A reactive transport model of neptunium migration from the potential repository at Yucca Mountain

Viswanathan, Hari; Robinson, Bruce A.; Valocchi, Albert J.; Triay, I.R.

doi:10.1016/s0022-1694(98)00122-x

Cited by 86 publications

(57 citation statements)

References 43 publications

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“…For a detailed description of the hydrologic and geochemical processes aecting the migration of 237 Np, see Viswanathan et al [25]. This problem demonstrates the selective coupling method for a complex, unstructured grid and a reactive transport system with speciation and competitive ion exchange.…”

Section: Examplementioning

confidence: 90%

“…The unstructured grid captures the complex stratigraphy at the site scale, while also allowing transport near the potential repository to be captured at a grid spacing of about 3 m, resulting in a mesh with 7070 spatial nodes. For details on the hydrologic models, parameters, and in®ltration¯uxes used to investigate 237 Np transport, see Viswanathan et al [25]. In the present study, the nonisothermal eects examined in that paper are ignored in favor of an isothermal model, so that the chemical transport processes and numerical schemes can be examined more directly.…”

Section: Examplementioning

confidence: 99%

“…The reactive transport equations solved by FEHM are described in greater detail in Viswanathan et al [25]. We will provide a brief summary in this section.…”

Section: Primary/secondary Variablesmentioning

confidence: 99%

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Efficient numerical techniques for modeling multicomponent ground-water transport based upon simultaneous solution of strongly coupled subsets of chemical components

Robinson

Viswanathan

Valocchi

2000

Advances in Water Resources

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An iterative solution technique for reactive transport problems is developed, which we call the selective coupling method, that represents a versatile alternative to traditional uncoupled iterative techniques and the fully coupled global implicit method. The chemical formulation studied allows a combination of equilibrium and kinetic reactions, and therefore is a more versatile model formulation than a purely equilibrium-based system. However, this is a very challenging system for obtaining an ecient numerical solution. Techniques that sequentially compute the concentrations of aqueous components possibly ignore important derivatives in the Jacobian matrix of the full system of equations. The selective coupling method developed here allows only the strongly coupled components to be solved together, and the transport iteration consists of solving groups of components simultaneously. We also develop a method denoted as coupled normalization to reduce the computational work and memory requirements for particular types of reactive transport problems. These approaches can result in computational savings relative to the global implicit method by achieving a similar iteration count while reducing the cpu time per iteration. More importantly, the memory requirements of the selective coupling technique are controlled by the maximum number of coupled components, rather than by the total number of components. For complex aqueous chemical systems and grids with a large number of nodes, memory eciency is the characteristic that makes the selective coupling method particularly attractive relative to the global implicit method. A series of example cases illustrate the eciency of the new approach. These test problems are also used to address the implementation issues surrounding the most ecient strategy for coupling the aqueous components when carrying out the chemical transport iteration. In-depth knowledge of the behavior of the chemical system is required to select an appropriate solution strategy. Published by Elsevier Science Ltd.

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Section: Examplementioning

confidence: 90%

Section: Examplementioning

confidence: 99%

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Efficient numerical techniques for modeling multicomponent ground-water transport based upon simultaneous solution of strongly coupled subsets of chemical components

Robinson

Viswanathan

Valocchi

2000

Advances in Water Resources

Self Cite

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“…Several groups (Hsi and Langmuir 1985;Ho and Miller 1986;Waite, Davis et al 1994;Duff 1996;Lenhart and Honeyman 1999) (Zyvoloski 1997) have been used to model transport of uranium and neptunium (Viswanathan, Robinson et al 1998) species in the saturated zone at Yucca Mountain.…”

Section: Uranium and Neptunium Solution Speciationmentioning

confidence: 99%

Long-term desorption behavior of uranium and neptunium in heterogeneous volcanic tuff materials /

Dean¹

2010

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“…Among them, network reactions have been used to model a large variety of contaminants. This includes the degradation of chlorinated solvents (e.g., Clement, 1997Clement, , 2001, the decay of radioactive species (e.g., Painter et al, 2007), and the transformation of pesticides, organic phosphates and nitrogen in the environment (e.g., van Genuchten, 1985;Mishra and Mishra, 1991;Vishwanathan et al, 1998). When contaminant concentrations are small, i.e., less than the Michaelis half-saturation constant in the Monod or MichaelisMenten enzyme kinetic model, the microbial biotransformation rates can be described by pseudo-first-order reaction rates (e.g., Bouwer et al, 1981;Vogel et al, 1987;Haston and McCarty, 1999;Burnell et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

A random walk solution for modeling solute transport with network reactions and multi-rate mass transfer in heterogeneous systems: Impact of biofilms

Henri

Fernàndez-García

2015

Advances in Water Resources

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The interplay between the spatial variability of aquifer properties, mass transfer and chemical reactions often complicates reactive transport simulations. It is well documented that hydro-biochemical properties are ubiquitously heterogeneous and that rate-limited mass transfer typically leads to the conceptualization of an aquifer as a multi-porosity system. Within this context, chemical reactions taking place in mobile/immobile water regions can be substantially different between each other. This paper presents a particle-based method that can efficiently simulate heterogeneity, network reactions and multi-rate mass transfer. The approach is based on the development of transition probabilities that describe the likelihood that particles belonging to a given species and mobile/immobile domain at a given time will be transformed into another species and mobile/immobile domain afterwards. The joint effect of mass transfer and sequential degradation is shown to be non-trivial. A characteristic double peak of daughter products occurs when the degradation capacity in the immobile domain is relatively small. This late rebound of concentrations is not driven by any change in the flow regime (e.g., pumping ceases in the pump-and-treat remediation strategy) but due to the natural interplay between mass transfer and chemical reactions. To illustrate that the method can simultaneously represent mass transfer, spatially varying properties and network reactions without numerical problems, we have simulated the degradation of tetrachloroethylene (PCE) in a three-dimensional fully heterogeneous aquifer subjected to rate-limited mass transfer. Two types of degradation modes were considered to compare the effect of an active biofilm with that of clay pods present in the aquifer. Results of the two scenarios display significantly differences. Biofilms that promote the degradation of compounds in an immobile region are shown to significantly enhance degradation, rapidly producing daughter products and less tailing.

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A reactive transport model of neptunium migration from the potential repository at Yucca Mountain

Cited by 86 publications

References 43 publications

Efficient numerical techniques for modeling multicomponent ground-water transport based upon simultaneous solution of strongly coupled subsets of chemical components

Efficient numerical techniques for modeling multicomponent ground-water transport based upon simultaneous solution of strongly coupled subsets of chemical components

Long-term desorption behavior of uranium and neptunium in heterogeneous volcanic tuff materials /

A random walk solution for modeling solute transport with network reactions and multi-rate mass transfer in heterogeneous systems: Impact of biofilms

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