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Ninomiya, Koji*; Yoshizawa, Hideaki*; Sato, Yasushi*; Onishi, Toshimitsu*
JNC TJ6420 2003-012, 200 Pages, 2004/02
JNC-TJ6420-2003-012.pdf:13.05MB
Layer to be applied for the capping of uranium mill tailings and waste rock yard at Ningyo-toge.In consideration of the business scale, operation efficiency and cost performance, etc, we selected the decomposed granite as a base soil, bentonite as an additive, and a Twister as a mixer for this research. Based on those materials and a mixer, we actually made the cover layer and measured the permeability, N2 ventilation, strength of the layer, using as a parameter different types of bentonite and different bentonite/sand mixture ratios.According to the permeability test results, permeability coefficient proved to be stand at below 1x10-9 m/s, regardless of any combination of bentonite/sand mixture ratios made with the twister. Through a series of laboratory tests, base soil and additive, we found out the optimum phase of combination, which are the 7wt% bentonite/sand mixture in case of Volclay; and 16wt% in case of Redhill. N2 ventilation tests were also carried out, using as a parameter the degree of moisture saturation of cover layer material. Test results showed that the gas ventilation is sensitive to changes of the degree of the saturation, and that under the conditions of moisture saturation of over 90%, the coefficient of N2 ventilation stands at below 1x10-10 m/s, under which conditions the radon barrier will work out in an efficient way.Lastly, we described the directions of future investigations and studies, including the necessity of gathering technical data on the quality variation of cover layer materials, the same caused by continuous mixing process, and the need of further investigations and designing into/of the comprehensive cover layer systems, including the capillary-break layer, etc.
*
JNC TJ7410 2001-004, 55 Pages, 2001/02
JNC-TJ7410-2001-004.pdf:1.36MB
no abstracts in English
Imai, Jun*
JNC TJ8400 2000-008, 196 Pages, 2000/02
JNC-TJ8400-2000-008.pdf:25.25MB
The objective of this research is to make clear long-term alteration processes of bentonite contacting with concrete under a repository condition for radioactive waste. The Uzu tunnel in yamagata prefecture in Japan, constructed during the term of December of 1963 to July 1967, was selected as an appropriate natural analogue: the tunnel wall was made of portland cement and which has been contacting with a bentonite bed during 
32 years. Sample analyses indicated that the original bentonite was Na
-type and it changed to Ca
-type in the range of a few millimeters from the contact. Although a Ca leaching was also observed from the concrete near the contact, neither transformation to zeolite nor to illite was recognized. On the other hand, sulfur increased and ettringite (3CaO 
Al
O
3CaSO
4 32HO) was recognized in the concrete within the depth about 30 mm from the contact.
*
JNC TJ7400 2000-013, 26 Pages, 2000/02
JNC-TJ7400-2000-013.pdf:1.25MB
no abstracts in English
Imai, Jun*
JNC TJ8400 99-043, 237 Pages, 1999/02
The objective of this research is to understand the long-term alteration processes of bentonite contacting with concrete under a repository condition for radioactive waste. The Uzu tunnel in yamagata prefecture in Japan, constructed during the term of December of 1963 to July 1967, was selected as an appropriate natural analogue: the tunnel wall was made of portland cement and which has been contacting with a bentonite bed during 32 years. Sample analyses indicated that the original bentonite was Na-type and Ca proportion was increased between the bentonite layers in the range of a few millimeters from the contacting part. On the other hand, the increase of sulfur and the preparation of ettringite (3CaO AlO 3CaSO 32HO) was recognized in the concrete within the depth approximately 20 mm from the contact.