Water, Vapor, and Salt Dynamics in a Hot Repository
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0985-NN13-06
Water, Vapor, and Salt Dynamics in a Hot Repository Davood Bahrami1, George Danko1, and John Walton2 1 Department of Mining Engineering, University of Nevada, Reno, 1664 N. Virginia St., Reno, NV, 89557 2 Department of Civil Engineering, University of Texas at El Paso, 500 W. University, El Paso, TX, 79968
ABSTRACT The purpose of this paper is to report the results of a new model study examining the high temperature nuclear waste disposal concept at Yucca Mountain using MULTIFLUX, an integrated indrift- and mountain-scale thermal-hydrologic model. The results show that a large amount of vapor flow into the drift is expected during the period of above-boiling temperatures. This phenomenon makes the emplacement drift a water/moisture attractor during the above-boiling temperature operation. The evaporation of the percolation water into the drift gives rise to salt accumulation in the rock wall, especially in the crown of the drift for about 1500 years in the example. The deposited salts over the drift footprint, almost entirely present in the fractures, may enter the drift either by rock fall or by water drippage. During the high temperature operation mode, the barometric pressure variation creates fluctuating relative humidity in the emplacement drift with a time period of approximately 10 days. Potentially wet and dry conditions and condensation on salt-laden drift wall sections may adversely affect the storage environment. Salt accumulations during the above-boiling temperature operation must be sufficiently addressed to fully understand the waste package environment during the thermal period. Until the questions are resolved, a below-boiling repository design is favored where the Alloy-22 will be less susceptible to localized corrosion. INTRODUCTION The goal of the new model study is to examine the high temperature nuclear waste disposal concept at Yucca Mountain (YM). The concept involves complex, nonlinear, coupled, typically multi-physics thermal-hydrologic processes in the emplacement area.1-3 Examination of such a complex thermalhydrologic problem requires an integrated, multi-scale solution. Models which include the edge-cooling phenomena must be used, such as multi-scale thermohydrologic models (MSTHM) applied for the baseline design by Buscheck et al.2, Danko and Bahrami4,5, Manepally and Fedors6and Birkholzer et al.7 Buscheck et al.2 applied the superposition of four sub-models: (a) a three-dimensional (3-D), smeared-source, mountain-scale heat conduction-only model; (b) a line-averaged, two-dimensional (2-D), drift-scale thermohydrologic model; (c) a smeared-heat-source, one-dimensional, drift-scale heat conduction model; and (d) a drift-scale, discrete-source, 3-D, heat conduction and radiation model, based on effective thermal conductivities. The effect of condensation was simulated separately with another, added model3. The effect of ventilation during pre-closure was also simulated separately, using an independent ventilation model8, de-coupled from the MSTHM. The effect of rock drying
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