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KMID : 0371819960280050458
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Nuclear Engineering and Technology
1996 Volume.28 No. 5 p.458 ~ p.466
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microstructural Analysis on UO2 and UO2-4wt% CeO2 by Using Additives in Reducing and Oxidizing Atmospheres
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Han Soo Kim
Si Hyung Kim/Young Woo Lee/and Sang Ho Na
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Abstract
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The effects of dopants on the modification of microstructure of UO2 and UO2-4wt%CeO2 sintered pellets have been studied in hydrogen and CO2/CO mixture atmospheres by using Ta2O5, TiO2 and Nb2O5 as sintering additives. The dopant were added as oxide powders and homogenized by attrition milling. The mixed powders were pressed, and then sintered in hydrogen at 1700?C , or in oxidizing atmosphere using Controlled CO2/CO mixtures at 1250?C. Both density and microstructure of UO2 are modified by the addition of dopants in reducing atmosphere. The sintered density is increased with Ta2O5 addition up to 0.33wt% and subsequently decreased with higher content of the additive. The effect on the densification and the gain growth are apparent with the addition of 0.24wt% Nb2O5. With 0.lwt% titania and 0.6wt% Ta2O5, the sintered density is decreased, but the grain size is increased. In oxidizing atmosphere, the grain sizes for UO2 doped with the above additives are smaller than that for pure UO2. The grain size of Ta or Nb-doped UO2 is decreased with increasing CO2/CO ratio, but that of pure UO2or T-doped UO2 is increased. A large portion of second phases is observed in UO2 doped with 0.lwt% TiO2 sintered in hydrogen atmosphere, while, in CO2/CO atmospheres, the second phases or dopant agglomerates are not observed. For UO2-4wt%CeO2 mixed oxide, the effect of additives on the gain growth is not so much as that for the pure UO2. This is attributed to the formation of clusters by dopant cations and Ce ions, so that the additives contribute to a lesser exent to the grain growth for the mixed oxide.
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