Proposed Yucca Mountain Repository Research Articles

Expected dose and associated uncertainty and sensitivity analysis results for all scenario classes in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. The conceptual structure and organization of the 2008 YM PA is based on decomposing the analysis into the following scenario classes: nominal, early waste package failure, early drip shield failure, igneous intrusive, igneous eruptive, seismic ground motion, and seismic fault displacement. This presentation describes how results obtained for the individual scenario classes are brought together in the determination of expected dose to the reasonably maximally exposed individual (RMEI) specified by the NRC in the regulatory requirements for the YM repository and presents associated uncertainty and sensitivity analysis results. The following topics are addressed: (i) determination of expected dose to the RMEI from all scenario classes, (ii) expected dose and uncertainty in expected dose to the RMEI for 0 to 20,000yr, (iii) expected dose and uncertainty in expected dose to the RMEI from for 0 to 106yr, (iv) justification for the decomposition procedure used to estimate expected dose to the RMEI from all scenario classes, and (v) effectiveness of individual barrier systems in reducing releases from the repository and thus dose to the RMEI. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Expected dose and associated uncertainty and sensitivity analysis results for the human intrusion scenario in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes the determination of expected (mean) dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository resulting from an inadvertent drilling intrusion into the repository. The following topics are addressed: (i) assumed properties of an inadvertent drilling intrusion and the determination of the associated dose and expected (mean) dose to the RMEI, (ii) uncertainty and sensitivity analysis results for expected dose to the RMEI, and (iii) the numerical stability of the sampling-based procedure used to estimate expected (mean) dose to the RMEI. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Expected dose for the seismic scenario classes in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes the determination of expected dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository for the seismic ground motion scenario class and the seismic fault displacement scenario class in the 2008 YM PA. The following topics are addressed: (i) definition of the seismic scenario classes and the determination of dose and expected dose to the RMEI, (ii) properties of the seismic ground motion scenario class, (iii) expected dose and uncertainty in expected dose to the RMEI for the seismic ground motion scenario class from 0 to 20,000yr, (iv) expected dose and uncertainty in expected dose to the RMEI for the seismic ground motion scenario class from 0 to 106yr, (v) properties of the seismic fault displacement scenario class including expected dose and uncertainty in expected dose to the RMEI from 0 to 20,000yr and 0 to 106yr, (vi) expected dose and uncertainty in expected dose to the RMEI for the combined ground motion and seismic fault displacement scenario class, and (vii) probabilities associated with seismic scenario classes. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Uncertainty and sensitivity analysis for the igneous scenario classes in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes uncertainty and sensitivity analysis results for the igneous intrusive scenario class and the igneous eruptive scenario class obtained in the 2008 YM PA. The following topics are addressed for the igneous intrusive scenario class: (i) engineered barrier system conditions, (ii) release results for the engineered barrier system, unsaturated zone, and saturated zone, (iii) dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository, and (iv) expected dose to the RMEI. In addition, expected dose to the RMEI for the igneous eruptive scenario class is also considered. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Expected dose for the nominal scenario class in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes the determination of expected (mean) dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository for the nominal scenario class (i.e., under nominal or undisturbed conditions) in the 2008YM PA. The following topics are addressed: (i) properties of the nominal scenario class and the determination of dose and expected (mean) dose to the RMEI, (ii) uncertainty in dose and resultant expected (mean) dose to the RMEI, (iii) expected (mean) dose to the RMEI from individual radionuclides, and (iv) numerical stability of the sampling-based procedure used to estimate the expected (mean) dose to the RMEI. The present paper is part of a special issue of Reliability Engineering and System Safety devoted to the 2008YM PA; additional papers in the issue describe other aspects of the 2008YM PA.

