A site-scale model for fluid and heat flow in the unsaturated zone of Yucca Mountain, Nevada

Wu, Yu‐Shu; Haukwa, C.; Bodvarsson, G.S.

doi:10.1016/s0169-7722(99)00014-5

Cited by 108 publications

(82 citation statements)

References 21 publications

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“…Different modeling approaches have been tested for handling fracture-matrix interaction at Yucca Mountain [7]. However, the DKM concept has been consistently used as the main modeling approach for simulating flow and transport in the UZ of Yucca Mountain [30], because of its ability to handle flow through both fracture and matrix continua.…”

Section: Numerical Model Gridsmentioning

confidence: 99%

“…The annual average surface temperature at Yucca Mountain was measured continuously for several years. Surface temperatures T s at any elevation Z are then computed as constants, according to the following equation [30]: …”

Section: Top Boundary Temperature Conditionmentioning

confidence: 99%

“…While the site characterization has been mostly carried out for analyzing unsaturated flow and radionuclide transport in ambient, isothermal conditions [30,31], the inherent nature of nonisothermal flow and transport processes, created by repository heating from radioactive decay, has also motivated many research efforts to understand thermal-hydrologic (TH) behavior and its impact on the repository performance within the UZ. In particular, significant progress has been made in quantitative TH modeling studies at Yucca Mountain [9,10,6].…”

Section: Introductionmentioning

confidence: 99%

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A mountain-scale thermal–hydrologic model for simulating fluid flow and heat transfer in unsaturated fractured rock

Mukhopadhyay

Zhang

et al. 2006

Journal of Contaminant Hydrology

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A multidimensional, mountain-scale, thermal-hydrologic (TH) numerical model is presented for investigating unsaturated flow behavior in response to decay heat from the radioactive waste repository in the Yucca Mountain unsaturated zone (UZ), Nevada. The model, consisting of both two-dimensional (2-D) and three-dimensional (3-D) representations of the UZ repository system, is based on the current repository design, drift layout, thermal loading scenario, and estimated current and future climate conditions. This mountain-scale TH model evaluates the coupled TH processes related to mountain-scale UZ flow. It also simulates the impact of radioactive waste heat release on the natural hydrogeological system, including heat-driven processes occurring near and far away from the emplacement tunnels or drifts. The model simulations predict thermally perturbed liquid saturation, gas-and liquid-phase fluxes, and water and rock temperature elevations, as well as the changes in water flux driven by evaporation/condensation processes and drainage between drifts. These simulations provide mountain-scale thermally perturbed flow fields for assessing the repository performance under thermal loading conditions. Key Words: thermal-hydrologic processes in subsurface, thermal load, Yucca Mountain, fluid and heat flow in porous media, heat pipe, reservoir simulation, fractured unsaturated rock * Corresponding author. Tel.: +1-510-486-7291; fax: +1-510-486-5686, E-Mail address: YSWu@lbl.gov. 2 IntroductionIn the past decade, the 500-700 m thick Yucca Mountain unsaturated zone (UZ) has been extensively investigated as a potential subsurface repository for storing high-level radioactive wastes. While the site characterization has been mostly carried out for analyzing unsaturated flow and radionuclide transport in ambient, isothermal conditions [30,31], the inherent nature of nonisothermal flow and transport processes, created by repository heating from radioactive decay, has also motivated many research efforts to understand thermal-hydrologic (TH) behavior and its impact on the repository performance within the UZ. In particular, significant progress has been made in quantitative TH modeling studies at Yucca Mountain [9,10,6].Emplacement of heat-generating high-level radioactive waste in the UZ system of unsaturated welded and unwelded fractured tuff at Yucca Mountain will perturb the ambient condition and create complex multiphase fluid flow and heat-transfer processes.The physical phenomena associated with repository heating include conduction and convection heat transfer, phase change (boiling and condensation), two-phase flow of liquid and gas phases under variably saturated conditions, enhanced fracture-matrix interaction caused by rapid matrix drying and subsequent imbibition, diffusion and dispersion of vapor and gas, and vapor-pressure-lowering effects. These TH processes will last hundreds to thousands of years after waste emplacement, and will significantly redistribute the in-situ moisture content and alter the per...

