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Sawaguchi, Takuma; Takai, Shizuka; Sasagawa, Tsuyoshi; Uchikoshi, Emiko*; Shima, Yosuke*; Takeda, Seiji
MRS Advances (Internet), 8(6), p.243 - 249, 2023/06
In the intermediate depth disposal of relatively high-level radioactive waste, a method to confirm whether the borehole for monitoring is properly sealed should be developed in advance. In this study, groundwater flow analyses were performed for the hydrogeological structures with backfilled boreholes, assuming sedimentary rock area, to understand what backfill design conditions could prevent significant water pathways in the borehole, and to identify the confirmation points of borehole sealing. The results indicated the conditions to prevent water pathways in the borehole and BDZ (Borehole Disturbed Zone), such as designing the permeability of bentonite material less than or equal to that of the host rock, and grouting BDZ.
Takai, Shizuka; Kimura, Hideo*; Uchikoshi, Emiko*; Munakata, Masahiro; Takeda, Seiji
JAEA-Data/Code 2020-007, 174 Pages, 2020/09
JAEA-Data-Code-2020-007.pdf:4.23MB
The MIG2DF computer code is a computer program that simulates groundwater flow and radionuclide transport in porous media for the safety assessment of radioactive waste disposal. The original version of MIG2DF was released in 1992. The original code employs a two-dimensional (vertical or horizontal cross-section, or an axisymmetric configuration) finite-element method to approximate the governing equations for density-dependent saturated-unsaturated groundwater flow and radionuclide transport. Meanwhile, for geological disposal of radioactive wastes, landscape evolution such as uplift and erosion needs to be assessed as a long-term geological and climate events, considering site conditions. In coastal areas, the impact to groundwater flow by change of salinity distribution to sea level change also needs to be considered. To deal with these events in the assessment, we have revised the original version of MIG2DF and developed the external program which enables MIG2DF to consider unsteady landscape evolution. In these developments, this report describes an upgrade of MIG2DF (Version 2) and presents the configuration, equations, methods, and verification. This reports also give the explanation external programs of MIG2DF: PASS-TRAC (the particle tracking code), PASS-PRE (the code for dataset preparation), and PASS-POST (the post-processing visualization system).
Shimada, Taro; Uchikoshi, Emiko*; Takai, Shizuka; Takeda, Seiji
no journal, ,
Long-term topographic change due to uplift, denudation and eustasy may change the field of groundwater flow and nuclide migration when radioactive wastes are disposed at the repository near the sea. In this report, we constructed the frame work for evaluating uncertainties of future topograophic changes. Using the evaluation code under developing at JAEA, we tried evaluating the future topographic change until 0.125k years after for catchment basin near the sea.
Takai, Shizuka; Shimada, Taro; Uchikoshi, Emiko*; Takeda, Seiji
no journal, ,
In geological disposal, landscape evolution by uplift, denudation, and sea-level change will change geological environment and decrease the depth of disposal. This may lower safety functions of disposal system: therefore, the effect needs to be evaluated properly. Landscape evolution can be evaluated quantitatively using landscape evolution models. In general, the evaluation is based on extrapolation of the past. However, the future sea-level change may differ from the past because of greenhouse gases. In this study, we constructed the evaluation method for future long-term landscape evolution based on the past landscape evolution. We confirm the applicability in the typical basin consisting of mountain, river, plain, and sea. The effect to future landscape evolution by uncertainties of sea-level change were evaluated.
Takai, Shizuka; Shimada, Taro; Uchikoshi, Emiko*; Takeda, Seiji
no journal, ,
In geological disposal, landscape evolution by uplift, denudation, and sea-level change will change geological environment and decrease the depth of disposal. This may lower safety functions of disposal system: therefore, the effect needs to be evaluated properly. In the assessment, landscape evolution needs to be evaluated considering topography, material properties, and environmental factors. In addition, uncertainty should be considered for future sea-level change, which will significantly different from previous glacial cycles due to anthropogenic greenhouse-gas emissions. In this study, we evaluated future landscape evolution for a glacial-interglacial cycle (125 ka) by numerical simulation. Then, we conducted groundwater simulation considering transient topography and sea-level change. The uncertainty of future global sea-level change was considered based on previous studies by glacial isostatic adjustment simulation. The impact on groundwater flow was evaluated at the typical basin consisting of mountain, river, plain, and sea in Japan.
Sawaguchi, Takuma; Takai, Shizuka; Uchikoshi, Emiko*; Takeda, Seiji
no journal, ,
In the intermediate depth disposal of radioactive waste, it is necessary to confirm that the monitoring boreholes are properly backfilled to prevent potential migration pathways for radioactive materials. In this study, groundwater flow analysis was performed to understand the effects of backfilled boreholes on radionuclide migration by varying conditions related to the boreholes and their surrounding hydrogeologic structure. The results showed that in the case of a single borehole in an aquifer isolated by clay layer, when the borehole was backfilled with highly permeable sand, groundwater flowing several tens of meters around the borehole changed the flow direction along the borehole and the average flow velocity was approximately three times greater than that in the case of no borehole. On the other hand, when the borehole was backfilled with low permeability bentonite, the flow direction and velocity were no different. In addition, assuming the presence of two boreholes backfilled with sand and spaced 20 m apart, the flow velocities through two boreholes and in the geological medium between their boreholes were increased. Furthermore, the effects of different hydrogeologic structures on flow direction and velocity associated with the borehole presence were evaluated.
