Hygrothermal Performance of an Engineered Clay Barrier

1990 ◽  
Vol 212 ◽  
Author(s):  
A.P.S. Selvadurai ◽  
S.C.H. Cheung
Keyword(s):  
Moisture Distribution ◽  
Experimental Simulation ◽  
Residual Moisture ◽  
Moisture Movement ◽  
Bentonitic Clay ◽  
Waste Container ◽  
Buffer Material ◽  
Deep Rock ◽  
High Level ◽  
Nuclear Fuel Waste

ABSTRACTA series of laboratory experiments was conducted to establish the heat-induced moisture movement in a bentonitic clay buffer. The buffer material is proposed as an engineered barrier to isolate a heat-emitting high-level nuclear fuel waste container from its emplacement borehole located in a deep rock repository. In the experimental simulation, the hygrothermal phenomena are initiated by a cylindrical heater placed within the compacted buffer material in a borehole centrally located in a granite block. The experimental results illustrate the time-dependent distribution of temperatures within the rock mass and the residual moisture distribution at the termination of the experiment.

Creep behaviour of a buffer material for nuclear fuel waste vault

1985 ◽  
Vol 22 (4) ◽  
pp. 541-550 ◽  
Author(s):  
Raymond N. Yong ◽  
Prapote Boonsinsuk ◽  
Demos Yiotis
Keyword(s):  
Finite Element ◽  
Nuclear Fuel ◽  
Host Rock ◽  
Creep Behaviour ◽  
Creep Model ◽  
Secondary Creep ◽  
Full Size ◽  
Waste Container ◽  
Buffer Material ◽  
Nuclear Fuel Waste

In the Canadian nuclear fuel waste disposal concept currently under study, one of the prime candidate procedures is the borehole emplacement technique. Each fuel waste container will be placed in a 1.1 m diameter hole in the floor of a disposal vault in deep plutonic rock. The container will be surrounded by buffer material consisting of a mixture of clay and sand. This study examines the creep behaviour of the buffer material in the borehole during interaction with the waste container and the host rock. It simulated the buffer – container – host rock interaction through a small-scale physical model using the loading pressures anticipated in the full-size system. The results from the model tests were compared with those predicted by a finite element analytical model. The creep behaviour of the full-size system was then predicted using the analytical model.From the results, it is evident that the creep behaviour of the buffer material depends significantly on interaction within the container – buffer – host rock system, overburden pressure, and water uptake. At relatively low overburden pressures, the waste container might settle, causing a separation between the buffer material and the container top. However, this could be alleviated by the swelling properties of the buffer material. The secondary creep rates are negligible, and creep in the buffer material is primarily governed by the primary creep stage. Key words: creep, model test, swelling soil, soil deformation, unsaturated soil, finite element analysis.

Modelling the in Situ Performance of Bentonite-Sand Buffer

1989 ◽  
Vol 176 ◽  
Author(s):  
H.S. Radhakrishna ◽  
K.-C Lau ◽  
B.H. Kjartanson ◽  
S.C.H. Cheung
Keyword(s):  
Boundary Conditions ◽  
Moisture Transport ◽  
Moisture Diffusivity ◽  
Moisture Movement ◽  
Waste Container ◽  
Buffer Material ◽  
Heat And Moisture Transport ◽  
Coupled Heat And Moisture ◽  
Heat And Moisture

ABSTRACTIn the Canadian nuclear fuel waste management concept, a number of engineered barriers, such as the bentonite-sand buffer which surrounds the waste container in the emplacement boreholes, are used to inhibit the transport of radionuclides. The buffer material is also required to effectively conduct heat from the fuel-waste containers to the surrounding rock. To a large extent, in situ buffer performance will depend on the degree of moisture within the buffer. The moisture content will in turn depend on temperature, temperature gradients, and buffer initial and moisture flux boundary conditions. Modelling of coupled heat and moisture transport in the buffer before resaturation is necessary to assess in situ buffer performance. This paper describes the results of a parametric study using the Philip and de Vries coupled heat and moisture transport model to assess the effects of variations in the moisture diffusivity parameters and the boundary conditions on buffer performance.The results show that the thermal performance of the buffer is affected by heat-induced moisture movement. In particular, the thermal vapour diffusivity, DTvap, has the most significant effect on thermal drying in a closed system. Work is currently underway to improve our capability to model coupled heat and moisture transport in buffer. Laboratory experiments are in progress to more accurately define the moisture diffusivity parameters and the model is being modified to include the effects of boundary moisture fluxes and pressure potentials so that the resaturation process may be modelled. A full scale buffer/container experiment is currently being planned for conduct in AECL's Underground Research Laboratory to assess further the effects of scale and in situ boundary conditions on buffer performance and to qualify the model.

