8 research outputs found
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Importance of creep failure of hard rock in the near field of a nuclear-waste repository
Potential damage resulting from slow creep deformation intuitively seems unlikely for a high-level nuclear waste repository excavated in hard rock. However, recent experimental and modeling results indicate that the processes of time-dependent microcracking and water-induced stress corrosion can lead to significant reductions in strength and alteration of other key rock properties in the near-field region of a repository. We review the small data base supporting these conclusions and stress the need for an extensive laboratory program to obtain the new data that will be required for design of a repository
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Methodology for determining time-dependent mechanical properties of tuff subjected to near-field repository conditions
We have established a methodology to determine the time dependence of strength and transport properties of tuff under conditions appropriate to a nuclear waste repository. Exploratory tests to determine the approximate magnitudes of thermomechanical property changes are nearly complete. In this report we describe the capabilities of an apparatus designed to precisely measure the time-dependent deformation and permeability of tuff at simulated repository conditions. Preliminary tests with this new apparatus indicate that microclastic creep failure of tuff occurs over a narrow strain range with little precursory Tertiary creep behavior. In one test, deformation under conditions of slowly decreasing effective pressure resulted in failure, whereas some strain indicators showed a decreasing rate of strain
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Use of chemical explosives for emergency solar flare shelter construction and other excavations on the Martian surface
The necessity to shelter people on the Martian surface from solar flare particles at short notice and the need for long-term habitats with thick cosmic ray shielding suggests that explosives could be used effectively for excavation of such structures. Modern insensitive high explosives are safe, efficient, and reliable for rock breakage and excavation. Extensive Earth-bound experience leads us to propose several strategies for explosively-constructed shelters based on tunneling, cratering, and rock casting techniques
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SUBSELENE: a nuclear powered melt tunneling concept for high-speed lunar subsurface transportation tunnels
High-speed lunar surface transportation between manned scientific, commercial, or logistical facilities will require subsurface tunnels because humans must be shielded from Galactic Cosmic Ray and Solar Proton Event irradiations. We present a concept called SUBSELENE in which heat from a nuclear reactor is used to melt rock and form a self-supporting, glass-lined tunnel suitable for Maglev or other high-speed transport modes. We argue that SUBSELENE is an optimal approach to forming transportation tunnels on the Moon because: (1) it uses a high-energy-density, high-efficiency, nuclear power supply; (2) it does not require water or other rare volatiles for upon system muck handling or cooling; (3) it can penetrate through a mechanically varied sequence of rock types without complicated configurational changes; (4) it forms its own support structure as it goes; and (5) it is highly amenable to unmanned, automated operation. We outline the R and D needed to develop a SUBSELENE device and give a cost estimate based on experience with small-scale, field-tested, rock-melting penetrators
Transpression and tectonic exhumation in the Heimefrontfjella, western orogenic front of the East African/Antarctic Orogen, revealed by quartz textures of high strain domains
The metamorphic basement of the Heimefrontfjella in western Dronning Maud Land (Antarctica) forms the western margin of the major ca. 500 million year old East African/East Antarctic Orogen that resulted from the collision of East Antarctica and greater India with the African cratons. The boundary between the tectonothermally overprinted part of the orogen and its north-western foreland is marked by the subvertical Heimefront Shear Zone. North-west of the Heimefront Shear Zone, numerous low-angle dipping ductile thrust zones cut through the Mesoproterozoic basement. Petrographic studies, optical quartz c-axis analyses and x-ray texture goniometry of quartz-rich mylonites were used to reveal the conditions that prevailed during the deformation. Mineral assemblages in thrust mylonites show that they were formed under greenschist-facies conditions. Quartz microstructures are characteristic of the subgrain rotation regime and oblique quartz lattice preferred orientations are typical of simple shear-dominated deformation. In contrast, in the Heimefront Shear Zone, quartz textures indicate mainly flattening strain with a minor dextral rotational component. These quartz microstructures and lattice preferred orientations show signs of post-tectonic annealing following the tectonic exhumation. The spatial relation between the sub-vertical Heimefront Shear Zone and the low-angle thrusts can be explained as being the result of strain partitioning during transpressive deformation. The pure-shear component with a weak dextral strike-slip was accommodated by the Heimefront Shear Zone, whereas the north–north-west directed thrusts accommodate the simple shear component with a tectonic transport towards the foreland of the orogen