A Turbulent Transport Network Model in MULTIFLUX Coupled with TOUGH2

A new numerical method is described for the fully iterated, conjugate solution of two discrete submodels, involving (a) a transport network model for heat, moisture, and airflows in a high-permeability, air-filled cavity; and (b) a variably saturated fractured porous medium. The transport network submodel is an integrated-parameter, computational fluid dynamics solver, describing the thermal-hydrologic transport processes in the flow channel system of the cavity with laminar or turbulent flow and convective heat and mass transport, using MULTIFLUX. The porous medium submodel, using TOUGH2, is a solver for the heat and mass transport in the fractured rock mass. The new model solution extends the application fields of TOUGH2 by integrating it with turbulent flow and transport in a discrete flow network system. We present demonstrational results for a nuclear waste repository application at Yucca Mountain with the most realistic model assumptions and input parameters including the geometrical layout of the nuclear spent fuel and waste with variable heat load for the individual containers. The MULTIFLUX and TOUGH2 model elements are fully iterated, applying a programmed reprocessing of the Numerical Transport Code Functionalization model-element in an automated Outside Balance Iteration loop. The natural, convective airflow field and the heat and mass transport in a representative emplacement drift during postclosure are explicitly solved in the new model. The results demonstrate that the direction and magnitude of the air circulation patterns and all transport modes are strongly affected by the heat and moisture transport processes in the surrounding rock, justifying the need for a coupled, fully iterated model solution such as the one presented in the paper

Forecast of thermal-hydrological conditions and air injection test results of the single heater test at Yucca Mountain

The heater in the Single Heater Test (SHT) in alcove 5 of the Exploratory Studies Facility (ESF) was turned on August 26, 1996. A large number of sensors are installed in the various instrumented boreholes to monitor the coupled thermal-hydrological-mechanical-chemical responses of the rock mass to the heat generated in the single heater. In this report the authors present the results of the modeling of both the heating and cooling phases of the Single Heater Test (SHT), with focus on the thermal-hydrological aspect of the coupled processes. Also in this report, the authors present simulations of air injection tests will be performed at different stages of the heating and cooling phase of the SHT

Sensitivity analysis for joint inversion of ground-penetratingradar and thermal-hydrological data from a large-scale underground heatertest

We describe a joint inversion approach that combinesgeophysical and thermal-hydrological data for the estimation of (1)thermal-hydrological parameters (such as permeability, porosity, thermalconductivity, and parameters of the capillary pressure and relativepermeability functions) that are necessary for predicting the flow offluids and heat in fractured porous media, and (2) parameters of thepetrophysical function that relates water saturation, porosity andtemperature to the dielectric constant. The approach incorporates thecoupled simulation of nonisothermal multiphase fluid flow andground-penetrating radar (GPR) travel times within an optimizationframework. We discuss application of the approach to a large-scale insitu heater test which was conducted at Yucca Mountain, Nevada, to betterunderstand the coupled thermal, hydrological, mechanical, and chemicalprocesses that may occur in the fractured rock mass around a geologicrepository for high-level radioactive waste. We provide a description ofthe time-lapse geophysical data (i.e., cross-borehole ground-penetratingradar) and thermal-hydrological data (i.e., temperature and water contentdata) collected before and during the four-year heating phase of thetest, and analyze the sensitivity of the most relevantthermal-hydrological and petrophysical parameters to the available data.To demonstrate feasibility of the approach, and as a first step towardcomprehensive inversion of the heater test data, we apply the approach toestimate one parameter, the permeability of the rock matrix

Comparative Simulation Syudy of Coupled THM Processes near Back-Filled and Open-Drift Nuclear Waste Repositories in Task D of International DECOVALEX Project

As part of the ongoing international DECOVALEX project, four research teams used five different models to simulate coupled thermal, hydrological, and mechanical (THM) processes near underground waste emplacement drifts. The simulations were conducted for two generic repository types, one with open and the other with back-filled repository drifts, under higher and lower post-closure temperature, respectively. In the completed first model inception phase of the project, a good agreement was achieved between the research teams in calculating THM responses for both repository types, although some disagreement in hydrological responses are currently being resolved. Good agreement in the basic thermal-mechanical responses was also achieved for both repository types, even though some teams used relatively simplified thermal-elastic heat-conduction models that neglect complex near-field thermal-hydrological processes. The good agreement between the complex and simplified process models indicates that the basic thermal-mechanical responses can be predicted with a relatively high confidence level

Summary Report on CO{sub 2} Geologic Sequestration & Water Resources Workshop

The United States Environmental Protection Agency (EPA) and Lawrence Berkeley National Laboratory (LBNL) jointly hosted a workshop on “CO{sub 2} Geologic Sequestration and Water Resources” in Berkeley, June 1–2, 2011. The focus of the workshop was to evaluate R&D needs related to geological storage of CO{sub 2} and potential impacts on water resources. The objectives were to assess the current status of R&D, to identify key knowledge gaps, and to define specific research areas with relevance to EPA’s mission. About 70 experts from EPA, the DOE National Laboratories, industry, and academia came to Berkeley for two days of intensive discussions. Participants were split into four breakout session groups organized around the following themes: Water Quality and Impact Assessment/Risk Prediction; Modeling and Mapping of Area of Potential Impact; Monitoring and Mitigation; Wells as Leakage Pathways. In each breakout group, participants identified and addressed several key science issues. All groups developed lists of specific research needs; some groups prioritized them, others developed short-term vs. long-term recommendations for research directions. Several crosscutting issues came up. Most participants agreed that the risk of CO{sub 2} leakage from sequestration sites that are properly selected and monitored is expected to be low. However, it also became clear that more work needs to be done to be able to predict and detect potential environmental impacts of CO{sub 2} storage in cases where the storage formation may not provide for perfect containment and leakage of CO{sub 2}–brine might occur