Advances in Earth Science ›› 2017, Vol. 32 ›› Issue (10): 1050-1061. doi: 10.11867/j.issn.1001-8166.2017.10.1050

• Orginal Article • Previous Articles     Next Articles

Mechanisms and Models for Bentonite Erosion Used for Geologic Disposal of High Level Radioactive Waste: A Review

Yongfu Xu( )   

  1. 1.Department of Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
    2.Wentian College of Hohai University, Anhui Maanshan 243000, China
  • Received:2017-04-20 Revised:2017-08-03 Online:2017-12-20 Published:2017-10-20
  • About author:

    First author:Xu Yongfu (1967-), male, Taixing County, Jiangsu Province, Professor. Research areas include mechanics of fractal media, unsaturated soil mechanics and ground

  • Supported by:
    Project supported by the National Natural Science Foundation of China “Geological disaster and its control method due to bentonite erosion under seepage at the bentonite/granite interface of a deep geological radioactive waste repository” (No.41630633).

Yongfu Xu. Mechanisms and Models for Bentonite Erosion Used for Geologic Disposal of High Level Radioactive Waste: A Review[J]. Advances in Earth Science, 2017, 32(10): 1050-1061.

The performance of the bentonite buffer in nuclear waste repository concept relies to a great extent on the buffer surrounding the canister having sufficient dry density. Loss of buffer material caused by erosion remains as the most significant process reducing the density of the buffer. In the worst case, the process is assumed to last as long as the free volume between the pellets in the pellets filled regions is filled with groundwater. Erosion rate and mass erosion are calculated based on the erosion model, and the measures are presented to prevent the geological disaster due to bentonite erosion. The groundwaters may solubilise the smectite particles in the bentonite and carry them away as colloidal particles. A dynamic model is developed for sodium gel expansion in fractures where the gel soaks up groundwater as it expands. The model is based on a force balance between and on smectite particles, which move in the water. Attractive van der Waals forces, repulsive electric diffuse layer (DDL) forces, gravity and buoyancy forces and forces caused by the gradient of chemical potential of the particles act to move the particle in the water. The effect of the fracture width and the frictions between particles and water and surrouding rock is analysed based on erosion model. The DDL forces strongly depend on the type of clay minerals and the type of ion and concentration in the water surrounding the particles. In the designed safe use of nuclear waste disposal (tens of thousands of years to hundreds of thousands of years), the safety of nuclear waste disposal is affected by the hydrodynamic and chemical effects, and bentonite erosion. Due to the bentonite erosion, the buffer/backfill layers become loose, and their permeability increases, which causes the nuclear element diffusion and convection, and even the nuclear disaster. In this paper, the mechanisms, models, experiments and control measures of bentonite erosion were systematically summarized. The current deficiencies of bentonite erosion were pointed out, and new methods were put forward to carry out the research for bentonite erosion. The measures were presented to prevent the geological disaster due to bentonite erosion through changes. The project is not only academic innovation, but also has a large practical significance. The research results of this project can be widely applied to the design, construction and maintenance of the bentonite buffer in nuclear waste repository.

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