Temporal Damping Effect of the Yucca Mountain FracturedUnsaturated Rock on Transient Infiltration Pulses

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Performance assessment of the Yucca Mountain unsaturated zone (UZ) as the site for an underground repository of high-level radioactive waste relies on the crucial assumption that water percolation processes in the unsaturated zone can be approximated as a steady-state condition. Justification of such an assumption is based on temporal damping effects of several geological units within the unsaturated tuff formation. In particular, the nonwelded tuff of the Painbrush Group (PTn unit) at Yucca Mountain, because of its highly porous physical properties, has been conceptualized to have a significant capacity for temporally damping transient percolation fluxes. The objective of this study ... continued below

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Zhang, Keni; Wu, Yu-Shu & Pan, Lehua May 2, 2005.

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Performance assessment of the Yucca Mountain unsaturated zone (UZ) as the site for an underground repository of high-level radioactive waste relies on the crucial assumption that water percolation processes in the unsaturated zone can be approximated as a steady-state condition. Justification of such an assumption is based on temporal damping effects of several geological units within the unsaturated tuff formation. In particular, the nonwelded tuff of the Painbrush Group (PTn unit) at Yucca Mountain, because of its highly porous physical properties, has been conceptualized to have a significant capacity for temporally damping transient percolation fluxes. The objective of this study is to investigate these damping effects, using a three-dimensional (3-D) mountain-scale model as well as several one-dimensional (1-D) models. The 3-D model incorporates a wide variety of the updated field data for the highly heterogeneous unsaturated formation at Yucca Mountain. The model is first run to steady state and calibrated using field-measured data and then transient pulse infiltrations are applied to the model top boundary. Subsequent changes in percolation fluxes at the bottom of and within the PTn unit are examined under episodic infiltration boundary conditions. The 1-D model is used to examine the long-term response of the flow system to higher infiltration pulses, while the damping effect is also investigated through modeling tracer transport in the UZ under episodic infiltration condition. Simulation results show the existence of damping effects within the PTn unit and also indicate that the assumption of steady-state flow conditions below the PTn unit is reasonable. However, the study also finds that some fast flow paths along faults exist, causing vertical-flux quick responses at the PTn bottom to the episodic infiltration at the top boundary.

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  • Journal Name: Journal of Hydrology; Journal Volume: 327; Journal Issue: 1-2; Related Information: Journal Publication Date: 07/30/2006

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  • Report No.: LBNL--57539
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 891199
  • Archival Resource Key: ark:/67531/metadc882183

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  • May 2, 2005

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  • Sept. 21, 2016, 2:29 a.m.

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  • March 23, 2018, 4:10 p.m.

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Zhang, Keni; Wu, Yu-Shu & Pan, Lehua. Temporal Damping Effect of the Yucca Mountain FracturedUnsaturated Rock on Transient Infiltration Pulses, article, May 2, 2005; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc882183/: accessed August 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.