Oklo, the Two Billion Year Old Nuclear Reactor

In 1972, French scientists were testing some uranium taken from the Oklo mine in Gabon, in Central Africa, where they had noticed something odd. They had a lot less usable uranium than they thought they did. Enough uranium to make six nuclear bombs was just… missing. Normally the uranium found in ore comes in three different varieties, or “isotopes,” each with a different number of neutrons in its nuclei. Since their atomic make-ups are slightly different, they all react in different ways. But when you’re looking for the stuff that releases enough energy to light up a city or vaporize an island when you split it, the isotope you’re looking for is Uranium-235. Now, Uranium ore should contain the same ratios of different isotopes no matter where it’s found in the world. So the French scientists knew that, in the ore they were studying, they were supposed to find a concentration of Uranium-235 that was exactly 0.72%. But it turns out they only had a concentration of 0.717%. Now it might not sound like a lot, but spread out over the giant mine at Oklo it looked like 200 kilograms of Uranium-235 had disappeared. After a few weeks of frantic investigation, the scientists realized that they were NEVER going to find the missing Uranium because it had been gone for two billion years. What they had discovered was the remains of an ancient natural nuclear reactor. Some physicists had theorized that certain kinds of nuclear reactors could exist naturally, but only under very specific conditions. And it turns out that the Uranium deposits at the Oklo mine and the area around it fulfilled ALL of those conditions. Basically, a natural nuclear reactor needs the same ingredients that modern nuclear power plants do. You need an atom that you can split pretty quickly and easily, you need neutrons to do the splitting, and you need a way to control that reaction, so once the atoms start breaking apart and releasing face-melting amounts of energy, you don’t have a nuclear Armageddon on your hands. When the first ingredient, an atom of Uranium-235, is struck by the second ingredient, a stray neutron, the atom becomes so unstable that it splits, releasing a ton of energy, plus a few more neutrons that fly off and split other Uranium atoms, creating a chain reaction. And way back, a couple of billion years ago, Oklo had both of those ingredients. Back then, natural concentrations of Uranium-235 pretty much everywhere on the planet were at a healthy 3%, which is about as much as nuclear power plants use in their fuel rods today. And in addition to all that potential fuel, Oklo also has lots of neutrons flying around just because, over time, Uranium-235 naturally decays into element, an isotope of Thorium, and in the process, it releases a neutron. Now, in a natural, uncontrolled reaction, all of those neutrons being released would be moving WAY too fast to split an atom. Instead of hitting another atom, they’d mostly just rocket away without hitting anything, and the reaction would simply stop. But this didn’t happen at Oklo because the deposit also had the third major ingredient: a way to control the reaction. The Oklo deposit was full of water. Groundwater, to be precise, which continuously flowed into the site, slowing the neutrons down enough that they had time to hit other atoms of Uranium-235 and keep the chain reaction going. Now you’d think with all these atoms getting split and energy being released, things would spin out of control pretty fast. But it turns out that the groundwater prevented that from happening as well. As more and more Uranium split, the energy being released made the water hotter. After about half an hour of that, the water would get so hot that it would start to boil off. And without the groundwater to slow them down, the neutrons would start moving too fast to hit any more Uranium which would quickly stop the reaction. But eventually, the water would come back and slow down the neutrons enough that the chain reaction would start over. And on and on this cycle went, likely for hundreds of thousands of years. All told, the deposits in the Oklo area probably had an average ongoing power output of about a hundred kilowatts, which is enough to power about a hundred washing machines FOR EONS. None of the energy was ever put to any use; eventually, the reaction used up so much of the U-235 in the deposit that the concentration got too low, and the reaction stopped. So, the energy produced by Oklo’s natural nuclear reactor quietly dissipated, leaving only that missing Uranium and a few byproducts as evidence that it ever existed. It’s pretty cool that nature actually figured out how to build a nuclear reactor before we did! Thank you for watching this SciShow Dose! If you have any questions for us, we’re on Facebook and Twitter and Tumblr and down in the comments below, and if you wanna keep getting smarter with us, you can go to youtube.com/SciShow and subscribe.

100 thoughts on “Oklo, the Two Billion Year Old Nuclear Reactor

  1. If the concentration back then was 3% globally and now is 0.17% doesnt that mean that all the iranium 235 will one day be gone

  2. Wait a second. If this was a working reactor how could the French scientists get ANY useable material. It would all be depleted! And in fact maybe the only reason it stopped working is lack of material. Only way they could of gotten close to it if it was dead and half life was timed out. Go figure

  3. I hate when people with terrible voices talk loudly and quickly and constantly — as if to convince us of something? If they really had something to say, wouldn't they let the content calmly speak for itself?

  4. israel adding to its undeclared nuclear arsenal, to blackmail nations. Which it isn't doing because it's undeclared nuclear arsenal is undeclared.

  5. No I believe humans have been here alot longer than we think what about those man harved balls that are a billion years old the same age as this nuclear reactor hmmm

  6. BS. You say that there was the right conditions… from were did you get that? Why do you say it? What about the water… show us proofs.

  7. Stupid internet monkeys are supposed to believe all of that crap,.. right babe?! How about, our modern view of the world is so ignorant that we collectively have a hard time to accept the possibility of an advanced civilisation way back in time so we can't find any remains of them except for some ancient nuclear wasteland. Nahhh, don't think out of the box, go back in there little sheep and believe what we try to stuff into you.

  8. No – more impressive than a natural reactor 2 billion years ago…….is that when the 235 concentration got below threshold …..

    …..the natural reactor …decommissioned itself. SAFELY.


    Humans on the other hand still cant build a reactor that will run that long. Unattended. Without ever blowing up.

