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Title: The Influence of Proposed Repository Thermal Load on MultiphaseFlow and Heat Transfer in the Unsaturated Zone of Yucca Mountain

Abstract

This paper investigates the impact of proposed repositorythermal-loading on mountain-scale flow and heat transfer in theunsaturated fractured rock of Yucca Mountain, Nevada. In this context, amodel has been developed to study the coupled thermal-hydrological (TH)processes at the scale of the entire Yucca Mountain. This mountain-scaleTH model implements the current geological framework and hydrogeologicalconceptual models, and incorporates the latest rock thermal andhydrological properties. The TH model consists of a two-dimensionalnorth-south vertical cross section across the entire unsaturated zonemodel domain and uses refined meshes near and around the proposedrepository block, based on the current repository design, drift layout,thermal loading scenario, and estimated current and future climaticconditions. The model simulations provide insights into thermallyaffected liquid saturation, gas- and liquid-phase fluxes, and elevatedwater and rock temperature, which in turn allow modelers to predict thechanges in water flux driven by evaporation/condensation processes, anddrainage between drifts.

Authors:
; ; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE Office of Civilian Radioactive WasteManagement
OSTI Identifier:
919751
Report Number(s):
LBNL-59783
R&D Project: G71780; TRN: US0806479
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Conference
Resource Relation:
Conference: 2006 International High Level Radioactive WasteManagement Conference, Las Vegas, Nevada, 30 April - 4 May2006
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; CROSS SECTIONS; DESIGN; DRAINAGE; HEAT TRANSFER; MULTIPHASE FLOW; NEVADA; RADIOACTIVE WASTE MANAGEMENT; SATURATION; WATER; YUCCA MOUNTAIN

Citation Formats

Wu, Y.-S., Mukhopadhyay, Sumit, Zhang, Keni, and Bodvarsson, G.S. The Influence of Proposed Repository Thermal Load on MultiphaseFlow and Heat Transfer in the Unsaturated Zone of Yucca Mountain. United States: N. p., 2006. Web.
Wu, Y.-S., Mukhopadhyay, Sumit, Zhang, Keni, & Bodvarsson, G.S. The Influence of Proposed Repository Thermal Load on MultiphaseFlow and Heat Transfer in the Unsaturated Zone of Yucca Mountain. United States.
Wu, Y.-S., Mukhopadhyay, Sumit, Zhang, Keni, and Bodvarsson, G.S. Tue . "The Influence of Proposed Repository Thermal Load on MultiphaseFlow and Heat Transfer in the Unsaturated Zone of Yucca Mountain". United States. doi:. https://www.osti.gov/servlets/purl/919751.
@article{osti_919751,
title = {The Influence of Proposed Repository Thermal Load on MultiphaseFlow and Heat Transfer in the Unsaturated Zone of Yucca Mountain},
author = {Wu, Y.-S. and Mukhopadhyay, Sumit and Zhang, Keni and Bodvarsson, G.S.},
abstractNote = {This paper investigates the impact of proposed repositorythermal-loading on mountain-scale flow and heat transfer in theunsaturated fractured rock of Yucca Mountain, Nevada. In this context, amodel has been developed to study the coupled thermal-hydrological (TH)processes at the scale of the entire Yucca Mountain. This mountain-scaleTH model implements the current geological framework and hydrogeologicalconceptual models, and incorporates the latest rock thermal andhydrological properties. The TH model consists of a two-dimensionalnorth-south vertical cross section across the entire unsaturated zonemodel domain and uses refined meshes near and around the proposedrepository block, based on the current repository design, drift layout,thermal loading scenario, and estimated current and future climaticconditions. The model simulations provide insights into thermallyaffected liquid saturation, gas- and liquid-phase fluxes, and elevatedwater and rock temperature, which in turn allow modelers to predict thechanges in water flux driven by evaporation/condensation processes, anddrainage between drifts.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Feb 28 00:00:00 EST 2006},
month = {Tue Feb 28 00:00:00 EST 2006}
}

