• Title/Summary/Keyword: UO2

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A Study on Calcination and Reduction of AUC (Ammonium Uranyl Carbonate) -Characteristics and Phase Change of Powder- (AUC(Ammonium Uranyl Carbonate)의 하소 및 환원 반응 -분말의 특성 및 상변화-)

  • 김응호;최청송;박진호;장인순
    • Journal of the Korean Ceramic Society
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    • v.30 no.4
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    • pp.279-288
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    • 1993
  • A study on calcination and reduction of AUC(ammonium uranyl carbonate, (NH4)4UO2(CO3)3) has been carried out by using TG-DTA in N2, air and H2 atmospheres, respectively. Phases of various intermediate obtained during thermal analysis of AUC in different atmospheres were confirmed by XRD. Powder characteristics of each intermediate were investigated by measuring particle size and specific surface area, and also observed by SEM. As a results, regardless of applied atmosphere AUC was calcined into amorphous UO3, which was converted to $\alpha$-U3O8 Via $\alpha$-UO3 in both H2 and N2 atmosphere, but directly into $\alpha$-UO3 in air atmosphere. Further reduction of U3O8 was only detectable in hydrogen atmosphere. During calcination and reduction, average particle size was reduced to less than 30% of original value without morphology change. Specific surface area was dramatically increased with release of NH3, CO2 and H2O from AUC powder and reached maximum value around 25$0^{\circ}C$, and then gradually decreased with the increase of temperature due to sintering effect of uranium oxides such as UO3 and U3O8. It was also found that the change of average crystallite size and pore size were closely related to the changes of specific surface area of uranium oxides.

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Microstructure Development during Sintering of $Nb_2O_5$-doped $UO_2$ pellets under $H_2$ and $CO_2$ atmospheres ($Nb_2O_5$ 첨가 $UO_2$ pellet의 수소 분위기와 이산화탄소 분위기 소결 중 미세조직의 형성에 대한 연구)

  • Song, K.W.;Kim, S.H.;Kim, B.G.;Lee, Y.W.;Yang, M.S.;Park, H.S.
    • Nuclear Engineering and Technology
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    • v.26 no.4
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    • pp.484-492
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    • 1994
  • Microstructures of Nb$_2$O$_{5}$-doped UO$_2$ pellets have been investigated during sintering under H$_2$ and $CO_2$ atmospheres. Pellets are sintered at 1$700^{\circ}C$ in H$_2$ atmosphere and at 130$0^{\circ}C$ in $CO_2$ atmosphere for 1 to 41 hr. The addison of Nb$_2$O$_{5}$ causes the formation of large pores, which shrink to some extent in H$_2$ atmosphere but very little in $CO_2$. Fine pores in the Nb$_2$O$_{5}$-doped UO$_2$ pellet are almost annihilated when sintered under H$_2$ atmosphere but little changed under $CO_2$ atmosphere. The increase in grain size due to Nb$_2$O$_{5}$ addition is much larger in H$_2$ atmosphere than in $CO_2$. Thus the enhancement of uranium diffusion in UO$_2$ due to the Nb$_2$O$_{5}$ addition is thought to be more significant in H$_2$ atmosphere. Microstructures of Nb$_2$O$_{5}$-doped UO$_2$ pellets sintered in H$_2$ atmosphere are discussed from the viewpoint of in-reactor performance. Possible defects formation due to Nb$_2$O$_{5}$ addition is discussed to explain the enhancement of uranium diffusion in H$_2$ and $CO_2$ atmospheres.> atmospheres.

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