Transport of radon gas into a tunnel at Yucca Mountain; estimating large-scale fractured tuff hydraulic properties and implications for the operation of the ventilation system

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doi: 10.1016/j.jconhyd.2003.07.001
Authors:Unger, André; Finsterle, Stefan; Bodvarsson, Gudmundur
Author Affiliations:Primary:
University of Waterloo, Earth Sciences Department, Waterloo, ON, Canada
Lawrence Berkeley National Laboratory, United States
Volume Title:Journal of Contaminant Hydrology
Source:Journal of Contaminant Hydrology, 70(3-4), p.153-171. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0169-7722
Publication Date:2004
Note:In English. Based on Publisher-supplied data
Summary:Radon gas concentrations have been monitored as part of the operation of a tunnel (the Exploratory Studies Facility--ESF) at Yucca Mountain to ensure worker safety. The objective of this study was to examine the potential use of the radon data to estimate large-scale formation properties of fractured tuffs. This objective was examined by developing a numerical model, based upon the characteristics of the ESF and the Topopah Spring welded (TSw) tuff unit, capable of predicting radon concentrations for prescribed ventilation conditions. The model was used to address two specific issues. First, it was used to estimate the permeability and porosity of the fractures in the TSw at the length scale of the ESF and extending tens of meters into the TSw, which surrounds the ESF. Second, the model was used to understand the mechanism leading to radon concentrations exceeding a specified level within the ESF. The mechanism controlling radon concentrations in the ESF is a function of atmospheric barometric fluctuations being propagated down the ESF along with ventilated air flow and the slight suction induced by the ventilation exhaust fans at the South Portal of the ESF. These pressure fluctuations are dampened in the TSw fracture continuum according to its permeability and porosity. Consequently, as the barometric pressure in the ESF drops rapidly, formation gases from the TSw are pulled into the ESF, resulting in an increase in radon concentrations. Model calibration to both radon concentrations measured in the ESF and gas-phase pressure fluctuations in the TSw yielded concurrent estimates of TSw fracture permeability and porosity of 1×10-11 m2 and 0.00034, respectively. The calibrated model was then used as a design tool to predict the effect of adjusting the current ventilation-system operation strategy for reducing the probability of radon gas concentrations exceeding a specified level. Abstract Copyright (2004) Elsevier, B.V.
Subjects:Calibration; Cenozoic; Concentration; Controls; Design; Experimental studies; Fractured materials; Fractures; High-level waste; Igneous rocks; Inverse problem; Isotopes; Mechanism; Migration of elements; Miocene; Monitoring; Neogene; Noble gases; Numerical models; Permeability; Physical properties; Pollution; Porosity; Prediction; Pyroclastics; Radioactive isotopes; Radon; Reservoir rocks; Rn-222; Soils; Tertiary; Topopah Spring Member; Tunnels; Underground disposal; Ventilation; Volcanic rocks; Waste disposal; Welded tuff; Nevada; Nye County Nevada; United States; Yucca Mountain
Coordinates:N364400 N370000 W1162500 W1163500
Record ID:2008123312
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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