[en] Water infiltrating down a fracture in unsaturated rock experiences complex fluid-flow and heat-transfer phenomena when entering above-boiling rock temperature regions. Such conditions are expected, for example, after emplacement of heat-generating nuclear waste in underground repositories. A new, efficient semi-analytical method is proposed in this paper that simulates the flow processes of infiltration events subject to vigorous boiling from the adjacent hot rock. It is assumed that liquid flow forms in localized preferential flow paths, and that infiltration events are typically short in duration but large in magnitude relative to the average net infiltration. The new solution scheme is applied to several test cases studying sensitivity to a variety of input parameters. Sample simulations are performed for conditions representative of the potential nuclear waste repository at Yucca Mountain, Nevada. A characteristic parameter is introduced that provides a quick estimate of the relative significance of boiling at a given location of interest

[en] This report describes the code TH(₎PULSE developed at the Ernest Orlando Lawrence Berkeley National Laboratory (Berkeley Lab). The code handles gravity-driven flow of episodic infiltration events entering above-boiling rock-temperature regions. Such temperature conditions are expected, for example, after emplacement of heat-generating nuclear waste in underground repositories. Complex fluid-flow and heat-transfer phenomena occur, as the infiltrating water is subject to vigorous boiling from the hot rock. A new efficient semi-analytical method is presented herein that simulates such phenomena. It is assumed that flow forms in localized preferential flow paths (referred to as ''fingers''). The first section of this report gives the conceptual and mathematical background for the solution scheme. The second section is a user's manual for TH(₎PULSE, providing all information required to run the code, including a detailed description of the input and output files. In the third section, the new solution scheme is applied to several test cases. Sample simulations are performed for conditions representative of the potential nuclear waste repository at Yucca Mountain, Nevada. A brief summary is given in Section 4

[en] This paper describes numerical prediction of the coupled thermal-hydrological processes (TH) in the vicinity of waste emplacement drifts during the heating phase of the proposed geologic repository for nuclear waste at Yucca Mountain, Nevada. Heating of rock water to above-boiling conditions induces water saturation changes and perturbed water fluxes that affect the potential of water seepage into drifts. In addition to the capillary barrier at the rock-drift interface--independent of the thermal conditions--a second barrier exists to downward percolation at above-boiling conditions. This barrier is caused by vaporization of water in the fractured rock overlying the repository. A TOUGH2 simulation model was developed to analyze the combined effect of these two barriers; it accounts for all relevant TH processes in response to heating, while incorporating the capillary barrier condition at the drift wall. Model results are presented for a variety of simulation cases

[en] Predicting the amount of water that may seep into waste emplacement drifts is important for assessing the performance of the proposed geologic repository for high-level radioactive waste at Yucca Mountain, Nevada. The repository would be located in thick, partially saturated fractured tuff that will be heated to above-boiling temperatures as a result of heat generation from the decay of nuclear waste. Since infiltrating water will be subject to vigorous boiling for a significant time period, the superheated rock zone (i.e., rock temperature above the boiling point of water) can form an effective vaporization barrier that reduces the possibility of water arrival at emplacement drifts. In this paper, we analyze the behavior of episodic preferential flow events that penetrate the hot fractured rock, evaluate the impact of such flow behavior on the effectiveness of the vaporization barrier, and discuss the implications for the performance assessment of the repository. A semi-analytical solution is utilized to determine the complex flow processes in the hot rock environment. The solution is applied at several discrete times after emplacement, covering the time period of strongly elevated temperatures at Yucca Mountain

[en] Prediction of the amount of water that may seep into the waste emplacement drifts is an important aspect of assessing the performance of the proposed geologic nuclear waste repository at Yucca Mountain, Nevada. The repository is to be located in thick, partially saturated fractured tuff that will be heated to above-boiling temperatures as a result of heat generation from the decay of nuclear waste. Since water percolating down towards the repository will be subject to vigorous boiling for a significant time period, the superheated rock zone (i.e., rock temperature above the boiling point of water) can form an effective vaporization barrier that reduces the possibility of water arrival at emplacement drifts. In this paper, we analyze the behavior of episodic preferential flow events that penetrate the hot fractured rock, and we evaluate the impact of such flow behavior on the effectiveness of the vaporization barrier

