Comparison of lab-scale experiments for the determination of non-reactive tracer diffusion coefficients in Boom Clay

IF 3.1 3区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Delphine Durce , Marc Aertsens , Norbert Maes , Marc Van Gompel , Stéphane Brassinnes
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Abstract

The transport parameters of radionuclides, the diffusion coefficient and the retardation factor, in clay-rich host rocks investigated for deep geological disposal, can be determined using various types of laboratory experiments. The present study aimed at comparing three types of laboratory experiments commonly used in the context of radioactive waste for the determination of the transport properties of two non-reactive tracers, HTO and 125I, in Boom Clay. Two Boom Clay samples with orientation parallel and perpendicular to the bedding were selected to assess the role of sample heterogeneity and anisotropy. Each sample/orientation was subjected to through-diffusion experiments, pulse injection experiments with pressure differences over the clay core ranging from 5 to 19 bars and a back-to-back experiment.

In the case of HTO, the three types of experiments led to a consistent set of transport parameters for each Boom Clay sample. Over the three types of experiment, the average apparent diffusion coefficients and accessible porosity vary at maximum a factor 1.4 and 1.3, respectively for a same sample type/orientation. The porosity accessible to HTO was similar to the porosity calculated from the water content. In the case of 125I, the three types of experiments also showed consistency for the determination of the apparent diffusion coefficients with values varying within a factor 1.7 for the same sample type/orientation. However, variation in accessible porosity between the experiments revealed a physical modification of the Boom Clay sample occurring during the pulse injection experiments and affecting 125I transport.

Transport anisotropy was consistently observed in all the types of experiment and for both HTO and 125I with a higher anisotropy observed in the samples richer in clay. Slightly higher total porosity and lower 125I accessible porosity were noticed in the clay-rich samples in comparison to silt-rich samples.

测定布姆粘土中非反应性示踪剂扩散系数的实验室规模实验比较
放射性核素在富含粘土的主岩中的迁移参数、扩散系数和延迟因子,可通过各种类型的实验室实验来确定。本研究旨在比较放射性废物方面常用的三种实验室实验,以确定两种非放射性示踪剂 HTO 和 125I 在 Boom Clay 中的迁移特性。为了评估样品的异质性和各向异性的作用,选择了两个方向与垫层平行和垂直的 Boom Clay 样品。每个样品/取向都进行了穿透扩散实验、粘土核心压力差为 5 至 19 巴的脉冲注入实验和背靠背实验。在三种类型的实验中,对于相同的样品类型/方位,平均表观扩散系数和可进入孔隙度分别最大相差 1.4 倍和 1.3 倍。HTO 可进入的孔隙度与根据含水量计算出的孔隙度相似。就 125I 而言,三种类型的实验在确定表观扩散系数方面也表现出了一致性,对于相同的样品类型/方位,其数值变化在 1.7 倍以内。在所有类型的实验中,HTO 和 125I 的迁移各向异性都是一致的,粘土含量较高的样品的各向异性更高。与富含淤泥的样品相比,富含粘土的样品总孔隙率略高,而 125I 可及孔隙率较低。
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来源期刊
Applied Geochemistry
Applied Geochemistry 地学-地球化学与地球物理
CiteScore
6.10
自引率
8.80%
发文量
272
审稿时长
65 days
期刊介绍: Applied Geochemistry is an international journal devoted to publication of original research papers, rapid research communications and selected review papers in geochemistry and urban geochemistry which have some practical application to an aspect of human endeavour, such as the preservation of the environment, health, waste disposal and the search for resources. Papers on applications of inorganic, organic and isotope geochemistry and geochemical processes are therefore welcome provided they meet the main criterion. Spatial and temporal monitoring case studies are only of interest to our international readership if they present new ideas of broad application. Topics covered include: (1) Environmental geochemistry (including natural and anthropogenic aspects, and protection and remediation strategies); (2) Hydrogeochemistry (surface and groundwater); (3) Medical (urban) geochemistry; (4) The search for energy resources (in particular unconventional oil and gas or emerging metal resources); (5) Energy exploitation (in particular geothermal energy and CCS); (6) Upgrading of energy and mineral resources where there is a direct geochemical application; and (7) Waste disposal, including nuclear waste disposal.
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