Effective Diffusivities of Iodine, Chlorine, and Carbon in Bentonite Buffer Material

1999 ◽  
Vol 556 ◽  
Author(s):  
H. Kato ◽  
T. Nakazawa ◽  
S. Ueta ◽  
M. Muroi ◽  
I. Yasutomi ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Radioactive Waste ◽  
Pore Water ◽  
Effective Diffusivity ◽  
Radioactive Waste Disposal ◽  
Radioactive Isotopes ◽  
Dry Density ◽  
Bentonite Buffer ◽  
Buffer Material ◽  
Effective Diffusivities

AbstractEffective diffusivities of iodine, chlorine, and carbon in mixtures of bentonite and sand were determined by measuring the effective diffusivities of common chemical compounds labeled with radioactive isotopes of these elements. For carbon, both inorganic and organic carbon compounds were used in order to consider the variety of chemical forms of carbon possible in a radioactive waste repository. The bentonite content and dry density of the bentonite–sand mixture were varied. Two chemically different aqueous solutions, representing concrete pore water and bentonite pore water, were used to represent different conditions that could affect diffusivity in bentonite buffer material in a hypothetical radioactive waste disposal situation.The effective diffusivities of iodine, chlorine, and carbon tended to decrease with increasing bentonite content and dry density of the mixture. In the presence of simulated concrete pore water, the effective diffusivities for iodine, chlorine, and carbon in the bentonite mixtures were not higher than those obtained when simulated bentonite pore water was used. Except for some organic compounds, the measured effective diffusivities were lower than that of tritiated water under the same experimental conditions. This was attributed primarily to exclusion of anions from the bentonite pores. The effective diffusivity of carbon depended on its chemical form. The effective diffusivity of the anionic forms of organic carbon tested (carboxylic acids ) was as low as that of inorganic anionic carbon.Measured effective diffusivities were compared with those calculated using a model based on electrical double layer theory. The theory was applied to calculate distributions of electrolyte ions and diffusing ions in the bentonite pores. The calculated effective diffusivities showed good agreement with the measured values.

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.

Soil Based Barriers for a Low and Intermediate Level Radioactive Waste Disposal

2003 ◽  
Author(s):  
Dimitar Antonov
Keyword(s):  
Moisture Content ◽  
Radioactive Waste ◽  
Intermediate Level ◽  
Radioactive Waste Disposal ◽  
Dry Density ◽  
Paper Strength ◽  
Maximum Dry Density ◽  
Soil Cement ◽  
Intermediate Level Radioactive Waste ◽  
Cement Mixtures

The loess terrains near “Kozloduy” NPP are among the prospective areas for the disposal of low and intermediate level radioactive waste. The analysis of the loess properties has shown two main problems: a loess collapsibility and water permeability. Using a soil-cement cushion under the repository foundation and a soil-cement backfill between the containers is a possibility to avoid these disadvantages. In this connection loess-cement mixtures with bentonite and clinoptilolite additives have been investigated. The aim of mixtures is to improve the impermeability and sorbtion properties against radionuclide migration. In the paper strength parameters of two kind of mixtures are discussed. According to their water content some are compacted at the optimum moisture content until the maximum dry density and others are compacted at higher moisture content equal to the liquid limit of loess. For the first type of mixtures the unconfined compressive strength (UCS) varies from 2 to 6 MPa depending on the cement and additives percents. Permeability measurements have shown satisfactory results. The UCS for the second type of mixtures is less than the first type, but is sufficient for a backfill between the waste containers. The conclusion is that the loess-cement mixtures, especially these with clinoptilolite additive, are prospective as barriers of a low and intermediate level radioactive waste repository.

Ultrasonic Velocities Measurement in Compacted Bentonite-Sand Mixtures for Saturation Level Evaluation

2018 ◽  
Author(s):  
Shun Kimura ◽  
Hideharu Takahashi ◽  
Ari Hamdani ◽  
Masanori Aritomi ◽  
Susumu Ozaki ◽  
...  
Keyword(s):  
Water Content ◽  
Water Saturation ◽  
Radioactive Waste Disposal ◽  
Saturation Level ◽  
Degree Of Saturation ◽  
Ultrasonic Velocities ◽  
Compacted Bentonite ◽  
Bentonite Buffer ◽  
Buffer Material

Compacted bentonite materials are often considered as a buffer material in the geological radioactive waste disposal. This bentonite is expected to fill up the space between the waste and the surrounding ground by swelling. Therefore, understanding the surrounding ground, i.e., groundwater behavior in bentonite, as a buffer material, is essential in order to evaluate the bentonite buffer performance and guarantee long-term safety. The monitoring system of the water saturation level in compacted bentonite is required because water content in buffer material may influence its elastic properties. In this study, the correlation between water content and elasticity in unsaturated compressed bentonite was experimentally evaluated. The evaluation was done by measuring the sound velocity of both longitudinal wave and transverse wave. As a result, it can be confirmed that ultrasonic velocities could evaluate a degree of saturation and bulk modulus of compacted bentonite.

