|Alternative Title||Migration of Eu(III) in compacted bentonite-sand mixtures as buffer/backfill material
|Place of Conferral||兰州
研究表明：膨润土-砂混合物的水力传导系数K = 2.07×10-10～5.23×10-10 cm/s。随着掺砂率增大，混合物的水力传导系数没有明显增大，证实了混合物的水力传导系数能满足缓冲回填材料低渗透性的要求。
Eu(III)在混合物中的表观扩散系数Da = 1.44×10-14～9.41×10-14 m2/s；有效黏土密度增大，表观扩散系数减小，这主要是因为：1）混合物中主要起吸附作用的主要是膨润土，有效黏土密度增大，混合物对Eu(III)的吸附能力增强，Eu(III)的扩散减慢；2）有效黏土密度增大，混合物的比表面积增大，水力弯曲因子减小，所以扩散系数减小。|
|Other Abstract||Deep geological disposal has been regarded as a feasible way to dispose of the high-level radioactive waste (HLW). Radionuclides will diffuse to the outside in case that the overpack has been destroyed in the HLW disposal repository. Therefore, buffer/backfill material serves as a significant part of engineering barrier, preventing convective water due to the low permeability of bentonite, and retarding the migration of radionuclides through buffer by sorption to the matrix. Hence, the hydraulic conductivity and diffusion coefficient of radionuclides on compacted bentonite-sand mixtures play a very important role in assessing the performance of buffer/backfill material and in designing the deep geological disposal.
Bentonite has been considered as the ideal buffer/backfill material in HLW repositories due to its high absorption, high swelling property and low permeability. The GMZ bentonite is selected as the major ingredient and quartz sand is taken as the additive of the buffer/backfill material in this paper. And then, quartz sand is uniformly added into the bentonite with Rs = 0, 10, 20, 30, 40 and 50%, respectively, followed by compacting the mixtures to specimens with objective water contents and objective dry densities. The hydraulic conductivity and migration of Eu(III) are examined using a flexible wall permeameter for a solute concentration of 2.0×10-5 mol/L to assess the performance of buffer/backfill material.
The research shows that: hydraulic conductivities of compacted bentonite-sand mixtures with sand ratio varying from 0% to 50% are K = 2.07×10-10～5.23×10-10 cm/s, regarding 2.0×10-5 mol/L Eu(III) solution as influent. Moreover, there is not a significant change in hydraulic conductivity with sand ratio ranging from 0% to 50%. This indicates that even though a certain content of sand is added into bentonite, the bentonite-sand mixtures can still maintain the permeability as low as that of pure bentonite. This verifies again that the bentonite-sand mixtures as buffer/backfill materials can meet the requirement of low permeability.
The apparent diffusion coefficients of Eu(III) in compacted bentonite-sand mixtures are Da = 1.44×10-14～9.41×10-14 m2/s. Generally, apparent diffusion coefficient decreases as effective dry density increases. The reduce in Da with increasing effective dry density is mainly attributed to two factors: 1) The sorption of Eu(III) on mixtures is dominated by bentonite, thus an increase in clay content in pe...|
周浪. Eu(III)在混合型缓冲回填材料中的迁移研究[D]. 兰州. 兰州大学,2014.
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