Engineered barrier experiments and analytical studies on coupled thermal – hydraulic – chemical processes in bentonite buffer material
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- Suzuki Hideaki
- Geological Isolation Research Unit Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency
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- Fujisaki Kiyoshi
- Geological Isolation Research Unit Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency Nuclear Waste Management Organizaton of Japan
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- Fujita Tomoo
- Geological Isolation Research Unit Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency
Bibliographic Information
- Other Title
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- 緩衝材の地球化学プロセスに着目した熱－水－化学連成挙動に関する工学規模の人工バリア試験と解析評価
- カンショウザイ ノ チキュウ カガク プロセス ニ チャクモク シタ ネツ-ミズ-カガクレンセイキョドウ ニ カンスル コウガク キボ ノ ジンコウ バリア シケン ト カイセキ ヒョウカ
- Engineered barrier experiments and analytical studies on coupled thermal ^|^#8211; hydraulic ^|^#8211; chemical processes in bentonite buffer material
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Abstract
It is anticipated that thermal - hydraulic - mechanical - chemical (THMC) processes will be coupled in the bentonite buffer material of a high-level radioactive waste repository. The main contributors to these processes are heat arising from the radioactive decay of the vitrified waste, infiltration of groundwater from the host rock and/or leachate from the cementitious component of the repository, and the consequent increase in swelling pressure and chemical reactions. In order to evaluate these coupled processes in the bentonite buffer material, it is necessary to take steps towards the development of a credible and robust THMC model.<br> The current paper describes the measured data of an engineering-scale coupled THC process experiment and the calculated results of a THC model undergoing development. The coupled experiment used an electric heater, bentonite blocks and a mortar block, subjected to infiltrating water to simulate a high-alkaline porewater derived from the concrete tunnel support seeping into the bentonite buffer material under a thermal gradient provided by the vitrified waste. <br> Temperature and water content of the bentonite buffer material were measured by several sensors continuously for several months. After this time, the buffer material was sampled. The results of mineral analysis of the samples suggested that the precipitate of amorphous hydrate with silica was found in the buffer material in contact with the mortar. The developing THC model simulated C-S-H gel precipitation as a secondary mineral in the exact same locality because of the solution being saturated with respect to portlandite and chalcedony, thereby providing some confidence in the chemical feature of the developing THC model. <br> Some important issues in the future development of the model were also identified, including the concentration of porewater being influenced by vapor movement in the bentonite buffer material due to heating from the vitrified waste and geochemical reactions being affected by the water retention feature of the bentonite buffer material.
Journal
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- Journal of Nuclear Fuel Cycle and Environment
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Journal of Nuclear Fuel Cycle and Environment 16 (1), 43-56, 2009
Division of Nuclear Fuel Cycle and Environment, Atomic Energy Society of Japan
