(ORDO NEWS) — Nuclear reactors, artificial machines designed to generate energy from nuclear fission, have been around since 1942. However, some may be surprised to learn that although man-made nuclear reactors were created almost 80 years ago, natural nuclear reactors existed much earlier.
In fact, natural nuclear reactors existed for billions of years before artificial reactors appeared in various regions of the globe. In particular, the country of Gabon in Central Africa once had 16 natural nuclear reactors.
The Gabonese nuclear reactors were capable of generating about 100 kilowatts of power, enough to light about 1,000 light bulbs at once.
Many are wondering how nuclear reactors came about in Gabon, and how likely it is that natural nuclear reactors will form in the future elsewhere on Earth.
Scientists and researchers have been able to piece together some information about these reactors to give us a better idea of their functionality.
By looking at how these naturally occurring nuclear reactors came into being, we can analyze the potential for new reactors in the future, and perhaps even learn a lesson or two about energy production from Mother Nature herself.
Ludovic Ferrière, curator of the rock collection, holds the Oklo reactor at the Natural History Museum in Vienna
The original all-natural source of energy
Gabon, short for the Gabonese Republic, is located on the west coast of Central Africa. It has a population of nearly 2.2 million and originated as a French territory in the 1800s.
Therefore, the main language in Gabon is French. Gabon gained independence as a state from France in 1960 along with several other African countries that were formerly part of the French Community.
Geologically, Gabon is interesting in that it mainly consists of almost two billion years old igneous and metamorphic rocks of the Paleoproterozoic era. This ancient crust contains valuable natural resources including magnesium, iron, uranium, gold and oil.
Across the landscape, explorers and scientists can find ancient landforms such as the hydrocarbon-filled rift basins that formed during the division of Pangea 175 million years ago. Gabonese natural nuclear reactors are another ancient formation that was stumbled upon nearly 50 years ago.
In the 1970s, miners stumbled across these 16 nuclear reactors in Oklo, Gabon’s southeastern region, while searching for uranium to power French nuclear power plants. Uranium is the main element used to generate energy through nuclear fission.
At artificial nuclear power plants, uranium is converted into pellets, which are used as fuel in nuclear reactors. These uranium pellets are then placed into rods that are tied together to form fuel assemblies. The fuel assemblies are placed inside the reactor vessel, which is submerged in water for cooling.
Oklo specimens donated to the Natural History Museum Vienna
In nuclear fission, the original uranium atom splits, releasing a neutron. This neutron then hits other uranium atoms, which, in turn, also split.
As more neutrons fission more uranium atoms, these chemical reactions release heat, which is then used to turn water into steam.
This steam is then used to turn steam turbines to produce clean, renewable energy. The water in which the reactor vessel is immersed cools the elements and slows down the neutrons so that the reactions do not occur too quickly.
Uranium is in high demand in nuclear power plants due to its ability to easily split into smaller atoms compared to other elements.
When natural uranium was found by French miners in Oklo, researchers called to the area noticed that the concentration of 235U (an isotope of uranium 235 that is predominantly used in nuclear fission because it is easily fissile) was statistically significantly lower.
They also found traces of cesium, americium, curium and plutonium, which are usually waste products from nuclear reactors from the decay of uranium.
This indicated that a natural fission of nuclear matter was taking place in the mines. This was the first discovery indicating that nuclear fission could occur naturally in the earth.
Oklo Natural Nuclear Fission Reactors: (1) Nuclear Reactor Zones. (2) Sandstone. (3) Layer of uranium ore. (4) Granite
Units and details of natural nuclear installations
As researchers began to look deeper into the nuclear fission that occurs in nuclear reactors in Gabon, they began to wonder how nuclear fission occurs so randomly. In artificial nuclear reactors, coolants such as water are needed to slow down chemical reactions by reducing the speed of neutrons.
Reducing the speed of neutrons reduces the splitting of uranium atoms, which leads to a more controlled release of heat and steam. Without a coolant like water, nuclear fission would happen so fast that the reactor pressure vessel could get hot enough to melt, burn, or even explode.
A striking example of uncontrolled nuclear fission is the Chernobyl disaster, as a result of which the reactor core melted and several explosions occurred, which led to numerous casualties and severe radioactive contamination of the region.
Several more deaths occurred in the following years due to radiation exposure, which caused various cancers and illnesses in the victims.
A simple diagram of nuclear fission. In the first frame, the neutron is about to be captured by the nucleus of the U-235 atom. In the second frame, the neutron is absorbed and briefly transforms the nucleus into a highly excited U-236 atom. In the third frame, the U-236 atom has decayed, resulting in two fission fragments (Ba-141 and Kr-92) and three neutrons, all with very high kinetic energy
Analyzing nuclear reactors in Gabon, scientists realized for the first time that in order for natural nuclear fission to occur, at some point a significantly higher concentration of 235U had to be present in order to start a chain reaction.
