $U_3O_8$ powder and the sintered pellet properties of MnO-$Al_2O_3$ doped pellets showed that the pellet density and grain size of doped pellets were increased and then saturated by increasing the BET surface area of the recycled $U_3O_8$ powder. The density and grain size of the pellets were maximized when the BET surface area of the recycled $U_3O_8$ powder was in the vicinity of $3m^2/g$. Among the process variables applied in this study, the cyclic heat treatment followed by low temperature oxidation was a potential process combination to obtain the sinter-active $U_3O_8$ powder.

Impedance Spectroscopy of (Pb0.92La0.08)(Zr0.95Ti0.05)O3 Ceramics above Room Temperatures

  • Jong-Ho Park
    • Korean Journal of Materials Research
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    • v.34 no.5
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    • pp.242-246
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    • 2024
  • La modified lead zirconate titanate ceramics (Pb0.92La0.08)(Zr0.95Ti0.05)O3 = PLZT-8/95/5 were prepared using the conventional solid state reaction method in order to investigate the complex impedance characteristics of the PLZT-8/95/5 ceramic according to temperature. The complex impedance in the PLZT-8/95/5 ceramic was measured over a temperature range of 30~550 ℃ at several frequencies. The complex dielectric constant anomaly of the phase transition was observed near TU1 = 179 ℃ and TU2 = 230 ℃. A remarkable diffuse dielectric constant anomalous behaviour of the complex dielectric constant was found between 100 ℃ and 550 ℃. The complex impedance spectra below and above TU1 and TU2 were fitted by the superposition of two Cole-Cole types of impedance relaxations. The fast component in the higher frequency region may be due to ion migration in the bulk, and the slow component in the lower frequency region is interpreted to be the formation and migration of ions at the grain boundary or electrode/crystal interfacial polarization.

Spark plasma sintering of UO2 fuel composite with Gd2O3 integral fuel burnable absorber

  • Papynov, E.K.;Shichalin, O.O.;Belov, A.A.;Portnyagin, A.S.;Buravlev, I.Yu;Mayorov, V.Yu;Sukhorada, A.E.;Gridasova, E.A.;Nomerovskiy, A.D.;Glavinskaya, V.O.;Tananaev, I.G.;Sergienko, V.I.
    • Nuclear Engineering and Technology
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    • v.52 no.8
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    • pp.1756-1763
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    • 2020
  • The paper studies spark plasma sintering (SPS) of industrially used UO2-based fuel containing integral fuel burnable absorber (IFBA) of neutrons Gd2O3. Densification dynamics of pristine UO2 powder and the one added with 2 and 8 wt% of Gd2O3 under ultrasonication in liquid has been studied under SPS conditions at 1050, 1250, and 1450 ℃. Effect of sintering temperature on phase composition as well as on O/U stoichiometry has been investigated for UO2 SPS ceramics. Sintering of uranium dioxide added with Gd2O3 yields solid solution (U,Gd)O2, which is isostructural to UO2. SEM with EDX and metallography were implemented to analyze the microstructure of the obtained UO2 ceramics and composite UO2-Gd2O3 one, particularly, open porosity, defects, and Gd2O3 distribution were studied. Microhardness, compressive strength and density were shown to reduce after addition of Gd2O3. Obtained results prove the hypothesis on formation of stable pores in the system of UO2-Gd2O3 due to Kirkendall effect that reduces sintering efficiency. The paper expands fundamental knowledge on pros and cons of fuel fabrication with IFBA using SPS technology.

Study of HubWA Protein Folding Reaction by Measuring the Stability of Folding Intermediate (중간단계의 구조적 안정성을 통한 HubWA 단백질의 접힘(folding) 반응 탐색)

  • Soon-Ho Park
    • Journal of the Korean Chemical Society
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    • v.67 no.2
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    • pp.81-88
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    • 2023
  • The contribution of hydrophobic residues to the protein folding reaction was studied by using HubWA variant proteins with I and L to V mutation. Folding kinetics of all V variant proteins was observed to be satisfied by a three-state on-pathway mechanism, U ⇌ I ⇌ N, where U, I, and N represent unfolded, intermediate, and native state, respectively. Three-state folding reaction was quantitatively analyzed and the free energy of folding of each elementary reactions and overall folding reaction, ΔGoUI, ΔGoIN, and ΔGoUN, were obtained. From the ratio of free energy difference between the variant protein and HubWA, ΔΔGoUI/ΔΔGoUN (ΔΔGoUI = ΔGoUI (variant protein) - ΔGoUI (HubWA) and ΔΔGoUN = ΔGoUN (variant protein) - ΔGoUN(HubWA)), the contribution of hydrophobic residues to HubWA folding was analyzed. The residues which are located in the hydrophobic core between α-helix and β-sheet, I3, I13, L15, I30, L43, I61 and L67, showed ΔΔGoUI/ΔΔGoUN value of ~0.5 when each of these residues was mutated to V, indicating that these residues form relatively solid hydrophobic core in the intermediate state. Residues located at the end of secondary structures and loop, I23, L69 and I36 showed ΔΔGoUI/ΔΔGoUN value below 0.4 when each of these residues was mutated to V, indicating that the region containing these residues are loosely formed in the intermediate state. V17A, L50V and L56V showed fairly high ΔΔGoUI/ΔΔGoUN value of ~0.8. Since L50 and L56 are located in the region containing long loop (residue 46 to 62), it is suggested that the high ΔΔGoUI/ΔΔGoUN value of these residues prevents the formation of aggregate at the early stage of folding reaction.