THE TOTAL MANAGEMENT OF NORM IN THE OFFSHORE PETROLEUM INDUSTRY

1998 ◽  
Vol 38 (2) ◽  
pp. 151
Author(s):  
J. Kvasnicka
Keyword(s):  
Radioactive Waste ◽  
Gamma Radiation ◽  
Radiation Protection ◽  
Waste Disposal ◽  
Petroleum Industry ◽  
Radiation Monitoring ◽  
Radioactive Waste Disposal ◽  
Radioactive Isotopes ◽  
Radiation Doses ◽  
Offshore Petroleum

Naturally Occurring Radioactive Materials (NORMs) in the offshore petroleum industry are generally associated with the formation of scale in pipes and vessels. As scale and sludge contain radioactive isotopes of radium they are in the category of Low Specific Activity (LSA) NORMs. Handling of NORMs creates issues involving occupational health and safety, environmental protection and radioactive waste management and waste disposal. Barium(Radium)Sulfate scale is highly insoluble and can create serious production problems by clogging pipes and valves.The paper discusses the external gamma radiation monitoring at the external surfaces of well and oil production pipes which assists in establishing the scale thickness patterns in pipes and in identifying the optimum location of a scale inhibitor injection point.To minimise radiation doses received by workers special NORM handling Work Procedures and Instructions supported by radiation protection training need to be developed. If facility personnel are trained in radiation protection and Work Procedures and Instructions are adopted it is possible to effectively manage personal radiation exposures below the public limit of 1 millisievert per year. Under such conditions no personal radiation monitoring during routine operations is required and the assessment of routine annual external radiation doses may be carried out through yearly external gamma radiation surveys of of fshore petroleum production facilities.The NORM waste cannot be disposed of onshore within the same disposal sites used for general non-radioactive waste. In Australia only the NORM waste generated in Western Australia can be disposed of onshore in an official low level radioactive waste disposal facility. It is important that Governments of other States and Territories address the onshore NORM waste disposal option. Regulations should also address a screening method for scrap metal contaminated by NORMs to be released for smelting.

Preliminary stochastic investigations of pore water induced loss of host rock integrity in radioactive waste disposal

2021 ◽  
Author(s):  
Maximilian Bittens ◽  
Jobst Maßmann ◽  
Jan Thiedau
Keyword(s):  
Computational Complexity ◽  
Radioactive Waste ◽  
Pore Water ◽  
Waste Disposal ◽  
Safety Assessment ◽  
Radioactive Waste Disposal ◽  
Complex Geometries ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Two Dimensional Model

<p>Numerical studies on integrity of the geological barriers in heat generating radioactive waste disposal remain a challenging topic involving modelling of thermal, hydraulic and mechanical (THM) processes within complex geometries, as well as particularly long simulation time intervals . Due to this, unfeasible computational complexity emerges for many three-dimensional problems, resulting in the need of further model assumptions and simplification for many types of simulation. To make use of results of such simulations reliably as a tool in the decision-making process, uncertainties introduced by the modelling have to be addressed in the framework of safety assessment.</p><p>Consequently, the system describing partial differential equations are dependent on a set of parameters, each parameter possibly subject to uncertainty resulting from reduced knowledge or imprecise measurement. The treatment of uncertainties introduces additional dimensions into the physical system, resulting in a dramatic increase of computational complexity for each parameter considered uncertain.</p><p>For general applicability, the method chosen for uncertainty quantification should be problem-independent, i.e. an arbitrary set of stochastic input data is propagated through the physical system, while the output is again a freely selectable quantity of interest. To this end, sampling-based methods like Monte-Carlo methods and stochastic collocation seem to be favourable.</p><p>Since a full stochastic model is never computable, it is amenable to include only the most sensitive parameters into stochastic analyses, retaining all other parameters as deterministic, in order to spend available computational power efficiently. With aim of finding such a suitable set of stochastic parameters, preliminary studies of simplified two-dimensional models with less complex geometries and a less complex TH-process seem to be appropriate.</p><p>In this contribution, a simplified two-dimensional model of a radioactive waste disposal in clayey rock is proposed, as a starting point, and its results of the thermal induced increase in pore water pressure is compared with more sophisticated and established models for a set of deterministic input parameters. It will be demonstrated that the simplified two-dimensional model is suitable for first stochastic investigation of pore water induced tensile or shear failure.</p><p>Subsequently, the results of different stochastic simulations for this model are presented, giving rise to a better understanding of stochastic modelling as well as stochastic post-processing in discretized problems for computational safety assessment of radioactive waste disposal. In detail, sensitivity of the quantity of interest to changes in the input parameters can be studied and in addition, worst-case scenarios within the parameter interval can be found. Given known probability density functions for each input parameter, probability of occurrence of each scenario as well as expected values and variances can be calculated.</p><p> </p><p> </p>

scholarly journals Investigating the contribution of claystone to the swelling pressure of its mixture with bentonite

2020 ◽  
Vol 195 ◽  
pp. 03043
Author(s):  
Zhixiong Zeng ◽  
Yu-Jun Cui ◽  
Nathalie Conil ◽  
Jean Talandier
Keyword(s):  
Radioactive Waste ◽  
Safety Assessment ◽  
Swelling Pressure ◽  
Radioactive Waste Disposal ◽  
Inert Material ◽  
Dry Density ◽  
Test Results ◽  
Pressure Tests ◽  
Volume Swelling