Uncertainty and sensitivity analysis for the nominal scenario class in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes uncertainty and sensitivity analysis results for the nominal scenario class (i.e., for undisturbed conditions) obtained in the 2008 YM PA. The following topics are addressed: (i) uncertainty and sensitivity analysis procedures, (ii) drip shield and waste package failure, (iii) engineered barrier system conditions, (iv) radionuclide release results for the engineered barrier system, unsaturated zone, and saturated zone, and (v) dose to the reasonably maximally exposed individual specified in the NRC regulations for the YM repository. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Uncertainty and sensitivity analysis for the early failure scenario classes in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes uncertainty and sensitivity analysis results for the early waste package failure scenario class and the early drip shield failure scenario class obtained in the 2008 YM PA. The following topics are addressed: (i) engineered barrier system conditions, (ii) release results for the engineered barrier system, unsaturated zone, and saturated zone, (iii) dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository, and (iv) expected dose to the RMEI. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Expected dose for the igneous scenario classes in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes the determination of expected dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository for the igneous intrusive scenario class and the igneous eruptive scenario class in the 2008 YM PA. The following topics are addressed: (i) properties of the igneous scenario classes and the determination of dose and expected dose to the RMEI, (ii) expected dose and uncertainty in expected dose to the RMEI from the igneous intrusive scenario class, (iii) expected dose and uncertainty in expected dose to the RMEI from the igneous eruptive scenario class, (iv) expected dose and uncertainty in expected dose to the RMEI from the combined igneous intrusive and igneous eruptive scenario class, and (v) uncertainty in the occurrence of igneous scenario classes. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Expected dose for the early failure scenario classes in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes the determination of expected dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository for the early waste package (WP) failure scenario class and the early drip shield (DS) failure scenario class in the 2008 YM PA. The following topics are addressed: (i) properties of the early failure scenario classes and the determination of dose and expected dose the RMEI, (ii) expected dose and uncertainty in expected dose to the RMEI from the early WP failure scenario class, (iii) expected dose and uncertainty in expected dose to the RMEI from the early DS failure scenario class, (iv) expected dose and uncertainty in expected dose to the RMEI from the combined early WP and early DS failure scenario class with and without the inclusion of failures resulting from nominal processes, and (v) uncertainty in the occurrence of early failure scenario classes. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Assessment of compliance with ground water protection standards in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the U.S. Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes the assessment of compliance with ground water protection standards in the 2008 YM PA. The following topics are addressed: (i) regulatory background, (ii) analysis structure including characterization of uncertainty, and (iii) analysis results for each of the ground water protection standards. The present article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Conceptual structure and computational organization of the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the U.S. Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. This presentation describes the overall conceptual structure and computational organization of the 2008 performance assessment (PA) for the proposed YM repository carried out by the DOE in support of a licensing application to the U.S. Nuclear Regulatory Commission (NRC). The following topics are addressed: (i) regulatory background, (ii) the three basic entities underlying a PA, (iii) determination of expected, mean and median dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository, (iv) the relationship between probability, sets and scenario classes, (v) scenario classes and the characterization of aleatory uncertainty, (vi) scenario classes and the determination of expected dose to the RMEI, (vii) analysis decomposition, (viii) disjoint and nondisjoint scenario classes, (ix) scenario classes and the NRC’s YM review plan, (x) characterization of epistemic uncertainty, and (xi) adequacy of Latin hypercube sample size used in the propagation of epistemic uncertainty. This article is part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA and is intended as an introduction to following articles in the issue that provide additional analysis details and specific analysis results.

Uncertainty and sensitivity analysis for the seismic scenario classes in the 2008 performance assessment for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada

Extensive work has been carried out by the US Department of Energy (DOE) in the development of a proposed geologic repository at Yucca Mountain (YM), Nevada, for the disposal of high-level radioactive waste. In support of this development and an associated license application to the US Nuclear Regulatory Commission (NRC), the DOE completed an extensive performance assessment (PA) for the proposed YM repository in 2008. This presentation describes uncertainty and sensitivity analysis results for the seismic ground motion scenario class and the seismic fault displacement scenario class obtained in the 2008 YM PA. The following topics are addressed for the seismic ground motion scenario class: (i) engineered barrier system conditions; (ii) release results for the engineered barrier system, unsaturated zone, and saturated zone; (iii) dose to the reasonably maximally exposed individual (RMEI) specified in the NRC regulations for the YM repository; and (iv) expected dose to the RMEI. In addition, expected dose to the RMEI for the seismic fault displacement scenario class is also considered. The present article is the part of a special issue of Reliability Engineering and System Safety devoted to the 2008 YM PA; additional articles in the issue describe other aspects of the 2008 YM PA.

Uncertainty and variability of infiltration at Yucca Mountain: Part 1. Numerical model development

[1] The U.S. Nuclear Regulatory Commission investigated climate and infiltration at Yucca Mountain to (i) understand important controls and uncertainties influencing percolation through the unsaturated zone on multimillennial time scales and (ii) provide flux boundary conditions for up to 1 million years in performance assessment models of the proposed Yucca Mountain repository. This first part of a two-part series describes a procedure for abstracting the results from detailed numerical simulations of local-scale infiltration into a site-scale model considering uncertainty and variability in distributed net infiltration. Part 2 describes site-scale model results and corroboration. A detailed one-dimensional numerical model was used to estimate bare-soil net infiltration at the scales of hours and meters for 442 soil, bedrock, and climate combinations. The set of results are abstracted into three parametric response functions for decadal-average bare-soil infiltration given hydraulic and climatic parameters. The three abstractions describe deep soil, shallow soil over a coarser layer, and shallow soil over a finer layer. The site-scale model considers spatial variability and uncertainty of the input parameters on a 30 m grid, using the abstractions independently in each cell. Two additional abstractions account for overland flow and vegetation. The model uses Monte Carlo simulation, with all input parameters uncertain and spatially variable, to calculate the mean and standard deviation of net infiltration in each grid cell for selected climate states. Using abstractions rather than detailed simulations speeds calculation of infiltration realizations by many orders of magnitude relative to a detailed simulation.

