• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.2
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• pp.113-122
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• 2007

In this study, uranium migration experiments have been performed using a natural groundwater and a granite core with natural fractures in a glove-box constructed to simulate an appropriate subsurface environment. Groundwater flow experiments using the non-sorbing anionic tracer Br were carried out to analyze the flow properties of groundwater through the fracture of the granite core. The result of the uranium migration experiment showed a breakthrough curve similar to that of the non-sorting Br. This result may imply that uranium migrates as anionic complexes through the rock fracture since uranium can form carbonate complexes at a given groundwater condition. The distribution coefficient $K_d$ of the uranium between the groundwater and the fracture filling material was obtained as low as 2.7 mL/g from a batch sorption experiment. This result agrees well with the result from the migration experiment, showing a faster elution of the uranium through the rock fracture. In order to analyze retardation properties of the uranium through the rock fracture, the retardation factor $R_d({\sim}16.2)$ was obtained by using the $K_d$ obtained from the batch sorption experiment and it was compared with the $R_d({\sim}14.3)$ obtained by using the result from the uranium migration experiment. The values obtained from the both experiments were very similar to each other. This reveals that the retardation of the uranium is mainly occurred by the fracture filling material when the uranium migrates through the fracture of a granite core.

• Economic and Environmental Geology
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• v.41 no.6
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• pp.719-729
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• 2008

In this study, the speciation, adsorption, and transport of uranium in groundwater environments were simulated using geochemical models. The retarded transport of uranium by adsortption was effectively simulated using 3-D groundwater flow and reactive transport models. The results showed that most uranium was adsorbed(up to 99.5%) in a neutral pH(5.5$pCO_2(10^{-3.6}atm)$ condition. Under the higher $pCO_2(10^{-2.5}atm)$ condition, however, the pH range where most uranium was absorbed was narrow from 6 to 7. Under very low $pCO_2(10^{-4.5}atm)$ condition, uranium was mostly absorbed in the relatively wide pH range between 5.5 and 8.5. In the model including anion complexes, the uranium adsorption decreased by fluoride complex below the pH of 6. The results of this study showed that uranium transport is strongly affected by hydrochemical conditions such as pH, $pCO_2$, and the kinds and concentrations of anions($Cl^-$, ${SO_4}^{2-}$, $F^-$). Therefore, geochemical models should be used as an important tool to predict the environmental impacts of uranium and other hazardous compounds in many site investigations.

• Journal of the Mineralogical Society of Korea
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• v.25 no.4
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• pp.263-270
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• 2012

Two kinds of uranium species, oxidized uranium(VI) and reduced uranium(IV), were prepared to be interacted with goethite and montmorillonite to identify sorption characteristic of uranium species, which are very sensitive to the redox-reaction. The reduced uranium was prepared by diluting a substantial uranium(IV) that was concomitantly produced during a sulfate reduction via a sulfate-reducing bacterium. The sorption amount of uranium(IV) by the minerals was relatively lower than that of uranium(VI) because the aqueous uranium(IV) had fine colloidal forms to cause its weak adsorption onto the mineral surfaces. We found that the uranium(IV) phase has a nano-colloid character by the transmission electron microscope, suggesting that the uranium species possibly migrating with the flow of groundwater in underground environments can be the colloidal uranium(IV) as well as the ionic uranium(VI).

• Nuclear Engineering and Technology
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• v.29 no.6
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• pp.60-64
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• 1997

핵연료의 가공공정에서 발생하는 스러지를 건식처리공정으로 회수 정제할 수 있는 건식처리 방법에 대하여 논의하고자 하였다. 건식처리방법은 수용액을 전혀 사용하지 알기 때문에 폐기물의 발생량이 습식처리방법에 비해 훨씬 줄어든다. 산화우라늄은 고온의 용융염중에서 염소개스에 의해 염소화반응을 통하여 우라늄염화물을 생성되게 되어 이들은 전기적으로 이동이 가능한 형태로 바뀌므로 전극에 선택적으로 전착될 수 있기 때문에 다른 금속이온과 분리할 수 있다. 본 보고서에서는 산화우라늄의 염소화공정, 전착공정에 대하여 기술하였고 전착된 산화물의 물리적 특성에 대하여 요약하였다.

