Oklo’s “Natural Nuclear Reactor” is the only one on Earth: he is in Gabon and is 2 billion years old

As strange as it may seem, there is a “Natural Nuclear Reactor“, That is, a unique place where the nuclear fission – Although this energy is not then converted into electricity. It is in fact a particular mine discovered in 1972 in the Franceville basin, in Gabon. It is estimated that the reactor was active from over 1.7 billion years, When the concentration of theisotope u²³⁵ In the natural uranium it was more than four times higher than the current one.

The discovery of the natural nuclear reactor in Gabon

The uranium present in nature is characterized by well -defined proportions of his three radioactive isotopes: the 99,2743% of U²³⁸lo 0.7202% of U²³⁵ And it 0.0055% of U²³⁴. You can therefore imagine the surprise of the French physicist Francis Perrin When, in 1972, he measured a concentration of U235 equal to 0.7171% In a sample extracted from the Uraiifere rocks of the Franceville basin, in the region of OkloIn the Gabonin the’West Africa.

Although apparently minimal, the difference of the 0.0031% Compared to today’s standard value, it is unusual. Further isotopic analyzes, conducted after various recalibractions of the spectrometer, confirmed these results, excluding the possibility of an instrumental error. Subsequent samples in the Oklo mine revealed concentrations of U²³⁵ even lower. In a report published byInternational Atomic Energy Agency (Iaea) it is indicated that in about 500 tons of uranium analyzed in 1972, the average concentration of U²³⁵ was of the 0.62%with a champion who even went down to 0.44%. This means that about 500 kg of uranium u²³⁵ they had “disappeared”.

The only physical process capable of explaining such a significant reduction in the concentration of U²³⁵ In the champions of the Franceville basin is the nuclear fission.

Natural nuclear fission

Nuclear fission is a phenomenon in which an atom, in this case of uranium, comes I split in two Or more “children” nuclei and at the same time emits a number of neutrons. This is the same process exploited in nuclear power plants for the production of energy. Among the three uranium isotopes, the u²³⁵ is the only one fissilethat is, able to support a nuclear chain reaction. For this reason, in fact, the functioning of traditional nuclear reactors requires theenrichment of uraniumincreasing the concentration of U²³⁵ up to values ​​including between 3% and 5%.

Faced with the unusual isotopic concentrations detected in the Franceville basin, the first hypothesis formulated by scientists was that the champions were artificialproduced by a controlled reaction. However, this explanation was not compatible with the geological context in which they were found. The champions in fact came from mines in the subsoilin some cases at depth above 1000 metersand had been extracted from sedimentary rocks of Paleoproterozoic, today dated about 2.1 billion years ago . The only plausible explanation is therefore that the finds are the remains of a ancient natural nuclear reactor.

The possible causes of natural fission

The hypothesis of a natural nuclear reactor was theorized for the first time by the nuclear chemist and physicist Paul Kuroda In the 1952. The one discovered in the Oklo region is probably not the first natural reactor on Earth, but it is certainly the only one so far discovered.

Basically, it is a natural environment in which the nuclear fission reaction of Uranium isotopes can occur spontaneously. An environment of this type would be impossible today, due to the low concentrations of U²³⁵. However, over 1.7 billion years ago, the concentration of U²³⁵ In the natural uranium it was equal to about 3%a value comparable to that used in modern nuclear reactors, e sufficient to trigger a natural fission.

The functioning of Oklo’s natural reactor is not yet completely clear. In the paleoproterozoic the landscape was very different: the Oklo region was crossed by vast river systems and deltizi who transported heavy elementsproduced by the erosion of granite rocks, towards the pelvis. Some studies suggest that the increase in oxygen concentrations caused by “Great oxidation“have facilitated the dissolution of uranium in the water, allowing its migration through pores And fractures in the rock. In addition, the presence of organic matter may have favored the precipitation of uranium in high concentrations.

Finally, thewaterfall He would have played a crucial role both in the trigger and in maintaining the fission reactions. As he explains Peter Wood, Expert scientist in the production of uranium at AIEA.

As in the light nuclear reactors built by man, fission reactions, without a moderator who slows down neutrons, would stop. The water in Oklo acted as a moderator, absorbing neutrons and controlling the chain reaction.

To date, they have been identified 16 natural nuclear reactors in Franceville’s basin: 15 located near each other and one, the Bangombé reactor, to Over 30 km away. The largest of these measures about 12 meters long, 18 meters thick and up to 0.5 meters wide. Experts speculate that the natural fission process continued at intervals for a few hundred thousand years and probably never exceeded 100 kW of thermal power.