Applicability evaluation on geotomography for the high level waste geological disposal repository. Visualized monitoring in the near-field

The present study has reviewed principal and applicability of geotomography for visualized monitoring of high level wastes geological disposal repository in current techniques. One of the important issues in the high level wastes geological disposal is to monitor the physical properties of the disposal repository and the neighborhood (called 'near-field'). In the near-field, it is predicted that the heat generation from high level waste package, reflood of underground water, swelling of bentonite buffer and backfilling material, subsidence of overpack, deformation of bedrock, etc. for a very long term are occur. It is one of the effective methods to carry out visualized monitoring by the geotomography which is able to cut out internal structures just like a cross-sectional photograph, when evaluating the physical properties of near-field. Elastic wave tomography can be superior to infer the change of physical property inside the disposal holes and all over the near-field. The change of permeability and saturated/unsaturated zone of near-field can be estimated by the resistivity tomography. X-rays CT method can apply only the confirmation of the homogeneity and/or existence of internal crack in the buffer before back-filling. Muography which can visualized density is a great advantage to be no artificial radiation sources. However, there are few examples of application due to developing technique recently. If it develops more, it may be able to be applied to visualization. (author)