Uncertainty and variability of infiltration at Yucca Mountain: Part 2. Model results and corroboration

[2] The U.S. Nuclear Regulatory Commission actively investigated climate and infiltration at Yucca Mountain for two decades to (i) understand important controls and uncertainties influencing percolation through the unsaturated zone on multimillennial time scales and (ii) provide flux boundary conditions for up to 1 million years in performance assessment models of the proposed Yucca Mountain repository. This second part of a two-part series describes site-scale model results for present and potential future conditions and confirmatory analyses for present-day conditions. At both the grid-cell and site-average scale, the calculated uncertainty distribution for net infiltration is approximately lognormal, and the coefficient of variation decreases with increasing net infiltration. Smaller relative but larger absolute responses to climate change occur where net infiltration is large. Comparisons of distributed model estimates with temperature and geochemical observations from the unsaturated zone suggest that average estimates are generally consistent but exhibit significant variability. An observed seepage event in the South Ramp of the Exploratory Studies Facility, combined with related subsurface observations across the site, suggests that subsurface spreading from zones of high infiltration to zones of low infiltration may occur in stratabound fractures, laterally extensive discontinuities, or at transitions between welded and nonwelded tuff units. Two conceptual models for unsaturated-zone flow each explain the subsurface observations, collectively providing bounding estimates for net infiltration. Model-predicted uncertainty distribution for decadal-average site-scale net infiltration is generally consistent with estimated percolation fluxes using the bounding hypotheses, suggesting that the model-calculated uncertainty is reasonably consistent with the uncertainty in interpreting site observations.

Performance Assessment for Geological Disposal of Graphite Waste Containing TRISO Particles

This paper presents a deterministic performance assessment for spent fuel from deep-burn modular high-temperature reactors (DBMHRs) in the proposed Yucca Mountain repository. Typical DBMHR designs utilize fuel elements manufactured from graphite. The fuel itself is made of TRISO particles containing the fissile material. The performance of the DBMHR spent fuel (DBSF) was evaluated in terms of the annual dose to the reasonably maximally exposed individual (RMEI) under various hydrogeological conditions. Part of this evaluation was an analysis of the graphite waste matrix and of the TRISO particles under repository conditions, the result of which indicates that the lifetime of the graphite matrix greatly exceeds that of the TRISO particles and that it is the graphite, not the TRISO particles, that serves to sequester the radionuclides within the fuel matrix. Under all 14 cases considered, DBSF is seen to comply with the annual dose standards set in Part 197 of Title 40 of the Code of Federal Regulations, for exposure via groundwater contamination under current climatic conditions. Parametric studies for the effect of waste matrix lifetime on annual dose received by the RMEI indicate that repository performance is sensitively linked to waste matrix durability because most radionuclides including actinides are likely to be released congruently with the graphite matrix.

Used Fuel Disposition Campaign – Objectives, Mission, Plans and Current Activities

ABSTRACTThe safe management and disposition of used nuclear fuel and/or high level nuclear waste is a fundamental aspect of the nuclear fuel cycle. The United States currently utilizes a once-through fuel cycle where used nuclear fuel is stored on-site in either wet pools or in dry storage systems with ultimate disposal in a deep mined geologic repository envisioned. However, a decision not to use the proposed Yucca Mountain Repository will result in longer interim storage at reactor sites than previously planned. In addition, alternatives to the once-through fuel cycle are being considered and a variety of options are being explored under the U.S. Department of Energy’s Fuel Cycle Technologies Program.These two factors lead to the need to develop a credible strategy for managing radioactive wastes from any future nuclear fuel cycle in order to provide acceptable disposition pathways for all wastes regardless of transmutation system technology, fuel reprocessing scheme(s), and/or the selected fuel cycle. These disposition paths will involve both the storing of radioactive material for some period of time and the ultimate disposal of radioactive waste.To address the challenges associated with waste management, the DOE Office of Nuclear Energy established the Used Fuel Disposition Campaign in the summer of 2009. The mission of the Used Fuel Disposition Campaign is to identify alternatives and conduct scientific research and technology development to enable storage, transportation, and disposal of used nuclear fuel and wastes generated by existing and future nuclear fuel cycles. The near-and long-term objectives of the Fuel Cycle Technologies Program and its’ Used Fuel Disposition Campaign are presented.

