A sequential partly iterative approach for multicomponent reactive transport with CORE2D

Journal of Contaminant Hydrology

Montenegro

2011

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The performance assessment of a geological repository for radioactive waste requires quantifying the geochemical evolution of the bentonite engineered barrier. This barrier will be exposed to coupled thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. This paper presents a coupled THC model of the FEBEX (Full-scale Engineered Barrier EXperiment) in situ test which accounts for bentonite swelling and chemical and thermal osmosis. Model results attest the relevance of thermal osmosis and bentonite swelling for the geochemical evolution of the bentonite barrier while chemical osmosis is found to be almost irrelevant. The model has been tested with data collected after the dismantling of heater 1 of the in situ test. The model reproduces reasonably well the measured temperature, relative humidity, water content and inferred geochemical data. However, it fails to mimic the solute concentrations at the heater-bentonite and bentonite-granite interfaces because the model does not account for the volume change of bentonite, the CO 2 (g) degassing and the transport of vapor from the bentonite into the granite. The inferred HCO 3 -and pH data cannot be explained solely by solute Page 2 of 54 transport, calcite dissolution and protonation/deprotonation by surface complexation, suggesting that such data may be affected also by other reactions.

Section: Bentonite Swellingmentioning

confidence: 99%

A coupled THC model of the FEBEX in situ test with bentonite swelling and chemical and thermal osmosis

Zheng

Journal of Contaminant Hydrology

Montenegro

2011

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“…FADES allows the simulation of the coupled thermo-hydro-mechanical behaviour of unsaturated soils (Navarro and Alonso, 2000 Zhang et al, 2008), interpret the Redox Zone Experiment in a fracture zone of the Äspö site Molinero and Samper, 2006), evaluate the long-term geochemical evolution of radioactive waste repositories in clay (Yang et al, 2008) and granite (Yang et al, 2007), model the transport of corrosion products and their geochemical interactions with bentonite (Samper et al, 2008c), analyze stochastic transport and multicomponent competitive cation exchange in aquifers and study concrete degradation (Galíndez et al, 2006). (Xu et al, 1999;Samper et al, 2009). The feedback between reactive transport and THM processes is accounted for in an explicit manner when changes in porewater ionic strength are large (Juncosa 2001).…”

Section: Numerical Implementationmentioning

confidence: 99%

A coupled THMC model of a heating and hydration laboratory experiment in unsaturated compacted FEBEX bentonite

Zheng

Montenegro

et al. 2010

Journal of Hydrology

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“…The DR experiment was simulated with CORE 2D V4, a 2-D Galerkin finite element multicomponent reactive transport code which solves for groundwater flow, heat transport and multicomponent reactive solute transport in saturated/unsaturated steady or transient groundwater flow under general boundary conditions (Samper et al 2009. This code has been extensively used to model aquifer flow and solute transport in aquifers , in situ diffusion experiments in clay formations Samper et al 2006aSamper et al , 2008aSamper et al , 2010aSoler et al 2008;Naves et al 2012;Yi et al 2012), laboratory diffusion and retention experiments (Samper et al 2006b), including the CERBERUS experiment in the Boom clay (Zhang et al 2008) and the Redox Zone experiment in a fracture zone of the Ä spö site Molinero and Samper 2006).…”

Section: Computer Codementioning

confidence: 99%

A single-site reactive transport model of Cs+ for the in situ diffusion and retention (DR) experiment

Naves

et al. 2015

Environ Earth Sci

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In situ diffusion experiments are performed in underground research laboratories for understanding and quantifying radionuclide diffusion from underground radioactive waste repositories. The in situ diffusion and retention, DR, experiment was performed at the Mont Terri underground research laboratory, Switzerland, to characterize the diffusion and retention parameters of the Opalinus clay. Several tracers were injected instantaneously in the circulating artificial water and were then allowed to diffuse into the clay rock through two porous packed-off sections of a borehole drilled normal to the bedding of the clay formation. This paper presents a single-site multicomponent reactive transport model of Cs ? , a tracer used in the DR experiment which sorbs onto Opalinus clay via cation exchange. The reactive transport model accounts for the diffusive-reactive transport of 11 primary species and 22 aqueous complexes, and the water-rock interactions for 5 cation exchange and 3 mineral dissolution/precipitation reactions. Most of the solutes except for Cs ? diffuse from the Opalinus clay formation into the injection interval because the concentrations in the initial Opalinus clay pore water are larger than those of the initial water in the circulation system. Calcite dissolves near the borehole while dolomite precipitates. Dissolved Cs ? sorbs by exchanging with Ca 2? in the exchange complex. The computed dilution curve of Cs ? in the circulating fluid is most sensitive to the effective diffusion, D e , of the filter, the selectivity coefficient of Na ? to Cs ? , K Na-Cs and D e of the borehole disturbed zone. The apparent distribution coefficient of Cs ? , K a d , in the formation varies in space and time from 100 to 165 L/kg due to the temporal changes in the water chemistry in the formation. The results of a sensitivity run in which the initial chemical composition of the Opalinus pore water is the same as the initial chemical composition of the water in the circulation system show that the changes in K a d are negligible. The dilution curve of Cs ? computed with the reactive transport model coincides with that obtained with the K d model. The tracer concentrations along the overcoring profiles computed with the K d model, however, differ significantly from those computed with the reactive transport model. Therefore, a reactive transport model is needed for the appropriate interpretation of the Cs ? overcoring data from the DR diffusion experiment.