The Francevillian (Lower Proterozoic) uranium ore deposits of Gabon

Gauthier-Lafaye, F.; Weber, F.

doi:10.2113/gsecongeo.84.8.2267

Cited by 156 publications

(87 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Because the size of the uranium deposition in porous rock [21] is of the order of the grain size of those rock, i.e. tens of microns, which is much smaller than typical neutron mean-free-path (several centimeters), we can consider that uranium deposition in porous rock is homogeneously mixed with rock and water in an MCNP model.…”

Section: Methods and Geometriesmentioning

confidence: 99%

“…For fractured geometry I, the value of fracture aperture b is fixed at 1.0 cm as the reference value for the critical mass calculations. It is interesting to note that more than 700 MT of uranium with the enrichment of about 3.7% was involved in the sustainable chain reactions in reactor zones 1-6 of Oklo uranium deposit [21]. The highest grade uranium ore found in Oklo contains up to 15% of uranium by weight, which can be converted into the HMVF by assuming dry sandstone as 0.047.…”

Section: Critical Massmentioning

confidence: 99%

See 1 more Smart Citation

Conditions for criticality by uranium deposition in water-saturated geological formations

Liu

Ahn

Hirano

2014

Journal of Nuclear Science and Technology

View full text Add to dashboard Cite

This study focuses on neutronic analysis to examine the criticality conditions for uranium depositions in geological formations resulting from geological disposal of damaged fuels from Fukushima Daiichi reactors. MCNP models are used to evaluate the neutron multiplication factor (k eff ) and critical mass for various combinations of host rock and geometries. It has been observed that the k eff for the deposition become greater with (1) smaller concentrations of neutron-absorbing materials in the host rock, (2) larger porosity of the host rock, (3) heterogeneous geometry of the deposition, and (4) greater mass of uranium in the deposition. This study has revealed that the planar fracture geometry applied in the previous criticality safety assessment for geological disposal would not necessarily yield conservative results against the homogeneous uranium deposition.

show abstract

Section: Methods and Geometriesmentioning

confidence: 99%

Section: Critical Massmentioning

confidence: 99%

Conditions for criticality by uranium deposition in water-saturated geological formations

Liu

Ahn

Hirano

2014

Journal of Nuclear Science and Technology

View full text Add to dashboard Cite

show abstract

“…Under oxidizing conditions, U(IV) is unstable and is oxidized to U(VI), which is soluble in water and can be transported along with water (e.g., Langmuir, 1978). The major Proterozoic type of U mineralization is represented by the deposits of Oklo, Gabon, which are also called natural nuclear fission reactors (Gauthier Lafaye and Weber, 1989). The U mineralization has been dated to be ~ 1.95 Ga, whereas the sediments hosting them are ~ 2.15 Ga (Gauthier Lafaye and Weber, 2003).…”

Section: Detrital Uraninite Pyrite and Sideritementioning

confidence: 99%

Emerging views on the evolution of atmospheric oxygen during the Precambrian

Sreenivas

Murakami

2005

Journal of Mineralogical and Petrological Sciences

View full text Add to dashboard Cite

The oxygenation of the atmosphere produced some irreversible changes in the Earth's history, including evolution of higher biological forms. Several aspects of this important process, such as its timing and causes, have remained subjects of debate. The present review is an attempt to provide an update on issues related to the evolution of atmospheric oxygen during the Precambrian. It is generally believed that the amount of atmospheric oxygen increased during the Paleoproterozoic despite the fact that photosynthesis originated much earlier in the Earth's history. The pattern of Fe retention in paleosols and the record of mass independent fractionation in sulfur isotopes confirm that the transition to more oxidizing conditions took place during the Paleoproterozoic.Various mechanisms, ranging from an increase in the sources of oxygen to a decrease in its sinks, have been envisaged as processes causing the oxygen rise during the Paleoproterozoic. Conventionally, it is believed that the burial of photosynthetic carbon has allowed the establishment of oxygen. However, the transition in mantle oxidation states and the escape of hydrogen during photolysis of methane of biogenic origin have also been suggested as having played an important role in the establishment of free molecular oxygen in the atmosphere hydrosphere system. The coincidence of timing of the oxygen rise and the positive excursions in carbon isotope compositions of carbonate rocks during the Paleoproterozoic suggests an important role for the carbon cycle in atmospheric oxygen evolution.Better quantitative modeling of atmospheric oxygen levels may be essential to allow full comprehension of the timing, causes and consequences of the oxygen rise in the Earth's history. Quantitative modeling is essential as it can lead to an unraveling of the co evolutionary nature of the surface environment and the biosphere of the Earth.

show abstract

“…Geological study , on the Oklo uranium ore deposit has been reported by Gauthier-Lafaye and Weber (1989).…”

Section: Samplesmentioning

confidence: 99%

Reconstruction of cumulative fission yield curve and geochemical behaviors of fissiogenic nuclides in the Oklo natural reactors.

1992

View full text Add to dashboard Cite

The Francevillian (Lower Proterozoic) uranium ore deposits of Gabon

Cited by 156 publications

References 0 publications

Conditions for criticality by uranium deposition in water-saturated geological formations

Conditions for criticality by uranium deposition in water-saturated geological formations

Emerging views on the evolution of atmospheric oxygen during the Precambrian

Reconstruction of cumulative fission yield curve and geochemical behaviors of fissiogenic nuclides in the Oklo natural reactors.

Contact Info

Product

Resources

About