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Takachi, Kazuhiko; *; Tabei, Kazuto*; Noda, Masaru*; *; *
Saikuru Kiko Giho, (5), p.27 - 36, 1999/12
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Takachi, Kazuhiko; Sugino, Hiroyuki
JNC TN8400 99-043, 52 Pages, 1999/11
In the near field, as tunnels and pits are excavated, a redistribution of stresses in the surrounding rock will occur. For a long period of time after the emplacement of waste packages various events will take place, such as the swelling of the buffer, sinking of the overpack under its own weight, deformation arising from expansion of overpack corrosion products and the creep deformation of the rock mass. The evaluation of what effects these changes in the stress-state will have on the buffer and rock mass is a major issue from the viewpoint of safety assessment. Therefore, rock creep analysis, overpack corrosion expansion analysis and overpack sinking analysis have been made in order to examine the longterm mechanical stability of the near field and the interaction of various events that may affect the stability of the near field over a long period of time. As the results, rock creep behavior, the variations of the stress-state and the range of the influence zone differ from the rock strength, strength of buffer in the tunnel and side pressure coefficient etc. about the hard rock system and soft rock system established as basic cases. And the magnitude of the stress variations for buffer by the overpack sinking and rock creep deformation is negligible compared with it by the overpack corrosion expansion. Furthermore, though very limited zone of buffer around the overpack is close to the critical state by the overpack corrosion expansion, the engineered barrier system attains a comparatively stable state for a long period of time.
Takachi, Kazuhiko; Taniguchi, Wataru
JNC TN8400 99-042, 68 Pages, 1999/11
The buffer material is expected to maintain its low water permeability, self-sealing properties, radionuclides adsorption and retardation properties, thermal conductivity, chemical buffering properties, overpack supporting properties, stress buffering properties, etc. over a long period of time. Natural clay is mentioned as a material that can relatively satisfy above. Among the kinds of natural clay, bentonite when compacted is superior because (1)it has exceptionally low water permeability and properties to control the movement of water in buffer, (2)it fills void spaces in the buffer and fractures in the host rock as it swells upon water uptake, (3)it has the ability to exchange cations and to adsorb cationic radioelements. In order to confirm these functions for the purpose of safety assessment, it is necessary to evaluate buffer properties through laboratory tests and engineering-scale tests, and to make assessments based on the ranges in the data obtained. This report describes the procedures, test conditions, results and examinations on the buffer material of dynamic triaxial tests, measurement of elastic wave velocity and liquefaction tests that aim at getting hold of dynamic mechanical properties. MWe can get hold of dependency on the shearing strain of the shearing modulus and hysteresis damping constant, the application for the mechanical model etc. by dynamic triaxial tests, the acceptability of maximum shearing modulus obtained from dynamic triaxial tests etc. by measurement of elastic wave velocity and dynamic strength caused by cyclic stress etc. by liquefaction tests.
Takachi, Kazuhiko; Suzuki, Hideaki*
JNC TN8400 99-041, 76 Pages, 1999/11
The buffer material is expected to maintain its low water permeability, self-sealing properties, radionuclides adsorption and retardation properties, thermal conductivity, chemical buffering properties, overpack supporting properties, stress buffering properties, etc. over a long period of time. Natural clay is mentioned as a material that can relatively satisfy above. Among the kinds of natural clay, bentonite when compacted is superior because (1)it has exceptionally low water permeability and properties to control the movement of water in buffer, (2)it fills void spaces in the buffer and fractures in the host rock as it swells upon water uptake, (3)it has the ability to exchange cations and to adsorb cationic radioelements. In order to confirm these functions for the purpose of safety assessment, it is necessary to evaluate buffer properties through laboratory tests and engineering-scale tests, and to make assessments based on the ranges in the data obtained. This report describes the procedures, test conditions, results and examinations on the buffer material of unconfined compression tests, one-dimensional consolidation tests, consolidated-undrained triaxial compression tests and consolidated-undrained triaxial creep tests that aim at getting hold of static mechanical properties. We can get hold of the relationship between the dry density and tensile stress etc. by Brazillian tests, between the dry density and unconfined compressive strength etc. by unconfined compression tests, between the consolidation stress and void ratio etc. by one-dimensional consolidation tests, the stress pass of each effective confining pressure etc. by consolidated-undrained triaxial compression tests and the axial strain rate with time of each axial stress etc. by consolidated-undrained triaxial creep tests.
