Transport simulation of Pu through fractured media based on continuous time random walk model

HUANG Shi-qi; HU Li-tang; LIU Dong-xu; LIN Jian-feng; TIAN Lei; WANG Dao

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China Environmental Science ›› 2023, Vol. 43 ›› Issue (12) : 6321-6328.

Water Pollution Control

Transport simulation of Pu through fractured media based on continuous time random walk model

HUANG Shi-qi¹, HU Li-tang¹, LIU Dong-xu², LIN Jian-feng², TIAN Lei¹, WANG Dao¹

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Abstract

Non-Fickian dispersion occurs in the migration of nuclides in groundwater, which is influenced by geological media heterogeneity and physicochemical processes. To improve the accuracy of the simulation of this phenomenon, an alternative model is required. To analyze Pu (plutonium) migration in one-dimensional fractured rock columns, we employed the continuous time random walk (CTRW) model together with the traditional advection-dispersion equation (ADE) to effectively represent Pu breakthrough curves (BTCs). The goodness of fit and feasibility of the ADE, CTRW-TPL, CTRW-TPLA, and CTRW-ETA models were later compared to identify the superior model for simulating Pu transport in fractured media with varying colloidal concentrations. The results indicated that the CTRW-TPL model, which incorporated adsorption, outperformed the traditional ADE in describing non-Fickian migration characteristics. Although the CTRW-ETA model lacked comprehensive migration characterization, its inversion process was more feasible. Furthermore, the migration capacity of Pu in fractured media was significantly enhanced due to colloidal effects. However, beyond a certain concentration threshold, the migration capacity of Pu decreased with increasing colloidal concentrations. Regarding the theoretical framework of the CTRW model, our analysis showed that the generalized transport velocity and dispersion coefficient first increased and then decreased, while the average adsorption rate of solute particles first decreased and then increased. These findings serve as a valuable reference for future research on the parameters of the CTRW model in fractured media.

Key words

advection-dispersion equation(ADE) / colloid- facilitated transport / continuous time random walk (CTRW) / non-Fickian / nuclides / Pu

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HUANG Shi-qi, HU Li-tang, LIU Dong-xu, LIN Jian-feng, TIAN Lei, WANG Dao. Transport simulation of Pu through fractured media based on continuous time random walk model[J]. China Environmental Science. 2023, 43(12): 6321-6328

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