Experimental study on the thermo- and hydro- properties of two bentonites as buffer materials

2020 ◽  
Author(s):  
Wei-Hsing Huang
Keyword(s):  
Heat Transfer ◽  
Characteristic Curve ◽  
Swelling Pressure ◽  
Moisture Distribution ◽  
Experimental Program ◽  
Heat Transfer Characteristics ◽  
Geological Disposal ◽  
Mechanical Coupling ◽  
Buffer Material ◽  
High Level

<p>This study aims at investigating the hydraulic and thermal properties which are important for buffer materials to be used for geological disposal of high-level radioactive wastes. MX-80 bentonite and Kunigel V1 bentonite, originated from Wyoming USA and Japan, respectively, were used in the experimental program. The characteristics of these 2 bentonites, including soil-water characteristic curve, swelling pressure, hydraulic conductivity, and thermal conductivity were determined in the laboratory. And these data are applied in the simulation of the resaturation processes of buffer material in a deposition hole, such that a comparison can be made on the thermo-hydro-mechanical coupling effects of the buffer material can be evaluated. It is found that the two bentonites do not behave very differently in terms of the moisture distribution and heat transfer characteristics with the same boundary conditions assumed. </p>

scholarly journals Experimental study on effect by cementation on self-sealing capability of bentonite buffer material

2020 ◽  
Vol 205 ◽  
pp. 10004
Author(s):  
Daichi Ito ◽  
Hideo Komine ◽  
Hailong Wang
Keyword(s):  
High Pressures ◽  
Swelling Pressure ◽  
Swelling Properties ◽  
Bentonite Buffer ◽  
Waste Container ◽  
Buffer Material ◽  
The Difference ◽  
Property Changes ◽  
High Level

In Japanese project for disposal of high-level radioactive waste, the self-sealing capability of bentonite buffer material, which results from the swelling deformation to fill the gaps between waste container and wall of disposal pit, must be retained thousands of years. However, because of the effect of high pressures, occurrence of cementation and property changes of the buffer material are a concern. Few studies had examined cementation effects because of the difficulties for simulating long-term alteration process experimentally. In this paper, swelling properties of consolidated buffer are regarded as similar as those of naturally consolidated bentonite ore. Therefore, three kinds of bentonite ores were used for experiments to elucidate influences of cementation on self-sealing capabilities. Undisturbed and reconstituted specimens were prepared to assess their swelling pressures after filling a preset gap in a swelling pressure apparatus. Results show that for Japanese ores, the swelling pressure of undisturbed specimens is about half that of reconstituted specimens. For American and Chinese ores, the difference of swelling pressure is greater when the preset gap is smaller. Results imply that effects of cementation on self-sealing capability are smaller when swelling deformation is allowed.

Moisture Movement in a Clay based Buffer Material under Isothermal Conditions

1993 ◽  
Vol 333 ◽  
Author(s):  
A.M.O. Mohamed ◽  
I. Shooshpasha ◽  
R.N. Yong ◽  
C. Onofrei
Keyword(s):  
Water Potential ◽  
Water Content ◽  
Soil Water ◽  
Volume Change ◽  
Soil Water Potential ◽  
Volumetric Water Content ◽  
Moisture Distribution ◽  
Dry Density ◽  
Moisture Movement ◽  
Buffer Material

ABSTRACTSeveral series of one dimensional tests were performed to examine the moisture and soil water potential distributions in the buffer material compacted to a dry density of 1.67 Mg/m3 and volumetric water content of 0.28. Diffusivity parameters were calculated using the measured moisture profiles combined with the finite difference method. Powell’s optimization was used to determine the material parameters.It is experimentally demonstrated that the moisture distribution is highly dependent on the test boundary conditions. When volume change was allowed to take place during infiltration process, the buffer material adsorbs more water than in the case of no volume change. This is attributed to an increase in hydraulic conductivity by one order of magnitude. As the volumetric water content increases soil water diffusivity increases and soil water potential decreases.

