Borehole geophysics in nuclear power plant siting
Miniaturized borehole geophysical equipment designed for use in ground-water investigations can be adapted to investigations of nuclear power plant sites. This equipment has proved to be of value in preliminary and comprehensive studies of interior basins where thick sequences of Quaternary clastic sediment, occasionally with associated volcanic rocks, pose problems of stratigraphic correlation. The unconsolidated nature of the deposits generally requires that exploratory holes be cased, which ordinarily restricts the borehole geophysical studies to the radiation functions—natural gamma, gamma-gamma, neutron-gamma, and neutron-epithermal neutron logs. Although a single log response may be dominant in a given area, correlations derive from consideration of all log responses as a composite group. Because major correlations usually are based upon subtle differences in the physical properties of the penetrated sediment, high-resolution logging procedures are employed with some sacrifice of the quantitative parameters important to petroleum technology. All geophysical field data are recorded as hard copy and as digital information on punched paper tape. Digital data are subsequently computer processed and plotted to scales that enhance the stratigraphic data being correlated. Retention of the data in analog format permits rapid review, whereas computer plotting allows playback and detailed examination of log sections and sequences that may be attenuated on hard copy because of the logarithmic nature of the response to the physical property being examined.
Figures & Tables
During the “great decade” of siting and construction of nuclear power plants that ended in 1975, the nuclear industry mustered the largest geologic task force in this country’s history, resulting in rapid advances in geologic technologies. Many of the advances are discussed in this volume, a major contribution to engineering geology. Subjects treated are the regulatory, siting, and licensing processes; seismicity of the central and western U.S., with a consumer’s guide to instrumental methods for determination of hypocenters; and techniques, such as remote-sensing, microfacies analysis, dating techniques in faults, trenching as an exploratory method, borehole geophysics, and ground-water studies. Includes a useful glossary.