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Aoyagi, Takayoshi*; *; Mihara, Morihiro; Okutsu, Kazuo*; Maeda, Munehiro*
JNC TN8400 2001-024, 103 Pages, 2001/06
JNC-TN8400-2001-024.pdf:8.84MB
In the disposal concept of TRU waste, concentrated disposal of wastes forms in large cross-section underground cavities is envisaged, because most of TRU waste is no-heat producing in spite of large generated volume as compared with HLW. In the design of engineered barrier system based on large cross-section cavities, it is necessary to consider the long-term mechanical process such as creep displacement of the host rock from the viewpoint of the stability of engineered barrier system. In this study, the long-term creep displacement of the host rock was calculated using the non-linear viscoelasticity model and the effects on the stability of engineered barrier system was evaluated. As a result, in the disposal concept of crystalline rock, no creep displacement occurred at the time after 1 milion year. On the other hand, in the disposal concept of sedimentary rock, creep displacement of 80
90mm occurred at the time after 1 milion year. Also, in this calculation, a maximum reduction of 45mm concerned with the thickness of buffer material was estimated. But these values resulted within allowance of design values. Therefore, these results show that the effects of the creep displacement on the stability of engieered barrier system would not be significant.
Aoyagi, Takayoshi*; Maeda, Munehiro*; Mihara, Morihiro; Tanaka, M.*
JNC TN8400 98-002, 62 Pages, 1998/11
Tests to determine the swelling pressure, permeability, compressive strength and elastic modulus of Ca-Na exchanged bentonite, Na-bentonite and Ca-bentonite at the Power Reactor and Nuclear Fuel Development Corporation have mainly used distilled water. However, disposal facilities for TRU waste will use cementateous material for packaging, backfill as well as structural support. In this case, a large amount of calcium will dissolve in groundwater flowing through the cementateous material. Therefore, it is important to investigate the mechanical properties of bentonite in calcium-rich water as part of the disposal research program for TRU waste. In order to understand the effect of the chemical composition of water on the basic mechanical properties of bentonite - part of evaluating the disposal concepts for TRU waste disposal - we tested the permeability of compacted bentonite under saturated conditions using a calcium hydroxide solution. The aqueous solution represents water dominated by the calcium component. Na-bentonite, Ca-Na exchanged bcntonite and Ca-bentonite were used for swelling pressure measurement tests and permeability testing. Measures of the maximum and equilibrium swelling pressure as well as permeability were obtained. The dry density of bentonite was varied between tests. Results show that swelling pressure and permeability are dependent on dry density. In separate tests usig Ca-bentonite, the bentonite-mixing rate was varied as an independent parameter. Results show that there is little change in the swelling pressure and permeability between tests usig calcium hydroxide solution and distilled water for all bentonite types.
Maeda, Munehiro*; Tanai, Kenji; Ito, Masaru; Mihara, Morihiro; Tanaka, M.*
PNC TN8410 98-021, 136 Pages, 1998/03
The buffer material component of the engineered barrier system of the radioactive waste repository, functions to maintain low groundwater flow and mechanical stability in the repository for long periods of time. If Na bentonite is used as a buffer material, it is possible that the Na bentonite will change to Ca bentonite by exposure to Ca ions derived from calcite in the ground water. In the TRU waste disposal repository if cementitious materials are used, the change from Na to Ca bentonite may be almost immediate. Therefore it is important to investigate the mechanical properties of Ca bentonite as part of TRU waste disposal research and development. This paper reports the results of swelling pressure, water permeability and compressive strength tests for compacted Ca bentonite and for bentonite which has undergone Na-Ca exchange. Maximum and equilibrium swelling pressure tests and water permeability tests were performed. Compressive strength tests produced compressive strength and elastic modulus values for unsaturated compacted bentonite. The results of these test correlate with the dry density and sand mixing contents of bentonite. Finally, the relative properties of Ca, Na and Ca-Na exchanged bentonite were compared. It is clear that the maximum and equilibrium swelling pressures and hydraulic conductivity of compacted Ca-Na exchanged bentonite are the same as Na bentonite when both their dry density was about 1.8 g/cm
. The compressive strength and elastic modulus of compacted Ca-Na exchanged bentonite are a little higher than Na bentonite. When compacted, results are the same for either Ca bentonite (dry density 1.4g/cm) or Ca-Na exchanged bentonite compared with Na bentonite (dry density 1.6-1.8g/cm).
Maeda, Munehiro*; Ito, Masaru; Mihara, Morihiro; Tanaka, M.*
PNC TN8410 97-314, 48 Pages, 1997/12
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Maeda, Munehiro*; ; Mihara, Morihiro; Okutsu, Kazuo*; Akasaka, Naoto*
NO.104 (1997.12), (104), p.107 - 114, 1997/12
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