Nature built a nuclear reactor 2 billion years ago

The uranium extracted from the Oklo region of Gabon contained a percentage too low of coveted isotope 235. Has anyone adulterated the uranium? Is this an artifact of an ancient and unknown civilization? Or, perhaps, something even stranger: had uranium simply feding?

“This is not possible.” This was the first idea that went through the physical mind Francis Perrin In May 1972, when he examined a dark piece of uranium ore in a nuclear fuel processing center in southern France.

The uranium sample, extracted from a mine in Gabon, Africa, contained a secret that challenged everything that scientists knew About natural uranium.

Normally, uranium exists in a consistent proportion of isotopes: Uranium-238, Uranio-234 and the coveted uranium-235the main fuel used in civil nuclear reactors to produce electricity.

This isotope is fissile, that is, may suffer nuclear fission: Its core can be divided into two smaller nuclei when bombarded by a neutrão, releasing a large amount of energy – and more neutrons.

Throughout the earth’s crust, the proportion of uranium-235 remains stable at 0.720%. However, Gabon’s sample analyzed by Perrin contained only 0.717% of isotope 235.

It was a tiny deviation “But enough to raise questions and trigger alarms.” The simplest explanation would be that Uranium had suffered fission. But how could this be, since this was a natural sample?

Someone would have tampered with uranium? Is this an artifact of an ancient and unknown civilization? Or, perhaps, something even stranger?

Fission in nature

The more the scientists investigated, the stranger the case became, tells. In some uranium samples in the region of Oklo, in Gabonthe proportion of uranium-235 It was even lower, reaching 0.4%.

This had to be more than a statistical chance “It meant something deep had altered the ore.” Later analyzes revealed that uranium had really suffered fissionthe same process used in nuclear reactors.

The evidence pointed to an event that occurred two billion years ago, but this fission was not the result of human interference, nor of any alien species that had the earth at the time.

Suddenly, The unthinkable became clear. After his analysis, Perrin and colleagues confirmed that the natural sample had suffered fission when the earth was still a young planet: Nature had created its own nuclear reactor.

Artificial nuclear fission reactors work carefully controlling a chain reaction where uranium-235 atoms are divided by neutrons, releasing energy and more neutronswhich continue to divide additional atoms.

To support this reaction, Enriched uranium is required -where uranium-235 concentration is increased. The creation of such reactors requires Advanced technology, precise engineering and security protocols strict. It is not something that would be expected to find naturally.

However, in Oklo, thousands of millions of years ago, nature spontaneously provided the certain combination of uranium concentration, water and geological stability to support a controlled fission reaction.

How to form a natural reactor

In 1956, a chemist called Paul K. Kuroda predicted that, under the right circumstances, natural fission reactors could form.

His work received some attention, but it was not an instant success, since The conditions seemed very unlikelyand few people (if any) really expected to find something like that.

Kuroda estimated that the uranium deposit needs to be at least 66 centimeters to support a natural nuclear fission reaction. If the deposit is less than that, cannot reach the critical mass. Then it is necessary to have sufficient uranium-235 in the warehouse.

Two billion years ago, Uranium-235 was much more abundant of what it is today. At that time, it constituted about 3% of natural uranium – A percentage similar to that of enriched uranium used in modern nuclear reactors.

As in the reactors, The process needed a moderator to slow neutrons and make fission more likely. In Oklo, it was the groundwater to play this crucial role. The water slowed the neutrons, facilitating a sustained chain reaction.

“As in a nuclear reactor of artificial light water, fission reactions, with nothing to slow neutrons, to moderate them, Simply stop“Said Peter Woods, a team leader responsible for the production of uranium at the International Association of Atomic Energy.“The water acted in Oklo as a moderatorabsorbing neutrons, controlling the chain reaction. ”

It was also necessary that Elements like Boro or Lithiumwhich absorb neutrons and interrupt fission, were absent. Oklo didn’t have these “contaminants”, which allowed the reaction to continue. When these conditions aligned perfectly, The result was a natural nuclear reactor.

The old oklo reactor It did not work continuously. After dating the rocks and analyzing the past activity of the samples, the researchers found that the oklo reactor Cycles operated.

As groundwater infiltrated uranium deposits, it moderated neutrons, allowing the fission to occur. The reaction warmed the waterthat ends up evaporating as steam. Without water to moderate neutrons, the reaction stopped.

After the area cools, and more groundwater to infiltrate, the reaction began again. This cycle Repetured for hundreds of thousands of years.

One on the oklo reactor, conducted in 1976 by George A. Cowana researcher at the University of California, concluded that, during a period of several hundred thousands of years, Okla uranium produced approximately 15,000 megawatt-fission energy megatat – The equivalent of the operation of a major reactor of 1,500 MW for ten years. ”

Oklo uranium mines currently are exhaustedbut the legacy of the only known natural nuclear reactors in the world continues. There are samples of oklo reactors preserved in museums, such as the Vienna Natural History Museum, where visitors can see rocks produced by the natural fission reactor.

It is possible that there are other natural reactors – We just haven’t found them yet. Meanwhile, humanity is focusing on its own reactors of fission.