Bulk and thermal properties of the functional Tuffaceous Beds in holes USW G-1, UE-25 No. 1, and USW G-2, Yucca Mountain, Nevada

One emplacement horizon considered for a nuclear-waste repository at Yucca Mountain, Nevada, adjacent to the Nevada Test Site, consists of a zeolitized section. This section is defined here as an informal functional unit called the Tuffaceous Beds. This report describes the logic, data, and uncertainties involved in picking the boundaries of the functional unit in exploratory Holes USW G-1, UE-25a No. 1, and USW G-2. It also includes frequency profiles for grain density and porosity within the unit in the three exploratory holes. Results indicate that the functional Tuffaceous Beds range from 143 to 312 m in total thickness in the three holes studied. Unit-wide average grain densities and porosities of nonwelded ash-flows are 2.39 g/cm{sup 3} and 0.33, respectively. The average matrix thermal conductivity of heavily zeolitized tuffs is constant at 1.95 W/m.K. This value leads to average estimated conductivities of saturated and dehydrated nonwelded ashflows within the functional Tuffaceous Beds of 1.3 and 0.9 W/m.K, respectively. Available confined measurements indicate an average predehydration linear-expansion coefficient of 6.7 x 10{sup -6} K{sup -1}; individual values range from 2.8 to 13.2 x 10{sup -6} K{sup -1}. Transdehydration expansion behavior is variable, with average coefficients ranging from -56 to -29 xmore » 10{sup -6} K{sup -1}, depending on relative zeolite and (quartz + feldspar) contents. Postdehydration behavior is also sensitive to mineralogy, with average unconfined coefficients ranging from -4.5 to +7.8 x 10{sup -6} K{sup -1} for the different subunits within the functional Tuffaceous Beds. For the nonwelded ashflows dominant within the unit, pre-, trans-, and postdehydration expansion coefficients of +6.7, -56, and -4.5 x 10{sup -6} K{sup -1} are most representative. 21 refs, 7 figs., 12 tabs.« less