Deep Geologic Repositories
Deep Geologic Repositories reviews the success stories of underground waste isolation. It focuses on repositories that did, do, and will permanently and safely isolate dangerous materials from the near-surface biosphere. Complementary topics address the isolation capability of average crustal rock, investigations at one representative underground research laboratory, and the geologic preservation of fission products from Precambrian nuclear reactors. An international cast of contributors presents proven practical solutions to a formerly confounding issue in environmental and engineering geology: What do we do with wastes that retain their dangerous characteristics in human terms forever? The principal answer: Recycling into the lithosphere by “reverse” mining.
Carbonaceous substances in Oklo reactors—Analogue for permanent deep geologic disposal of anthropogenic nuclear waste
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Published:January 01, 2008
Abstract
Seventeen known natural nuclear fission reactors sustained criticality in hydrothermally altered low-grade metasedimentary rocks of the Proterozoic Franceville Series ca. 1968 ± 50 Ma. About half of these reactors contain only traces of carbonaceous substances, and in these, fission products including strontium, cesium, rubidium, and boron migrated away from the reactors and were nearly completely lost. The others are rich in carbonaceous substances, particularly solid, partly graphitized bitumen and kerogen, as well as liquid oil in fluid inclusions. In these carbonaceous substance–rich reactors, uranium and fissiogenic isotopes are held in uraninite, which became enclosed in liquid bitumen during criticality and was subsequently fixed when the bitumen solidified. The preservation of liquid oil in fluid inclusions for over two billion years suggests that time is not a parameter that controls petroleum degradation. This is viewed as a potentially important aspect in engineered nuclear waste containment projects. Likewise, because of the hydrophobic qualities of solid bitumen, its inducible plasticity, and its capability of conversion to nonflammability, it deserves serious consideration for use in permanent deep geologic disposal sites. Indications are that at Oklo, Gabon, carbonaceous substances have combined to restrain the migration of radionuclides and limit the extent to which migration occurs. The strength of the Oklo analogue lies in the fact that it represents more extreme conditions than those likely to be met in a deep geologic repository. The carbonaceous substance–rich reactors of Oklo stand as time-tested analogues for anthropogenic nuclear waste containment strategies.
- Africa
- carbonaceous composition
- Central Africa
- clastic rocks
- environmental analysis
- fluid dynamics
- fluid inclusions
- Francevillian
- Gabon
- human activity
- inclusions
- lithofacies
- metamorphic rocks
- metasedimentary rocks
- Oklo
- Paleoproterozoic
- Precambrian
- Proterozoic
- radioactive waste
- sandstone
- sedimentary rocks
- site exploration
- textures
- underground disposal
- upper Precambrian
- waste disposal