Diffusive transport of neptunium and plutonium through compacted sand-bentonite mixtures under anaerobic conditions

Yamaguchi, Tetsuji; Nakayama, Shinichi; Nagao, Seiya; Kizaki, Minoru

doi:10.1524/ract.2007.95.2.115

Cited by 12 publications

(15 citation statements)

References 21 publications

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“…Acrylic diffusion cells 28) were used in this study. Each side of the bentonite/sand mixture was covered with sintered stainless steel filters with a porosity of 40% and 1 mm thickness, to avoid expansion of the bentonite into the reservoirs.…”

Section: Through-diffusion Experimentsmentioning

confidence: 99%

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Iida¹,

Yamaguchi²,

Tanaka³

2011

J. Nucl. Sci. Technol.

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Effective diffusion coefficients of selenium through bentonite/sand mixtures were obtained by the through-diffusion method under reducing conditions where selenium was dissolved as HSe À and Se 4 2À . Experiments were carried out under variable bentonite content and porewater salinity. Bentonite contents in bentonite/sand mixtures varied from 20 to 70 wt%. The salinities of experimental solutions varied from 0.05 to 0.5 mol dm À3 , simulating brackish groundwater and seawater. Effective diffusion coefficients were also obtained under anaerobic conditions where the dominant selenium species was determined to be SeO 3 2À . The effective diffusion coefficients of selenium species decreased with increasing bentonite content and with decreasing salinity. This tendency is primarily due to anion exclusion that was caused by the negative surface charge of montmorillonite. A diffusion model for anionic species was developed based on the electric double layer theory and the pore diffusion model, to evaluate the diffusion behaviors of HSe À , Se 4 2À , and SeO 3 2À in bentonite porewater. In this model, pores in bentonite/sand mixtures are assumed to consist of two types of space; one is the space between mineral particles and the other is the space between layers of montmorillonite. The scope of application of this model is limited to less than or equal to 1,600 kg m À3 in dry density. The effective diffusion coefficients of selenium species predicted using this model showed good agreement with experimentally measured ones.

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Section: Through-diffusion Experimentsmentioning

confidence: 99%

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Iida¹,

Yamaguchi²,

Tanaka³

2011

J. Nucl. Sci. Technol.

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“…In addition, the concentration of naturally occurring colloids is too low to provide a substantial transport vector for radionuclides that escape to the far field of the repository. Experiments by Yamaguchi et al (2007) offer some corroboration for Vilks' argument; they found that Pu transport through a compacted bentonite-sand mixture is retarded relative to Np, because the Pu is present dominantly as colloids, which are too big to travel through the tight clay pores.…”

Section: Models For Transport Of Radionuclides By Colloidsmentioning

confidence: 83%

Radioactivity, Geochemistry, and Health

Siegel

Bryan

2014

Treatise on Geochemistry

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“…After performing series-2 diffusion runs for 363 days, a series of post-experimental analyses were performed for the diffusion tests and the blank test. The pH and E H were measured with electrodes, and the ratio of Np(IV) to the total dissolved Np was determined using the thenoyltrifluoroacetone (TTA) extraction technique (Yamaguchi et al, 2007). Np(IV) is extracted by TTA, while the other oxidation states of Np remain in the aqueous phase (Foti & Freiling, 1964) in 1 mol l À1 HCl.…”

Section: Conditionsmentioning

confidence: 99%

“…We also applied the above-mentioned method to analyse the Cs diffusion data in a similar diffusion experiment using a 0.3/0.03 mol l À1 NaHCO 3 / Na 2 S 2 O 4 solution by Yamaguchi et al (2007), and re-estimated D e and D a .…”

Section: Fig 2 Initial and Boundary Conditions For The Through-diffmentioning

confidence: 99%

“…At high ionic strength (series-1À2, series-1À3, series-2, and Yamaguchi et al, 2007), the effective diffusivities through the column, including the filters, were corrected for the filter effect to obtain effective diffusivity through the specimens using equation 8. On the other hand, the effective diffusivity through the column for low ionic strength (series-1À1) was higher than the value expected when only the filter was placed in the column (2.4610 À9 m 2 s À1 ), and could not be corrected using equation 8.…”

Section: Diffusivities Of Csmentioning

confidence: 99%

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Diffusion of Cs, Np, Am and Co in compacted sand-bentonite mixtures: evidence for surface diffusion of Cs cations

et al. 2013

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AB ST R ACT : We studied the diffusive transport of Cs, Np, Am and Co in compacted sandbentonite mixtures by using the through-diffusion method. The experiments for Cs were performed under various aqueous compositions. Effective diffusivity (D e ) values of 4.7610 À10 to 5.9610 À9 m 2 s À1 were obtained with a somewhat large variation. Apparent diffusivity (D a ) values, on the other hand, showed less variation, ranging from 2.0610 À12 to 6.2610 À12 m 2 s À1 . The results indicated that diffusive flux was proportional to the concentration gradient on the basis of the amount of Cs in the unit volume of the compacted sand-bentonite mixtures rather than the Cs concentration gradient in pore water. Because the former concentration gradient in the mixtures was nearly equal to that of adsorbed Cs, the diffusion of Cs in the mixtures was probably dominated by the concentration gradient of the Cs adsorbed on the mixtures. In addition, the effective/apparent diffusivity of 237 Np(IV) and apparent diffusivity of 241 Am(III) and 60 Co(II) in the mixtures were determined in 0.3/0.03 mol l À1 (NH 4 ) 2 CO 3 /Na 2 S 2 O 4 solution.

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Diffusive transport of neptunium and plutonium through compacted sand-bentonite mixtures under anaerobic conditions

Abstract: Diffusive transport of neptunium, plutonium, tritiated water (HTO), Cs

Cited by 12 publications

References 21 publications

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Experimental and Modeling Study on Diffusion of Selenium under Variable Bentonite Content and Porewater Salinity

Radioactivity, Geochemistry, and Health

Diffusion of Cs, Np, Am and Co in compacted sand-bentonite mixtures: evidence for surface diffusion of Cs cations

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