Bentonite as a Backfill Material in a High-Level Waste Repository

Grauer, R.

doi:10.1557/s0883769400048697

Cited by 27 publications

(21 citation statements)

References 20 publications

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“…Previous discussions on the stability of bentonite in HLW repositories generally focus on the potential for the conversion of smectite to illite (Pusch, 1993;Grauer, 1994;Madsen, 1998;Meunier et al, 1998).…”

Section: High-level Nuclear Waste Disposalmentioning

confidence: 99%

“…Long-term ambient temperature conditions are expected to be less than 100°C. Temperatures of 60 and 45°C are envisaged for the Swiss and Japanese disposal concepts respectively (Grauer, 1994;JNC, 1999). The temperatures at which significant smectite chloritisation is observed may therefore be higher than those expected to occur over prolonged periods in a HLW repository.…”

Section: Natural Analoguesmentioning

confidence: 99%

See 1 more Smart Citation

The effect of iron on montmorillonite stability. (I) Background and thermodynamic considerations

Wilson

Savage

Cuadros

et al. 2006

Geochimica et Cosmochimica Acta

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Section: High-level Nuclear Waste Disposalmentioning

confidence: 99%

Section: Natural Analoguesmentioning

confidence: 99%

The effect of iron on montmorillonite stability. (I) Background and thermodynamic considerations

Wilson

Savage

Cuadros

et al. 2006

Geochimica et Cosmochimica Acta

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“…In addition, some geologic disposal concepts for HLW propose the emplacement of a barrier of compacted bentonite, composed mainly of montmorillonite, between the waste containers and the surrounding rocks to limit the potential movement of radionuclides from the repository (Grauer 1994). For these reasons, a quantitative knowledge of radionuclide sorption onto clay minerals is desirable.…”

Section: Introductionmentioning

confidence: 99%

Neptunium(V) Sorption on Montmorillonite: An Experimental and Surface Complexation Modeling Study

Turner

1998

Clays and clay miner.

118

121

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Abstract--Batch sorption experiments at fixed initial Np(V) concentration (-1 • 10 6 M 237Np), M/V ratio (4 g L-l), and ionic strength (0.1 molal NaNO3) were conducted to determine the effects of varying pH and Pco2 on Np(V) sorption on SAz-1 montmorillonite. The results show that Np(V) sorption on montmorillonite is strongly influenced by pH and Pco2. In the absence of CO2, Np(V) sorption increases over the entire pH range examined (~3 to --10), with measured sorption coefficients (Ko) of about 10 mL g-1 at pH < 6 to K o ~ 1000 mL g-~ at a pH of 10.5. However, for experiments open to atmospheric CO2 (Pco2 = 10 3.5 arm), Np(V) sorption peaks at Ko -100 mL g-1 at pH of 8 to 8.5 and decreases at higher or lower pH. A comparison of the pH-dependence of Np(V) sorption with that of Np(V) aqueous speciation indicates a close correlation between Np(V) sorption and the stability field of the Np(V)-hydroxy complex NpO2OH ~ (aq). In the presence of CO2 and aqueous carbonate, sorption is inhibited at pH > 8 due to formation of aqueous Np(V)-carbonate complexes. A relatively simple 2-site DiffuseLayer Model (DLM) with a single Np(V) surface complexation reaction per site effectively simulates the complex sorption behavior observed in the Np(V)-H20-CO2-montmorillonite system. The good agreement between measured and DLM-predicted sorption values suggests that surface complexation models based on parameters derived from a limited set of data could be useful in extrapolating radionuclide sorption over a range of geochemical conditions. Such an approach could be used to support transport modeling and could provide a better alternative to the current use of constant K o values in performance assessment transport calculations.

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“…Because clay minerals are ubiquitous components of rocks, soils, and sediments, radionuclide sorption onto these minerals may play a key role in retarding radionuclide migration in many geologic environments. In addition, some disposal concepts for nuclear wastes propose the emplacement of a barrier of compacted bentonite, comprised mainly of montmorillonite, between the waste containers and the surrounding rocks in order to limit the potential movement of radionuclides from the repository (Grauer, 1994). Thus, a quantitative knowledge of radionuclide sorption onto clay minerals is important.…”

Section: Introductionmentioning

confidence: 99%

Uranium(6+) sorption on montmorillonite: Experimental and surface complexation modeling study

1997

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Sorption interactions with montmorillonite and other clay minerals in soils, sediments, and rocks are potentially important mechanisms for attenuating the mobility of U(6+) and other radionuclides through the subsurface environment. Batch experiments were conducted (in equilibrium with atmospheric Pco2) to determine the effects of varying pH (2 to 9), solid-mass to solution-volume ratio (M/V = 0.028 to 3.2 g/L), and solution concentration (2 x 10 -7 and 2 x 10 -6 M 233U) on U(6+) sorption on SAz-1 montmorillonite. The study focused on U(6+) surface complexation on hydroxylated edge sites as the sorption mechanism of interest because it is expected to be the predominant sorption mechanism at pHs typical of natural waters (pH ~6 to ~9). Thus, the experiments were conducted with a 0.1 M NaNO3 matrix to suppress ion-exchange between U(6+) in solution and interlayer cations. The results show that U(6+) sorption on montmorillonite is a strong function ofpH, reaching a maximum at near-neutral pH (,~6 to ~6.5) and decreasing sharply towards more acidic or more alkaline conditions. A comparison of the pH-dependence of U(6+) sorption with that of U(6+) aqueous speciation indicates a close correspondence between U(6+) sorption and the predominance field of U(6+)-hydroxy complexes. At high pH, sorption is inhibited due to formation of aqueous U(6+)-carbonate complexes. At low pH, the low sorption values indicate that the 0.1 M NaNO3 matrix was effective in suppressing ion-exchange between the uranyl (UO] +) species and interlayer cations in montmorillonite. At pH and carbonate concentrations typical of natural waters, sorption of U(6+) on montmorillonite can vary by four orders of magnitude and can become negligible at high pH.The experimental results were used to develop a thermodynamic model based on a surface complexation approach to permit predictions of U(6+) sorption at differing physicochemical conditions. A Diffuse-Layer model (DLM) assuming aluminol (>A1OH °) and silanol (>SiOH °) edge sites and two U(6+) surface complexation reactions per site effectively simulates the complex sorption behavior observed in the U(6+)--H20----4202-montmorillonite system at an ionic strength of 0.1 M and pH > 3.5. A comparison of model predictions with data from this study and from published literature shows good agreement and suggests that surface complexation models based on parameters derived from a limited set of data could be useful in extrapolating radionuclide sorption over a range of geochemical conditions. Such an approach could be used to support transport modeling by providing a better alternative to the use of constant K~ s in transport calculations.

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Bentonite as a Backfill Material in a High-Level Waste Repository

Cited by 27 publications

References 20 publications

The effect of iron on montmorillonite stability. (I) Background and thermodynamic considerations

The effect of iron on montmorillonite stability. (I) Background and thermodynamic considerations

Neptunium(V) Sorption on Montmorillonite: An Experimental and Surface Complexation Modeling Study

Uranium(6+) sorption on montmorillonite: Experimental and surface complexation modeling study

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