Effect of a Low-Permeability Layer on Calculated Gas Flow at Yucca Mountain

by Ning Lu, Disposal Safety Inc, Washington, United States,
Steven Amter, Disposal Safety Inc, Washington, United States,
Benjamin Ross, Disposal Safety Inc, Washington, United States,

Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1991


Yucca Mountain is being studied to determine its suitability as a location for a high-level nuclear waste repository. The mountain is a steep-sided linear ridge which is underlain by a 500-meter thick unsaturated zone composed of alternating layers of ash-flow and bedded tuffs. An understanding of the velocity, trajectories, and mixing of the gas in Yucca Mountain is necessary both as input for a model of the carbon-14 movement in the unsaturated zone and evaluation of the net vapor flux. This paper describes a systematic sensitivity study that was designed to test several aspects of the TGIF model when used to simulate gas flow under Yucca Mountain. Values of three important inputs to the model were systematically varied to form a matrix of 80 runs. The matrix consisted of five values of permeability contrast between a bedded tuff layer and surrounding welded units (in all cases, bulk permeabilities were used to represent the combined effect of both fractures and matrix permeability), four temperature profiles representing different stages of repository cooldown, and four finite-difference grids.

Subject Headings: Gas flow | Matrix (mathematics) | Permeability (soil) | Permeability (material) | Radioactive wastes | Flow simulation | Sensitivity analysis | Volcanic deposits

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