Analysis of Uranium Diffusion Coefficients in Compacted FEBEX Bentonite

2003 ◽  
Vol 807 ◽  
Author(s):  
M. García-Gutiérrez ◽  
J. L. Cormenzana ◽  
T. Missana ◽  
M. Mingarro ◽  
U. Alonso
Keyword(s):  
Radioactive Waste ◽  
Diffusion Coefficients ◽  
Solid Phase ◽  
Dry Density ◽  
Compacted Clay ◽  
Spent Fuel ◽  
Apparent Diffusion Coefficients ◽  
Theoretical Approaches ◽  
Through Diffusion ◽  
High Level

ABSTRACTIn the Spanish concept of a high level radioactive waste (HLRW) repository, the canister with the spent fuel would be surrounded by a layer of FEBEX bentonite (Ca-Mg smectite clay) compacted to a dry density of 1.65 g/cm3. Since the permeability of the compacted bentonite is very low, the main mechanism for radionuclide transport in the clay barrier is expected to be diffusion, retarded by the sorption on the solid. Since the mayor component of the radioactive waste is uranium it is very important to study its diffusion behaviour in the compacted clay.Generally, effective (De) and apparent (Da) diffusion coefficients are obtained from "through-diffusion" and "in-diffusion" experiments, respectively. The obtention of both parameters in the same sample is a very interesting issue because the former includes the information on the porous medium structure (connectivity, constrictivity, tortuosity) and the latter takes into account the sorption on the solid phase. In this work, through-diffusion experiments were carried out for studying uranium diffusion and both effective and apparent diffusion coefficients were estimated, from the same experiment, by using different theoretical approaches.

Hydraulic and Diffusive Properties of Clay-Based Backfill Material for a Low-and Intermediate-Level Waste Repository

1994 ◽  
Vol 353 ◽  
Author(s):  
W.J. Cho ◽  
J.O. Lee ◽  
P.S. Hahn ◽  
H.H. Park
Keyword(s):  
Diffusion Coefficients ◽  
Experimental Studies ◽  
Clay Content ◽  
Dry Density ◽  
Compacted Clay ◽  
Southeastern Part ◽  
Apparent Diffusion Coefficients ◽  
Crushed Granite ◽  
Apparent Diffusion ◽  
Water Saturated

AbstractThe results of experimental studies performed to determine the radionuclide diffusion coefficients in a compacted clay and the hydraulic conductivities of clay/crushed granite mixtures with various clay contents are presented. Clay used in the experiments is a natural clay from the southeastern part of Korea, and it contains mainly calcium bentonite. The hydraulic conductivities of clay/crushed granite mixtures decreased with increasing clay content. In case of clay content of 50 wt.%, they maintain the considerably lower values even at the dry density of 1.5 Mg/m3. The diffusion coefficients for 90Sr, 137Cs, 60Co and 125I in water saturated clay at a dry density of 1.4 Mg/m3 were measured at room temperature. The average apparent diffusion coefficients obtained are 4.5 × 10−12 m2/s, 9.0 ×10−13 m2/s, 3.4 × 10−13 m2/s and 6.7 × 10−11 m2/s for 90Sr, 137Cs, 60Co, and 125I, respectively.

The Dependence of the Diffusion Coefficients of 3H and Cs on Grain Size in Compacted Montmorillonite

1997 ◽  
Vol 506 ◽  
Author(s):  
Mamoru Nakajima ◽  
Tamotsu Kozaki ◽  
Hiroyasu Kato ◽  
Seichi Sato ◽  
Hiroshi Ohashi
Keyword(s):  
Grain Size ◽  
Diffusion Coefficients ◽  
Dry Density ◽  
Formation Factor ◽  
Apparent Diffusion Coefficients ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Apparent Diffusion ◽  
Different Grain Size ◽  
High Level

ABSTRACTCompacted bentonite is a candidate buffer material in geological disposal of high-level radioactive waste. The transport of radionuclides in compacted bentonite is dominated by diffusion, because of its very low permeability. In this study, we focused on the grain size of clay mineral, which is considered to be closely related to the formation factor in the pore water diffusion model[1,2]. The apparent diffusion coefficients (Da) of HTO and cesium ions in compacted clays were determined using montmorillonite samples with different grain size and dry density, and the effect of the grain size on diffusion behavior was discussed.