Compacted MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been considered as a possible sealing/backfilling material in the French deep geological radioactive waste disposal. The swelling pressure of such mixture is an important factor in the design and long-term safety assessment of deep geological repositories. In this study, constant-volume swelling pressure tests were performed on the mixtures with different claystone fractions and dry densities. The test results show that the swelling pressure of the mixtures decreased with the increasing claystone fraction and decreasing dry density. According to the experimental results, the contribution of claystone to the global swelling pressure was further investigated. It was found that the deformation of claystone and its contribution to swelling pressure was highly dependent on the claystone fraction. As the claystone fraction was larger than 30%, the claystone in the mixture swelled, contributing to the global swelling pressure; On the contrary, as the claystone fraction was less than 30%, the swelling of claystone was inhibited by the bentonite and it worked an inert material without any contribution to the swelling pressure.

scholarly journals Study Of Factors Affecting The Thermal Conductivity Of Iraqi Bentonite

2012 ◽  
Vol 9 (3) ◽  
pp. 548-553
Author(s):  
Baghdad Science Journal
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Volume Fraction ◽  
Dry Density ◽  
Factors Affecting ◽  
Compacted Bentonite ◽  
Bentonite Buffer ◽  
Buffer Material ◽  
Major Factors ◽  
Water Contents

Thermal conductivity of compacted bentonite is one of the most important properties where this type of clay is proposed for use as a buffer material. In this study, Lee's disc method was used to measure the thermal conductivity of compacted bentonite specimens. The experimental results have been analyzed to observe the three major factors affecting the thermal conductivity of bentonite buffer material. While the clay density reaches to a target value, the measurement is taken to evaluate the thermal conductivity. By repeating this procedure, a relationship between clay dry density and thermal conductivity has been established in specimens after adjusting the water contents of the bentonite by placing its specimens in a drying oven for different periods. So relationships of thermal conductivity with each of these major factors (clay density, water content, and sand volume fraction) are established in this study. The relevance of these relationships be analyzed together using experimental data on many compacted bentonites.

Swelling characteristics of bentonites in artificial seawater

2009 ◽  
Vol 46 (2) ◽  
pp. 177-189 ◽  
Author(s):  
Hideo Komine ◽  
Kazuya Yasuhara ◽  
Satoshi Murakami
Keyword(s):  
Radioactive Waste ◽  
Swelling Pressure ◽  
Radioactive Waste Disposal ◽  
Exchangeable Cation ◽  
Deformation Characteristics ◽  
High Level Radioactive Waste ◽  
Disposal Facility ◽  
Buffer Material ◽  
Swelling Characteristics ◽  
High Level

Bentonite is currently designated for use as a buffer material for the repository of high-level radioactive waste because such a material requires swelling characteristics to seal the waste. A high-level radioactive waste disposal facility may be built in a coastal area of Japan because transportation of this waste by ships is feasible. Therefore, it is important to investigate the effects of seawater on a bentonite-based buffer. This study is intended to investigate the influence of seawater on the swelling pressure and swelling deformation characteristics of five common types of bentonite. The experiments described herein clarify the relations between the influence of seawater grade and compaction density, type of exchangeable cation, montmorillonite content of the bentonite, and vertical pressure condition. Based on experimental results, suitable specifications have been defined for a bentonite-based buffer that can withstand the effects of seawater.

scholarly journals The Healing Process of the Joints between Buffer Material Blocks and the Influence on Solute Migration

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Rui Zhou ◽  
Yuemiao Liu ◽  
Tao Xu ◽  
Yufeng Gao
Keyword(s):  
Diffusion Coefficient ◽  
Healing Process ◽  
Design Parameters ◽  
Dry Density ◽  
Mechanical Coupling ◽  
Water Head ◽  
Bentonite Buffer ◽  
Buffer Material ◽  
External Water ◽  
And Diffusion

A set of thermo-hydro-mechanical coupling control equations was established, and the healing process of the joints between Gaomiaozi bentonite (GMZ01) buffer material blocks and the influence of the joint parameters were numerically simulated. The calculations consider the effect of joints on solute migration, the permeability and thermal conductivity of the buffer material, and the evolution of the healing effect. The effects of the joint design parameters, including the type, number, width, splicing form, and average dry density of the joint, are investigated. Studies show that, under an external water head, the joints will become hydraulic priority channels due to their higher permeability, which will shorten the saturation time of the blocks. As the bentonite gradually saturates, the swelling force compresses the joint material. This action improves the overall uniformity of the buffer material and reduces the priority channel effect. Meanwhile, the final average permeability and diffusion coefficient of the buffer material are found to mainly depend on the average dry density of the buffer material. The higher the average dry density of the buffer material is, the lower the final average permeability and diffusion coefficient are, whereas the distribution of joints and the block splicing are less affected by the average dry density of the buffer material. The findings of this study can provide a reference for the design of bentonite buffer material blocks in the repository.

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