Experimental tests of enhancement of vapor diffusion in Topopah Spring Tuff

The potential enhancement of thermally driven water vapor diffusion in Topo pah Spring Tuff was investigated using a transient-state thermal conductivi ty measurement. Thermal conductivity was measured as a function of pressure , temperature, and water content by the method of Parikh et al. (1979), whi ch allows separation of thermal conductivity from thermally induced Intent heat transport. The measured thermal conductivity of Topopah Spring Tuff ra nged from 0.99 W/mK to 2.07 W/mK and showed an increase with increasing tem perature above approximately 40 degreesC. These values are slightly lower t han the range of values measured for other samples from the Yucca Mountain, Nevada site (e.g., Nimick, 1990). Enhancement of vapor diffusion in tuff w as not observed at any of the investigated combinations of water contents, temperatures, and pressures. The method of Parikh et al. (1979) was subsequ ently tested on a mixture of quartz sand and 10% kaolinite. A considerable degree of enhancement was observed in the soil for a water saturation of 14 %, demonstrating the capability of the method to estimate enhancement of va por diffusion.