Development of MIG2DF Version 2

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).

Geosphere stability project, 5; Estimation of groundwater recharge rate in consideration of long-term changes in surface hydrological environment

Takeuchi, Ryuji; Onoe, Hironori; Yasue, Kenichi

no journal, , 

In geological disposal for high-level radioactive waste, time scale for assessment is equal to or more than several hundreds of thousand years. During this time, the surface hydrological environment might change. Especially, changes of precipitation, evapotranspiration and runoff volume might cause a change of groundwater recharge rate (GRR), which is upper boundary condition of groundwater flow for deep underground. This study shows the method to estimate GRR considering the influence of changes for climate condition and landform condition as an example in Tono area. The GRRs of 0.45 Ma are estimated 118% to 237% of the current GRR, and the GRRs of 0.14 Ma are estimated 81% to 196% of the current GRR. In the result of current topography in the glacial period, the recharge rate is estimated 58% to 72% of the current GRR. However it's not possible to estimate the runoff volume based on the topography of 1.0 Ma, which is estimated poor undulations and flat terrains.

Outline of research on the safety of decommissioning, storage and disposal of radioactive waste

Takeda, Seiji

no journal, , 

no abstracts in English

Numerical study on the impact of long-term landscape evolution and sea-level change on groundwater flow

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.

Data collection and predictive analysis of river denudation

Kawamura, Makoto; Jia, H.*; Koizumi, Yukiko*; Nishiyama, Nariaki; Umeda, Koji*

no journal, , 

Using topographical analysis with GIS using 10 m DEM, we created 2 km river crossing lines on each side of the three rivers, Abegawa, Oigawa and Kumanogawa, starting from the estuary and going straight to the course of the river every 3 km. In addition, the geological information of the river transverse line was extracted. When the cross-sectional lines of the three rivers are displayed together, it can be seen that the river bed rises and the undulations increase as it goes upstream. A comparison of the cross-sectional shapes of the three rivers reveals similar trends, with peaks of undulations on both sides of the rivers in the middle to upper reaches located approximately 500-1,500 m from the center of the river. The relative height between bed and peak also tends to be around 200-600 m. The difference in elevation between the peaks on both sides of the river and the river bed increased in the upstream direction, that is, the depth of the valley to the river bed increased in the upstream direction. When the riverbed slope of the river longitudinal created from the riverbed elevation was taken, an inflection points where the slope trend rose from the upstream area was seen in all three rivers regardless of the geology and geological structure. Although the trend of elevation of the riverbed and increase in undulations from the relatively flat landform near the mouth of the river upstream is pseudo, it suggests a temporal process of landform formation due to uplift and denudation from the flat lowland. This will be information that contributes to verification of the validity of future predictions and performance evaluation models that incorporate topographical changes, such as topographical change simulations.