• Economic and Environmental Geology
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• v.42 no.5
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• pp.471-477
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• 2009

An experimental removal of dissolved uranium (U) exsiting as uranyl ion (${UO_2}^{2+}$) was carried out using Shewanella p., iron-reducing bacterium. By the microbial reductive reaction, initial U concentration ($50{\mu}M$) was constantly decreased, and most U were removed from solution after 2 weeks. Major mechanism that U was removed from the solution was adsorption, precipitation and mineralization on the microbe surface. Under the transmission electron microscopy, the U adsorbed on the microbe was observed as being crystallized and eventually enlarged to several ${\mu}m$ sizes of minerals by combining with individual microbes and organic exudates. It seems that such U growth and mineralization on the microbial surface could affect the U behavior in a radioactive waste disposal site. Thus, the biogechemical reaction of metal-reducing bacteria observed in this experiment could give an affirmative measure that the microbial activity may retard U movement in subsurface environment.

• Economic and Environmental Geology
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• v.51 no.2
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• pp.77-85
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• 2018

There would be a possibility of uranium contamination around the nuclear power plants and the underground waste disposal sites, where the uranium could further migrate and diffuse to some distant places by groundwater. It is necessary to understand the biogeochemical behaviors of uranium in underground environments to effectively control the migration and diffusion of uranium. In general, various kinds of microbes are living in soils and geological media where the activity of microbes may be closely connected with the redox reaction of nuclides resulting in the changes of their solubility. We investigated the adsorption and precipitation behaviors of dissolved uranium on some solid materials using hydrogen gas as an electron donor instead of organic matters. Although the effect of hydrogen gas did not appear in a batch experiment that used granite as a solid material, there occurred a reduction of uranium concentration by 5~8% due to hydrogen in an experiment using bentonite. This result indicates that some indigenous bacteria in the bentonite that have utilized hydrogen as the electron donor affected the behavior (reduction) of uranium. In addition, the bentonite bacteria have showed their strong tolerance against a given high temperature and radioactivity of a specific waste environment, suggesting that the nuclear-biogeochemical reaction may be one of main mechanisms if the natural bentonite is used as a buffer material for the disposal site in the future.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.351.1-351
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• 2001

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.3
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• pp.235-243
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• 2006

In this study, an experimental study on the sorption properties of uranium(VI) onto a bentonite colloid generated from Gyeongju bentonite which is a potential buffer material in a high-level radioactive waste repository was performed as a function of the pH and the ionic strength. The bentonite colloid prepared by separating a colloidal fraction was mainly composed of montmorillonite. The concentration and the size fraction of the prepared bentonite colloid measured using a gravitational filtration method was about 5100 ppm and 200-450 nm in diameter, respectively. The amount of uranium removed by the sorption reaction bottle walls, by precipitation, and by ultrafiltration was analyzed by carrying out some blank tests. The removed amount of uranium was found not to be significant except the case of ultrafiltration at 0.001 M $NaClO_4$. The ultrafiltration was significant in the lower ionic strength of 0.001 M $NaClO_4$ due to the cationic sorption onto the ultrafilter by a surface charge reversion. The distribution coefficient $K_d$ (or pseudo-colloid formation constant) of uranium(VI) for the bentonite colloid was about $10^4{\sim}10^7mL/g$ depending upon pH and ionic strength of $NaClO_4$ and the $K_d$ was highest in the neutral pH around 6.5. It is noted that the sorption of uranium(VI) onto the bentonite colloid is closely related with aqueous species of uranium depending upon geochemical parameters such as pH, ionic strength, and carbonate concentration. As a consequence, the bentonite colloids generated from a bentonite buffer can mobilize the uranium(VI) as a colloidal form through geological media due to their high sorption capacity.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2006.09a
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• pp.283-291
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• 2006

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2006.11a
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• pp.208-209
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• 2006