Taniguchi, Wataru; Takachi, Kazuhiko; *; Mori, Koji*
JNC TN8400 99-055, 168 Pages, 1999/09
In Japan, where many earthquakes have been occurring, it's very important to evaluate aseismatic mechanical stability of the engineered barrier system (EBS) of high-level radioactive waste (HLW) repository. In this study as a cooperative project of JNC with National Research Institute for Earth Science and Disaster Prevention Science and Technology Agency, that started from 1992, aseismatic mechanical stability of the EBS of HLW repository have been evaluated based on the engineering scale vibration test of the engineered barrier and the analytical methods. In this report, the results of the engineering scale vibration test of the engineered barrier and the development of the analytical computer code for seismic response of the engineered barriers are described, following Study of Vibration Behavior Deep Underground Cavity and Internal Structure (1). From this study, the following conclusions are obtained (1)Engineering scale vibration test of engineered barrier. From the results of sweep wave vibration tests conducted to examine the effect of natural frequency of the EBS, the natural frequency of the EBS tends to decrease as the acceleration increases. From the results of vibration tests with the actual seismic waves characteristics, both of the simulated overpack and the buffer have no significant response against seismic and then simulated engineered barriers behave dynamically as a rigid body. (2)Development of the analytical computer code for seismic response of the engineered barrier. The analytical computer code has been developed considering the non-linear dynamic properties of the buffer material between stress and strain. verification analysis results for the engineering scale vibration test of the engineered barrier mentioned above, using the analytical computer code, agree with vibration test of the engineered barrier.
Taniguchi, Wataru; Takachi, Kazuhiko; Sugino, Hiroyuki; Mori, Koji*
JNC TN8400 99-054, 140 Pages, 1999/09
For the buffer material of geological disposal of high-level radioactive waste (HLW) in Japan, it is considered to use a compacted bentonite or a compacted sand-mixture bentonite that is one kind of clay. The buffer material is expected to maintain long-term mechanical stability, to hold the waste in designated place, and to avoid the effects on the radionuclides migration. It is considered that the cyclic load due to seismic activities affects long-term mechanical stability in Japan, where many earthquakes have been occurring. In this report, aseismic mechanical stability of engineered barrier of HLW is studied by dynamic analysis based on equation of vibration, mainly in the view point of mechanical stability of the buffer. The analytical computer code that has been developed by JNC in cooperative project with National Research Institute for Earth Science and Disaster Prevention Science and Technology Agency is used in this study. Seismic wave at the disposal depth in the assumed geological environment is established by multiple reflection theory analysis, and then seismic wave at the disposal depth is used for the aseismic mechanical stability analysis. For the aseismic mechanical stability, total stress analyses (single-phase system) with the target field of near field are conducted to evaluate the shear failure of the buffer, the displacement of overpack, and vibrational behavior of the engineered barrier, and then effective stress analyses (two-phase system) with the target field of the engineered barrier are conducted to evaluate excursion in the pore water pressure within the buffer (i. e. liquefaction), concerning the non-linear dynamic properties of the buffer material. From the results, the following conclusions are obtained. (1)From the results of the total stress analyses, it is confirmed that the buffer must not reach a shear failure condition from the stresses caused by an earthquake and the overpack must not move significantly due to the ...
Takachi, Kazuhiko
Donen Giho, (2), p.9 - 17, 1999/03
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