21 research outputs found
Core Softening in Cavernously Weathered Tonalite
Tonalite exhibiting cavernous weathering at Catavina, Baja California, was investigated to determine the
factors which contribute to differential hardness within the rock. Soft cores have a high degree of chemical
weathering as indicated by kaolinite content. Hematite formed from the leaching of biotite occurs in
coatings on rock surfaces, but the hardening effect of the coating is insignificant compared to the core-softening
of the interior. The hardness, measured by an abrasion resistance hardness tester, is inversely
correlated with kaolinite content in the tonalite. A one-dimensional water flow model was developed for
core-softened. cavernously weathered boulders. It indicates that during infiltration and dessication the
moisture flux is greatest through the cavern interior wall because of changes in the hydraulic conductivities
induced by core softening. Therefore, the cavern interior wall should have the greatest weathering rate in
the boulder
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Radiolytic effects of plutonium.
Plutonium isotopes, most of them a-emitters, cause radiolytic changes in the matrix, in whic h they are embedded. The internal irradiation of Pu metal or its alloys results in physical changes, largel y as a result of the formation of helium bubbles, well-known to material scientists and weapons specialists . In all other media where plutonium occurs, usually as Pu'+ in an ionic form, the results of irradiation ar e chemical in nature. Homogenous media containing Pu, are often aqueous or non-aqueous solutions o f plutonium compounds, mostly originating during processing of spent nuclear fuel or from Pu processing . Heterogenous matrices containing plutonium are more complex from the point of view of radiolysis; they usually contain a variety of combinations of common materials contaminated with radionuclides . This class of radioactive materials represents a challenge for the management of plutonium waste . One has to consider a range of time scales for radiolytic effects (and consequently a several orders o f magnitude range of the cumulative dose) beginning with waste generation, through packaging, transportation, to the period of final storage . Final storage could be for thousands of years in deep geologic repositories . At every ' stage of that time scale, radiolysis proceeds continuously an d cumulative effects c an complicate operating procedures and final disposition . The results presented here have been obtained from experiments that have irradiated of model materials, which are typically the objects of contamination with plutonium . They were irradiated with linearly accelerated electrons up to very high dose rates, adjusted to simulate any contamination at any point on the time scale
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Summary and Synthesis Report on Radionuclide Retardation for the Yucca Mountain Site Characterization Project - Yucca Mountain Site Characterization Program Milestone 3784M
Case hardening of sandstone
The case-hardened crust developed on the Aztec Sandstone in the Valley of Fire,
Nevada, has been characterized by a variety of techniques, including electron microscopy
and infrared spectroscopy. The case-hardened crust consists mainly of host rock, with a
fine-grained cement and wind-deposited kaolinite. The cement is usually calcite, but in
some cases the hydrated calcium borate, colemanite, was found to be the case-hardening
cement