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Sawaguchi, Takuma; Miwa, Kazuji*; Shimada, Taro; Takeda, Seiji
no journal, ,
In the previous dose assessment for the radioactive waste disposal, the dissolved radionuclides leaking from the repository were assumed to flow directly into the living environment (ocean, lake, river, etc.) through natural barriers. However, based on the knowledge after the Fukushima Daiichi Nuclear Power Plant accident, it was considered that radionuclides via groundwater could sorb and desorb with soil near spring water points, and that radiocesium was mainly transferred as sorbed to suspended particles in the living environment. In this study, in order to contribute to the dose assessment for intermediate-depth disposal, we analytically understood the influence on the migration in the living environment with or without consideration of the nuclide sorption on the seabed soil during spring water inflow into a coastal zone. In addition, the effects were also evaluated for the presence or absence of the nuclide sorption/desorption on suspended particles and the particle sedimentation. As a result, the radioactivity concentrations in seabed soil and seawater immediately above the seabed were higher in the estimate that considered the sorption/desorption and the sedimentation than in the estimate that did not. These results indicate that it is important to consider the radionuclide sorption on the seabed soil and the migration of radionuclides sorbed on suspended particles in the estimation of radionuclide migration in the living environment because these phenomena could cause the increase of radionuclide concentrations in the interface layer and the seabed soil and the higher exposure due to benthic fish and shellfish ingestion, etc.
Shimada, Taro; Sasaki, Toshihisa*; Takai, Shizuka; Takeda, Seiji
no journal, ,
In Japan, shallow land disposal sites have already been and may be constructed in the future on marine terraces. It has been reported that deep-seated landslides, which are rapid erosions on terrace cliffs and hillslopes of streams formed on terrace faces, are dominant in the erosion of marine terraces. Therefore, the ability to handle deep-seated landslides is necessary to evaluate the effects of erosion on disposal sites during long-term topographic change. The Landlab code can evaluate deep-seated landslides as well as gradual erosion, mainly on hillslopes in mountainous areas. However, its applicability to marine terraces needs to be confirmed. In order to confirm the applicability of the evaluation model for deep-seated landslide of the Landlab to marine terraces, we first evaluated the occurrence points of deep-seated landslides using the Landlab with 2m DEM for an area with marine terraces. We then compared the points extracted by the Landlab with the hillslopes extracted by the manuals to determine the applicability of the Landlab's evaluation model. The target area was selected as an area with evidence of deep-seated landslides on marine terraces and streams. The points where deep-seated landslides are likely to occur in the future were evaluated for the field profile using the 2m DEM. The two manuals target the field profile and extract hillslopes where deep-seated landslides are likely to occur in the future based on the characteristics of the slope distribution considering the past landslide and topographic quantities in the same area using 2mDEM. Comparison of the extracted results of deep-seated landslides shows that most of the extracted points of deep-seated landslides by the Landlab were included in the possible deep-seated hillslopes extracted by the two manual methods. The results confirm that the Landlab's evaluation model is capable of extracting points where deep-seated landslides are likely to occur in the future.