Laboratory gas injection tests of compacted bentonite buffer material for TRU waste disposal

2014 ◽  
Vol 400 (1) ◽  
pp. 521-529 ◽  
Author(s):  
Kazuto Namiki ◽  
Hidekazu Asano ◽  
Shinichi Takahashi ◽  
Tomoyuki Shimura ◽  
Ken Hirota
Keyword(s):  
Waste Disposal ◽  
Gas Injection ◽  
Compacted Bentonite ◽  
Bentonite Buffer ◽  
Buffer Material

A Study on Gas Migration Behavior in Buffer Material using X-ray CT Method

2006 ◽  
Vol 932 ◽  
Author(s):  
K. Tanai ◽  
M. Yui
Keyword(s):  
Water Saturation ◽  
Gas Injection ◽  
Swelling Pressure ◽  
Digital Data ◽  
Migration Behavior ◽  
Gas Migration ◽  
Migration Test ◽  
X Ray ◽  
Compacted Bentonite ◽  
Buffer Material

ABSTRACTThis paper presents a study on gas migration behavior in a bentonite specimen with the aid of X-ray computer tomography (CT) scan data. The laboratory experiment was carried out to clarify gas migration behavior through saturated, compacted bentonite. X-ray CT was used to estimate the spatial distribution of gas and water saturation during gas migration test in the bentonite. For the gas migration test, the controlled flow rate of gas injection was adopted for pre-compacted samples of Kunigel V1 bentonite using helium gas, which is safer than hydrogen gas.A specimen was isotropically consolidated and saturated by synthetic seawater, simultaneously, by applying a backpressure. This was followed by injecting the gas using a syringe pump. Inlet and outlet gas fluxes were monitored. This test exhibited a significant threshold pressure for breakthrough, somewhat larger than the sum of the swelling pressure and the backpressure.The procedure of the X-ray CT measurement is as follows; i) measurement of the initial condition (saturated condition) of the compacted bentonite, ii) measurement of the gas injection condition as a function of time. The digital data obtained from the X-ray CT usually includes some noise. The stacking method can reduce the noise in CT values and enables to identify the gas migration area. The results indicate that gas is transported through preferential pathways in compacted bentonite, and is not homogenous.

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.

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.

scholarly journals Performance evaluation of compacted bentonite buffer material at shear failure

2010 ◽  
Vol 5 (2) ◽  
pp. 207-218
Author(s):  
Takeshi KODAKA ◽  
Yuko TERAMOTO ◽  
Toshio HIRATE ◽  
Yasuhisa MOTOYAMA
Keyword(s):  
Performance Evaluation ◽  
Shear Failure ◽  
Compacted Bentonite ◽  
Bentonite Buffer ◽  
Buffer Material

scholarly journals Longitudinal and Shear Wave Velocities Measurement in Compacted Bentonite for Water Content

2018 ◽  
Vol 43 ◽  
pp. 01016
Author(s):  
Shun Kimura ◽  
Kazumi Kitayama ◽  
Hideharu Takahashi ◽  
Kazushi Kimoto ◽  
Katsuyuki Kawamura ◽  
...  
Keyword(s):  
Bulk Modulus ◽  
Water Content ◽  
Degree Of Saturation ◽  
Ultrasonic Velocities ◽  
Compacted Bentonite ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Bentonite Buffer ◽  
Buffer Material

Bentonite is a good candidate of buffer material for disposal repository of high-level radioactive waste. Understanding groundwater behavior in bentonite buffer material is important in order to evaluate the bentonite buffer performance and guarantee long-term safety. Elastic constants of the bentonite buffer material are important parameters for the long-term safety. Water content in buffer material may have an influence on its elastic properties. For this reason, the monitoring system of the water saturation level in compacted bentonite is required. In this study, the ultrasonic velocity measurement method for evaluation of water content in compacted bentonite was proposed. At first, the effect of a degree of saturation in compacted bentonite on the longitudinal and shear wave velocities was investigated experimentally. In addition, the elastic property, bulk modulus, in unsaturated compacted bentonite were evaluated by ultrasonic velocities. As a result, it can be confirmed that ultrasonic velocities can evaluate a degree of saturation and bulk modulus of compacted bentonite.

scholarly journals Modeling early in situ wetting of a compacted bentonite buffer installed in low permeable crystalline bedrock

2016 ◽  
Vol 52 (8) ◽  
pp. 6207-6221 ◽  
Author(s):  
B. Dessirier ◽  
A. Frampton ◽  
Å. Fransson ◽  
J. Jarsjö
Keyword(s):  
Compacted Bentonite ◽  
Crystalline Bedrock ◽  
Bentonite Buffer

Coupling Swelling and Water Retention Processes in Compacted Bentonite

2011 ◽  
Vol 6 (1) ◽  
Author(s):  
Antti Lempinen
Keyword(s):  
Water Retention ◽  
Spent Nuclear Fuel ◽  
Effective Strain ◽  
Swelling Pressure ◽  
Model Parameters ◽  
Confined Water ◽  
Swelling Properties ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Swelling Factor

Compacted bentonite is the main candidate for buffer material in several plans for spent nuclear fuel repositories. One of its important properties is high swelling capacity, which is caused by interaction between water molecules and exchangeable cations. This interaction makes bentonite behave differently from capillary materials. In this article, a model for thermo-hydro-mechanical state of partially water saturated bentonite is presented. It couples the water retention and swelling properties with introduction of the swelling factor in effective strain. The Helmholz energy density determines the state with a relatively small set of independent parameters: swelling pressure, swelling factor, maximum confined water content and the reference state. The model parameters are determined from experimental data for FEBEX bentonite, and as a simple consistency check, confined suction curves are calculated and compared to test results. Consistency of the model with observations on nano- and microscale of bentonite is also discussed.

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