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Section: Numerical Model Gridsmentioning

confidence: 99%

Section: Top Boundary Temperature Conditionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A mountain-scale thermal–hydrologic model for simulating fluid flow and heat transfer in unsaturated fractured rock

Mukhopadhyay

Zhang

et al. 2006

Journal of Contaminant Hydrology

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“…Thus, the temporal change of water in the drift element represents the cumulative seepage collected in a capture system installed in the drift. The background percolation flux at the experimental site is extracted from the UZ site-scale model (Wu et al, 1999) and applied uniformly as a constant flux across the top model boundary. The fluxes of 2.54 mm/yr for Niche 3107 and 2.02 mm/yr for Niche 4788 are significantly lower than the injection flux applied during the liquid-release tests, and thus are not expected to greatly affect the simulation results.…”

Section: Model Developmentmentioning

confidence: 99%

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confidence: 99%

Inverse and predictive modeling of seepage into underground openings

Finsterle

Ahlers

Trautz

et al. 2003

Journal of Contaminant Hydrology

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Abstract. We discuss the development and calibration of a model for predicting seepage into underground openings. Seepage is a key factor affecting the performance of the potential nuclear-waste repository at Yucca Mountain, Nevada. Three-dimensional numerical models were developed to simulate field tests in which water was released from boreholes above excavated niches. Data from air-injection tests were geostatistically analyzed to infer the heterogeneous structure of the fracture permeability field. The heterogeneous continuum model was then calibrated against the measured amount of water that seeped into the opening. This approach resulted in the estimation of model-related, seepage-specific parameters on the scale of interest.The ability of the calibrated model to predict seepage was examined by comparing calculated with measured seepage rates from additional experiments conducted in different portions of the fracture network. We conclude that an effective capillary-strength parameter is suitable to characterize seepage-related features and processes for use in a prediction model of average seepage into potential waste emplacement drifts.Keywords: capillary barrier, unsaturated zone, parameter estimation * Corresponding author: Fax: +1-510-486-5686; e-mail: SAFinsterle@lbl.gov 2 IntroductionSeepage of water into emplacement drifts for nuclear waste is considered a key factor affecting the long-term safety of a potential repository at Yucca Mountain, Nevada. The number of waste packages contacted by water, the corrosion rate of engineered barriers and waste containers, the dissolution and mobilization of radioactive contaminants, and their release and migration towards the accessible environment all depend on the rate, the chemical composition, and the spatial and temporal distribution of water seeping into the waste-emplacement drifts.Accurately estimating seepage into underground openings excavated from an unsaturated fractured formation requires process understanding on a wide range of scales. Processes to be studied include (1) the mountain-scale distribution of percolation flux, (2) the intermediate-scalechanneling, bifurcation, and dispersion of flow in the fracture network, (3) the small-scale capillary-barrier effect in the boundary layer around the opening, and (4) the micro-scale phenomena of film flow, drop formation, and drop detachment at the drift surface. In addition, the thermodynamic environment in the drift (temperature, relative humidity, ventilation regime, etc.) must be known as it impacts the boundary condition at the drift wall.Developing a comprehensive, physically based seepage model that covers all scales discussed above would require a large amount of characterization data that are difficult or practically impossible to measure in the field. Moreover, a suite of model assumptions would have to be made to relate fracture and surface properties to hydrogeologic model parameters.Finally, the spatial and temporal resolution of a numerical model necessary to accurately and explicitly ca...

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Permeability tensor of three‐dimensional fractured porous rock and a comparison to trace map predictions

2014

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The reduction from three‐ to two‐dimensional analysis of the permeability of a fractured rock mass introduces errors in both the magnitude and direction of principal permeabilities. This error is numerically quantified for porous rock by comparing the equivalent permeability of three‐dimensional fracture networks with the values computed on arbitrarily extracted planar trace maps. A method to compute the full permeability tensor of three‐dimensional discrete fracture and matrix models is described. The method is based on the element‐wise averaging of pressure and flux, obtained from a finite element solution to the Laplace problem, and is validated against analytical expressions for periodic anisotropic porous media. For isotropic networks of power law size‐distributed fractures with length‐correlated aperture, two‐dimensional cut planes are shown to underestimate the magnitude of permeability by up to 3 orders of magnitude near the percolation threshold, approaching an average factor of deviation of 3 with increasing fracture density. At low‐fracture densities, percolation may occur in three dimensions but not in any of the two‐dimensional cut planes. Anisotropy of the equivalent permeability tensor varies accordingly and is more pronounced in two‐dimensional extractions. These results confirm that two‐dimensional analysis cannot be directly used as an approximation of three‐dimensional equivalent permeability. However, an alternative expression of the excluded area relates trace map fracture density to an equivalent three‐dimensional fracture density, yielding comparable minimum and maximum permeability. This formulation can be used to approximate three‐dimensional flow properties in cases where only two‐dimensional analysis is available.

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A site-scale model for fluid and heat flow in the unsaturated zone of Yucca Mountain, Nevada

Cited by 108 publications

References 21 publications

A mountain-scale thermal–hydrologic model for simulating fluid flow and heat transfer in unsaturated fractured rock

A mountain-scale thermal–hydrologic model for simulating fluid flow and heat transfer in unsaturated fractured rock

Inverse and predictive modeling of seepage into underground openings

Permeability tensor of three‐dimensional fractured porous rock and a comparison to trace map predictions

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