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Effective thermal conductivity of silica sand bed as a filling material for crevices around radioactive- waste canisters

A method for measuring the effective thermal conductivity, λ e , of free-falling silica sand bed is described. The sand, made artificially from quartzite, was allowed to fall into cylindrical vessels 110 mm in diameter and120 mm high. Commercial grain size number of the sand ranged from 2 to 8 (corresponding peak diameters of the sand grains were 1680 to 74 μm). Bulk density of the sand, ρ B , was 1180-1460 kg m - 3 , and its porosity, Φ, was 45%-55%. λ e was measured at the temperatures of 25, 45, 65, and 85°C, in that order, under dry conditions, by the transient heat probe method. The measured values were found to vary with grain size number, porosity, and temperature from 0.17 to 0.46 W m - 1 K - 1 . The experimental results were analysed to evaluate λ e of the sand bed in situ by means of a three-phase model previously presented.