Implications of Stability Analysis for Heat Transfer at Yucca Mountain

Ross, Benjamin; Zhang, Yiqiang; Lu, Ning; ,

Implications of Stability Analysis for Heat Transfer at Yucca Mountain

by Benjamin Ross, Disposal Safety Inc, Washington, United States,
Yiqiang Zhang, Disposal Safety Inc, Washington, United States,
Ning Lu, Disposal Safety Inc, Washington, United States,

Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993

Abstract:

An analytical solution has been obtained to the stability problem for an infinite horizontal layer of gas with its humidity constrained to 100%. Latent heat transfer makes convective heat transfer much more important for this moist gas than for a dry gas. The critical Rayleigh number for the onset of convective flow in the moist gas, with a lower no-flow boundary at 97?C and an upper no-flow boundary at 27?C, is 0.18, much less than the value of 4?² for a dry gas. Although the heat source at Yucca Mountain will be finite in extent, the solution for an infinite horizontal layer still gives a useful criterion for the qualitative importance of convective heat transfer. The critical Rayleigh number of 0.18 corresponds to a permeability of 4 ? 10^-12 m² if other parameters are given values measured at Yucca Mountain. This value falls roughly in the middle of the range of measured permeabilities. The analysis also gives a time constant for the onset of convection, which at twice the critical Rayleigh number is 1000 yr. Thus convection will probably make an important contribution to heat transfer at Yucca Mountain if the rock permeability falls in the upper portion of the range of measurements to date, but only at times after a few hundred or thousand years.

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