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Shimada, Taro; Takubo, Kazuya; Takeda, Seiji; Tanaka, Tadao
no journal, ,
In long-term safety assessment of geological disposal system, it is necessary to evaluate the impact on the nuclides migration where groundwater flow and water composition are changed with decreasing a depth of the repository by uplifts and denudation. Therefore, we developed an integrated safety assessment methodology for uplifts and denudation where nuclides migration was evaluated reflecting temporal and spatial changes of parameters of natural and engineered barriers such as distribution coefficient, porosity and groundwater velocity, which were obtained by calculation of groundwater flow, salt water distribution and long-term transition of engineered barriers. The methodology was applied to an assumed disposal site composed of sedimentary rocks with uplift and denudation. Migration parameters of engineered barrier such as coefficient of water permeability and porosity of buffer material were evaluated considering the interaction between overpack and surrounding bentonite clay under the condition of water composition. Migration parameters of the natural barrier such as distribution coefficient were determined by the combination of the geology section and water composition section on the migration pathway from the repository to the outlet of the natural barrier at the depth of 40m from the surface. The migration fluxes of some radionuclides at the outlet of natural barrier were evaluated and then the impacts on nuclides migration by uplifts and denudation were compared.
Shimada, Taro; Takubo, Kazuya; Takai, Shizuka; Takeda, Seiji; Tanaka, Tadao
no journal, ,
There is a residual uncertainty not able to avoid geological and climate events because some indications of them are difficult to be detected, while direct damage by the events such as active fault is avoided at site selection. Therefore radionuclide migration analysis was carried out considering safety functions of engineered barrier decreased or lost by intersection of fault and temporal and spatial changes of nuclide migration pathway under the assumption that concealed spray fault reaches the disposal system. And we evaluated the affects by inflow of fluid from deep region and of acidic groundwater from the surface along the grown spray fault. Based on the results of groundwater flow analysis, we calculated the nuclides migration fluxes at the outlet of engineered and natural barriers using nuclides migration parameters such as migration pathway, its length and groundwater velocity and sorption distribution coefficients estimated by combination of groundwater composition and geology. And important factors to affect the fluxes were extracted.
