Thermal conductivity of silicic tuffs: predictive formalism and comparison with preliminary experimental results

Abstract

Allen R. Lappin Geological Projects Division 4537Sandia Laboratories Albuquerque, NM 87185 ABSTRACT Performance of both near-and far-field thermomechanical calculations to assess the feasibility of waste disposal in silicic tuffs requires a formalism for predicting thermal conductivity of a broad range of tuffs. This report summarizes the available thermal conductivity data for silicate phases that occur in tuffs and describes several grain-density and conductivity trends which may be expected to resul e from post-emplaceweat alteration. A bounding curve is drawn that predicts the minimum theoretical matrix (zero-porosity) conductivity for most tuffs as a function of grain density. Comparison of experimental results with this curve shows that experimental conductivities are consistently lower at any given grain density. Use of the lowered bounding curve and an effective gas conductivity of 0.12 W/m°C allows conservative prediction of conductivity for a broad range of tuff types. For the samples measured here, use of the predictive curve allows estimation of conductivity to within 15% or better, with one exception. Application and ~ossible improvement of the formalism are also discussed. Introduction and Objectives

Studying the thermal conductivity of a deep Eocene clay formation: Direct measurements vs back-analysis results

“…Temperature dependence of thermal conductivity (mainly associated with its dependence on quartz and water) is expected not to greatly affect the measured valueswithin the temperature range used. In this temperature range, the decrease in thermal conductivity of quartz with increase in temperature is around -0.0235 Wm -1 K -1 /K[28] and the increase in thermal conductivity of water around 0.0015 Wm -1 K -1 /K, which compensates the temperature sensitivity of clay thermal conductivity.The time evolutions of inflow and outflow heat fluxes (Eq. (2)) are plotted inFigure 6for these two samples.…”

Thermal conductivity, bulk properties, and thermal stratigraphy of silicic tuffs from the upper portion of hole USW-G1, Yucca Mountain, Nye County, Nevada

“…4 6 In fact, the confined conductivity of 1330 after dehydration is "identical" to that reported in the literature for obsidian (1.26, 1.42 W /m°C), fused silica (1.33 to 1.36 W /m°C), and basaltic glasses (1.37 W /m°C). 9 The porosity of Sample 1330 (¢ = 0.03) is so low that the increase in glass conductivity with increasing temperature more than makes up for any decrease in total conductivity resulting from dehydration near 200°C.…”

“…This is almost certainly not the case. 9 In the case of devitrified tuffs, while the conductivity of feldspars may increase slightly with increasing temperature, that of quartz is well documented to decrease. Many of the samples of devitrified tuff analyzed here show a slight decrease in saturatd conductivity with increasing temperature.…”

“…In Figure 2, Curve A represents approximate changes in grain density and matrix conductivity resulting from zeolite formation at the expense of primary anhydrous glass having a density of 2.41 g/cm 3 and conductivity of 1.35 W /m°C. 9 There is little apparent change in thermal conductivity because of zeolitization, though conductivity data for zeolites are sparse; none are available for clinoptilolite. Hydration of initially anhydrous glass (as in the case of Sample 1330) decreases jts conductivity and grain density 18 below values shown in the figure.…”

Preliminary stratigraphic and petrologic characterization of core samples from USW-G1, Yucca Mountain, Nevada

“…For example, Wolfsberg et al (1979), Johnstone and Wolfsberg (1980), and Vine et al (1980) show that sorption data for tuff can be broadly grouped into two categories based on kind and degree of devitrification, and especially on the presence and abundance of zeolite and clay minerals. Lappin (1980) described grain density vs thermal conductivity trends for tuffs and developed a predictive curve for theoretical conductivity of tuff as a function of grain density. Heiken and Bevier (1979) described the petrology of tuff units from drill hole J-13 located in Forty Mile Wash on the western edge of Jackass Flat and adjacent to Yucca Mountain (Fig.…”