Given the extremely high half-life of uranium (700 million years), this concentration must have been present almost two billion years before the discovery of uranium ores.
At this high concentration, the atoms should have collided and split naturally, leading to further reactions. The researchers believe that such a high concentration of uranium was most likely caused by a combination of weathering of igneous rocks and high bacterial activity in ancient times.
With such a high concentration of 235U, some sort of refrigerant would be required to control the reactions and prevent an explosion in the mine.
It is believed that earlier, two billion years ago, there was a significant amount of water in Oklo, which could serve as a natural coolant for the mines. This would prevent any uncontrolled reactions occurring in the mine over time.
For some scientists, the most interesting thing about Gabon’s nuclear reactors is not the fact that they once produced nuclear power. The most interesting fact is that the tests did not reveal signs of high radioactivity in the region.
The once toxic cesium and plutonium have now decayed into barium, which is harmless to humans. There are also no signs of radioactive exposure of wildlife in the area, which would naturally be expected in the region of 16 natural nuclear reactors.
This discovery about nuclear reactors in Gabon suggests that nature has found a way to naturally rid the area of significant radioactivity over time, and scientists are quickly trying to learn from this.
The terrain surrounding the natural nuclear reactors at Oklo suggests that groundwater infiltration above the bedrock layer may be a necessary ingredient to produce rich uranium ore capable of spontaneous fission
Series of natural nuclear events
Researchers believe Gabon’s nuclear reactors have been in operation for more than a million years after being formed almost two billion years ago.
The reactors could function normally underwater until the water eventually evaporated due to the high temperature of the nuclear reactions. This is the same reaction that occurs in artificial reactors, only the water is recycled rather than completely evaporated.
About a million years earlier, the high concentration of 235U would have been significantly depleted. At this point, the reactors probably stopped actively producing power. Although the natural reactors were shut down, they miraculously survived for millions of years thereafter thanks to the protection of the surrounding clay and carbonaceous matter.
These substances protected the reactors from sources of high oxygen content, which would corrode or dissolve all traces of a nuclear reaction over the past few million years.
As for the future of Gabon’s natural nuclear reactors, French miners continued to mine the remaining uranium for use in artificial nuclear reactors. The mines have now exhausted most of the usable uranium, eliminating any possibility that reactors will produce more power sometime in the future.
Scientists now refer to these mines as “fossil” natural nuclear fission reactors, as they are no longer operational but still contain evidence of their former ability to generate power.
Professor François Gauthier-Lafayer (University of Strasbourg) shows the contact zone of the natural nuclear reactor No. 10 to a group of Swiss journalists at the Oklo uranium mine (Gabon) in 1997
Can natural energy come back?
Although Gabon’s nuclear reactors have already produced all usable uranium, miners have taken steps to reclaim the mines. Mine reclamation is a human activity aimed at minimizing the environmental consequences of mining by returning mined-out areas to their original state.
Remediation may include reducing erosion, stabilizing slopes, and removing any impact on local wildlife. It is believed that, over time, the reclamation of mines can lead to the replenishment of the Earth’s own resources, although we will not see some of the consequences of mine reclamation during our lifetime. Many developed areas are being converted into wildlife habitats or agricultural fields.
As regards the fossil natural nuclear reactors in Oklo, mine reclamation is still ongoing. The plan for this region is not entirely clear, given its history as the site of natural nuclear reactors, but scientists are actively working in the region to implement the best plan possible.
These reclamation plans have led some to doubt that the mines could ever start generating power again. Given the significantly low concentration of uranium in the mines at present, it is highly unlikely that any chain reaction will occur in the near future.
Because uranium is a finite resource on Earth and cannot be produced, it is also impossible for the concentration of uranium in mines to increase over time.
While the future of nuclear reactors in Gabon looks bleak, scientists acknowledge that it is entirely possible that other naturally occurring nuclear reactors exist elsewhere on Earth.
Although none of them have been found at the moment, in the future, miners and researchers may discover another natural nuclear reactor in various regions.
Since there is a high concentration of uranium in the ocean (estimated at about “four billion tons”), some scientists suggest that natural nuclear reactors may function in the oceanic crust at the bottom of the ocean.
The sea water will act as a natural coolant to prevent the uncontrolled fission of uranium, similar to the Gabon reactors two billion years ago. Considering that about 80% of the ocean has not yet been mapped and explored, it is quite possible that a natural nuclear reactor may be hiding somewhere in the depths.
As renewable energy sources are explored and further introduced, uranium will continue to be mined for artificial nuclear reactors. Nuclear scientists are still analyzing the long-term consequences of using nuclear energy, such as the need to dispose of nuclear waste without contaminating the Earth with radioactivity.
Using the information gathered from Gabon’s nuclear reactors, scientists may be able to develop an efficient and safe way to dispose of this waste in the future. With any luck, the Gabonese nuclear reactors will one day become an achievable example of how nuclear power can be generated in an environmentally friendly way.
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