Natural uranium reactor

World annual uranium requirements in 1993 were estimated at about 58,382 t natural uranium equivalent. Reactor-related requirements are expected to rise about 1015 t/yr on the average, reaching 75,700 t U total requirements in the year 2010. The cumulative aggregate world uranium requirements for the period 1993—2010 are estimated to be about 1.185 X 10 t U metal (29). 

The GANDU Reactors. The Canadian deuterium uranium (CANDU) reactors are unique among power reactors in several respects. Heavy water is used as moderator natural uranium having 235u... 

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

Toulhoat, P., Gallien, J. P. et al. 1996. Preliminary studies of groundwater flow and migration of uranium isotopes around the Oklo Natural Reactors (Gabon). Journal of Contaminant Hydrology, 21, 3-17. 

Del Nero, M., Salah, S., Miura, T., Clement, A. Gauthier-Lafayf., F. 1999a. Sorption/deso-rption processes of uranium in clayey samples of the Bangombe natural reactor zone, Gabon. Radiochimica Acta, 87, 135-149. 

Salah, S. 2000. Weathering Processes at the Natural Reactor of Bangombe (Gabon). Identification and Geochemical Modeling of the Retention and Migration Mechanisms of Uranium and Rare Earth Elements. PhD thesis, Strasbourg, France. 

Natural uranium consists of different isotopes of uranium. Natural uranium is 0.7% U-235 and 99.3% U-238. Uranium-238 is nonfissionable, and therefore naturally occurring uranium must be enriched to a concentration of approximately 4% to be used as fuel for nuclear reactors or 90% for weapons-grade uranium. Yellow cake is shipped to conversion plants... 

CANDU Reactor A pressurized heavy-water, natural-uranium power reactor designed by a consortium of Canadian government and private industry participants. CANDU utilizes natural, unenriched uranium oxide as fuel. Because unenriched uranium is cheaper, this kind of reactor is attractive to developing countries. The fuel is contained in hundreds of tubes that are pressure resistant. This means that a tube can be refueled while the reactor is operating. CANDU is a registered trademark of the CANDU consortium. 

Analysis of the natural reactors at Oklo gives valuable information about the migration behaviour of fission products and actinides in the geosphere. Uranium and the lanthanides have been redistributed locally. Plutonium produced in the Oklo reactors did not move during its lifetime from the site of its formation 85-100% of the lanthanides, 75-90% of the Ru and 60-85% of the Tc were retained within the reactor zones. Small amounts of U, lanthanides, Ru and Tc moved with the water over distances of up to 20-50 m. 

Another more sensitive way to detect a natural reactor is to look for fission products such as ruthenium, palladium, or tellurium which are rare elements in the earth s crust. As a result of preliminary experiments conducted at the Idaho National Engineering Laboratory ruthenium from spontaneous fission of 238U has been detected in a natural uranium ore, thus illustrating the sensitivity of the method and also the possibility of using ruthenium to uranium ratios to date uranium ores. The burn-up of... 

In the future we plan to make use of mass spectrometry of both uranium and ruthenium in a continuing investigation of natural reactors, the formation of rich, economic ore deposits, their rates of survival or destruction, and the relationship of ore deposit stability to long term storage of reactor products. 

Some billion years ago natural nuclear reactors must have operated and generated Tc as a high yield fission product by induced fission of with slow neutrons. The relics of a natural reactor were discovered in 1972 at the Oklo uranium mines in the Republic of Gabon, Africa. lire Oklo phenomenon occurred 1.72 billion years ago and produced a greater amount of Tc than detected in other uranium ores [20. Ruf-fenach et al. [21] reported values of integrated flux of thermal neutrons for the Oklo uranium ores of up to 1. . 2 10 n cm and a atomic ratio down to 0.00410,... 

A small portion of the 94 39 produced may also be changed to 94 4o by absorption of neutrons. The neutronic reactors referred to above may be called isotope converters in that one thermally fissionable isotope is formed (94 ) as another thermally fissionable isotope (U33B) is used up. However, this conversion is not c6m-plete, and the natural uranium, which acts to supply both the reaction isotope (U s) the absorption isotope (U ), will contain two different thermally fissionable isotopes after the reactor has been started. Certain presently known uranium-graphite reactors have been found to have a conversion factor of. 78, U to 94 3 . However, it may be desirable to form other fissionable isotopes in quantity such, as for example, U . Isotopes such as U 3 and Th , which arc not thermally fissionable isotopes, but which, upon absorption of a neutron, produce a thermally fissionable istotope, are called fertile isotopes. ... 

A neutronic reactor according to claim 1 wherein the fissionable material is plutonium diluted in a 1 1 proportion with natural uranium, the reactor is cylindrical, the reactor critical volume is 9 liters, the critical weight is 40 kg. and the thickness of the blanket is 30 cm. 

It will be understood that other means may be utilized 10 proportion with natural uranium, the reactor is cylin-... 

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