We carried out the centrifuge model test to evaluate the long-term behavior during the resaturation surrounding the deep geological disposal repository. The centrifuge model is the vertical emplacement concept repository and 1/50-size, and the sedimentary rock is drilled a single disposal tunnel and hole, and then the model-overpack, Na-type bentonite buffer, and backfill material are placed in. And the test was conducted at 50 G with the effective stress of 3 MP for equivalent to about 200 years based on centrifugal similarity law. As a result, the displacement of the overpack was measured to be several times larger than that of the tests without the backfill material and disposal tunnel. In addition, it was confirmed that the buffer significantly expanded to the disposal tunnel after the test and visual confirmation. Test results implied that the displacement of the overpack is affected by the stiffness of the backfill material.
The high level radioactive waste (HLW) disposal repository in Japan will be built in deeper than 300 m in the underground (JNC, 2000). The vitrified waste is enclosed in a metallic overpack. It is then packed, surrounded by buffer material made of clay bentonite, into a disposal hole drilled deep into the bedrock. The near-field is composed of such a heterogeneous composite. In the near-field, various processes will occur under the effect of heat from the waste, rock stress and underground water. This thermal-hydraulic-mechanical (THM) transition will dominate and continue for hundreds of years in the initial construction, operation, and closure stage. These states are transition period of artificial disturbance and resaturation, and phenomena dominates THM, mechanically unstable.
Long-term behavior in the near-field is finally evaluated by numerical analysis. In order to improve the reliability of the numerical analysis, it is necessary to validate the numerical analysis by comparing it with test results. To validate the numerical analysis, Nishimoto et al. (2016) conducted centrifuge model tests, which are time-acceleration tests based on the similarity law of static fields, and Sawada et al. (2017) compared the test results with those of the numerical analysis.
