The in-situ long-term sorption and diffusion (LTDE-SD) experiment performed at the Äspö Hard Rock Laboratory in Sweden aims at increasing knowledge of sorption and diffusion processes of radionuclides in natural fractures and granodiorite matrix under in-situ conditions. This paper presents a comprehensive modeling exercise focusing on the scaling approach for sorption and diffusion parameters from laboratory to in-situ conditions using the LTDE-SD data set for six representative radionuclides. The near-surface heterogeneities at both the fracture surface and rock matrix were evaluated by the conceptual model with high porosity, diffusivity, and sorption capacity, as well as their gradual changes at the near-surface zones. The modeling results for non-sorbing Cl-36 and weak-sorbing Na-22 validated the model concept and parameter estimation of porosity and diffusivity by considering a 5-mm-thick disturbed zone with gradual parameter changes and an undisturbed matrix characterized by constant parameters. The effective diffusivities (D_e) of these cationic and anionic tracers showed typical cation excess and anion exclusion effects; however, the cation excess diffusion was more pronounced due to the heterogeneous pore networks in this granodiorite. The modeling results for high-sorbing tracers (Cs-137, Ra-226, Ni-63, and Np-237) with different sorption mechanisms validated the scaling approaches of distribution coefficients (K_d) as a function of particle size and their relation to near-surface disturbances. Sorption dependence on particle size could be understood in relation to different sorption mechanisms and mineralogical features. This modeling exercise provided key recommendations toward better scaling approaches for estimating reliable D_e and K_d parameters under in-situ conditions.

中文翻译：

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结晶岩石保留特性的缩放方法：瑞典 Äspö Hard Rock 实验室的原位长期吸附和扩散实验 (LTDE-SD) 的案例研究

在瑞典 Äspö Hard Rock 实验室进行的原位长期吸附和扩散 (LTDE-SD) 实验旨在增加对原位条件下天然裂缝和花岗闪长岩基质中放射性核素吸附和扩散过程的了解。本文使用 LTDE-SD 数据集为六种代表性放射性核素提供了一个综合建模练习，重点是从实验室到原位条件的吸附和扩散参数的缩放方法。裂缝表面和岩石基质的近地表非均质性通过具有高孔隙率、扩散率和吸附能力的概念模型以及它们在近地表区域的逐渐变化来评估。非吸附性 Cl-36 和弱吸附性 Na-22 的建模结果验证了孔隙度和扩散率的模型概念和参数估计，考虑了参数逐渐变化的 5 mm 厚扰动区和具有恒定参数特征的未扰动基体. 有效扩散系数 (D _e ) 这些阳离子和阴离子示踪剂表现出典型的阳离子过量和阴离子排斥作用；然而，由于该花岗闪长岩中的非均质孔隙网络，阳离子过量扩散更为明显。具有不同吸附机制的高吸附示踪剂（Cs-137、Ra-226、Ni-63 和 Np-237）的建模结果验证了分布系数 ( K _d ) 作为粒度函数的缩放方法及其关系近地表扰动。可以通过不同的吸附机制和矿物学特征来理解吸附对粒度的依赖性。这对于更好地缩放提供重要建议造模运动估计可靠方法d _ë和ķ_d原位条件下的参数。