Oklo natural reactor full#
Oklo natural reactor code#

This containment is reassuring, because Nature did not take any precautions. It was found that an environment of phosphates (apatites) was conducive to the retention of the radioelements. The Oklo study has shown that there was little or no uranium migration, and has revealed that minerals in the subsoil effectively trapped certain actinides and fission products. It is possible to study the migration of radioactive elements in the subsoil over a very long period, as well as their containment. Detailed analyses show the presence in those seams of a fossil record of radioactive waste that remained where it was and uranium ore with a low uranium-235 content. The Oklo site offers a unique example of the natural disposal of residues from a reactor core. At Oklo, the fission reactions occurred slowly over nearly 100,000 years, like a smouldering fire.

Oklo natural reactor full#

There is no comparison between these natural reactors – there had been several on the site – and their man-made counterparts that have been running at full power for decades. Water played the role of neutron moderator. a similar content to that of the enriched fuel of a modern nuclear reactor, so the uranium deposit at Oklo in Gabon could function like a reactor given the right environment. Two billion years ago, a uranium ore contained approximately 3.5 % of the uranium-235 isotope, i.e. These variations were surprising because isotope content on Earth is generally uniform in an ore.īecause its half-life is six times shorter than that of the more prevalent uranium-238 isotope, the uranium-235 concentration had diminished over time. They realised that there were major variations in the isotope content in different parts of the deposit. When some Soviet customers complained about an ore delivery with a low uranium-235 content, the quality of deliveries and the honour of the CEA were at stake. It was noticed by chance in the 1970s that a uranium ore deposit in Gabon being mined for its particularly rich uranium content, had functioned as a nuclear reactor two billion years ago. A conjunction of favourable factors, including its content of fissile uranium-235, which was much higher then than it is now, contributed to this extraordinary phenomenon. Sixteen ‘natural’ reactors were in operation at Oklo for several hundreds of thousands of years, two billion years ago. These calculations are in progress.This piece of cliff on the site of the Oklo uranium mines in Gabon contains traces of the operation of a fossil reactor, discovered during the 1970s. Further improvement of the accuracy of the limits can be achieved by taking account of the core burn-up. We obtain new, more accurate limits of -4×10 -17⩽α Following tradition, we have used formulas of Damour and Dyson to estimate the rate of change of the fine structure constant α. Contrary to the results of previous papers, we found no evidence of a change of the samarium cross section: a possible shift of the resonance energy is given by the limits -73⩽ΔE r⩽62 meV. The averaged cross section of 62 149Sm and its dependence on the shift of a resonance position E r (due to variation of fundamental constants) are significantly different from previous results. As would be expected, we found for the fresh core a significant difference between reactor and Maxwell spectra, which had been used before for averaging cross sections in the Oklo reactor. We also estimated the temperature and void effects for the fresh core. Multiplication factors, reactivities, and neutron fluxes were calculated. The calculations were performed for three fresh cores with different uranium contents. We constructed a computer model of the Oklo reactor zone RZ2 which takes into account all details of design and composition.

Oklo natural reactor code#

For reliability, we used recent versions of two Monte Carlo codes: the Russian code MCU-REA and the well-known international code MCNP. Using modern methods of reactor physics, we performed full-scale calculations of the Oklo natural reactor.