HISTORICAL DEVELOPMENT AND EVOLUTION OF EPRI'S POST-CLOSURE DOSE ASSESSMENT OF POTENTIAL RELEASES TO THE BIOSPHERE FROM THE PROPOSED HLW REPOSITORY AT YUCCA MOUNTAIN

This paper describes the development and evolution of the Electric Power Research Institute's (EPRI) post-closure dose assessment for potential releases of radionuclides from the proposed High Level Waste repository at Yucca Mountain. The starting point for this work was the 1995 publication of Technical Bases for Yucca Mountain Standards by the Commission on Geosciences, Environment and Resources of the National Research Council. This report proposed the development and application of an individual risk-based standard for releases from the repository to replace the existing one, which was based on radionuclide release limits. This in turn implied the development and application of methods to assess radiation doses to humans. Accordingly, EPRI produced a methodology for such dose assessment as part of its Total System Performance Assessment program for the proposed Yucca Mountain repository site. The methodology initially addressed releases via groundwater and then releases associated with extrusive igneous events. The methodology was updated and applied over the following years to take account of regulatory developments, changes in estimates of the source term to the biosphere, peer review through international model comparison exercises, new site generic data, and new data concerning conditions at the point of compliance in Amargosa Valley. The main outputs were Biosphere Dose Conversion Factors, which relate radionuclide levels in environmental media to the annual individual doses to a member of a hypothetical critical group and to the regulator-defined Reasonably Maximally Exposed Individual. Most recently, consideration has been given to uncertainty in the dose estimates based on a probabilistic analysis. The paper provides a perspective on the evolution of the dose assessments in response to the developments listed above.

Fuel Cycle Research and Development Program, Used Fuel Disposition Campaign Objective, Mission, Plans, and Activity Status

AbstractThe safe management and disposition of used nuclear fuel and/or high level nuclear waste is a fundamental aspect of the nuclear fuel cycle. The United States currently utilizes a once-through fuel cycle where used nuclear fuel is stored on-site in either wet pools or in dry storage systems with ultimate disposal in a deep mined geologic repository envisioned. However, a decision not to use the proposed Yucca Mountain Repository will result in longer interim storage at reactor sites than previously planned. In addition, alternatives to the once-through fuel cycle are being considered and a variety of options are being explored under the U.S. Department of Energy's Fuel Cycle Research and Development Program.These two factors lead to the need to develop a credible strategy for managing radioactive wastes from any future nuclear fuel cycle in order to provide acceptable disposition pathways for all wastes regardless of transmutation system technology, fuel reprocessing scheme(s), and/or the selected fuel cycle. These disposition paths will involve both the storing of radioactive material for some period of time and the ultimate disposal of radioactive waste.To address the challenges associated with waste management, the DOE Office of Nuclear Energy established the Used Fuel Disposition Campaign within its Fuel Cycle Research and Development Program in the summer of 2009. The mission of the Used Fuel Disposition Campaign is to identify alternatives and conduct scientific research and technology development to enable storage and disposal of used nuclear fuel and wastes generated by existing and future nuclear fuel cycles. The near-and long-term objectives of the Fuel Cycle Research and Development Program and it's Used Fuel Disposition Campaign are presented.

Modeling acid-gas generation from boiling chloride brines.

BackgroundThis study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate.ResultsSimple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150°C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimental data from other studies.ConclusionThe combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC) processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual and modeled distillation experiments do not represent expected conditions in an emplacement drift, but nevertheless illustrate the potential for acid-gas generation at moderate temperatures (<150°C).

Coupled In-Rock and In-Drift Hydrothermal Model Study for Yucca Mountain

A thermal-hydrologic natural-ventilation model is configured for simulating temperature, humidity, and condensate distributions in the coupled domains of the in-drift airspace and the near-field rock mass in the proposed Yucca Mountain repository. The multiphysics problem is solved with MULTIFLUX, in which a lumped-parameter computational fluid dynamics (CFD) model is iterated with TOUGH2. The iterative process ensures that consistent boundary conditions are used on the drift wall in both the CFD and the TOUGH2 model-elements. The CFD solution includes natural convection, conduction, and radiation for heat, as well as moisture convection and diffusion for moisture transport with half waste package-scale details in the drift. The TOUGH2 solution for the rock mass is generalized with the use of the Numerical Transport Code Functionalization technique in order to include both mountain-scale heat and moisture transport in the porous and fractured rock, and fine half waste package-scale details at the drift wall. The method provides fast convergence on a personal computer computational platform. Numerical examples and comparison with a TOUGH2-based integrated model are presented.