Post-test Comparison of Thermal-mechanical Measurements Vs. Analyses for the In-Situ Single Heater Test, Yucca Mountain, Nevada

Journal of Contaminant Hydrology

Tsang

2003

A coupled thermal, hydrologic and mechanical (THM) analysis is conducted to evaluate the impact of coupled THM processes on the performance of a potential nuclear waste repository at Yucca Mountain, Nevada. The analysis considers changes in rock mass porosity, permeability, and capillary pressure caused by rock deformations during drift excavation, as well as those caused by thermo-mechanically induced rock deformations after emplacement of the heat-generating waste. The analysis consists of a detailed calibration of coupled hydraulic-mechanical rock mass properties against field experiments, followed by a prediction of the coupled thermal, hydrologic, and mechanical behavior around a potential repository drift. For the particular problem studied and parameters used, the analysis indicates that the stress-induced permeability changes will be within one order of magnitude and that these permeability changes do not significantly impact the overall flow pattern around the repository drift.

Section: Drift Wall Inelastic Behaviormentioning

confidence: 95%

mentioning

confidence: 99%

Analysis of thermal–hydrologic–mechanical behavior near an emplacement drift at Yucca Mountain

Journal of Contaminant Hydrology

Tsang

2003

“…These included three‐dimensional simulations of TH processes conducted by Lawrence Berkeley National Laboratory using the TOUGH2 code [ Birkholzer and Tsang , 1997, 2000] and by Lawrence Livermore National Laboratory using the NUFT code [ Buscheck et al , 1997]. Coupled TM processes were first simulated by the Sandia National Laboratories using the JAS3D code [ Francis et al , 1997; Sobolik et al , 1998, 1999] and by Lawrence Livermore National Laboratory using the 3‐DEC code [ Blair , 2001; Blair et al , 2001]. In the pretest prediction of coupled TM processes Francis et al [1997] applied a ubiquitously fractured continuum model approach that was based on previous experiences in modeling the SHT [ Sobolik et al , 1998].…”

Section: Development Of Conceptual Understanding and Modelsmentioning

confidence: 99%

“…Coupled TM processes were first simulated by the Sandia National Laboratories using the JAS3D code [ Francis et al , 1997; Sobolik et al , 1998, 1999] and by Lawrence Livermore National Laboratory using the 3‐DEC code [ Blair , 2001; Blair et al , 2001]. In the pretest prediction of coupled TM processes Francis et al [1997] applied a ubiquitously fractured continuum model approach that was based on previous experiences in modeling the SHT [ Sobolik et al , 1998]. A reasonably good agreement between simulated and measured displacements during the heating phase confirmed the appropriateness of the continuum approach.…”

Section: Development Of Conceptual Understanding and Modelsmentioning

confidence: 99%

Multiphysics processes in partially saturated fractured rock: Experiments and models from Yucca Mountain

Tsang

2012

Reviews of Geophysics

The site investigations at Yucca Mountain, Nevada, have provided us with an outstanding data set, one that has significantly advanced our knowledge of multiphysics processes in partially saturated fractured geological media. Such advancement was made possible, foremost, by substantial investments in multiyear field experiments that enabled the study of thermally driven multiphysics and testing of numerical models at a large spatial scale. The development of coupled‐process models within the project have resulted in a number of new, advanced multiphysics numerical models that are today applied over a wide range of geoscientific research and geoengineering applications. Using such models, the potential impact of thermal‐hydrological‐mechanical (THM) multiphysics processes over the long‐term (e.g., 10,000 years) could be predicted and bounded with some degree of confidence. The fact that the rock mass at Yucca Mountain is intensively fractured enabled continuum models to be used, although discontinuum models were also applied and are better suited for analyzing some issues, especially those related to predictions of rockfall within open excavations. The work showed that in situ tests (rather than small‐scale laboratory experiments alone) are essential for determining appropriate input parameters for multiphysics models of fractured rocks, especially related to parameters defining how permeability might evolve under changing stress and temperature. A significant laboratory test program at Yucca Mountain also made important contributions to the field of rock mechanics, showing a unique relation between porosity and mechanical properties, a time dependency of strength that is significant for long‐term excavation stability, a decreasing rock strength with sample size using very large core experiments, and a strong temperature dependency of the thermal expansion coefficient for temperatures up to 200°C. The analysis of in situ heater experiments showed that fracture closure/opening caused by changes in normal stress across fractures was the dominant mechanism for thermally induced changes in intrinsic fracture permeability during rock mass heating/cooling and that fracture shear dilation appears to be less significant. Significant effort was devoted to predicting the long‐term stability of underground excavations under (mechanical) strength degradation and seismic loading, perhaps one of the most challenging tasks within the project. We note that such long‐term strength degradation is actually an example of a chemically mediated process governed by underlying (microscopic) stress corrosion and chemical diffusion processes. In the Yucca Mountain Project, such chemically mediated mechanical changes were considered implicitly through model calibrations against laboratory and in situ heater experiments at temperatures anticipated to be experienced by the rock. A possible future research direction would be to simulate such processes mechanistically in a complete coupled THMC framework where C denotes chemical processes.

“…Coupled TM processes have been simulated by the Sandia National Laboratories using the JAS-3D code [18,191 and by the Lawrence Livermore National Laboratory using the 3-DEC code [20]. In a pre-test prediction of coupled TM processes at the DST, Francis et al [18, 191 applied a ubiquitously fractured continuum model approach that was also based on previous experiences in modeling the SHT [22]. The TM analyses of the DST and SHT, showed that rock-mass deformations in the Tptpmn unit were reasonably well captured with the continuum approach and linear-elastic or nonlinear-elastic mechanical model [ 19,20, and 321.…”

Section: Previous Coupled Th and Tm Analyses Of The Dstmentioning

confidence: 99%

Coupled thermal–hydrological–mechanical analyses of the Yucca Mountain Drift Scale Test—Comparison of field measurements to predictions of four different numerical models

International Journal of Rock Mechanics and Mining Sciences

Barr²,

Datta

et al. 2005

38permeability. The generally good agreement between simulated and measured THM data shows that adopted continuum model approaches are adequate for simulating relevant coupled THM processes at the DST. Moreover, TM-induced rock-mass deformations were reasonably well predicted using elastic models, although some individual displacements appeared to be better captured using an elasto-plastic model. It is concluded that fracture closure/opening caused by change in normal stress across fractures is the dominant mechanism for TM-induced changes in intrinsic fracture permeability at the DST, whereas fracture shear dilation appears to be less significant. This indicates that TM-induced changes in intrinsic permeability at the DST, which are within one order of magnitude,, tend to be reversible.