Hydraulic Fracturing R&D at Sandia National Laboratories
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The essential characteristics of the issue of radioactive waste management can be conceptualized as complex, with a variety of facets and uncertainty. These characteristics tend to cause people to perceive the issue of radioactive waste management as a 'risk'. This study was initiated in response to a desire to understand the perceptions of risk that the Korean public holds towards radioactive waste and the relevant policies and policy-making processes. The study further attempts to identify the factors influencing risk perceptions and the relationships between risk perception and social acceptance.
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There is a long history of testing crushed salt as backfill for the Waste Isolation Pilot Plant program, but testing was typically done at 100 C or less. Future applications may involve backfilling crushed salt around heat-generating waste packages, where near-field temperatures could reach 250 C or hotter. A series of experiments were conducted to investigate the effects of hydrostatic stress on run-of-mine salt at temperatures up to 250 C and pressures to 20 MPa. The results of these tests were compared with analogous modeling results. By comparing the modeling results at elevated temperatures to the experimental results, the adequacy of the current crushed salt reconsolidation model was evaluated. The model and experimental results both show an increase in the reconsolidation rate with temperature. The current crushed salt model predicts the experimental results well at a temperature of 100 C and matches the overall trends, but over-predicts the temperature dependence of the reconsolidation. Further development of the deformation mechanism activation energies would lead to a better prediction of the temperature dependence by the crushed salt reconsolidation model.
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43rd U.S. Rock Mechanics Symposium and 4th U.S.-Canada Rock Mechanics Symposium
The disturbed rock zone (DRZ) is an important feature which is evaluated in the Waste Isolation Pilot Plant (WIPP) performance assessment (PA) to predict post-closure repository performance. Mining of a WIPP disposal room disturbs the stress state sufficiently to cause fracturing of the surrounding rock, and this fracturing will alter the mechanical and hydrological properties of the salt. DRZ extent, and permeability, controls the majority of the brine that enters or exits the repository in PA modeling of the undisturbed scenario. Extensive laboratory data from experiments performed on rock salt demonstrate that damage can be modeled in terms of stress invariants. In this paper the DRZ extent is calculated based on a dilatant damage criterion. The calibrated damage factor C in the damage criterion is determined by comparing ultrasonic wave velocity field measurements obtained in the S-90 drift with a numerical analysis that predicts the salt's behavior. Ultrasonic velocities decrease in the presence of microcracks and loosened grain boundaries associated with salt damage. The most extensive DRZ exists during early times, within the first ten years of mining. The maximum predicted DRZ surrounding a WIPP disposal room is approximately 2.25 m below, 4.75 m above, and 2 m laterally. This paper also presents several lines of evidence, based on previous studies, that support the prediction of DRZ size by applying a WIPP specific damage criterion calibrated using ultrasonic velocity measurements. Copyright 2009 ARMA, American Rock Mechanics Association.
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