A Proposed Model for the Thermal Conductivity of Dry And Water-Saturated Tuff

ABSTRACTThe room-temperature thermal conductivities of two kinds of tuff from the Nevada Test Site have been measured on a linear-heat-flow thermal comparator. The results are the basis for an empirical model of the conductivity of these rocks in the dry and water-saturated conditions as a function of porosity. Tuff is one medium being considered for nuclear waste disposal. Devitrified, non-zeolitized tuffs with 6-22% porosity, and non-welded, zeolitized tuffs with 24-35% porosity were examined. The empirical geometric mean model is used to characterize the porosity-dependent thermal conductivity. We consider the rock matrix conductivity and the effective fluid conductivity as adjustable parameters in fitting the model to data for saturated and dehydrated samples, separately. For each rock type, the fitted value of matrix conductivity is the same in both the saturated and dehydrated cases; 2.3 and 1.1 W/(m.K) for the non-zeolitized and zeolitized tuffs, respectively. The fitted values for fluid conductivities are different for the the zeolitized and non-zeolitized tuffs, but the ratio of fitted water conductivity to fitted gas conductivity is very nearly the same for both rock types. This permits the use of a single equation to predict with good accuracy the ratio of saturated to dry rock conductivity.