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OKLO REACTORS : 2 Billion Years Before Fermi !

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OKLO REACTORS : 2 Billion Years Before Fermi ! OKLO REACTORS : 2 billion Years before Fermi ! Bertrand BARRÉ, AREVA « The italian Navigator has landed in the New World » And not even a photographer… 2 - B. Barré OKLO séminaire GIFT - 2005 Then and Now X 2000 million years ago X Today 3 - B. Barré OKLO séminaire GIFT - 2005 Detective Story X June 1972 X Pierrelatte Nuclear Fuel Enrichment plant was using ore from Gabon (deposits discovered in 60’s) X Shipment of U routine mass spec. measurements of 235U/ 238U ratio (0.7171% instead of 0.7202%), and no 236U… X Talk about paying attention to details! X Pierrelatte > Malvesi > Gueugnon > Mounana > Oklo (north) 4 - B. Barré OKLO séminaire GIFT - 2005 Where is Oklo? 5 - B. Barré OKLO séminaire GIFT - 2005 Franceville Basin 6 - B. Barré OKLO séminaire GIFT - 2005 7 - B. Barré OKLO séminaire GIFT - 2005 Oklo, Gabon (CEA 1974) 8 - B. Barré OKLO séminaire GIFT - 2005 OKLO Mining Operations Nov1970-Dec1971 9 - B. Barré OKLO séminaire GIFT - 2005 Open Pit Mining in Oklo Mined ore Excavation Ore in place Drillings Very rich « lens » 10 - B. Barré OKLO séminaire GIFT - 2005 The OKLO Mine 11 - B. Barré OKLO séminaire GIFT - 2005 Mounana Plant Nov1970-Dec1971 U concentration in ore vs 235U abundance 12 - B. Barré OKLO séminaire GIFT - 2005 Reminder… X 235U is desired form of Uranium for thermal fission X Reactors (other than CANDU and Magnox) require enrichment : X MTR (old) :93% X MTR (new): 20% X LWR : 3.2-4.5% 13 - B. Barré OKLO séminaire GIFT - 2005 A Window in Time X Before 2.2 billion years ago, no uranium deposit, because not enough oxygen in atmosphere and therefore water X After 1.4 billion years ago, 235U abundance too low Remember… The Americas separated from EurAsia and Africa less than 200 million years ago 14 - B. Barré OKLO séminaire GIFT - 2005 Oklo Events… How’d it Happen? 15 - B. Barré OKLO séminaire GIFT - 2005 X Mobilization of Uranium: source of U for reactors came from tiny amounts scattered about Earth’s crust. Major biological event: photosynthesis and atmospheric oxygen z Water acquires its ‘oxidizing nature’, dissolve Uranium from crustal rocks into streams and rivers X Uranium ore/reactor formation: Uranium was deposited thinly and low concentration over large area (by water) Thousands of meters of sand deposited on top Earth lifted (45o), rain percolated down, re-mobilized uranium, which eventually re-deposited in very high concentrations (up to 70% UO2) 16 - B. Barré OKLO séminaire GIFT - 2005 Stratigraphy of Zones 5-6 Reactor faciès Intact Reactor clay sandstone 17 - B. Barré OKLO séminaire GIFT - 2005 Reactor Operation: ~1 million years (can tell by dating byproducts) Waste Movement: All radioactive waste products have decayed (2000million years to degrade) 18 - B. Barré OKLO séminaire GIFT - 2005 Fossil Reactor # 15 Yellow is Uranium Oxide and white is recrystallized quartz 19 - B. Barré OKLO séminaire GIFT - 2005 Calculating the Reactors X Compare Absolute Cumulative Fission Yields Oklo vs. modern nuclear reactors Oklo was fissioning both 238U and 239Pu as well as 235U. 239 z But no Pu present on the earth when Oklo formed 239 z Oklo Reactors have 'BRED' the Pu 236 232 z U decayed in Th 20 - B. Barré OKLO séminaire GIFT - 2005 Fission yields for 235U, or « the camel’s back » 21 - B. Barré OKLO séminaire GIFT - 2005 22 - B. Barré OKLO séminaire GIFT - 2005 The main nuclear Reactions 23 - B. Barré OKLO séminaire GIFT - 2005 Correlation between « enrichment » and U concentration in the Ore % 235U % U in Ore 24 - B. Barré OKLO séminaire GIFT - 2005 Average « Core » Temperature vs Fluence 25 - B. Barré OKLO séminaire GIFT - 2005 26 - B. Barré OKLO séminaire GIFT - 2005 Correlation between Reactor operation & Clay Formation 27 - B. Barré OKLO séminaire GIFT - 2005 OKLO as a Waste Disposal « Analogue » ? Le Point Nov 2004 28 - B. Barré OKLO séminaire GIFT - 2005 Bure Underground Laboratory 29 - B. Barré OKLO séminaire GIFT - 2005 Bangombé : Near Surface, best Analogue 30 - B. Barré OKLO séminaire GIFT - 2005 Oklo: The Natural Waste Disposal Experiment X Nature dealing with tonnes of concentrated radioactive waste near surface X Large parts of reactor holding original waste still intact! hope that nuclear fission waste may be stored in suitable geological repositories. 31 - B. Barré OKLO séminaire GIFT - 2005 32 - B. Barré OKLO séminaire GIFT - 2005 33 - B. Barré OKLO séminaire GIFT - 2005 Summary X 16 reactors 10 to 30 m wide & 1 m thick , 3 500 m deep. X Operation : 100 000 to 1 million years X Flux 107 to 108 n.cm-2.s-1 X Fluence 1.3 1021 n.cm-2 X Temperature ~300°C (from 176Lu) X Water controlled. Water/U ~20 to 30% volume X Total Energy produced 16 500 W.year X Plutonium production ~3 t 34 - B. Barré OKLO séminaire GIFT - 2005 One of a Kind ?? 35 - B. Barré OKLO séminaire GIFT - 2005.
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