Unique natural nuclear reactor in Oklo, history of its opening and principle of operation

We are all accustomed to the fact that a nuclear reactor is a complex engineering structure, which was relatively recently invented by mankind and made to bring benefits through a controlled nuclear reaction.

But our nature is so unique and diverse that it has created its own natural nuclear reactor, which has managed to work for more than one hundred years, and it was almost two billion years ago. The history of the discovery and the principle of operation of this natural phenomenon will be discussed in today's material.

How a natural nuclear reactor was discovered

So, 1956, the so-called Cold War is in full swing, and every more or less large country is striving to get uranium 235 in order to enter the closed club of nuclear powers. France also showed the same desire, but it failed to find uranium deposits on its territory.

But luckily, French specialists managed to find the rich Oklo region in a country like Gabon (France had power over this country as a metropolis). But the uranium mined in this deposit turned out to be very strange. After all, he looked as if he had already visited an operating reactor.

This became known after the usual mass spectrometric analysis performed in 1972 at the concentrator.

It's just that engineers were faced with a unique natural phenomenon - a natural nuclear reactor, which, as it turned out, had successfully worked for about two billion years.

The principle of nuclear reaction and the half-life of uranium 235

Several isotopes of uranium can be found in nature, but only uranium 235 is suitable for work in nuclear reactors and for filling nuclear bombs. Moreover, the half-life of this isotope is 700 million years, and as a result of this decay, thorium 231 is formed.

But one has only to influence uranium 235 with a slow neutron, as it immediately decays. This is what makes this element so unique.

There are many sources of neutron radiation in nature that are quite capable of triggering a decay reaction. But they are moving too fast to interact with uranium 235, which means they must go through a stage of deceleration by external influences.

It turns out that if you put U235 in ordinary water, then it slows down enough neutrons, and they will be absorbed by uranium 235. This will produce the isotope uranium 236, which is extremely unstable and rapidly decays into barium 141 and krypton 92, as well as three high-energy neutrons.

So, as soon as the allocated three neutrons are slowed down by water, they can also be absorbed already three isotopes of uranium 235, which, in turn, will also undergo a decay process with the release of fast neutrons. This will provoke an exponentially increasing chain reaction of nuclear fission.

Scientists have long learned how to perform the so-called carbon analysis, which is precisely based on the determination of the residual fraction of uranium 235. In this regard, everything is simple, if you know when uranium was formed and that every 700 million years its share in the ore is halved, then it is a matter of technology to determine what its content is in the ore.

So it is believed that absolutely all uranium on our planet was formed then, then our Sun became a supernova, that is, about 6 billion years ago. Based on these data, we find that the concentration of uranium 235 in uranium ore on Earth should be 0.72%.

But the analysis of the ore from the Oklo deposit showed a grade of 0.717%. At first glance, the difference is not significant, but given the volume of the deposit, it was estimated that in Oklo about 200 kg of pure uranium is missing, and this will be enough for a minute to create several atomic bombs.

I don't think it's worth saying that there was no limit to the surprise of the French, since, given the entire political situation and the unfolding arms race between the Soviet Union and the United States, the "loss" of such a quantity of uranium caused great concern and many questions.

But with a more thorough study of the ore in the deposit, scientists also discovered a large amount of the so-called decay products of uranium 235.

This suggested that the mined uranium 235 had already worked out in the reactor and was returned to the ground.

And, at first glance, this is sheer nonsense, but further work on the deposit showed that this is a unique object - the world's only natural nuclear reactor.

The principle of operation of a natural nuclear reactor in Oklo

The reactor was in the active phase for a very long time, namely about 2 billion years ago. Moreover, at that time the concentration of uranium in the ore was 3%, just like in modern nuclear reactors.

Nature solved the problem of slowing down neutrons at the expense of groundwater, since it turned out that uranium ore was immersed in the groundwater layer. And it was this water that slowed down the neutrons that reacted and set off a nuclear chain reaction.

And if the water was constantly in the "reactor", then the ever increasing reaction would pass into a supercritical state and an explosion would inevitably occur.

But the natural reactor at Oklo never went into such a critical state. After all, water both starts the reaction and can stop it.

The above figure shows a cross-section of the Oklo reactor. So the passing water through the reactor triggered a chain reaction and made this area very hot, then after a certain time the water boiled and evaporated. Thus, the reaction stopped, since there was nothing to slow down the neutrons.

When the reactor cooled down, water was again collected in it and the reaction was started. The reactor stayed in this "working" state for many years, until the uranium concentration dropped to such a level that it was no longer possible to reach the criticality state.

This is how the unique natural reactor in Oklo worked, and scientists even calculated that its power was about 100 kW.

This fact indicates that, at first glance, an impossible phenomenon in nature may well exist and nature is still an inventor.

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