    And again, decommission itself. ….unattended. wow huh?

    Maybe we should look closer at "nature's" (read God) that dont kill living organisms in horrible ways while poisoning the enviroment and deny us use of the area for hundreds of thousands of years.

    But I dont think humans ever will because of our collectively worse flaw.


  9. Omg this is so funny ., up next ; nature builds a starship and it flew coincidently and landed coincidently in mars lol

  10. So the ground itself around this oklo place was essentially like an electric plug that we all now have in the walls of our houses?  Makes me think about how Nikola Tesla used to harness unlimited energy from the ground

  11. As soon as people start saying 'Billions of years' I know a fairy tale is coming up, long ago and far away, we don't know we cannot say but it sure sounds good so it must be true even when we have no proof. tell something long enough and loud enough people will believe it, people will believe anything even iff it is a lie. So we can make our money and keep our jobs.

  12. On the one hand, I enjoyed the common sense, i.e., scientific exploration of, a.) What was found, and b.) How that find could be interpreted using logic and common sense–not so common these days in the US of A.
    I was, however, a little taken aback, by the moronic, standard American stupidity, comments it inspired from the hard-core stupid, we-hate-anything-we-don't-understand, American juveniles so common it that benighted culture these days. Their welfare-reject high school teachers must be very proud of them as they seem to have learned the "make fun of anything you don't understand" lesson very well indeed–albeit too well to keep the crumbling American social system afloat much longer.

  13. Yes, somewhat belatedly, I have a question. I don't understand the concept "going too fast to hit other atoms" and conversely "going slow enough to hit…".

  14. Actually there were about 20 small reactor zones in Oklo. What is interesting is that all the waste products were contained within a distance of 1-2 metres and for 2 billion years too! So who says that nuclear waste cannot be contained?

  15. Not that it has been gone for 2 billion years, but it had been decaying over the 2 billion years. It didn't happen all at once, it happened over the period of time.

  16. How would humans harness the power of a natural nuclear reactor? I’d guess we’d use a turbine to catch the steam and generate it but where would the best and most feasible place to put it? Would we harness it like geothermal? How much energy would it generate in the span of a human life? Would it do it often or would it do just short bursts that released high amounts of energy?

  17. If the water really vaporized under pressure that would mean there must have been some vapor geysers I guess. Any evidence of that?

  18. NERD
    i thought this video was going to be cool but you talk way above my intellect
    this is why u got picked on

  19. The claims of "natural" and "reactor" is nothing more than groundless claim to hide the truth of ancient nuclear war.

  20. The question here how did they count 2billion year age? The bigger the lie the more believable it appears isn't it.

  21. Sorry, this guy and his wavy arms and seconds saving split time video comes across as particularly annoying, so even though the facts are quite interesting, I gave up fairly early trying to watch and listen. Why must these announcements have to be done as if the earth’s about to end by maniacal hyped up on coffee, ( or something) extroverts?.

  22. Nobody that actually makes things for a living says zero point XX. Only academics that talk for a living speak like that.

  23. __from okla take must uranium and transported at reactor s nuclear for product of ellectricity__arcahicxnc

  24. So, does that mean all the water flowing and/or boiling out of that area was contaminated with radiation?

  25. meh.. really,? nature did is before us?? We are born from space dust.. WTF.-. Ya a Answeare of lack missing evidence was.. Thorium.. Thing for yourself..

  26. So if thorium is sum sort of power supply additive y don't they use that to power cars,planes,households and other things on the planet instead of mining other natural resources,…from wut I heard Cadillac done sumthin like that to a concept car sum years ago claiming it could run for a million yrs off of one thorium fuel cell,is this true???

  27. An MP suggested that it would be possible to survive without nuclear energy.My question would be;”How are you going to turn off the Sun?”

  28. Very likely it was remnants of space trash like the crap we send up to power our devices and let fall on who knows what and where millions of years later, like the nuclear powered space junk heading out of our solar system right now. The test indicate it was refined and decaying nuclear material, not ore grade, and food thought to the wise, figure out ahead of time where your garbage and junk will seep into.

  29. AND NOW FOR EARTH'S NEXT TRICK! "The right conditions causes Earth to manifest itself into all natural time traversing ball- istic space vehicle!"…"lol"

  30. The whole earth was at a certain dept a natural nuclear reactors that powered the mist coming out if the earth watering the earth according to the word of God.

  31. All uranium dates back to The Flood 4,350 years ago when it was created by massive piezo-electrical burst due to Earth's crust being shattered.
    Study quartz and piezoelectrical energy and forget the silly Planet of Apes billions of years nonsense.
    The reason you are told and believe the lie that lead is depleted uranium is beacuse lead is a ntural element in the hot water inside Earth and naturally dueing teh flood it seeped through the shattered crust – just where the piezo-electricity had created radioactive matter we call uranium.

  32. I like picturing those French scientists going to conferences to share their results with other French scientists and the conversation basically being, "Non! C'est impossible!" and, "Oui! C'est possible!" "Non!" "Oui!" "Non!" "Oui!" etc… =)

  33. It is far more likely that there were advanced civilizations in the past, than this happened naturally. I just don't buy it.

  34. Why you are speaking so so so fast? This theme interrests me, but I can't understand anything. You are a bad boy. Speaking to speak, not for understatement of your visitors. Make it again AND MAKE IT SLOW!

  35. We had Nukes back in Mahabharathas days. And buried the tech cuz we knew the world isn’t ready for that shite. So kind of “been there, done that”. Love from India 🇮🇳

  36. Actually, different isotopes (of uranium) DON'T react (chemically) in different ways. Yes there are plenty of examples of hot springs heated by natural radioactivity. Nothing new here.

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