Management of Commercially Generated Radioactive Waste - U.S. ...

5.18
(Witherspoon 1977). Pulse injection tests aid in determining permeability in low permea-
bility rocks (Ballou 1979). Moreover, pressure decay curves for gases pressurized at
selected borehole intervals can be used to estimate the permeability of the very tight rocks
expected at repository horizons. Although present measurement techniques for hydraulic con-
ductivity in nearly impermeable rocks may be in error by up to a few orders of magnitude
(Bredehoeft et al. 1978), even the higher, most conservative values indicate that water
moves extremely slowly in these rocks.
Hydrologic R&D Studies
For rocks that possess a natural fracture system (e.g., granite, basalts, some shales,
limestones, sandstones) the determination of near-field flow mechanisms is also evolving.
Because fracture networks are not random, their nature and orientation within the system
will be statistically determined. Methods designed to assess fracture effects on hydrologic
flow are currently being developed at the Nevada Test Site (Johnstone 1980), the Stripa mine
in Sweden (Gale et al. 1979), and the Los Medanos site in New Mexico (Gonzales et al. 1979).
The direct determination of hydrologic parameters in fracture networks includes conventional
pump testing with multiple-point piezometers, tracer studies, and flow-meter tests performed
in wells or subsurface facilities constructed at the repository site or in rock bodies that
provide a close analog of site conditions.
Water influx at mines in crystalline rocks is a well-known phenomenon. However, where
permeabilities are very low, mine ventilation commonly evaporates and removes most, if not
all, of this water (Gale et al. 1979). Thus, the mines are usually "dry," although a small
amount of water may continually flow into them. By sealing a room with airtight bulkheads
and circulating controlled quantities of warm air, the amount of seepage water can be deter-
mined by measuring the humidity and mass of the circulating air. Data on fluid gradients
around the sealed-off chamber permit calculations of nearby rock permeabilities. Such an
experiment is being performed at the Stripa mine in Sweden (Gale et al. 1979 and Lawrence
Berkeley Laboratory 1978).
Site-Specific R&D
The thermal properties of potential host rocks can be measured in the laboratory by
accepted methods (Stephens et al. and Jaeger et al. 1979). Standard sized cylindrical spe-
cimens are subjected to a controlled thermal power source at one end; increasing tempera-
tures and dimensions are measured either along the axes or along the outside lengths of the
specimens. The results are then used to calculate volumetric expansion coefficients and
thermal conductivity. The specific heat of a rock is determined by standard calorimetry
(Stephens et al.).
Mechanical properties of potential host rocks can also be measured in the laboratory
by standard techniques and apparatus (Jaeger et al. 1979); the results are used in prelimi-
nary models of the repository's response and to help determine which properties require
better definition by field testing (Chan et al. 1980). The compressive strengths of