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Nagao, Rina; Namekawa, Maki*; Totsuka, Masayoshi*; Nakata, Hisakazu; Sakai, Akihiro
JAEA-Technology 2021-009, 139 Pages, 2021/06
JAEA-Technology-2021-009.pdf:13.96MB
Japan Atomic Energy Agency is the implementing body of the near surface disposal of low-level radioactive waste (LLW) generated from research facilities and other facilities. Concrete-pit disposal are considered as a method of disposing of the LLW. Since the concrete-pits are placed at deeper position than the groundwater level, we need to consider that radionuclides might migrate with the flow of groundwater. Accordingly, in order to explain the safety of the concrete-pit disposal facility, it is necessary to investigate the flow of groundwater and the volumetric flow rate of leaching water from the facility. Therefore, in this report, sensitivity analysis of the volumetric flow rate of leaching water from concrete-pit was carried out by varying the permeability of cover-soil filled with in outside of the lateral sides of the bentonite mixed soil (BMS) and the conditions of the BMS on the upper part of the concrete-pits. As a result of the analysis, when the BMS is normal condition, the volumetric flow rate of leaching water from the concrete-pits is reduced by lowering permeability of the lateral cover-soil. However, in the case of occurring the deterioration of the function of BMS on the upper part of the concrete-pit, significant reduction of the volumetric flow rate of leaching water is not seen even if the permeability of the lateral cover-soil is lowered. Therefore, taking into consideration the possibility of the deterioration of the function of BMS on the upper part of the concrete-pit, it is necessary to consider that cover-soil with low permeability is equipped on the upper part of the BMS.
Munakata, Masahiro; Namekawa, Maki; Sakai, Ryutaro; Kimura, Hideo
no journal, ,
In the safety assessment for a geological disposal of long-lived radioactive waste such as high-level radioactive waste and TRU waste etc, it is important to estimate radionuclide migration to human society associated with groundwater flow. Japan Atomic Energy Agency (JAEA) has started to investigate a sedimentary rock area in the Yoro river basin, in Chiba Prefecture. The analytical study on regional groundwater flow system was performed by numerical code using FEM. As a result, a range of flow rates was estimated from 0.5 m/y to 30.0 m/y in this region and frow direction was generally from south-east to north-west. These numerical results show the local and regional flow system is reasonable to the observed data.
Kimura, Hideo; Munakata, Masahiro; Hanatani, Ikuo; Sakai, Ryutaro; Namekawa, Maki; Matsuba, Hisashi
no journal, ,
Site selection of high-level radioactive waste geologic disposal on the detailed site investigation will be performed in the early of Heisei 20 years. In such case, the regulatory authority will be need to be concerned on the safety of geologic disposal, migration of radionuclides by groundwater flow from the disposal facility to human environment on the ground surface is very important key issue. We have been developed for the safety assessment methodologies of the regional groundwater flow on the geologic disposal site taking account of the naturally occurring events such as up-lift and erosion, variation of sea level.
Fuchiwaki, Hirotaka; Namekawa, Maki; Munakata, Masahiro; Kimura, Hideo
no journal, ,
no abstracts in English
Namekawa, Maki; Matsuba, Hisashi; Munakata, Masahiro; Kimura, Hideo
no journal, ,
no abstracts in English
Munakata, Masahiro; Kimura, Hideo; Sakai, Ryutaro; Namekawa, Maki; Fuchiwaki, Hirotaka
no journal, ,
no abstracts in English
Namekawa, Maki; Munakata, Masahiro; Fuchiwaki, Hirotaka; Kimura, Hideo
no journal, ,
no abstracts in English
Takeda, Seiji; Munakata, Masahiro; Namekawa, Maki; Sakai, Ryutaro; Shimada, Taro; Tanaka, Tadao
no journal, ,
In long-term safety assessment of geological disposal system, it is necessary to evaluate the impact on the radionuclides migration where groundwater flow and water composition are changed with decreasing a depth of the repository by uplifts (two types: uniform and tilted) and denudation. We developed an integrated safety assessment methodology for uplifts and denudation where radionuclides migration analysis was combined with calculation results of groundwater flow and salt concentration distribution in a disposal site and of long-term transition of engineered barriers to estimate their properties and migration parameters. Assuming disposal site composed of sedimentary rocks with uplifts and denudation, we carried out the sensitivity analyses on groundwater velocity and salt concentration and indicated the requirements for future investigation of natural barrier related to uplifts and denudation at a candidate site from the estimation results.