18 research outputs found
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Models and methods summary for the FEHMN application
This models and methods summary provides a detailed description of the mathematical models and numerical methods employed by the finite element heat and mass tranfer code (FEHMN) application
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Calibration of the Site-Scale Saturated Zone Flow Model
The purpose of the flow calibration analysis work is to provide Performance Assessment (PA) with the calibrated site-scale saturated zone (SZ) flow model that will be used to make radionuclide transport calculations. As such, it is one of the most important models developed in the Yucca Mountain project. This model will be a culmination of much of our knowledge of the SZ flow system. The objective of this study is to provide a defensible site-scale SZ flow and transport model that can be used for assessing total system performance. A defensible model would include geologic and hydrologic data that are used to form the hydrogeologic framework model; also, it would include hydrochemical information to infer transport pathways, in-situ permeability measurements, and water level and head measurements. In addition, the model should include information on major model sensitivities. Especially important are those that affect calibration, the direction of transport pathways, and travel times. Finally, if warranted, alternative calibrations representing different conceptual models should be included. To obtain a defensible model, all available data should be used (or at least considered) to obtain a calibrated model. The site-scale SZ model was calibrated using measured and model-generated water levels and hydraulic head data, specific discharge calculations, and flux comparisons along several of the boundaries. Model validity was established by comparing model-generated permeabilities with the permeability data from field and laboratory tests; by comparing fluid pathlines obtained from the SZ flow model with those inferred from hydrochemical data; and by comparing the upward gradient generated with the model with that observed in the field. This analysis is governed by the Office of Civilian Radioactive Waste Management (OCRWM) Analysis and Modeling Report (AMR) Development Plan ''Calibration of the Site-Scale Saturated Zone Flow Model'' (CRWMS M&O 1999a)
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Evaluation of the second hot dry rock geothermal energy reservoir: results of Phase I, Run Segment 5
The results of a long-term (286 day) flow test of the second hot dry rock reservoir at the Fenton Hill field site are presented. This second reservoir was created by fracturing an interval of granitic rock located at a depth of 2.93 km (9620 ft) in the same wellbore pair used in the creation of the first, smaller reservoir. The new fracture system has a vertical extent of at least 320 m (1050 ft), suggesting that the combined heat-transfer area of the old and new fracture systems is much greater than that of the old system. The virgin rock temperature at the bottom of the deeper interval was 197/sup 0/C (386/sup 0/F). Downhole measurements of the water temperature at the reservoir outlet, as well as temperatures inferred from geothermometry, showed that the thermal drawdown of the reservoir was about 8/sup 0/C, and preliminary estimates indicate that the minimum effective heat-transfer area of the new reservoir is 45,000 m/sup 2/ (480,000 ft/sup 2/), which is six times larger than the first reservoir
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Some results of a long-term flow test of a hot-dry-rock reservoir
Results from a 286-day flow test of a new hot dry rock reservoir created at Fenton Hill in the Jemez Mountains in northwest New Mexico are presented. The reservoir was created by fracturing an interval of granitic rock at a depth of 2.93 km (9620 ft). The system was formed from a recemented wellbore pair used to create the first hot dry rock reservoir. The undisturbed rock temperature at the bottom of the new reservoir was 197/sup 0/C. With a nominal outlet flow of 5.7 x 10/sup -3/ m/sup 3//s (95 gpm), the reservoir showed a thermal drawdown of about 8/sup 0/C. A preliminary estimate of the heat transfer area is 45,000 m/sup 3/ (480,000 ft/sup 2/). The water loss rate to the formation was 4.6 x 10/sup -4/ m/sup 3//s (7 gpm). The flow impedance was 1.6 GPa s/M/sup 3/ (15 psi/gpm). The results of the flow test show that in comparison with the earlier smaller hot dry rock system at the same site, the large increase in heat transfer area was accompanied by only a small increase in the water loss and with the impedance staying essentially constant
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Users Manual for the FEHMN application
The user`s manual documents the use of the Yucca Mountain Site Characterization Projects Finite element heat and mass transfer code (FEHMN) application. The manual covers: Program considerations, data files, input data, output, system interface, and examples
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Economics of a conceptual 75 MW Hot Dry Rock geothermal electric power station