Diffusion of Technetium in Compacted Bentonites in the Reducing Condition with Corrosion Products of Iron

1996 ◽  
Vol 465 ◽  
Author(s):  
Yuji Kuroda ◽  
K. Idemitsu ◽  
H. Furuya ◽  
Y. Inagaki ◽  
T. Arima
Keyword(s):  
Carbon Steel ◽  
Diffusion Coefficients ◽  
Corrosion Products ◽  
High Level Waste ◽  
Dry Density ◽  
Apparent Diffusion Coefficients ◽  
Reducing Conditions ◽  
Apparent Diffusion ◽  
Reducing Environment ◽  
High Level

ABSTRACTIn the vicinity of a high-level waste repository, corrosion of carbon steel overpacks will create a reducing environment. Reducing conditions are expected to retard the migration of redox-sensitive radionuclides such as technetium.The apparent diffusion coefficients of technetium were measured in compacted bentonites (Kunigel VI® and Kunipia F®, JAPAN) in contact with carbon steel and its corrosion products under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusion coefficients measured were 10-12 to 10-13 m2/s under oxidizing conditions and 10-12 to 10-13 m2/s under reducing conditions. There were significant effects of redox condition, dry density (0.2 to 2.3 g / cm3) and montmorillonite content (50% for Kunigel VI or 100% for Kunipia F) on the apparent diffusion coefficients. Montmorillonite density could be a good index to explain density dependence of the diffusion coefficients under both reducing and oxidizing conditions.

Migration Rates of Brine Inclusions in Single Crystals of Nacl

1981 ◽  
Vol 6 ◽  
Author(s):  
I-Ming Chou
Keyword(s):  
Radioactive Waste ◽  
Temperature Gradients ◽  
Spent Fuel ◽  
Ion Diffusion ◽  
Cold Side ◽  
Migration Rates ◽  
Permanent Storage ◽  
Salt Brine ◽  
Salt Deposits ◽  
High Level

Rock-salt deposits have been considered as a possible medium for the permanent storage of high-level radioactive wastes and spent fuel. Brine inclusions present in natural salt can migrate toward the waste if the temperature and the temperature gradients in the vicinity of the radioactive waste are large enough. This migration is due to the dissolution of salt at the hot side of the salt-brine interface, ion diffusion through the brine droplet, and the precipitation of salt at the cold side of the salt brine interface.

scholarly journals Thermal Conductivity of Compacted GO-GMZ Bentonite Used as Buffer Material for a High-Level Radioactive Waste Repository

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Yong-Gui Chen ◽  
Xue-Min Liu ◽  
Xiang Mu ◽  
Wei-Min Ye ◽  
Yu-Jun Cui ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Radioactive Waste ◽  
Water Content ◽  
Radioactive Waste Disposal ◽  
Dry Density ◽  
Gmz Bentonite ◽  
High Level Radioactive Waste ◽  
Buffer Material ◽  
High Level ◽  
Crucial Parameter

In China, Gaomiaozi (GMZ) bentonite serves as a feasible buffer material in the high-level radioactive waste (HLW) repository, while its thermal conductivity is seen as a crucial parameter for the safety running of the HLW disposal. Due to the tremendous amount of heat released by such waste, the thermal conductivity of the buffer material is a crucial parameter for the safety running of the high-level radioactive waste disposal. For the purpose of improving its thermal conductivity, this research used the graphene oxide (GO) to modify the pure bentonite and then the nanocarbon-based bentonite (GO-GMZ) was obtained chemically. The thermal conductivity of this modified soil has been measured and investigated under various conditions in this study: the GO content, dry density, and water content. Researches confirm that the thermal conductivity of the modified bentonite is codetermined by the three conditions mentioned above, namely, the value of GO content, dry density, and water content. Besides, the study proposes an improved geometric mean model based on the special condition to predict the thermal conductivity of the compacted specimen; moreover, the calculated values are also compared with the experimental data.

