29 July, 2015

The 2 Billion Year Old Nuclear Reactor - Gabon, Africa

Two billion years ago parts of an African uranium deposit spontaneously underwent nuclear fission.

Sometime a bit less than 2 billion years ago, and lasting for about 300,000 years, the Oklo reactors held a series of stable nuclear fission reactions.

Upon their discovery, the central question about these reactors was simply: How could they possibly work? One early hypothesis was that the fundamental physical constants that restrict nuclear reactions today may have been different 2 billion years ago. Analysis of the wastes at Oklo, running all the way up to this very month, suggest that the physical constants have indeed been constant all along. That means the reactor would have needed a fissionable isotope in the same concentrations we require today.

If we have such trouble making raw uranium usable in stable fission reactions, how could an inanimate planet possibly do it?

Well, it didn’t. Back when these Oklo reactors first fired themselves up, Earth was barely half as old as it is today. That means that less time had passed since its initial formation from bits of galactic dust and rock. As a result, fewer radioactive half-lives had played out, and unstable isotopes were found in much higher concentrations.

Scientists estimate the Oklo reactors would have had samples with roughly 3.6% uranium-235.

These small details led to further investigations which showed that least a part of the mine was well below the normal amount of uranium 235: some 200 kilograms appeared to have been extracted in the distant past, today, that amount is enough to make half a dozen nuclear bombs. Soon, researchers and scientists from all over the world gathered in Gabon to explore what was going on with the Uranium from Oklo. 

What was found in Oklo surprised everyone gathered there, the site where the uranium originated from is actually an advanced subterranean nuclear reactor that goes well beyond the capabilities of our present scientific knowledge. Researchers believe that this ancient nuclear reactor is around 1.8 billion years old and operated for at least 500,000 years in the distant past. Scientists performed several other investigation at the uranium mine and the results were made public at a conference of the International Atomic Energy Agency. According to News agencies from Africa, researchers had found traces of fission products and fuel wastes at various locations within the mine area.

Incredibly, compared with this huge nuclear reactor, our modern-day nuclear reactors are really not comparable both in design and functionality. According to studies, this ancient nuclear reactor was several kilometers long. Interestingly, for a large nuclear reactor like this, thermal impact towards the environment was limited to just 40 meters on all sides. What researchers found even more astonishing, are the radioactive wastes that have still not moved outside the limits of the site as they are still held in place tanks to the geology of the area.

What is surprising is that a nuclear reaction had occurred in a way that the plutonium, the by-product, was created and the nuclear reaction itself had been moderated something considered as a “holy grail” for atomic science. The ability to moderate the reaction means that once the reaction was initiated, it was possible to leverage the output power in a controlled way, with the ability to prevent catastrophic explosions or the release of the energy at a single time.

Researchers have dubbed the Nuclear Reactor at Oklo as a “natural Nuclear Reactor”, but the truth about it goes far beyond our normal understanding.
Meanwhile, French nuclear scientists carried out a detailed survey of the Oklo site, discovering not just one reactor zone but up to 17 of them over an area of several tens of square kilometres. Some of these were close to the surface and so had been influenced by weathering processes, while others were at depths of up to 400 metres and were more or less pristine.

In addition to the depleted uranium-235, these zones contained numerous fission fragments such as isotopes of zirconium, yttrium, neodymium and cerium. The unusual ratios of these isotopes was an important indicator of what had gone on there almost 2 billion years earlier.

The presence of these fission by-products immediately piqued the interest of nuclear scientists

The Workings of an Ancient Nuclear Reactor - Scientific American
2 billion-year-old African nuclear reactor proves that Mother Nature still has a few tricks up her sleeve | ExtremeTech
2 billion year old nuclear reactor in Gabon | News24
In the 1970s, Scientists Discovered a 2 Billion-Year-Old Nuclear Reactor in West Africa — The Physics arXiv Blog — Medium


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