Man-made, Hot Dry Rock (HDR) geothermal energy reservoirs have been investigated for over ten years. As early as 1977 a research-sized reservoir was created at a depth of 2.9 km near the Valles Caldera, a dormant volcanic complex in New Mexico, by connecting two wells with hydraulic fractures. Thermal power was generated at rates of up to 5 MW(t) and the reservoir was operated for nearly a year with a thermal drawdown less than 10/sup 0/C. A small 60kW(e) electrical generation unit using a binary cycle (hot geothermal water and a low boiling point organic fluid, R-114) was operated. Interest is now worldwide with field research being conducted at sites near Le Mayet de Montagne, France; Falkenberg and Urach, Federal Republic of Germany; Yakedake, Japan; and Rosemanowes quarry in Cornwall, United Kingdom. To assess the commercial viability of future HDR electrical generating stations, an economic modeling study was conducted for a conceptual 75 MW(e) generating station operating at conditions similar to those prevailing at the New Mexico HDR site. The reservoir required for 75 MW(e), equivalent to 550 MW of thermal energy, uses at least 9 wells drilled to 4.3 km and the temperature of the water produced should average 230/sup 0/C. Thermodynamic considerations indicate that a binary cycle should result in optimum electricity generation and the best organic fluids are refrigerants R-22, R-32, R-115 or R-600a (Isobutane). The break-even bus bar cost of HDR electricity was computed by the levelized life-cycle method, and found to be competitive with most alternative electric power stations in the US
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A New Ghost-Node Method for Linking Different Gound-Water Models and Initial Investigation of Heterogeneity and Nonmatching Grids
A method was developed for flexible and robust grid refinement of ground-water models that use different types of numerical methods. One application is the use of a child (local scale) finite-element model to solve for local heat and (or) solute transport by using boundary conditions derived from a parent (regional scale) finite-difference model. This paper presents a new iterative method that uses ghost nodes to link different models. The models are solved iteratively based on the shared-node method for coupling a parent model that encloses a child model described by Steffen W. Mehl and Mary C. Hill in 2002. Ghost nodes are located within the parent model along a line or plane that passes through nodes of parent cells along the model interface. The links between the parent and child models-specified-flow boundary conditions for the parent model and specified-head boundary conditions for the child model-are achieved by using heads at ghost nodes and flows through the material in model cells between the child and ghost nodes. The ghost-node method can be used to link nonmatching grids that occur when parent-model cell edgedfaces do not coincide with child-model cell edgedfaces and the parent model nodes do not coincide with a ghost node. The ghost-node method is tested for two- and three-dimensional systems that are either homogeneous or moderately heterogeneous, and for matching and nonmatching grids. The coupled models are simulated by using the finite-difference MODFLOW and finite-element FEHM models for the parent and child grids, respectively. Results for models of two-dimensional, homogeneous systems having matching or nonmatching grids indicate that the new method is as accurate as coupling using shared-node method of two MODFLOW models having matching grids. The three-dimensional systems exhibit similar errors to the two-dimensional homogeneous systems with both matching and nonmatching grids
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A Coupled Modeling System to Simulate Water Resources in the Rio Grande Basin
Limited availability of fresh water in arid and semi-arid regions of the world requires prudent management strategies from accurate, science-based assessments. These assessments demand a thorough understanding of the hydrologic cycle over long time periods within the individual water-sheds that comprise large river basins. Measurement and simulation of the hydrologic cycle is a tremendous challenge, involving a coupling between global to regional-scale atmospheric precipitation processes with regional to local-scale land surface and subsurface water transport. Los Alamos National Laboratory is developing a detailed modeling system of the hydrologic cycle and applying this tool at high resolution to assess the water balance within the upper Rio Grande river basin. The Rio Grande is a prime example of a river system in a semiarid environment, with a high demand from agricultural, industrial, recreational, and municipal interests for its water supply. Within this river basin, groundwater supplies often augment surface water. With increasing growth projected throughout the river basin, however, these multiple water users have the potential to significantly deplete groundwater resources, thereby increasing the dependence on surface water resources