Conference:
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  • This paper investigates the impact of proposed repository thermal-loading on mountain-scale flow and heat transfer in the unsaturated fractured rock of Yucca Mountain, Nevada. In this context, a model has been developed to study the coupled thermal-hydrological (TH) processes at the scale of the entire Yucca Mountain. This mountain-scale TH model implements the current geological framework and hydrogeological conceptual models, and incorporates the latest rock thermal and hydrological properties. The TH model consists of a two-dimensional north-south vertical cross section across the entire unsaturated zone model domain and uses refined meshes near and around the proposed repository block, based onmore » the current repository design, drift layout, thermal loading scenario, and estimated current and future climatic conditions. The model simulations provide insights into thermally affected liquid saturation, gas- and liquid-phase fluxes, and elevated water and rock temperature, which in turn allow modelers to predict the changes in water flux driven by evaporation/condensation processes, and drainage between drifts.« less
  • The 500-700 m thick Yucca Mountain unsaturated zone (UZ) is under extensive investigation as a subsurface repository for the permanent disposal of high-level nuclear wastes. The site characterization has been mostly carried out for analyzing unsaturated flow and radionuclide transport under ambient, isothermal conditions. However, significant research effort has also been devoted to understand the nature of flow and transport processes under non-isothermal conditions. In particular, substantial repository heating from radioactive waste decay has motivated investigations of the coupled thermo-hydrologic (TH) behavior of the UZ under repository heating and its potential impact on repository performance. Significant progress has been mademore » in quantitative coupled TH studies in the last decade. Despite the significant advances made so far in modeling and understanding TH processes, the previous studies have been in general limited to modeling in 1-D and 2-D (instead of the full 3-D representation), and/or small spatial and temporal scale analysis. In addition to these limited modeling exercises, multidimensional modeling has been carried out for large-scale (at the scale of the entire mountain) TH analyses. However, these previous large, mountain-scale TH models utilized the effective continuum model (ECM), rather than the more rigorous dual-continuum model (DKM). This is primarily due to numerical difficulties and computational burden involved with simulating highly non-linear coupled two-phase fluid flow and heat transfer in the fractured unsaturated rock with over one hundred thousand grid blocks (required for mountain-scale simulations). In general, 3-D, mountain-scale, DKM investigations of coupled TH processes in the fractured rock of Yucca Mountain is lacking in the literature. In parallel to the TH modeling studies, significant progress has also been made in site characterization of UZ flow and transport processes. For example, field and modeling studies conducted over the past few years have updated and enhanced our understanding, and revealed many new insights into how the UZ system works under the natural, ambient conditions. As a result, both geological and conceptual models have been updated by model calibration and verification efforts, and fracture-matrix properties and model parameters are better estimated. In addition, the repository design and drift layout plan, which are different from the ones used in previous modeling studies, are also revised. These advances in site characterization, data collection and parameter estimates motivate this work for updated TH modeling efforts. This paper presents the results of our latest effort to develop a representative 3-D, mountain-scale TH model to investigate the coupled TH processes for the repository under thermal load. More specifically, the TH model implements the current geological framework and hydrogeological UZ flow conceptual models, and incorporates the most updated, best-estimated input parameters from the 3-D model calibration (Wu et. al., 2003). Using the more rigorous DKM approach, the TH model consists of (1) a 2-D north-south cross section modeling studies with refined meshes near and around the repository block and (2) a full 3-D representation of the repository and UZ system, which explicitly includes every waste emplacement drift of the repository. For better description of the ambient geothermal condition of the UZ system, the TH model is first calibrated against measured borehole temperature data. The temperature calibration provides the needed surface and water table boundary and initial conditions for the TH model.« less
  • This paper presents a numerical study on the response of the unsaturated zone (UZ) system of Yucca Mountain to heat generated from decaying radioactive wastes emplaced at the proposed repository. The modeling study is based on the current thermal-hydrological (TH) mountain-scale model, which uses a locally refined 2D north-south cross section and dual-permeability numerical approach. The model provides a prediction of the mountain-scale TH response under the thermal-load scenario of 1.45 kW/m, while accounting for future climatic changes and the effects of drift ventilation. The TH simulation results show that ventilation of the repository drifts has a large impact onmore » thermal-hydrologic regimes and moisture-flow conditions at the repository. In both cases, with and without ventilation, the TH model predicts dry or reduced liquid saturation near the drifts for over 1,000 years, during which liquid flux through the drifts is reduced to either zero or less than the ambient flux. Without ventilation, the model predicts higher temperatures at the repository, but no major moisture redistribution in the UZ except in the areas very near the heated drifts.« less
  • The design of the potential Yucca Mountain repository is subject to many thermal goals related to the compliance of the site with federal regulations. This report summarizes a series of sensitivity studies that determined the expected temperatures near the potential repository. These sensitivity studies were used to establish an efficient loading scheme for the spent fuel canisters and a maximum areal power density based strictly on thermal goals. Given the current knowledge of the site, a design-basis areal power density of 80 kW/acre can be justified based on thermal goals only. Further analyses to investigate the impacts of this design-basismore » APD on mechanical and operational aspects of the potential repository must be undertaken before a final decision is made.« less
  • The MultiScale ThermoHydrologic Model (MSTHM) predicts thermohydrologic (TH) conditions in emplacement drifts and the adjoining host rock throughout the proposed nuclear-waste repository at Yucca Mountain. The MSTHM is a computationally efficient approach that accounts for TH processes occurring at a scale of a few tens of centimeters around individual waste packages and emplacement drifts, and for heat flow at the multi-kilometer scale at Yucca Mountain. The modeling effort presented here is an early investigation of the repository and is simulated at a lower temperature mode and with a different panel loading than the repository currently being considered for license application.more » We present these recent lower temperature mode MSTHM simulations that address the influence of repository-scale thermal-conductivity heterogeneity and the influence of preclosure operational factors affecting thermal-loading conditions. We can now accommodate a complex repository layout with emplacement drifts lying in non-parallel planes using a superposition process that combines results from multiple mountain-scale submodels. This development, along with other improvements to the MSTHM, enables more rigorous analyses of preclosure operational factors. These improvements include the ability to (1) predict TH conditions on a drift-by-drift basis, (2) represent sequential emplacement of waste packages along the drifts, and (3) incorporate distance- and time-dependent heat-removal efficiency associated with drift ventilation. Alternative approaches to addressing repository-scale thermal-conductivity heterogeneity are investigated. We find that only one of the four MSTHM submodel types needs to incorporate thermal-conductivity heterogeneity. For a particular repository design, we find that the most influential parameters are (1) percolation-flux distribution, (2) thermal-conductivity heterogeneity within the host-rock units, (3) the sequencing of waste-package emplacement, and (4) the duration of the preclosure ventilation period.« less