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

5.19
potential host rocks are determined in accordance with well-accepted methods by observing
which states of stress and temperature cause fracturing. Standard tests are also performed
to determine the tensile strength of rocks.
Synergistic effects between thermal and mechanical properties are determined for labor-
atory samples by obtaining data on mechanical response as a function of rock temperature or
obtaining thermal conductivity data as a function of rock stress. The effects of the rock's
fluid content on specific heat, critical stress, and thermal conductivity are also being
investigated.
Sorption capacities are currently determined by passing water doped with radionuclides
through the rock and measuring the amounts of radionuclides retained. Transient batch
methods for determining sorption are currently being standardized (Brandstetter et al.
1979). Techniques are also being developed to identify minerologic and molecular affinities
for sorbed radionuclides, allowing a better understanding of the materials and mechanisms
responsible for the sorption process.
Laboratory tests are being validated by field determinations of thermal, mechanical,
and chemical behavior under expected repository conditions. Field tests generally involve
single or multiple heat sources emplaced in drill holes with an array of measuring instru-
ments surrounding the heat source. A monitor array can be designed to measure rock tempera-
tures, deformation, water content, chemistry, and rock stresses as a function of time and
distance from the heat source.
Regional Geologic Forecasting Studies. Predicted performance of a geologic system has
not matured to the point enjoyed by conventional engineering disciplines. Geologic research
has largely concentrated on characterizing present-day natural processes and events and on
historically reconstructing the distribution, magnitude, and sequence of past events. How-
ever, future tectonic activity, including volcanic eruptions, folding, epeirogeny, fault
movements, salt diapirism, and seismic activity, need to be predicted to the degree that the
likelihood and the consequences of changes in the natural system with regard to containment
and isolation can be estimated.
Plotting space-time relationships of past events allows a calculation of past rates and
distributions of occurrence for tectonic events (Crowe 1978 and Rogers et al. 1977). The
probabalistic extrapolation of these rates into the future must be weighted against deter-
ministic tectonic models such as plate tectonics to determine whether observed space-time
distributions are likely to continue or be modified. The geographic scale for which data
are compiled is of critical importance and needs to be evaluated. In general, for larger
areas, consensus is more readily obtained among earth scientists about tectonic processes.
Conversely, averaging probabalistic projections for individual events over large areas
decreases their reliability for a given site. Thus, a reasoned interpretation of probabil-
istic and deterministic approaches is required to assess the likelihood of tectonic events
that might disrupt a repository's natural system. This combination of methods is most
developed for assessing seismic hazards (Algermissen 1976 and Glass et al. 1978).