Variability of effective diffusivity in fractured and mineralized metamorphic host rock from Bukov URF, Bohemian Massif (CZ)

IF 3.4 3区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Applied Geochemistry Pub Date : 2025-09-25 DOI:10.1016/j.apgeochem.2025.106574

Wenyu Zhou , Johannes Kulenkampff , Milan Zuna , Filip Jankovský , Christoph Butscher , Robin Kammel , Thorsten Schäfer , Cornelius Fischer

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引用次数: 0

Abstract

Crystalline rocks are considered host rocks for high-level radioactive waste (HLW) disposal because of their mechanical, thermal, and chemical properties. However, fractures and associated mineral precipitates, e.g. calcite, introduce significant heterogeneity that complicates predictions of radionuclide (RN) transport in fractured crystalline rock systems. This study combines positron emission tomography (PET) imaging and transport modeling to investigate the effects of calcite-filled fractures on predominantly diffusive transport in crystalline rocks. Diffusion experiments using a conservative iodine tracer (¹²⁴I) were performed on rocks from the BUKOV underground research facility (Czech Republic), and CT-based calcite-filled fracture geometries were incorporated into RTM simulations. The results show two types of transport modifications due to calcite precipitation in fractures: enhanced transport in porous calcite generations and suppressed transport in low-porosity calcite fracture fillings. The spatial distribution of fracture-filling calcite, its porosity, and the porosity of the surrounding matrix materials can lead to heterogeneous or anisotropic diffusion behavior. This suggests that important transport characteristics in heterogeneous systems may be overlooked by conventional modeling using homogenized diffusion coefficients. The apparent diffusivity of the fractured and variously sealed BUKOV rock ranges from 10⁻¹³ to 10⁻¹⁰ m²/s. We conclude that exploiting the variability and anisotropy of diffusive flux behavior is beneficial for improving the accuracy of RN migration predictions in fractured and mineralized crystalline rock systems. This work demonstrates the value of integrating advanced imaging and modeling techniques to better characterize solute transport in fractured crystalline host rocks.

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波西米亚地块Bukov URF破碎矿化变质寄主岩有效扩散系数的变异

结晶岩由于其机械、热学和化学性质，被认为是高放射性废物（HLW）处置的寄主岩。然而，裂缝和伴生的矿物沉淀，如方解石，引入了显著的非均质性，使裂缝结晶岩石系统中放射性核素（RN）输运的预测复杂化。本研究结合正电子发射断层成像（PET）和输运模型来研究方解石充填裂缝对结晶岩石中主要扩散输运的影响。使用保守碘示踪剂（124I）对来自BUKOV地下研究设施（捷克共和国）的岩石进行了扩散实验，并将基于ct的方解石充填裂缝几何形状纳入RTM模拟。结果表明，裂缝中方解石的沉积导致两种类型的输运变化：多孔方解石世代的输运增强和低孔隙方解石充填体的输运抑制。裂缝充填方解石的空间分布、其孔隙度以及周围基质材料的孔隙度会导致非均质或各向异性扩散行为。这表明，使用均质扩散系数的传统建模可能会忽略非均质系统中的重要输运特征。裂缝和不同密封BUKOV岩石的表观扩散系数为10−13 ~ 10−10 m2/s。我们认为，利用扩散通量行为的变异性和各向异性有助于提高裂缝和矿化结晶岩系统中RN迁移预测的准确性。这项工作证明了整合先进的成像和建模技术的价值，可以更好地表征裂缝性结晶寄主岩石中的溶质运移。

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来源期刊

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.