[en] A general approach is presented here which allows estimation of field-scale thermal properties of unsaturated rock using temperature data collected from in situ heater tests. The approach developed here is used to determine the thermal conductivities of the unsaturated host rock of the Drift Scale Test (DST) at Yucca Mountain, Nevada. The DST was designed to obtain thermal, hydrological, mechanical, and chemical (THMC)data in the unsaturated fractured rock of Yucca Mountain. Sophisticated numerical models have been developed to analyze these THMC data. However, though the objective of those models was to analyze 'field-scale' (of the order of tens-of-meters) THMC data, thermal conductivities measured from 'laboratory-scale' core samples have been used as input parameters. While, in the absence of a better alternative, using laboratory-scale thermal conductivity values in field-scale models can be justified, such applications introduce uncertainties in the outcome of the models. The temperature data collected from the DST provides a unique opportunity to resolve some of these uncertainties. These temperature data can be used to estimate the thermal conductivity of the DST host rock and, given the large volume of rock affected by heating at the DST, such an estimate will be a more reliable effective thermal conductivity value for field scale application. In this paper, thus, temperature data from the DST are used to develop an estimate of the field-scale thermal conductivity values of the unsaturated host rock of the DST. An analytical solution is developed for the temperature rise in the host rock of the DST; and using a nonlinear fitting routine, a best-fit estimate of field-scale thermal conductivity for the DST host rock is obtained. Temperature data from the DST show evidence of two distinct thermal regimes: a zone below boiling (wet) and a zone above boiling (dry). Estimates of thermal conductivity for both the wet and dry zones are obtained in this paper. Sensitivity of these estimates to the input heating power of the DST is also investigated in this paper. These estimated thermal conductivity values are compared with core measurements and those estimated from geostatistical simulations. Note that the approach presented here is applicable to other host rock and heater test settings, provided suitable modifications are made in the analytical solution to account for differences in test geometry

[en] The calculations presented in this report are performed to obtain seepage rates into drift and boreholes for two alternative designs of drift and waste emplacement at Yucca Mountain. The two designs are defined according to the Scope of Work 14012021M1, activity 399621, drafted October 6, 1998, and further refined in a conference telephone call on October 13, 1998, between Mark Balady, Jim Blink, Rob Howard and Chin-Fu Tsang. The 2 designs considered are: (1) Design A--Horizontal boreholes 1.0 m in diameter on both sides of the drift, with each borehole 8 m long and inclined to the drift axis by 30 degrees. The pillar between boreholes, measured parallel to the drift axis, is 3.3 m. In the current calculations, a simplified model of an isolated horizontal borehole 8 m long will be simulated. The horizontal borehole will be located in a heterogeneous fracture continuum representing the repository layer. Three different realizations will be taken from the heterogeneous field, representing three different locations in the rock. Seepage for each realization is calculated as a function of the percolation flux. Design B--Vertical boreholes, 1.0 m in diameter and 8.0 m deep, drilled from the bottom of an excavated 8.0 m diameter drift. Again, the drift with the vertical borehole will be assumed to be located in a heterogeneous fracture continuum, representing the rock at the repository horizon. Two realizations are considered, and seepage is calculated for the 8-m drift with and without the vertical 1-m borehole at its bottom

[en] Dual-continuum models have been widely used in modeling flow and transport in fractured porous rocks. Among many other applications, dual-continuum approaches were utilized in predictive models of the thermal-hydrological conditions near emplacement tunnels (drifts) at Yucca Mountain, Nevada, the proposed site for a radioactive waste repository in the U.S. In unsaturated formations such as those at Yucca Mountain, the magnitude of mass and heat exchange between the two continua fracture network and matrix is largely dependent on the flow characteristics in the fractures, because Channelized finger-type flow strongly reduces the interface area between the matrix surfaces and the flowing liquid. This effect may have important implications, for example, during the time period that the fractured rock near the repository drifts would be heated above the boiling point of water. Depending on the magnitude of heat transfer from the matrix, water percolating down the fractures will either boil off in the hot rock region above drifts or may penetrate all the way to the drift walls and possibly seep into the open cavities. In this paper, we describe a sensitivity analysis using a variety of approaches to treat fracture-matrix interaction in a three-dimensional dual-continuum setting. Our simulation example is a laboratory heater experiment described in the literature that provides evidence of rapid water flow in fractures, leading to drift seepage despite above-boiling conditions in the adjacent fractured rock. The experimental finding can only be reproduced when the interface area for heat transfer between the matrix and fracture continua is reduced to account for flow channeling

[en] The paper examines the pressure increase resulting from injection of CO2 into a 1D radial system with closed boundaries. The finding is that unacceptably high pressures are obtained when only 1% or less of the pore volume is occupied by injected CO2. These results are used to make the general conclusion that large-scale CCS is not feasible.

[en] The Single Heater Test (SHT) is one of two in-situ thermal tests included in the site characterization program for the potential underground nuclear waste repository at Yucca Mountain. The heating phase of the SHT started in August 1996, and was completed in May 1997 after 9 months of heating. The coupled processes in the unsaturated fractured rock mass around the heater were monitored by numerous sensors for thermal, hydrological, mechanical and chemical data. In addition to passive monitoring, active testing of the rock mass moisture content was performed using geophysical methods and air injection testing. The extensive data set available from this test gives a unique opportunity to improve the understanding of the thermal-hydrological situation in the natural setting of the repository rocks. The present paper focuses on the 3-D numerical simulation of the thermal-hydrological processes in the SHT using TOUGH2. In the comparative analysis, they are particularly interested in the accuracy of different fracture-matrix-interaction concepts such as the Effective Continuum (ECM), the Dual Continuum (DKM), and the Multiple Interacting Continua (MINC) method