Experimental Investigation on the Active Range of Sulfate-Reducing Bacteria for Geological Disposal

1994 ◽  
Vol 353 ◽  
Author(s):  
S. Fukunaga ◽  
H. Yoshikawa ◽  
K. Fujiki ◽  
H. Asano
Keyword(s):  
Experimental Investigation ◽  
Environmental Conditions ◽  
Desulfovibrio Desulfuricans ◽  
Sulfate Reducing Bacteria ◽  
Geological Disposal ◽  
Sulfate Reducing ◽  
Buffer Material ◽  
Ph Range ◽  
High Level ◽  
Reducing Bacteria

AbstractThe active range ofDesulfovibrio desulfuricans. a species of sulfate-reducing bacteria, was examined in terms of pH and Eh using a fermenter at controlled pH and Eh. Such research is important because sulfate-reducing bacteria (SRB) are thought to exist underground at depths equal to those of supposed repositories for high-level radioactive wastes and to be capable of inducing corrosion of the metals used in containment vessels.SRB activity was estimated at 35°C, with lactate as an electron donor, at a pH range from 7 to 11 and Eh range from 0 to -380 mV. Activity increased as pH approached neutral and Eh declined. The upper pH limit for activity was between 9.9 and 10.3, at Eh of -360 to -384 mV. The upper Eh limit for activity was between -68 and -3 mV, at pH 7.1. These results show that SRB can be made active at higher pH by decreasing Eh, and that the higher pH levels of 8 to 10 produced by use of the buffer material bentonite does not suppress SRB completely.A chart was obtained showing the active range ofDesulfovibrio desulfuricansin terms of pH and Eh. Such charts can be used to estimate the viability of SRB and other microorganisms when the environmental conditions of a repository are specified.

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.

A resistivity-based approach to determining the rates of groundwater seepage into buffer materials

2019 ◽  
Vol 482 (1) ◽  
pp. 205-212 ◽  
Author(s):  
T. Ishii ◽  
M. Kawakubo ◽  
H. Asano ◽  
I. Kobayashi ◽  
P. Sellin ◽  
...  
Keyword(s):  
Water Solution ◽  
High Level Waste ◽  
Dry Density ◽  
Chemical Alteration ◽  
Constant Rate ◽  
Buffer Material ◽  
The Status ◽  
Engineered Barriers ◽  
High Level ◽  
Saturation Front

AbstractBentonite-based buffer materials play an important safety role in engineered barriers planned for use in geological disposal repositories for radioactive high-level waste (HLW) in Japan. The effectiveness of buffer materials is dependent on the status of groundwater saturation during resaturation of the repository. Accordingly, it is important to determine the behaviour of buffer materials during saturation and predict post-saturation conditions such as the distribution of residual dry density and chemical alteration.In this study, the rate of groundwater uptake into a buffer material was determined to clarify the behaviour of the material during the saturation process. As mechanical changes and chemical alteration of buffer materials are generated by groundwater permeation, knowledge of the water uptake rate is necessary for the prediction of post-permeation conditions. In the experiment reported here, one-dimensional permeation by distilled water and a NaCl water solution at a constant rate was monitored over a period of more than seven years. The results indicated that the seepage and saturation front moved in proportion to the square root of the seepage time. The coefficient of the relationships between the seepage and the saturation fronts with time of the reference bentonite used in Japan was determined.

The Use of Repassivation Potential in Predicting The Performance of High-Level Nuclear Waste Container Materials

1994 ◽  
Vol 353 ◽  
Author(s):  
Narasi Sridhar ◽  
Darrell Dunn ◽  
Gustavo Cragnolino
Keyword(s):  
Field Tests ◽  
Localized Corrosion ◽  
High Level Waste ◽  
Repassivation Potential ◽  
Waste Container ◽  
Highly Sensitive ◽  
Plant Equipment ◽  
Robust Parameter ◽  
High Level Nuclear Waste ◽  
High Level

AbstractLocalized corrosion in aqueous environments forms an important bounding condition for the performance assessment of high-level waste (HLW) container materials. A predictive methodology using repassivation potential is examined in this paper. It is shown, based on long-term (continuing for over 11 months) testing of alloy 825, that repassivation potential of deep pits or crevices is a conservative and robust parameter for the prediction of localized corrosion. In contrast, initiation potentials measured by short-term tests are non-conservative and highly sensitive to several surface and environmental factors. Corrosion data from various field tests and plant equipment performance are analyzed in terms of the applicability of repassivation potential. The applicability of repassivation potential for predicting the occurrence of stress corrosion cracking (SCC) and intergranular corrosion in chloride containing environments is also examined.

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