Assessment of Redox Conditions in the Near Field of Nuclear Waste Repositories: Application to the Swiss high-level and intermediate level waste disposal concept

2003 ◽  
Vol 807 ◽  
Author(s):  
Paul Wersin ◽  
Lawrence H. Johnson ◽  
Bernhard Schwyn
Keyword(s):  
Solid Phase ◽  
Near Field ◽  
Intermediate Level ◽  
Redox Conditions ◽  
High Level Waste ◽  
Redox Potentials ◽  
Spent Fuel ◽  
Reducing Conditions ◽  
High Level ◽  
Waste Repositories

ABSTRACTRedox conditions were assessed for a spent fuel and high-level waste (SF/HLW) and an intermediate-level waste (ILW) repository. For both cases our analysis indicates permanently reducing conditions after a relatively short oxic period. The canister-bentonite near field in the HLW case displays a high redox buffering capacity because of expected high activity of dissolved and surface-bound Fe(II). This is contrary to the cementitious near field in the ILW case where concentrations of dissolved reduced species are low and redox reactions occur primarily via solid phase transformation processes.For the bentonite-canister near field, redox potentials of about -100 to -300 mV (SHE) are estimated, which is supported by recent kinetic data on U, Tc and Se interaction with reduced iron systems. For the cementitious near field, redox potentials of about -200 to -800 mV are estimated, which reflects the large uncertainties related to this alkaline environment.

European Concepts for Shared Storage and Disposal Facilities for Radioactive Wastes?

2007 ◽  
Author(s):  
Ewoud Verhoef ◽  
Hans Code´e ◽  
Vladan Sˇtefula ◽  
Charles McCombie
Keyword(s):  
Radioactive Waste ◽  
Implementation Strategies ◽  
Practical Implementation ◽  
Spent Fuel ◽  
Pilot Studies ◽  
Eu Member States ◽  
Waste Storage ◽  
Geological Conditions ◽  
European Development ◽  
High Level

Geological disposal is an essential component of the long-term management of spent fuel and high-level radioactive waste. Implementation of a suitable deep repository may, however, be difficult or impossible in some (especially small) countries because of challenging geological conditions or restricted siting options, or because of the high costs involved. For these countries, shared regional or international storage and disposal facilities are a necessity. The European Parliament and the EC have both expressed support for concepts that could lead to regional shared facilities being implemented in the EU. The EC, therefore, funded two projects that form the first two steps of a staged process towards the implementation of shared regional or international storage and disposal facilities. In the period 2003 to 2005, the EC funded SAPIERR I, a project devoted to pilot studies on the feasibility of shared regional storage facilities and geological repositories, for use by European countries. The studies showed that shared regional repositories are feasible, but also that, if they are to be implemented, even some decades ahead, efforts must already be increased now. The first step would be to establish a structured framework for the work on regional repositories. This is the goal of SAPIERR II (2006–2008): to develop possible practical implementation strategies and organisational structures. These will enable a formalised, structured European Development Organisation (EDO) to be established in 2008 or afterwards for working on shared EU radioactive waste storage and disposal activities. The EDO can work in parallel with national waste programmes. Participating EU Member States will be able to use the structures developed as, when and if needed for the furtherance of their individual national policies.

Transport of radioselenium oxyanions by diffusion in unsaturated soils

2015 ◽  
Vol 103 (7) ◽  
Author(s):  
David Aldaba ◽  
Miguel García-Gutiérrez ◽  
Taufik Abrão ◽  
Anna Rigol ◽  
Miquel Vidal
Keyword(s):  
Radioactive Waste ◽  
Waste Disposal ◽  
Diffusion Coefficients ◽  
Unsaturated Soils ◽  
Diffusion Profile ◽  
Gaussian Functions ◽  
Apparent Diffusion Coefficients ◽  
Apparent Diffusion ◽  
Planar Source ◽  
First Time

AbstractThere is a lack of data on the diffusion of long-lived radionuclides in soils, especially of those originated from the leaching of radioactive waste in waste disposal facilities. Here, the simultaneous diffusion of two radioselenium species, which were postulated to be radioselenite and radioselenate, was examined for the first time in four soils at laboratory level by applying the planar-source method. The Gaussian-shaped experimental diffusion profile was deconvoluted into two Gaussian functions, and then the apparent diffusion coefficients (

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